"R. Ton" <[EMAIL PROTECTED]> made an utterance to the drakelist gang ---------------------------------------------------------------------- Garey-
It's sure looking like the tubes, odd as that seems. Here are the readings I'm getting (measured at the tube socket): Pin 1 - 255VDC RX, 247VDC TX Pin 2 - -58 VDC Pin 3 - 155VDC RX, 0VDC TX Pin 4, 5 - Filaments (good - tubes light, get hot, RX works) Pin 6 - -58 VDC (Same as pin 2) Pin 7 - 255VDC RX, 247VDC TX (Same as pin 1) Pin 8 - Ground Plate cap - 748VDC (+/- 1VDC, all 3) Definately agree that all three tubes would have to be open to draw no current, but there doesn't seem to be another explanation. It sure seems odd. Almost impossible, even. You would think that opening the meter shunt resistor would actually protect the tubes -- they were obviously drawing plenty of current when the resistor blew. Not knowing the history of this rig though, it's hard to say. I pulled the tubes -- nothing obvious to be seen there. The above readings were taken after I put the tubes back in. Wish like heck I had a spare set to try, but I now have a set on order. (BTW -- I've never dealt with Antique Electronic Supply - tubesandmore.com before, but if anyone's interested, they have 6JB6A's on 'sale' for $14.60 apiece until 5/14 and claim they'll match them for $1.25 apiece.) A tube sale??? So... unless someone sees something wierd with the voltage readings, I guess I'm waiting on tubes. Oh... also checked the meter switch on the load control -- it ohms out fine. The factory selected resistor (R13) in this rig is 39 ohms. Many thanks again! 73, Rob (KFØRT) > -----Original Message----- > From: Garey Barrell [mailto:[EMAIL PROTECTED] > Sent: Sunday, April 16, 2006 4:45 PM > To: R. Ton > Cc: Drakelist > Subject: Re: [drakelist] TR-4C transmitter troubleshooting > > > Rob - > > I find it hard to believe that ALL three tubes are totally dead, > assuming the filaments are lit! > > First, have you measured the screen voltage on the tubes? Each tube > should have about 250VDC on the screen pin via a 68 ohm, 1W resistor. > > Where are you measuring the plate voltage? Measure at the plate cap of > each tube. > > Again, if there is 750 VDC on the plate cap, 250 VDC on the screen, 0 > VDC on the grid and 0 VDC at the cathode, each one of those tubes would > draw over an amp of cathode current. To control this current, you > apply a negative voltage to the grid, and typically ~ -55 VDC should > limit that current to ~ 30 mA. IF these conditions are met at the tube > pins, then the only remaining answer is three completely open tubes, > which I still find hard to comprehend. The three tubes are in parallel, > so if any one of them is even slightly good, you should see plate current! > > If the cathode PINS are at 0 VDC in transmit, then the RFC, meter shunt > and relay contact are OK. There are two RF chokes in series between the > HV feedthrough under the chassis and the plate caps of all three tubes. > > 73, Garey - K4OAH > Atlanta > > Drake B & C-Line Service CDs > <http://www.k4oah.com> > > > > R. Ton wrote: > > Great idea, Garey... > > > > With my meter set as low as it'll go, I'm showing about 0.3 mV across > > the shunt resistor in transmit. This thing isn't drawing any current > > at all! In receive, I'm getting a cathode voltage of about 155V and > > a plate voltage of about 754V. The 754V plate reading is the same > > as my AC-4 under no load. In transmit, there is no change in plate > > voltage, but the cathode voltage goes to zero. > > > > According to the schematic, the cathodes are grounded via the T/R relay, > > the 2 ohm shunt resistor, an RF choke and a 15 ohm resistor (one 15 > > ohm resistor for each tube). Even through the 15 ohm resistor, I'm > > showing 0V on the cathode in transmit. > > > > Wierd. This would sure seem to indicate that the finals aren't > > conducting at all. Still, very weak on my tube theory here -- > > could a grid condition cause this? I'm showing a good -60V on > > pins 2 and 6. > > > > I was also thinking that a 1 watt, 2 ohm resistor should be able > > to handle about 700ma without cooking. When I got the rig, this > > resistor was burned in half. Maybe it's time to pull the tubes > > and see if anything is rattling around inside? :( > > > > Is my thinking halfway straight? :) Hoping like heck the plate > > current meter isn't shot -- I have a feeling those are hard to > > get. > > > > Thanks again everyone! > > > > 73, Rob (KFØRT) > > > > > > > >> -----Original Message----- > >> From: [EMAIL PROTECTED] > >> [mailto:[EMAIL PROTECTED] Behalf Of Garey Barrell > >> Sent: Sunday, April 16, 2006 9:57 AM > >> To: R. Ton > >> Cc: Drakelist > >> Subject: Re: [drakelist] TR-4C transmitter troubleshooting > >> > >> > >> > >> Garey Barrell <[EMAIL PROTECTED]> made an utterance to the > >> drakelist gang > >> ---------------------------------------------------------------------- > >> Rob - > >> > >> OK, a little more information..... > >> > >> When the 2 ohm meter shunt resistor opens up, the Final cathode current > >> is routed through a "slide switch" mounted up on the LOAD capacitor > >> shaft, (activated by pushing in the LOAD control,) a series resistor > >> that is selected at test, (mounted on the slide switch terminals,) of > >> typically ~200 ohms, and the plate meter. It wouldn't take much > >> current to damage that resistor and/or meter with the shunt resistor > >> open. Or if the slide switch contacts are not closing properly in the > >> "out" position of the LOAD control. > >> > >> Perhaps your finals are drawing idle current, it's just not showing on > >> the meter!? Measure the voltage drop across the meter shunt resistor. > >> 100 mA should read 200 mV. > >> > >> By the way, if you're not used to working on tube gear, keep in mind > >> that 650V (OR 250v) BITES! An AC-4 bleeds down pretty quickly when > >> turned off, but only your meter knows for sure before you stick your > >> fingers in there! > >> > >> 73, Garey - K4OAH > >> Atlanta > >> > >> Drake B & C-Line Service CDs > >> <http://www.k4oah.com> > >> > >> > >> > >> R. Ton wrote: > >> > >>> Thanks to all (!!) -- more coming when I get a chance (life is > >>> > >> getting in > >> > >>> the way of fun right now). > >>> > >>> So far, I've had the chance to change out the relay -- the ONE > >>> > >> spare part > >> > >>> I had on hand. No difference. The rig does go into transmit > >>> > >> when switched > >> > >>> to CW mode (no key plugged in). Both relays respond and the > >>> > >> receiver mutes. > >> > >>> I just noticed this AM that the .025 plate current reading I > >>> > >> get is there > >> > >>> even with the power off. Meter moves about a needle's width > >>> > >> when put into > >> > >>> transmit and the S-meter reads about 7-8 in transmit -- may be > >>> > >> another clue? > >> > >>> And thanks for the hollow-state theory Garey. It's been a > >>> > >> REALLY long time > >> > >>> since I've worked on any tube gear, but it's slowly coming back > >>> > >> to me. :) > >> > >>> I'll be digging some more in a bit here and will report back. > I'll also > >>> see if I can catch the technical net this afternoon. 7.238 @ > >>> > >> 2000Z, right? > >> > >>> Thanks again everyone! > >>> > >>> 73, Rob (KFØRT) > >>> > >>> > >>> > >>>> -----Original Message----- > >>>> From: [EMAIL PROTECTED] > >>>> [mailto:[EMAIL PROTECTED] Behalf Of Garey Barrell > >>>> Sent: Sunday, April 16, 2006 8:41 AM > >>>> To: Drakelist > >>>> Subject: Re: [drakelist] TR-4C transmitter troubleshooting > >>>> > >>>> > >>>> > >>>> Garey Barrell <[EMAIL PROTECTED]> made an utterance to the > >>>> drakelist gang > >>>> > ---------------------------------------------------------------------- > >>>> Hi Kevin - > >>>> > >>>> Expertise is just experience clouded by memory! :-) > >>>> > >>>> I don't think I've ever come across a PAIR of finals that > "lit up", but > >>>> wouldn't draw at least a couple hundred mA if they had the DC > >>>> > >> potentials > >> > >>>> applied to them. In fact, I can only remember one tube that > >>>> > >> was "open", > >> > >>>> but lit. I still think it had a broken weld inside it!! :-) > >>>> > >>>> But then I've been wrong before. A favorite med school phrase, "when > >>>> you hear hoof beats, think horses, not zebras" comes to mind! > >>>> > >>>> Hopefully Rob will get it fixed in spite of my help and let > us know the > >>>> truth!! > >>>> > >>>> 73, Garey - K4OAH > >>>> Atlanta > >>>> > >>>> Drake B & C-Line Service CDs > >>>> <http://www.k4oah.com> > >>>> > >>>> > >>>> > >>>> kbgluxford wrote: > >>>> > >>>> > >>>>> kbgluxford <[EMAIL PROTECTED]> made an utterance to > the drakelist > >>>>> gang > >>>>> > ---------------------------------------------------------------------- > >>>>> I certainly don't have Garey's expertise or long > experience, but I did > >>>>> have a similar problem on one of my TX4 transmitters recently. I > >>>>> changed out the PA tubes and the problem disappeared. > >>>>> > >>>>> 73 > >>>>> Kevin > >>>>> VK3DAP / ZL2DAP > >>>>> > >>>>> Garey Barrell wrote: > >>>>> > >>>>> > >>>>>> Garey Barrell <[EMAIL PROTECTED]> made an utterance to the > >>>>>> drakelist gang > >>>>>> > >>>>>> > >> ---------------------------------------------------------------------- > >> > >>>>>> Rob - > >>>>>> > >>>>>> You don't mention anything about "keying" the transmitter. > You have > >>>>>> to "key" the Push-To-Talk (PTT) of the microphone to switch it to > >>>>>> transmit to see the idling plate current. You should hear > the relay > >>>>>> click when it closes. > >>>>>> > >>>>>> If the final tubes have plate voltage, screen voltage and filament > >>>>>> voltage, and the cathodes are returned to the negative > pole of those > >>>>>> supplies, they WILL draw plate current! The grid voltage is the > >>>>>> only thing that keeps them from drawing AMPS of current in the > >>>>>> presence of the other voltages. > >>>>>> > >>>>>> There are two RF chokes in series between the +650VDC > supply and the > >>>>>> plate caps of the tubes. There is a 15 ohm, 1W resistor in series > >>>>>> with each of the final tube cathodes to another RF choke, > through the > >>>>>> meter shunt resistor, and then through a relay contact to ground. > >>>>>> > >>>>>> 73, Garey - K4OAH > >>>>>> Atlanta > >>>>>> > >>>>>> Drake B & C-Line Service CDs > >>>>>> <http://www.k4oah.com> > >>>>>> > >>>>>> > >>>>>> > >>>>>> R. Ton wrote: > >>>>>> > >>>>>> > >>>>>>> "R. Ton" <[EMAIL PROTECTED]> made an utterance to the > drakelist gang > >>>>>>> > >>>>>>> > >> ---------------------------------------------------------------------- > >> > >>>>>>> I'm finally digging into a TR-4C I bought used some time ago. It > >>>>>>> "worked > >>>>>>> fine" when it was shipped here, but I haven't been able to get any > >>>>>>> power out > >>>>>>> of the transmitter. It at least oscillates -- I can hear it on a > >>>>>>> receiver > >>>>>>> in the same room. > >>>>>>> > >>>>>>> Starting at the beginning... > >>>>>>> > >>>>>>> The manual says to adjust the bias on the AC-4 so that the plate > >>>>>>> meter reads > >>>>>>> .1 amp. This is with the sideband switch > counter-clockwise and the > >>>>>>> xmtr > >>>>>>> gain all the way down. The meter seems to read about .025 in > >>>>>>> receive and > >>>>>>> goes up just a little when the rig is switched to CW. > Adjusting the > >>>>>>> bias > >>>>>>> has no effect on the plate meter, but it does indeed > adjust the bias > >>>>>>> voltage. Setting it to -60 volts is no problem, but I'm unable to > >>>>>>> get any > >>>>>>> "real" plate current no matter what I do. Any ideas? > >>>>>>> > >>>>>>> I haven't done anything to the radio since I got it > except spray the > >>>>>>> switches with Deoxit D5 and replace R45 (2 ohms -- plate > meter shunt > >>>>>>> resistor!!). This resistor was fried in half. > >>>>>>> > >>>>>>> What am I in for? > >>>>>>> > >>>>>>> Many thanks in advance! > >>>>>>> > >>>>>>> 73, Rob (KFØRT) > >>>>>>> > >>>>>>> > >> ---------------------------------------------------------------------- > >> Submissions: drakelist@www.zerobeat.net > >> Unsubscribe: [EMAIL PROTECTED] - unsubscribe > >> drakelist in body > >> Hopelessly Lost: [EMAIL PROTECTED] - help in body > of message > >> Zerobeat Web Page: www.zerobeat.net - sponsored by www.tlchost.net > >> ---------------------------------------------------------------------- > >> > >> > > > > > > > ---------------------------------------------------------------------- Submissions: drakelist@www.zerobeat.net Unsubscribe: [EMAIL PROTECTED] - unsubscribe drakelist in body Hopelessly Lost: [EMAIL PROTECTED] - help in body of message Zerobeat Web Page: www.zerobeat.net - sponsored by www.tlchost.net ----------------------------------------------------------------------
