Re: [Drakelist] 6JB6 vs.6JB6A
Date: Wed, 29 Sep 2010 20:49:08 -0500 From: Curt rhule...@comcast.net Subject: Re: [Drakelist] 6JB6 vs.6JB6A To: drakelist@zerobeat.net I'll never again buy vacuum tubes off of the internet, after buying from a regular store on the auction site two matched 6JB6s, both soft as pillows and useless above 40M. Of course, everything there is always as-is. I'll also never buy anything from a big tube seller in Florida who is a small-time liar and crook. Only bonafide companies for me, the products are no more expensive, and at least its a big outfit ripping me off. Good to know that a 6GJ5 is equal to a 6JB6, surprised had never read that before. Unfortunately, maybe most tubes sold are pretty much worn out. Even most of the companies selling tubes draw the line at providing much warranty for sweep tubes ( 10 days conditional from the outfit I use a lot ). Curt KB5JO -- A 6GJ5 is not quite equivalent to a 6JB6. There is a pin difference. That caused problems with National transceivers such as the NCX-5 and the NCX-3 that used 6GJ5's. The 6GJ5 internally ties its suppressor grid to the cathode, the 6JB6 does not. The Nationals used one base pin as a tie point, that had to be separated out when tube types were swapped. Since I don't know how the Drakes are wired, I'm not sure if a similar problem exists. There are other minor differences between the tubes. 73, Doug/WA1TUT ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] 6JB6 vs.6JB6A
Hi Doug Yes, as I mentioned, there is no effect in the Drake transmitter. To quote Garey some years ago: NO modifications are needed to either the T-4(any) or the TR-4(any) to use the 6GJ5s. Pin 3 in the Drake 4 Line transmitters is the cathode of the final tubes. Pin 8 in the transmitters is grounded at the socket. With 6JB6s, K is connected internally to Pin 3, and G3 is connected internally to Pin 8. With 6GJ5s, K AND G3 are connected internally to Pin 3, AND there is _NO_ connection to Pin 8. So everything works the same, except G3 is connected directly to K rather than via a 15 ohm and 3.3 ohm resistor. The only difference is the interelectrode capacitance, which is small enough (0.5 pF) that the neutralization circuit is able to take care of it. I stocked a lifetime supply of these tubes NOS at $2 and $3 ea some years ago.and they are to me, indistinguishable from the JB6s. John k5mo At 02:25 AM 9/30/2010, Douglas wrote: Date: Wed, 29 Sep 2010 20:49:08 -0500 From: Curt rhule...@comcast.net Subject: Re: [Drakelist] 6JB6 vs.6JB6A To: drakelist@zerobeat.net I'll never again buy vacuum tubes off of the internet, after buying from a regular store on the auction site two matched 6JB6s, both soft as pillows and useless above 40M. Of course, everything there is always as-is. I'll also never buy anything from a big tube seller in Florida who is a small-time liar and crook. Only bonafide companies for me, the products are no more expensive, and at least its a big outfit ripping me off. Good to know that a 6GJ5 is equal to a 6JB6, surprised had never read that before. Unfortunately, maybe most tubes sold are pretty much worn out. Even most of the companies selling tubes draw the line at providing much warranty for sweep tubes ( 10 days conditional from the outfit I use a lot ). Curt KB5JO -- A 6GJ5 is not quite equivalent to a 6JB6. There is a pin difference. That caused problems with National transceivers such as the NCX-5 and the NCX-3 that used 6GJ5's. The 6GJ5 internally ties its suppressor grid to the cathode, the 6JB6 does not. The Nationals used one base pin as a tie point, that had to be separated out when tube types were swapped. Since I don't know how the Drakes are wired, I'm not sure if a similar problem exists. There are other minor differences between the tubes. 73, Doug/WA1TUT ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] 6JB6 vs.6JB6A
I own a few pairs of 6GJ5's, one pair is too high to fit into the 4-line PA compartment. Neither set of tubes would neutralize in a T-4XC. I havent tried adding or removing capacitance to the neutalizing trimmer to see if I could get them to work. Just a heads up. 73, Gary ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] 6JB6 vs.6JB6A
Gary - I have run into the size problem also. The RCA manual specifies outline 18A and 32 for the 6GJ5 and 6GJ5A respectively. As discussed yesterday, I have also seen 6JB6(A) that were too tall, but not of the 'four' brands. Do you have a transmitter open where you can measure the ACTUAL internal height of the cage. I've done it before, but can't find the info. I have NOT run into the failure to neutralize though, but I stick to the 'four'. Some 6JB6(A) of off brands will not neutralize, and I assume the GJ's that fail are made by the same manufacturer! It's perhaps possible to neutralize these by adding or subtracting the neutralizing capacitance, but I figure if they need that, then there may well be something else that could cause trouble later. Bottom line is these are 15 kHz tubes, NOT 30 MHz tubes.! 73, Garey - K4OAH Glen Allen, VA Drake 2-B, 2-C/2-NT, 4-B, C-Line TR-4/C Service Supplement CDs www.k4oah.com Gary Poland wrote: I own a few pairs of 6GJ5's, one pair is too high to fit into the 4-line PA compartment. Neither set of tubes would neutralize in a T-4XC. I havent tried adding or removing capacitance to the neutalizing trimmer to see if I could get them to work. Just a heads up. 73, Gary ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] 6JB6 vs.6JB6A
Hello! Just to complicate a bit more this subject ;-), some years ago I worked on a TR-4C which had 6JM6 tubes on it. You can read about that here: http://jvgavila.com/dktr4c_1.htm They had a professional-looking adaptor on their bases but, definitely, worked. And were labeled as 6JB6A! So it seems that, with some imagination, you can get a Drake transmitter working with slightly different tubes. Of course, I would stick with 6JB6 while they last. Regards, JOSE -- 73 EB5AGV - JOSE V. GAVILA - IM99sm La Canyada - Valencia(SPAIN) Vintage Radio and Test Equipment... http://jvgavila.com RadioRepair BLOG... http://radiorepair.blogspot.com ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] 6JB6 vs.6JB6A
I have both, a BK emisions tester and a Hickok 6000A transconductance tester. The emisions tester is useless for testing 6JB6's beyond shorts or open filaments. Over the years I kept most of the 6JB6 pulls from my Drakes and others I repaired. With the Hickok I was able to go through them and pickout the ones with some life left and match them up. Its amazing how unevenly some pairs ( or three's ) aged and weakened. I suggest you buy tubes from RF Parts, Antique Radio Supply, Tube Depot, or SND. Do not buy used 6JB6's. 73, Gary___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] 6JB6 vs.6JB6A
?A comment regarding the height of various tube brands: A few years back, I bought a new set of 6550 finals for a CE 100V transmitter I was restoring. Unfortunately, they were too tall for the final cage. When I called the company I bought them from (Antique Electronic Supply in Arizona), they were extremely helpful and called me back after measuring the height of each of the various brands of 6550s they had in stock. Only one of the current manufacturers (Svetlana at that time) had the same height as the original tubes and AES happily exchanged my tubes for a pair of those. So, if you have problems with the physical size of any tube substitutes, it may be worth a call to AES to see if they have a brand that will fit. 73, Floyd - K8AC - Original Message - From: Garey Barrell k4...@mindspring.com To: drakelist Drakelist@zerobeat.net Sent: Thursday, September 30, 2010 9:10 AM Subject: Re: [Drakelist] 6JB6 vs.6JB6A Gary - I have run into the size problem also. The RCA manual specifies outline 18A and 32 for the 6GJ5 and 6GJ5A respectively. As discussed yesterday, I have also seen 6JB6(A) that were too tall, but not of the 'four' brands. Do you have a transmitter open where you can measure the ACTUAL internal height of the cage. I've done it before, but can't find the info. I have NOT run into the failure to neutralize though, but I stick to the 'four'. Some 6JB6(A) of off brands will not neutralize, and I assume the GJ's that fail are made by the same manufacturer! It's perhaps possible to neutralize these by adding or subtracting the neutralizing capacitance, but I figure if they need that, then there may well be something else that could cause trouble later. Bottom line is these are 15 kHz tubes, NOT 30 MHz tubes.! 73, Garey - K4OAH Glen Allen, VA ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] 6JB6 vs.6JB6A
6JB6's can be matched with a Drake transmitter. Set the bias on the AC-4 and leave it be. Then measure the voltage drop across each cathode resistor with the PTT keyed, no mic. Use ohms law to figure the current of each tube. You probably would want to check the resistance of each cathode resistor first. 73, Gary___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] 6JB6 vs.6JB6A
Garey, A TR-4 PA cage ( without the top cover installed ) is 3 3/8 inches tall. I have had good luck with GE's, Zenith, RCA, and Sylvania's of course. I hadn't seen any that were too tall, at least not yet, HI HI. The 6GJ5's are worth a try if you can find they cheap. I have a few that came from hamfest tube caddies. No one had grabbed them thinking they were of no use. Most tube caddies are picked through before I get to them. 73, Gary ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] 6JB6 vs.6JB6A
Yes, I really should do that, John. Bob was a Collins engineer and had many interesting experiences. I'll put that on the to do list. 73, Don, WB5HAK___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
[Drakelist] 6JB6 vs.6JB6A
Boy that was the first time I posted to the list. Thanks for all the info Mike, KB1EZL ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] 6JB6 vs.6JB6A
Many years ago, just before Drake stopped accepting TR-4 s for repair, my neighbor, WA5VGO sent his TR-4 to Drake for some repair. The radio came back with three different final tubes then when shipped to Drake. One of the three new tubes was as you described. A sweep tube with a printed circuit on the bottom changing the pin out of the tube. I don't know if it was a 6JM6 or not. However, the tube was put in there by Drake. Also, the three new tubes were taller then original and Drake had dimpled the top tube cage cover to accommodate the extra height of the new tubes. Strange indeed, but the radio worked just fine with these tubes. Lee, w0vt Hello! Just to complicate a bit more this subject ;-), some years ago I worked on a TR-4C which had 6JM6 tubes on it. You can read about that here: http://jvgavila.com/dktr4c_1.htm They had a professional-looking adaptor on their bases but, definitely, worked. And were labeled as 6JB6A! So it seems that, with some imagination, you can get a Drake transmitter working with slightly different tubes. Of course, I would stick with 6JB6 while they last. Regards, JOSE -- 73 EB5AGV - JOSE V. GAVILA - IM99sm La Canyada - Valencia(SPAIN) ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] 6JB6 vs.6JB6A
Upgrading to real RF-service tubes (6146's come to mind :) kinda pales when compared to that kind of mod. Curt LEE BAHR wrote: Many years ago, just before Drake stopped accepting TR-4 s for repair, my neighbor, WA5VGO sent his TR-4 to Drake for some repair. The radio came back with three different final tubes then when shipped to Drake. One of the three new tubes was as you described. A sweep tube with a printed circuit on the bottom changing the pin out of the tube. I don't know if it was a 6JM6 or not. However, the tube was put in there by Drake. Also, the three new tubes were taller then original and Drake had dimpled the top tube cage cover to accommodate the extra height of the new tubes. Strange indeed, but the radio worked just fine with these tubes. Lee, w0vt ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
[Drakelist] 6JB6 vs.6JB6A
Thanks for the info on 6jb6 vs. 6JB6A. I have seen a few 6JB6 of both varieties on line, often advertised as MATCHED. I wonder how they have matched them as some have listed an emmisson only tube tester as the match unit. I am very leary of these so called matched tubes! Even the ones from the large tube sellers may be useless! I was given a T4-R4 set which I took to WB4HFN. He went over them and said that I would need a new set of finals after I had used them for awhile. I am having some trouble getting a wire up for them, but I keeping my eyes open for a nice set of 6JB6 s. Mike, KB1EZL ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] 6JB6 vs.6JB6A
Hi Mike, From a thread re. Drake finals here of some two years ago, there was mention of the fact that the 6GJ5 is a direct substitute for the 6JB6, if you have no luck finding that latter tube... ~73~ de Eddy VE3CUI - VE3XZ - Original Message - From: m coffey To: drakelist@zerobeat.net Sent: Wednesday, September 29, 2010 4:56 PM Subject: [Drakelist] 6JB6 vs.6JB6A Thanks for the info on 6jb6 vs. 6JB6A. I have seen a few 6JB6 of both varieties on line, often advertised as MATCHED. I wonder how they have matched them as some have listed an emmisson only tube tester as the match unit. I am very leary of these so called matched tubes! Even the ones from the large tube sellers may be useless! I was given a T4-R4 set which I took to WB4HFN. He went over them and said that I would need a new set of finals after I had used them for awhile. I am having some trouble getting a wire up for them, but I keeping my eyes open for a nice set of 6JB6 s. Mike, KB1EZL -- ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] 6JB6 vs.6JB6A
Sylvania 6JB6's are on ebay, eham and QRZ normally for $25.00 each. I believe if the tubes have the same date code they are matched. On Wed, Sep 29, 2010 at 7:53 PM, Edward Swynar gswy...@durham.net wrote: *Hi Mike,* From a thread re. Drake finals here of some two years ago, there was mention of the fact that the *6GJ5* is a *direct substitute* for the 6JB6, if you have no luck finding that latter tube... *~73~ de Eddy VE3CUI - VE3XZ* - Original Message - *From:* m coffey r79b...@gmail.com *To:* drakelist@zerobeat.net *Sent:* Wednesday, September 29, 2010 4:56 PM *Subject:* [Drakelist] 6JB6 vs.6JB6A Thanks for the info on 6jb6 vs. 6JB6A. I have seen a few 6JB6 of both varieties on line, often advertised as MATCHED. I wonder how they have matched them as some have listed an emmisson only tube tester as the match unit. I am very leary of these so called matched tubes! Even the ones from the large tube sellers may be useless! I was given a T4-R4 set which I took to WB4HFN. He went over them and said that I would need a new set of finals after I had used them for awhile. I am having some trouble getting a wire up for them, but I keeping my eyes open for a nice set of 6JB6 s. Mike, KB1EZL -- ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] 6JB6 vs.6JB6A
Hi Eddy, It's the identical tube with the supressor grid internally connected. I've used them in several Drake Xmtrs with fine results. Others have reported difficulty with neutralization...but I've never seen that. The specs as I recall, were not close, they were identical. John K5MO At 07:53 PM 9/29/2010, Edward Swynar wrote: Hi Mike, From a thread re. Drake finals here of some two years ago, there was mention of the fact that the 6GJ5 is a direct substitute for the 6JB6, if you have no luck finding that latter tube... ~73~ de Eddy VE3CUI - VE3XZ - Original Message - From: mailto:r79b...@gmail.comm coffey To: mailto:drakelist@zerobeat.netdrakelist@zerobeat.net Sent: Wednesday, September 29, 2010 4:56 PM Subject: [Drakelist] 6JB6 vs.6JB6A Thanks for the info on 6jb6 vs. 6JB6A. I have seen a few 6JB6 of both varieties on line, often advertised as MATCHED. I wonder how they have matched them as some have listed an emmisson only tube tester as the match unit. I am very leary of these so called matched tubes! Even the ones from the large tube sellers may be useless! I was given a T4-R4 set which I took to WB4HFN. He went over them and said that I would need a new set of finals after I had used them for awhile. I am having some trouble getting a wire up for them, but I keeping my eyes open for a nice set of 6JB6 s. Mike, KB1EZL -- ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] 6JB6 vs.6JB6A
The same date code doesn't have much to do with matching, Richard, but they probably are close. There is a proceedure used for matching, but you'd have to have a basketfull of them to use it anymore. Drake original tubes have a number written on top of them in magic marker. I've been lucky enough over the years to find several of those. They are NEVER in a box, usually wrapped up in some paper like wrap and in a nondescrete box. If you spot those, with matching numbers at an estate sale or hamfest, GRAB THEM. I got three pairs with a radio set just because they weren't in a box, they were considered used!!! 73, Don, WB5HAK___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] 6JB6 vs.6JB6A
I have a matched pair (GE) from RF Parts I got maybe 10 years ago, packed in a wooden salt cod box. Counting on the sale proceeds to fund my retirement when I get to my 90's :) Chuck, K1OM On Wed, Sep 29, 2010 at 9:33 PM, Don Cunningham wb5...@martineer.netwrote: The same date code doesn't have much to do with matching, Richard, but they probably are close. There is a proceedure used for matching, but you'd have to have a basketfull of them to use it anymore. Drake original tubes have a number written on top of them in magic marker. I've been lucky enough over the years to find several of those. They are NEVER in a box, usually wrapped up in some paper like wrap and in a nondescrete box. If you spot those, with matching numbers at an estate sale or hamfest, GRAB THEM. I got three pairs with a radio set just because they weren't in a box, they were considered used!!! 73, Don, WB5HAK ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] 6JB6 vs.6JB6A
I'll never again buy vacuum tubes off of the internet, after buying from a regular store on the auction site two matched 6JB6s, both soft as pillows and useless above 40M. Of course, everything there is always as-is. I'll also never buy anything from a big tube seller in Florida who is a small-time liar and crook. Only bonafide companies for me, the products are no more expensive, and at least its a big outfit ripping me off. Good to know that a 6GJ5 is equal to a 6JB6, surprised had never read that before. Unfortunately, maybe most tubes sold are pretty much worn out. Even most of the companies selling tubes draw the line at providing much warranty for sweep tubes ( 10 days conditional from the outfit I use a lot ). Curt KB5JO ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] 6JB6 vs.6JB6A
If they were Sylvania, Chuck, you probably could, but GE's? I don't know about that. I think that's one of the brands that sometimes won't neutralize. I may be wrong, and it may be RCA, but some of them don't seem to make it. 73, Don, WB5HAK___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] 6JB6 vs.6JB6A
Of course this was only tongue-in-cheek. I plan on checking out in 2025, long before I get to my 90's. Chuck On Wed, Sep 29, 2010 at 9:53 PM, Don Cunningham wb5...@martineer.netwrote: If they were Sylvania, Chuck, you probably could, but GE's? I don't know about that. I think that's one of the brands that sometimes won't neutralize. I may be wrong, and it may be RCA, but some of them don't seem to make it. 73, Don, WB5HAK ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] 6JB6 vs.6JB6A
Meant to add, QCWA, 45 years. On Wed, Sep 29, 2010 at 9:59 PM, Chuck Grandgent ch...@chuckg.com wrote: Of course this was only tongue-in-cheek. I plan on checking out in 2025, long before I get to my 90's. Chuck On Wed, Sep 29, 2010 at 9:53 PM, Don Cunningham wb5...@martineer.netwrote: If they were Sylvania, Chuck, you probably could, but GE's? I don't know about that. I think that's one of the brands that sometimes won't neutralize. I may be wrong, and it may be RCA, but some of them don't seem to make it. 73, Don, WB5HAK ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] 6JB6 vs.6JB6A
And, as always, my snide comment was tongue FIRMLY planted in the cheek. Don't check out too early Chuck. I have a good friend in Richardson, TX, K5AY, in his 90's and you don't want to either challenge him to an electronic or antenna question, or challenge him to a CW speed run. He WILL win both. Sharp as a tack. Hope I'm half as sharp in the 80's, hi. 73, and good to see you on here, Don, WB5HAK___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] 6JB6 vs.6JB6A
Hi Don, Why not videotape an interview with this great OT and post it somewhere where we can all enjoy it. I have seen several similar interviews and they are really great. 73, John, W4AWM ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
[Drakelist] 6JB6 vs.6JB6A
Although I have been a member of the list for a while now, this is the first time that I have tried to post to it, so I hope that I have done this correctly! My question is that I have seen 6JB6A (vs. straight 6JB6) tubes listed for sale. I am wondering what difference(s) there are between the two and if eigther is suitable for use in the T4X series (or TR4s). Also, is a fairly close reading in mutual conductance ( ie. on my Heathkit TT1) consider as indicating a true match on the tubes? Mike, KB1EZL ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] 6JB6 vs.6JB6A
Mike - The 6JB6A is identical to the 6JB6 with the exception that the A version is spec'd for 11 second filament warmup. This was a spec that came along because many TV sets were series filament strings, (which is also where the 3, 16, 19, etc. filament tubes came from,) and tubes warming up at different rates stressed the filaments of other tubes. Either is suitable for the Drake 4 Series transmitters. I don't think Sylvania ever made an A version, the only ones I've seen are RCA and GE among the 'preferred' brands. One caveat, some of the later manufacture tubes were too tall to fit into the PA cages of the Drake transmitters. Despite the fact that the 6JB6 was specified as 2.91 - 3.17 seated height, and the 6JB6A as 2.875 - 3.125 my experience has been that just about all of the non-A tubes were toward the smaller size of their spec, while the A's seemed to be toward the high end of their spec. Just be aware that some tubes are too tall to fit. I don't recall what the exact height of the cage is, but it's right at 3 . Mutual conductance matching is good, but the final test is the bias voltage vs cathode current. Just the idle current exceeds the rated plate dissipation rating of the tubes, so you want them to be as close as possible. With a fixed bias voltage select two that draw between 32 and 38 mA each. 73, Garey - K4OAH Glen Allen, VA Drake 2-B, 2-C/2-NT, 4-B, C-Line TR-4/C Service Supplement CDs www.k4oah.com m coffey wrote: Although I have been a member of the list for a while now, this is the first time that I have tried to post to it, so I hope that I have done this correctly! My question is that I have seen 6JB6A (vs. straight 6JB6) tubes listed for sale. I am wondering what difference(s) there are between the two and if eigther is suitable for use in the T4X series (or TR4s). Also, is a fairly close reading in mutual conductance ( ie. on my Heathkit TT1) consider as indicating a true match on the tubes? Mike, KB1EZL ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
