Re: [AMRadio] Testing tubes
Jim, Here's a Site in Korean that has some graphs and info but the Eico 1030 P.S. shown is the perfect supply source for good regulated H.V as well as bias and filament. I have found several cheap at Fests and they seem to be a hidden gem for tube audio work. There are two 6L6's as pass tubes with the ratings of 400v at 150ma which is conservative. I put 6550's in mine, changed out the meters to read 500v and 250ma fs, upped some cap v ratings and can now get [EMAIL PROTECTED] no problem. I added several digital panel meters for precise V/A readings of all tube elements and it all cost less than $100. Perfect for most power tube specking as well as working on any type of tube gear. I will post the whole configuration when it's all reassembled. After all, where would our AM be without good AF power tubes. Enjoy, Bill KB3DKS --- StripMime Report -- processed MIME parts --- multipart/alternative text/plain (text body -- kept) text/html The reason this message is shown is because the post was in HTML or had an attachment. Attachments are not allowed. To learn how to post in Plain-Text go to: http://www.expita.com/nomime.html ---
RE: [AMRadio] Testing tubes
Thanks Jim Here is a very interesting article but I didn't write it. I aint that smart. But I think I can understand some of it. I think it may be worth printing and putting in a binder. http://www.john-a-harper.com/tubes201/#Physical%20Construction John, WA5BXO
RE: [AMRadio] Testing tubes
John, Wow! I have been inundated with stuff from higher minds than mine! Besides your excellent replies, I got a somewhat similar, yet different perspective from Patrick Turner from the R.A.T. group, (newsgroup: rec.audio.tubes) that I paste below. The guy wants me to calculate Mu, and plate resistance as well. After all, Gm = U / Ra. Patrick's reply: > What you are doing will broaden your ideas about tubes, > but why concentrate on the Gm? > > If I want to find out how to set up a tube I find out what > all three important parameters are, the Ra, U, and Gm. > > You can set up a tube with a choke load, and strap various values > of RL across the choke. > > Then after the bias is set apply a fixed signal input voltage to get about > half the maximum anode voltage swing before clipping, so thd is negligible. > Then measure the voltage gain, and do so for at least two different RLs, > say 5k, and say 10k. > > Voltage Gain, A, = U x RL / ( RL + Ra ), for all tubes. > > So since we know what A is, and RL is, we have two equations for the > two different loads, and from these we can work out > Ra, U and thus Gm, because for all tubes, > Gm = U / Ra. > > The most constant parameter for all tubes is the U, > because its determined mainly by electrode distances, > but Ra and Gm vary widely. > > The other way to measure Gm is to simply have no choke load, > or large value RL, and just have a 10 ohm R to the B+, > and measure the undistorted current change with grid voltage changes. > This don't tell you about Ra or U, which change dramatically > when G2 is connected to the anode. > > The first method of mine involves algebra. > But from one of with two equations, U can be expressed as a factor x Ra, > and this can be substituted where U appears in the second equation so that > this then has only numbers and Ra present, so Ra can be found, and its value > inserted into either equation, and the value of U found, > and thus Gm. > > The idle conditions for the tubes can be changed, and the 3 > parameters will change. > > The tests and measurements can be done using a class AB PP pair, > which will indicate what the 3 design values are when combined. > In AB circuits, the Gm usually drops a bit after one tube cuts off, > resulting in a flattening of the amplified sign wave, > which is compression, or lot of 3H present. > But when biased to near class B, the crossover distortion indicates > that Gm is initially low, then becomes greater as more tube current flows, > and the phase of the resulting 3H is opposite that of compression. > Some tubes, like the 6DQ6, display increasing Gm > even in class AB circuits at the extreme of the amplitude, > so that the wave peaks up before clipping, and again the 3H > is opposite phase to a compressed wave, so Gm is increasing lots, > even up to just before clipping. > > In triode signal tubes, such as 12AT7, 6DJ8, > quite large variations in Gm and Ra occur for different > idle currents, and some have deliberately engineered > variable parameters by means of variably spaced grid wires. > Many pentodes have also thus been made to have variable U and Gm, > to make the gain vary a heck of a lot, which is handy for > gain control in radio receivers, or to provide a more > constant sound level from microphones, regardless of the distance away from > the person using it becomes. > > Once you have established that a given load is ideal for > a pair of say 6L6GC tubes, then quite a few others might be substituted. > Speaker loads vary between say 4 and 40 ohms, so absolutely strict > load matches are impossible. > It pays to err on the conservative side, IMHO, > ie, allow for a high value RL than a low one, > as the best fidelity is then possible, and tube substitutions > are more successful. > > Patrick Turner. -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of John Coleman, ARS WA5BXO Sent: Monday, October 13, 2003 9:37 PM To: amradio@mailman.qth.net Subject: RE: [AMRadio] Testing tubes Actually Jim, You could probably use a 100 ohm resistor in series with the plate so as to have 1 volt measured change = 10 ma change. The 10 volt drop in plate voltage will not alter the plate current enough to be perceptible so long as the screen is constant. But it is easier to measure and you wouldn't need quite the large filter on the power supply. It need only be large enough capacitance to bypass the testing frequency. And if the testing frequency was at about 1000 CPS then it would be more accurate than at 60 CPS. I have drawn up what I think would be a good testing circuit for Gm. It might even show distortion factors if the scope was to be connected vertical to input and horizontal to outp
RE: [AMRadio] Testing tubes
Actually Jim, You could probably use a 100 ohm resistor in series with the plate so as to have 1 volt measured change = 10 ma change. The 10 volt drop in plate voltage will not alter the plate current enough to be perceptible so long as the screen is constant. But it is easier to measure and you wouldn't need quite the large filter on the power supply. It need only be large enough capacitance to bypass the testing frequency. And if the testing frequency was at about 1000 CPS then it would be more accurate than at 60 CPS. I have drawn up what I think would be a good testing circuit for Gm. It might even show distortion factors if the scope was to be connected vertical to input and horizontal to output. http://wa5bxo.shacknet.nu/HAMPICTURES/transconductance_check.gif What do you think? John, WA5BXO
RE: [AMRadio] Testing tubes
Hi Jim The idea that you have a triode connection is not exactly valid for this type of test because there is no series load resistor. The plate and screen voltage are held constant regardless of the plate current. It is however important that you measure the plate current separately from the screen current, if you want to measure the GM of a tetrode connection. Changes in screen current, is not what the test is about. The plate and screen voltage may come from the same source. The screen voltage is most critical and must be maintained constant as close as possible. Since plate and screen come from the same source then the source voltage should be monitored with a DVM and adjusted to be the constant of 250 Volts. This will require a little juggling each time you make a change in grid voltage. The actual plate current that you start with (90-110 ma) is not so important. But the change (delta) Ip with grid voltage change is what we are looking for. The only other thing that might be a problem is that the plate dissipation will be about 25 watts. Is this tube OK for that during the test? I would not use a delta Eg of more than 5 volts to make the test this would yield a change in plate current of more than 46.5 ma which is about 50 percent of the quiescent current of 100 ma. It is important that the increase in current when the Eg is made more negative be equal to the decrease in current when the Eg is made less negative by the same amount. In other words it should be linear. Keep in mind that when the plate current goes to 150 ma or more that the plate dissipation will be 50 percent more so make you measurement fast and don't for get to hold the EP constant with that DVM. You could also place a 1 ohm resistor in the plate lead and capacitively couple to a sensitive AC voltmeter (scope) and measure the AC current produced as a change in Eg AC. A 100 ma change would be represented as 0.1VPTP on the scope. You would need a very large capacitor to Filter the source with. 73 John, WA5BXO -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Jim candela Sent: Sunday, October 12, 2003 11:08 PM To: amradio@mailman.qth.net Subject: RE: [AMRadio] Testing tubes Hi Group, I got a wild hair, and made a setup to compare a set of used Genalex KT77's to a new MP (matched pair) of Sovetek EL34's. I was following a note in the KT77 data sheet that stated when a KT77 is considered bad (< 9.3 ma/volt transconductance when EP, Eg2 = 250 volts held constant, and IP = 100 ma). Following this criteria, I made a test setup. I am not too sure of my technique as it is a work in progress. I am curious that the Gm can vary considerably when changing Vg1 +/- 1 volt from the value used to obtain 100 ma plate current. Maybe this is all wrong, but I averaged the two numbers assuming that is the final answer. Since Genalex stated to run the screen and plate at 250 volts, I connected them together (Fluke 8012a looks at plate current only), so this test is in triode mode (or is it not?). For a high voltage supply I used my Sherwood S8000 stereo amp / FM with a variac (get ~ 250 vdc at 65 volts AC input). Hey it was there (awaiting a re-cap job), convenient, and able to do the job! Is the data I've taken valid? If not, can someone enlighten me? Maybe I need to vary Vg1 less than +/- 1 volt, for better data? Regards, Jim Candela Test results: http://pages.prodigy.net/jcandela/KT77/genalex_kt77.htm KT77 Data Sheet: http://pages.prodigy.net/jcandela/KT77/kt77.pdf Test Setup: http://pages.prodigy.net/jcandela/KT77/PA110015.JPG ___ AMRadio mailing list AMRadio@mailman.qth.net http://mailman.qth.net/mailman/listinfo/amradio
RE: [AMRadio] Testing tubes
Hi Group, I got a wild hair, and made a setup to compare a set of used Genalex KT77's to a new MP (matched pair) of Sovetek EL34's. I was following a note in the KT77 data sheet that stated when a KT77 is considered bad (< 9.3 ma/volt transconductance when EP, Eg2 = 250 volts held constant, and IP = 100 ma). Following this criteria, I made a test setup. I am not too sure of my technique as it is a work in progress. I am curious that the Gm can vary considerably when changing Vg1 +/- 1 volt from the value used to obtain 100 ma plate current. Maybe this is all wrong, but I averaged the two numbers assuming that is the final answer. Since Genalex stated to run the screen and plate at 250 volts, I connected them together (Fluke 8012a looks at plate current only), so this test is in triode mode (or is it not?). For a high voltage supply I used my Sherwood S8000 stereo amp / FM with a variac (get ~ 250 vdc at 65 volts AC input). Hey it was there (awaiting a re-cap job), convenient, and able to do the job! Is the data I've taken valid? If not, can someone enlighten me? Maybe I need to vary Vg1 less than +/- 1 volt, for better data? Regards, Jim Candela Test results: http://pages.prodigy.net/jcandela/KT77/genalex_kt77.htm KT77 Data Sheet: http://pages.prodigy.net/jcandela/KT77/kt77.pdf Test Setup: http://pages.prodigy.net/jcandela/KT77/PA110015.JPG
Re: [AMRadio] Testing tubes
John, Now that was what I wished to say, LOL!! I can't agree more with your observations and technique. It also explains my liking medium Mu 12AU7 based circuits over AX7's. As long as there is enough gain to properly drive the following stage hi Mu tubes are not really needed. I'm looking forward to getting the test set together again and looking at some of this under controlled conditions and doing proper documentation. I will not limit myself just to audio tubes but plan on being able to fire up just about any tube and run curves out. Anybody an A/D software GURU so the testing can be automated? Guess the SOFIA unit is no longer in production. Thanks, Bill KB3DKS --- StripMime Report -- processed MIME parts --- multipart/alternative text/plain (text body -- kept) text/html The reason this message is shown is because the post was in HTML or had an attachment. Attachments are not allowed. To learn how to post in Plain-Text go to: http://www.expita.com/nomime.html ---
Re: [AMRadio] Testing tubes: Cathode Interface
In a message dated 10/2/03 11:11:33 AM Eastern Daylight Time, [EMAIL PROTECTED] writes: > Could this be a form of cathode interface problem? Cathode interface is a > problem sometimes seen when old tubes are used in scope vertical amplifiers > with fast risetimes. Something happens to the tubes that causes the actual > rise > time to deteriorate as the tubes age. The "something" that happens is called > cathode interface. I have observed this effect personally on old Tek scopes > so I know it is real and apparently widely recognized. But I don't know if > anyone has done any work to see if cathode interface has an impact in other > tube applications like audio amplifiers. > > Anyway, I just thought I'd throw that idea into the discussion. I am no > expert and my ears prefer solid state audio. > > 73, Don Merz, N3RHT > > Don, Thanks for the reminder on that. I have several of the 500 series Tek mainframes and have read the advisory notices on cathode interface problems. Seems it was pointed at the 6DJ8/6922 tubes in particular in the sections you mentioned. I forgot completely about that trait and will look at the possibility that the problem lies there. Makes sense. Reduced rise time indicates a loss in H. F. response along with the inability to reproduce proper harmonic relationships. Enjoy, Bill KB3DKS --- StripMime Report -- processed MIME parts --- multipart/alternative text/plain (text body -- kept) text/html The reason this message is shown is because the post was in HTML or had an attachment. Attachments are not allowed. To learn how to post in Plain-Text go to: http://www.expita.com/nomime.html ---
RE: [AMRadio] Testing tubes
I can't stan it no more, I got to put in my 2 cents worth. HIHI I remember a VHF transceiver that I was responsible for maintaining while in the Air force. Radio was not my job in the Air Force but I was a ham, and so filled in on a number of disassociated assignments. Any way, this rig was a Class C plate modulated thing and it started having a reduction in output even though the grid drive and plate current was the same. I had no way to measure the plate temperature. But replacement of the 4CX150s brought the output back up. I could not explain it. But others in the work field said they had experienced the same thing over and over again with that type of rig. I never had the chance to experiment with the phenomenon of this VHF rig. I have never experienced any thing of this nature in HF and I have never built any VHF Class C rigs. I have however noticed a lot of different things about tubes in audio work. All phenomenons, I have found the reason for. If one goes to the trouble to actually graph a full set of plate characteristic curves on the tubes in question you will see that the tube characteristics have changed with age. All of which is associated with emission loss or space charge. Some also associated with the surface area that is actually emitting into the space charge. The ability for the space charge to be replenished by emission from the entire area of the cathode or just a small area that is still working is all part of the aging process. Most of the deterioration I think, is caused by a poor vacuum or loss of vacuum over time. Characteristics of tubes and especially aging are a hard thing to control. In my opinion circuit design should be adjusted to try to maintain a lower gain than might be described in many tube manuals and low distortion with changing characteristics. For instance, 1/2 of a 12AX7 has a circuit description in most tube manuals having a max gain of about 50. I tend to lean towards cathode bias for self adjusting bias and I leave the cathode resistor un-bypassed for a lower gain of about 10 and a lot less intermodulation and harmonic distortion. I will even test the circuit by reducing the filament voltage on the tube to 5 or even a little lower to simulate low emission if I have done my work right the gain will not measurably fall off nor will the distortion level increase. I have noticed a measurable drop in noise however and 5.5 volts and below. When the circuit is designed for max gain and the input resistor is high the tube takes on the characteristics of a reactance amplifier because the interelectrode capacitive reactance of the tube is a significant percentage of the input resistance. If the gain of the circuit is high and the frequency in question is high the reactance is equivalent to a capacitor across the input and the output will not maintain the exact 180 deg phase reversal that it does at lower frequencies. If the output circuit is forced to maintain gain at a higher frequency as with tuned circuits, the thing will break into oscillation as any un-neutralized HF tuned amplifier would. Designing a circuit for lower gain and lower input resistance coupling will help maintain its frequency response with aging as well as keeping the distortion down. By the way, if a graph is made of the dynamic transfer characteristics of the circuit with a gain 50 it will be found that the apparent linear portion of the curve is much less than the linear portion of the curve in the circuit with a gain of 10 and a un-bypassed cathode resistor. The un-bypassed cathode resistor is a form of inverse feed back within the current loop of the output. Even though the audiophiles say don't, I do. I'll compensate elsewhere for the effective rise in plate resistance. In a circuit of this kind you can barely detect the difference between the 12AX7 and a 12AY7. In short, yes, aging happens, make the circuit self compensating. Good discussion, I love it: John WA5BXO
Re: [AMRadio] Testing tubes
In a message dated 10/2/03 1:06:37 PM Eastern Daylight Time, [EMAIL PROTECTED] writes: > Comment: Below is a link about modyifing CD players where the op amp after > the D-A has a tremendous effect on the perceived audio quality. One > explanation is that many op-amps have very noticeable cross over distortion, > which > becomes more significant as the signal level drops into the lower portion of > the > available dynamic range. One solution for some op-amps is to use a pull up, > or down resistor from the output of the op-amp to a power buss. The idea is > to require the output stage to sink, or source a little current to in effect > keep only one half of the output running, or to put it in other words: make > it > act as a single ended amplifier, and therefore no cross over distortion. > You will also like the use of tubes following the D-A converter. Neat stuff! > > Jim > WD5JKO > > http://home.netcom.com/~wa2ise/radios/tubedac.htm > > . Thanks for the link. Have heard of that but hadn't found it yet. The early Magnavox/Phillips players were the subject of many Pooge (mod) articles in Audio Amateur Mag in the 80's. Nowadays everything is surface mount and next to impossible to play with. It's remarkable how the vacume tube has resurfaced as a viable interface with digital. Have been real interested in the motherboard out now with a tube in the sound circuit. I have a collection of tube type computer modules using pairs of dual triodes producing an op amp config.by Philbrick and single tube modules configured as other logic functions from a different mfg. Enjoy, Bill KB3DKS --- StripMime Report -- processed MIME parts --- multipart/alternative text/plain (text body -- kept) text/html The reason this message is shown is because the post was in HTML or had an attachment. Attachments are not allowed. To learn how to post in Plain-Text go to: http://www.expita.com/nomime.html ---
Re: [AMRadio] Testing tubes
On 2 Oct 2003 at 9:41, Jim Candela wrote: > > Gents, > >Bill wrote "It was real hard to count on a "new" tube working in an >old set". > > My reply: I can remember the mid 1970's where it seemed like 80% of > RCA 6GH8's had heater cathode leakage right out of the box. The 6U8, > or 6EA8 seemed like a better tube for whatever reason. And it was really bad when the RCA TV's of that era before the CTC-46 first solid state one ...well that had a WHOLE bunch of 6GH8's! Powell
Re: [AMRadio] Testing tubes
When I started working at a local TV shop in Senior H.S. in the late 60's, we had the 6000A Hickok tester and my boss said it wasn't how good the tubes tested as long as they worked in the set. That tester was one of the best for shorts and leakage indication I have ever worked with. I would not doubt some receiver problems are caused by the decline in tube quality since then. It's difficult to find any late mfg 6V6's that are reliable in the outputs of receivers like the SX42. I have had the best luck with older used ones and N OLD S myself. 6AU6's and BA6's commonly used in the IF areas have shown the same nature. The older ones seem to last and not develope shorts and leakage as much as the later mfg. Of course we are talking about miniature tubes. I have rarely have had to replace octals in a receiver rebuild but usually most of the Min's have had to go due to shorts and leakage. The 6SN7/6SL7 Octals are though to work and sound much better than their functional replacements,12AU7/12AX7 in audio apps. A subjective statement but one I think we all can agree on as far as the quality of construction. Enjoy, Bill KB3DKS . --- StripMime Report -- processed MIME parts --- multipart/alternative text/plain (text body -- kept) text/html The reason this message is shown is because the post was in HTML or had an attachment. Attachments are not allowed. To learn how to post in Plain-Text go to: http://www.expita.com/nomime.html ---
RE: [AMRadio] Testing tubes
Gents, Bill wrote: "example is in the difference in the sound and behavior of the various versions of the common 5532 and 5534 opamp. Originally a TI device and also Signetics mfg." Comment: Below is a link about modyifing CD players where the op amp after the D-A has a tremendous effect on the perceived audio quality. One explanation is that many op-amps have very noticeable cross over distortion, which becomes more significant as the signal level drops into the lower portion of the available dynamic range. One solution for some op-amps is to use a pull up, or down resistor from the output of the op-amp to a power buss. The idea is to require the output stage to sink, or source a little current to in effect keep only one half of the output running, or to put it in other words: make it act as a single ended amplifier, and therefore no cross over distortion. You will also like the use of tubes following the D-A converter. Neat stuff! Jim WD5JKO The reference here is at the bottom of this web page: http://home.netcom.com/~wa2ise/radios/tubedac.htm Jim candela <[EMAIL PROTECTED]> wrote: Gents, While going through my parallel connected 6L6 heising plate modulator in my Gonset G50, I too ran into gain compression whenever the plate voltage swing went below about 200 volts (had B+ at about 400, and G2 slightly below with a small series R, about 100 ohms). I wanted to maximize the dynamic range of the modulator to get more +/- modulation. In stock form the G50 modulator goes into limiting at about +50, -60 % modulation. Instead of fixing this, Gonset featured it as a high level limiter (that's marketing for you ---MBA's!). I got the + modulation up by running the 6L6's at maximum plate dissipation (decrease cathode resistor on TX, increase it on RX), but the (-) modulation suffered the gain compression prior to clipping. I found something similar to what Patrick did with the 6GH8's. Adding a screen dropping resistor to the paralleled 6L6's seemed to do the trick. It is important to note that keeping the screen unbypassed was key. I found that the symmetry of a sine wave was maintained to about 80% +/- this way. For me a value of 7K was the compromise between maximum power, and max symmetry. Bypassing G2 brought back the asymmetry. My theory here is that whenever the plate voltage got too low (during audio swing), the screen current rose, and progressively took over as the plate; only the plate was connected to the heising reactor (top end) so hence the gain compression. The series R, and unbypassed G2 kept the plate in charge because the screen voltage (instant by instant) stayed below the plate voltage. Maybe this is all hog wash, but heck it works for me! I can see how changing a tube can alter the DC operating point, and this will have an effect on the distortion products of an amplifier, especially if the tube is driven such that the available dynamic range is being used. H. By a changing to a Chinese 12A_7, shift the point, gain compress on one side, and then start writing stories on how wonderful the thing sounds! BTW gain compression on one side can be a valuable tool in a super modulated AM rig.. Regards, Jim -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of [EMAIL PROTECTED] Sent: Wednesday, October 01, 2003 10:24 PM To: amradio@mailman.qth.net Subject: Re: [AMRadio] Testing tubes OK Guys, I forgot I was addressing Radio ops, LOL ! I should have said most Audio tubes. I did real and subjective tests on the standard audio preamp tubes using a Sond Technology 1700 Distortion analyzer and Variable HT and Bias supply several years ago. Since it was just personal interest in finding good sounding tubes I really didn't document anything, just chose the best testing lowest noise tubes then did a subjective listening matchup in my amps. Now the test gear has been in storage since and I am setting it up again to do more advanced and documented testing including square wave and pulse behavior. Will post some actual figures before too long. But I agree that really there should not be an audible difference within tubes of the same type operating in the same identical voltages. My ears and experience with tube audio tell a different story tho and I also would like to see why there are noticable fidelity differences in various types of plate structure and mfg. I have a few suspicions that some of the difference may be caused by a change in plate resistance caused by differences in cathode composition, quality of mfg., and deterioration which would explain why NOS from the "Glory Days" of tube mfg. seem to hold up the best and are the most consistent. An interesting example is the now no longer available China Mfg 12AX7's that were highly regarded in audio but when used in guitar amplifiers for a year would still test almost as new but would be so dead sounding they were useless.
Re: [AMRadio] Testing tubes
Gents, Bill wrote "It was real hard to count on a "new" tube working in an old set". My reply: I can remember the mid 1970's where it seemed like 80% of RCA 6GH8's had heater cathode leakage right out of the box. The 6U8, or 6EA8 seemed like a better tube for whatever reason. Jim [EMAIL PROTECTED] wrote:In a message dated 10/2/03 9:33:13 AM Eastern Daylight Time, [EMAIL PROTECTED] writes: > I agree with Larry if for no other reason than this: considering the > bulk of tubes out there now (NOS and used) are of 20+ year manufacture > dates, how can the great response heard in so many fine receivers be > explained? Why also would the audiophools be paying so much for old > tubes, Amperex, Phillips, or otherwise, if the high end response was > somehow 'softened'? What is the mechanism for somehow attenuating > amplification in the same tube that would somehow pass all other > frequencies just fine, and why? Tuned Mechanical Plate filtering? If a > tube loses anything like this over the years, I'd suspect it would be > across the board myself. I'll even back that up with an equal amount of > proof and expertise as that given to support the 'softened highs' theory. > > OTOH, it *is* true that humans tend to lose their high frequency hearing > first compared to the rest of their aural range. Maybe the golden ear > crowd is looking to blame those poor old tubes for the inevitable > evolution of golden ears to tin? > > It's not the age of mfg. it's the quality. The older tubes hold up better and exibit less of the loss problems. I think we all are aware that at one time there was a real quality control but as the market for tubes dropped off the mfg's loosened that and in the end of American production only the Mil really had any QC. Ask anyone in the TV service business at the time. It was real hard to count on a "new" tube working in an old set. Respectfully, Bill KB3DKS --- StripMime Report -- processed MIME parts --- multipart/alternative text/plain (text body -- kept) text/html The reason this message is shown is because the post was in HTML or had an attachment. Attachments are not allowed. To learn how to post in Plain-Text go to: http://www.expita.com/nomime.html --- ___ AMRadio mailing list AMRadio@mailman.qth.net http://mailman.qth.net/mailman/listinfo/amradio --- StripMime Report -- processed MIME parts --- multipart/alternative text/plain (text body -- kept) text/html The reason this message is shown is because the post was in HTML or had an attachment. Attachments are not allowed. To learn how to post in Plain-Text go to: http://www.expita.com/nomime.html ---
Re: [AMRadio] Testing tubes
In a message dated 10/2/03 9:33:13 AM Eastern Daylight Time, [EMAIL PROTECTED] writes: > I agree with Larry if for no other reason than this: considering the > bulk of tubes out there now (NOS and used) are of 20+ year manufacture > dates, how can the great response heard in so many fine receivers be > explained? Why also would the audiophools be paying so much for old > tubes, Amperex, Phillips, or otherwise, if the high end response was > somehow 'softened'? What is the mechanism for somehow attenuating > amplification in the same tube that would somehow pass all other > frequencies just fine, and why? Tuned Mechanical Plate filtering? If a > tube loses anything like this over the years, I'd suspect it would be > across the board myself. I'll even back that up with an equal amount of > proof and expertise as that given to support the 'softened highs' theory. > > OTOH, it *is* true that humans tend to lose their high frequency hearing > first compared to the rest of their aural range. Maybe the golden ear > crowd is looking to blame those poor old tubes for the inevitable > evolution of golden ears to tin? > > It's not the age of mfg. it's the quality. The older tubes hold up better and exibit less of the loss problems. I think we all are aware that at one time there was a real quality control but as the market for tubes dropped off the mfg's loosened that and in the end of American production only the Mil really had any QC. Ask anyone in the TV service business at the time. It was real hard to count on a "new" tube working in an old set. Respectfully, Bill KB3DKS --- StripMime Report -- processed MIME parts --- multipart/alternative text/plain (text body -- kept) text/html The reason this message is shown is because the post was in HTML or had an attachment. Attachments are not allowed. To learn how to post in Plain-Text go to: http://www.expita.com/nomime.html ---
RE: [AMRadio] Testing tubes: Cathode Interface
Could this be a form of cathode interface problem? Cathode interface is a problem sometimes seen when old tubes are used in scope vertical amplifiers with fast risetimes. Something happens to the tubes that causes the actual rise time to deteriorate as the tubes age. The "something" that happens is called cathode interface. I have observed this effect personally on old Tek scopes so I know it is real and apparently widely recognized. But I don't know if anyone has done any work to see if cathode interface has an impact in other tube applications like audio amplifiers. Anyway, I just thought I'd throw that idea into the discussion. I am no expert and my ears prefer solid state audio. 73, Don Merz, N3RHT -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of Todd Bigelow - PS Sent: Thursday, October 02, 2003 9:25 AM To: amradio@mailman.qth.net Subject: Re: [AMRadio] Testing tubes Larry Szendrei wrote: >Bill sez: > > >>All tubes tend to loose high frequency tone with age. Kind of a softening of >>the high frq. response. But will still test good in a >>standard tester that uses line frq.as a signal source. >>The exception is the Weston testers which use an internal >>osc. at 5 khz which gives a more realistic test of the sound of >>the tube. >> >> > >and Larry respecfully sez: >I have a heard time swallowing this one. If tubes lose gain at the >higher audio feqs. with age, it then follows they'll stop amplifying RF >a heck of a lot sooner. I've never observed either phenomenon. > >But I'd be happy to be proven wrong with some hard data. :>) > >-Larry/NE1S > I agree with Larry if for no other reason than this: considering the bulk of tubes out there now (NOS and used) are of 20+ year manufacture dates, how can the great response heard in so many fine receivers be explained? Why also would the audiophools be paying so much for old tubes, Amperex, Phillips, or otherwise, if the high end response was somehow 'softened'? What is the mechanism for somehow attenuating amplification in the same tube that would somehow pass all other frequencies just fine, and why? Tuned Mechanical Plate filtering? If a tube loses anything like this over the years, I'd suspect it would be across the board myself. I'll even back that up with an equal amount of proof and expertise as that given to support the 'softened highs' theory. OTOH, it *is* true that humans tend to lose their high frequency hearing first compared to the rest of their aural range. Maybe the golden ear crowd is looking to blame those poor old tubes for the inevitable evolution of golden ears to tin? Hey Larry - you planning to be at HossTraders? de Todd/'Boomer' KA1KAQ ___ AMRadio mailing list AMRadio@mailman.qth.net http://mailman.qth.net/mailman/listinfo/amradio DISCLAIMER: The information contained in this e-mail may be confidential and is intended solely for the use of the named addressee. Access, copying or re-use of the e-mail or any information contained therein by any other person is not authorized. If you are not the intended recipient please notify us immediately by returning the e-mail to the originator.(A)
Re: [AMRadio] Testing tubes
In a message dated 10/2/03 7:45:41 AM Eastern Daylight Time, [EMAIL PROTECTED] writes: > I can see how changing a tube can alter the DC operating point, and > this > will have an effect on the distortion products of an amplifier, especially > if the tube is driven such that the available dynamic range is being used. > H. By a changing to a Chinese 12A_7, shift the point, gain compress on > one side, and then start writing stories on how wonderful the thing sounds! > > BTW gain compression on one side can be a valuable tool in a super > modulated AM rig.. > > Regards, > Jim > Yep,that's exactly the desired effect in guitar amps which yields increased note sustain and harmonic enrichment. I can see how the asymetrical soft clipping could be used in the proper phase for supermod. with little circuit modification. That's kind of the point of the whole discussion here. It's not so much how a tube or circuit behaves when within it's textbook operating conditions, it's when they are exceeded that the different characteristics show up. Most evident in power output ratings and clip points being dependent on the power supplys dynamic range. Max out the supply with your final current and there will be less available for the modulator. Usually the preceding audio and osc stages have a seperate supply so are not effected. I have heard FMing on quite a few of the smaller transmitters when pushed hard on their own. In Hi Fi tube gear with barely adequate common supplies that point is extremely critical since the linear operating point will be changed in several places in the circuit with supply sag and recovery. Enjoy, Bill KB3DKS --- StripMime Report -- processed MIME parts --- multipart/alternative text/plain (text body -- kept) text/html The reason this message is shown is because the post was in HTML or had an attachment. Attachments are not allowed. To learn how to post in Plain-Text go to: http://www.expita.com/nomime.html ---
Re: [AMRadio] Testing tubes
Larry Szendrei wrote: Bill sez: All tubes tend to loose high frequency tone with age. Kind of a softening of the high frq. response. But will still test good in a standard tester that uses line frq.as a signal source. The exception is the Weston testers which use an internal osc. at 5 khz which gives a more realistic test of the sound of the tube. and Larry respecfully sez: I have a heard time swallowing this one. If tubes lose gain at the higher audio feqs. with age, it then follows they'll stop amplifying RF a heck of a lot sooner. I've never observed either phenomenon. But I'd be happy to be proven wrong with some hard data. :>) -Larry/NE1S I agree with Larry if for no other reason than this: considering the bulk of tubes out there now (NOS and used) are of 20+ year manufacture dates, how can the great response heard in so many fine receivers be explained? Why also would the audiophools be paying so much for old tubes, Amperex, Phillips, or otherwise, if the high end response was somehow 'softened'? What is the mechanism for somehow attenuating amplification in the same tube that would somehow pass all other frequencies just fine, and why? Tuned Mechanical Plate filtering? If a tube loses anything like this over the years, I'd suspect it would be across the board myself. I'll even back that up with an equal amount of proof and expertise as that given to support the 'softened highs' theory. OTOH, it *is* true that humans tend to lose their high frequency hearing first compared to the rest of their aural range. Maybe the golden ear crowd is looking to blame those poor old tubes for the inevitable evolution of golden ears to tin? Hey Larry - you planning to be at HossTraders? de Todd/'Boomer' KA1KAQ
RE: [AMRadio] Testing tubes
Gents, While going through my parallel connected 6L6 heising plate modulator in my Gonset G50, I too ran into gain compression whenever the plate voltage swing went below about 200 volts (had B+ at about 400, and G2 slightly below with a small series R, about 100 ohms). I wanted to maximize the dynamic range of the modulator to get more +/- modulation. In stock form the G50 modulator goes into limiting at about +50, -60 % modulation. Instead of fixing this, Gonset featured it as a high level limiter (that's marketing for you ---MBA's!). I got the + modulation up by running the 6L6's at maximum plate dissipation (decrease cathode resistor on TX, increase it on RX), but the (-) modulation suffered the gain compression prior to clipping. I found something similar to what Patrick did with the 6GH8's. Adding a screen dropping resistor to the paralleled 6L6's seemed to do the trick. It is important to note that keeping the screen unbypassed was key. I found that the symmetry of a sine wave was maintained to about 80% +/- this way. For me a value of 7K was the compromise between maximum power, and max symmetry. Bypassing G2 brought back the asymmetry. My theory here is that whenever the plate voltage got too low (during audio swing), the screen current rose, and progressively took over as the plate; only the plate was connected to the heising reactor (top end) so hence the gain compression. The series R, and unbypassed G2 kept the plate in charge because the screen voltage (instant by instant) stayed below the plate voltage. Maybe this is all hog wash, but heck it works for me! I can see how changing a tube can alter the DC operating point, and this will have an effect on the distortion products of an amplifier, especially if the tube is driven such that the available dynamic range is being used. H. By a changing to a Chinese 12A_7, shift the point, gain compress on one side, and then start writing stories on how wonderful the thing sounds! BTW gain compression on one side can be a valuable tool in a super modulated AM rig.. Regards, Jim -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of [EMAIL PROTECTED] Sent: Wednesday, October 01, 2003 10:24 PM To: amradio@mailman.qth.net Subject: Re: [AMRadio] Testing tubes OK Guys, I forgot I was addressing Radio ops, LOL ! I should have said most Audio tubes. I did real and subjective tests on the standard audio preamp tubes using a Sond Technology 1700 Distortion analyzer and Variable HT and Bias supply several years ago. Since it was just personal interest in finding good sounding tubes I really didn't document anything, just chose the best testing lowest noise tubes then did a subjective listening matchup in my amps. Now the test gear has been in storage since and I am setting it up again to do more advanced and documented testing including square wave and pulse behavior. Will post some actual figures before too long. But I agree that really there should not be an audible difference within tubes of the same type operating in the same identical voltages. My ears and experience with tube audio tell a different story tho and I also would like to see why there are noticable fidelity differences in various types of plate structure and mfg. I have a few suspicions that some of the difference may be caused by a change in plate resistance caused by differences in cathode composition, quality of mfg., and deterioration which would explain why NOS from the "Glory Days" of tube mfg. seem to hold up the best and are the most consistent. An interesting example is the now no longer available China Mfg 12AX7's that were highly regarded in audio but when used in guitar amplifiers for a year would still test almost as new but would be so dead sounding they were useless. I will include some of those that I still have in my testing. A little non tube issue but similiar. Published spec and actual real world function of many devices do not necessarily agree with each other as a verifiable example is in the difference in the sound and behavior of the various versions of the common 5532 and 5534 opamp. Originally a TI device and also Signetics mfg. I have yet to find a currently made version from EXAR, NEC, etc that exibits the same characteristics in regards to output impedance and current capability, i.e. sound. Even tho these are "supposed" to be the same device. Sorry for the subjective length of this but I will follow up with hard data as soon as I can derive it. Thanks for listening ! Bill KB3DKS --- StripMime Report -- processed MIME parts --- multipart/alternative text/plain (text body -- kept) text/html The reason this message is shown is because the post was in HTML or had an attachment. Attachments are not allowed. To learn how to post in Plain-Text go to: http://www.expita.com/nomime.html --- _
Re: [AMRadio] Testing tubes
OK Guys, I forgot I was addressing Radio ops, LOL ! I should have said most Audio tubes. I did real and subjective tests on the standard audio preamp tubes using a Sond Technology 1700 Distortion analyzer and Variable HT and Bias supply several years ago. Since it was just personal interest in finding good sounding tubes I really didn't document anything, just chose the best testing lowest noise tubes then did a subjective listening matchup in my amps. Now the test gear has been in storage since and I am setting it up again to do more advanced and documented testing including square wave and pulse behavior. Will post some actual figures before too long. But I agree that really there should not be an audible difference within tubes of the same type operating in the same identical voltages. My ears and experience with tube audio tell a different story tho and I also would like to see why there are noticable fidelity differences in various types of plate structure and mfg. I have a few suspicions that some of the difference may be caused by a change in plate resistance caused by differences in cathode composition, quality of mfg., and deterioration which would explain why NOS from the "Glory Days" of tube mfg. seem to hold up the best and are the most consistent. An interesting example is the now no longer available China Mfg 12AX7's that were highly regarded in audio but when used in guitar amplifiers for a year would still test almost as new but would be so dead sounding they were useless. I will include some of those that I still have in my testing. A little non tube issue but similiar. Published spec and actual real world function of many devices do not necessarily agree with each other as a verifiable example is in the difference in the sound and behavior of the various versions of the common 5532 and 5534 opamp. Originally a TI device and also Signetics mfg. I have yet to find a currently made version from EXAR, NEC, etc that exibits the same characteristics in regards to output impedance and current capability, i.e. sound. Even tho these are "supposed" to be the same device. Sorry for the subjective length of this but I will follow up with hard data as soon as I can derive it. Thanks for listening ! Bill KB3DKS --- StripMime Report -- processed MIME parts --- multipart/alternative text/plain (text body -- kept) text/html The reason this message is shown is because the post was in HTML or had an attachment. Attachments are not allowed. To learn how to post in Plain-Text go to: http://www.expita.com/nomime.html ---
Re: [AMRadio] Testing tubes
Bill sez: > All tubes tend to loose high frequency tone with age. Kind of a softening of > the high frq. response. But will still test good in a > standard tester that uses line frq.as a signal source. > The exception is the Weston testers which use an internal > osc. at 5 khz which gives a more realistic test of the sound of > the tube. and Larry respecfully sez: I have a heard time swallowing this one. If tubes lose gain at the higher audio feqs. with age, it then follows they'll stop amplifying RF a heck of a lot sooner. I've never observed either phenomenon. But I'd be happy to be proven wrong with some hard data. :>) -Larry/NE1S
RE: [AMRadio] Testing tubes
Bill, I liked your response very much. I few questions do come to mind however. Many an audiophile will make statements about "sounds warm", or a "little tinny", etc. I was wondering about your statement about "losing high frequency tone with age." Is there a way to quantify this with test equipment, or is this one of those things left to the listener of a home audio system to judge for themselves? I can see for example on a scope when a triode isn't biased correctly, the AC sine wave as it starts to fill out the available dynamic range will compress more on one side than the other. You might say that the peak to average ratio of a pure sinusoidal waveform is being altered each 1/2 cycle, and in terms of distortion products, a rise in even order distortion products. The listener may then start using all kinds of catchy phrases praising the quality of the sound, etc. while advocating the use of Teflon insulated wire, and $100.00 / pair RCA to RCA cables, etc. I guess I am trying to get at a way to sift through the "bull", and quantify the merits of one circuit versus another, and maybe even a given circuit with one tube brand or another (all the same type, i.e. 12AX7). I was warned by one audiophile that a tube like the 12AT7 which is in current production today for audio use may not work in a RF circuit like a TV tuner where a old NOS 12AT7 works fine. If true, that means that the standards for manufacturing a given tube type have been violated in recent years. Things like interelectrode capacitance, and tube interconnection paths / lengths may not be constrained like they used to be. I have a "Realistic Lifetime" 12AX7 that I just put into my Sherwood S8000 amplifier. It has gold colored pins (really gold?), and says it is made in Poland. It too warms up with a brilliant glow that is brief in duration. I wonder if the inrush current may be too high, and if ramping the filament up in a soft start circuit may be of any benefit? You also say "All tubes tend to loose high frequency tone with age." Going to say 20,000 cycles / second for most any tube should be no big deal. So what do you think happens with aging tubes? Is it the cathode oxide changing every 1000 hours or so, or is it a rise in Miller capacitance due to some mechanism of tube aging? Also consider that many a tube amplifier with 12AX7's use DC on the low level stages, and sometimes less than 12.6/6.3 volts to heat these tubes. My Fisher X-101-B amplifier for example runs 4 seriesed 12AX7 filaments as the cathode resistor for the 7591A output tubes, and the cathode voltage is set to 40 volts. That means 10 volts per 12AX7 filament (if they share evenly). Maybe a situation like this where the tube is "emission starved" will show a degradation in emission with rising frequency? Sorry for all the commentary, but with me a nerve is struck whenever I hear the catchy phrases that often come from a audiophile peddling some form of "snake oil" to line their wallets with...I prefer a technical explanation for things which means taking the subjectivity out of the equation. PS Still looking for a "live one" to buy my pair of Genelax "Gold Lion" pair of KT-77's. First $250.00 takes them. Very rare, best sounding EL34 out there with such magnificence in the sound that is indescribable in the purest of tunes. listening to an amplifier with these tubes will bring tears to your eyes, and thereafter no other amplifier will even begin to sound the same I bought a Gonset G50 from Ebay for $43.00, and the KT77's were in there as modulators in place of 6L6's! Big surprise! Regards, Jim Candela WD5JKO -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of [EMAIL PROTECTED] Sent: Monday, September 29, 2003 6:46 PM To: amradio@mailman.qth.net Subject: Re: [AMRadio] Testing tubes Gentlemen, If you look at the mfg. of the tubes that light up like that you will probably find that they are Telefunken or Amperex (Holland). While not all tubes labeled such will have that characteristic that does indicate they were made in the same facility regardles of label. I don't remember the exact reason for the momentary incandescence but believe it has to do with the construction of the filament from that Mfg. It's actually a good sign since that type are regarded highly by the audio world. As for the offscale readings... check the tester calibration as "new" tubes readings will depend on the mfg. and year made. I have quite a few new Phillips/ECG late production 12AX7's that do not test close to what a NOS RCA or GE, or even some of the used Mullards do. My Cardamatic, the WE ,KS series version of the Hikock 123A tests 12AX7's with a different card than ECC83's in that the bias is slightly different. Actually the parameters of the
Re: [AMRadio] Testing tubes
Gentlemen, If you look at the mfg. of the tubes that light up like that you will probably find that they are Telefunken or Amperex (Holland). While not all tubes labeled such will have that characteristic that does indicate they were made in the same facility regardles of label. I don't remember the exact reason for the momentary incandescence but believe it has to do with the construction of the filament from that Mfg. It's actually a good sign since that type are regarded highly by the audio world. As for the offscale readings... check the tester calibration as "new" tubes readings will depend on the mfg. and year made. I have quite a few new Phillips/ECG late production 12AX7's that do not test close to what a NOS RCA or GE, or even some of the used Mullards do. My Cardamatic, the WE ,KS series version of the Hikock 123A tests 12AX7's with a different card than ECC83's in that the bias is slightly different. Actually the parameters of the 5751 and ECC83 are the same. All tubes tend to loose high frequency tone with age. Kind of a softening of the high frq. response. But will still test good in a standard tester that uses line frq.as a signal source. The exception is the Weston testers which use an internal osc. at 5 khz which gives a more realistic test of the sound of the tube. Beware of most of the Sov. 12AX7's as they tend to be very thin sounding with their small plate structure. IMHO the long plate Euro mfg. or NOS US long plate styles have the best overall tone. Excuse the long reply. Hope it helps. Bill KB3DKS --- StripMime Report -- processed MIME parts --- multipart/alternative text/plain (text body -- kept) text/html The reason this message is shown is because the post was in HTML or had an attachment. Attachments are not allowed. To learn how to post in Plain-Text go to: http://www.expita.com/nomime.html ---
Re: [AMRadio] Testing tubes
Hello Barrie: Barrie Smith escribió: Attempting to discover why an old Luxman tube-preamplifier didn't sound too good, I drug out the Hickok Cardmatic tube-tester this morning. I noticed that 6 of the 7 12AX7s tested off-scale (to the right, above 100). New 12AX7s that I tested ran from 80 to 90 on the scale. Which scale is this?, plate mA, relative performance? Is there a problem with an off-scale reading? There was no indication of leakage or gas in any of the tubes. Also, all of the tubes that tested off-scale had another characteristic: Upon powering them up in the tester, the wires in the base that evidently connect to the cathode lit up bright red to almost white for a short period of time, perhaps a second or two. I have a few of them with the same behaviour, I figure it's because the heater is a very low resistance at startup (cold), and so there's a high inrush current when heater voltage is applied, bringing them nearly white for a short period. These work fine anyway. Good luck Guillermo - LU8EYW. The new tubes that I tested did not exhibit that characteristic. Any thoughts on this subject? 73, Barrie, W7ALW ___ AMRadio mailing list AMRadio@mailman.qth.net http://mailman.qth.net/mailman/listinfo/amradio
