Re: [Drakelist] R4B Audio Distortion
Yep - wound up being lucky this time - didn't even have to buy another tube! Someone else had mentioned the Sherwood audio amp, and this particular R-4C has that mod. Overall, it sounds good now. Steve Wedge, W1ES/4 Live free or die: Death is not the worst of evils. John Stark. All my computers have my signature with various pearls of wisdom appended thereto. -- From: Garey Barrell k4...@mindspring.com Sent: Saturday, March 10, 2012 11:20 AM To: Steve Wedge w1es1...@earthlink.net Cc: Mike Bryce proso...@sssnet.com; Randy WB4SPB wb4...@earthlink.net; drakelist@zerobeat.net Subject: Re: [Drakelist] R4B Audio Distortion Steve - Yes, the tube noise only seems to be a problem in the 3rd Mixer, and 'noisy' tubes can often be used in the IF with no problem. I guess it has something to do with the way the stages are biased, but I've never really investigated it. I'm lazy, I'll just select a good tube, and it usually outlasts the radio. I've had a couple (three?) guys who doubted me on this, and all three replaced every component in the AF Output stage. All three eventually ended up selecting a 6EH5! :-) It's a tough sell, cause 'I put in a NEW tube'.. :-) It's kinda like the IDLE current in a PA. If the supply voltages are there, the PA tubes WILL draw current. The only question is how much, and there you have an adjustable bias to take care of minor differences. Except in this case you don't have 'easily' adjustable bias. If you have the right cathode resistor, and the voltages are present, the tube WILL draw ~30 mA. However, (there's always a however',) when the tube gets _hot_ if the grid starts emitting electrons, or there are gas particles in the 'vacuum', the 'natural order of things' is screwed up and the tube starts drawing a little more current. Which gets a little more grid current, which gets the tube a little hotter, which 73, Garey - K4OAH Glen Allen, VA Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line and TR-4/C Service Supplement CDs www.k4oah.com Steve Wedge wrote: I just wound up fixing an R-4C - and one of the things I did was to swap V4 and V6. That single exchange did more to reduce the noise in the receiver than anyting else I could have done. I did go on and convert the third mixer to cathode-feed, and that improved things a bit more, but you're on to something with respect to the audio output. OTOH, I still sit here and wonder. At audio frequencies, is everything as designed by Drake really that critical? It might be a good time to replace components to find out... Yeah - I'm a troublemaker... Steve Wedge, W1ES/4 I can't complain, but sometimes I still do. - Joe Walsh If the above message appears, it came from Steve's Son of Laptop! - Original Message - From: Garey Barrell k4...@mindspring.com To: Mike Bryce proso...@sssnet.com Cc: Randy WB4SPB wb4...@earthlink.net; drakelist@zerobeat.net Sent: Friday, March 09, 2012 10:21 PM Subject: Re: [Drakelist] R4B Audio Distortion Mike - I think the problem is that 'new' tubes are 50 years old.. Even a few molecules of air a day adds up after that long. When Drake assembled the radios, the tubes were _really_ new!! The 6EH5 gets 'really' hot in normal operation, and perhaps the heat/cool cycles are harder on the metal/glass seals at the pins. Some tubes definitely are more prone to 'gas' (grid emission), the 12BA6 comes to mind. That one shows as a 'drifting' S-Meter as the tubes heat up. The 6EJ7 is prone to noise in 3rd Mixer service, probably for a similar reason. The only answer I have come up with is to keep trying tubes until you get a 'good' one. 73, Garey - K4OAH Glen Allen, VA Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line and TR-4/C Service Supplement CDs www.k4oah.com Mike Bryce wrote: I wonder. when drake assembled the radios, did they go through three or fours tubes per radio to get one that worked correctly? dosen't seem logical. And although you can't argue with the fact that the subing out the tube fixed the problem, I wonder if there is something hidden down someplace in the design that causes the problem just a thought Mike, wb8vge On Mar 9, 2012, at 4:25 PM, Randy WB4SPB wrote: Altogether, I bought two 6EH5s and one 6CA5. I already had a spare 6EH5, so, considering those alone, I had to try three to get one. If I count the 6CA5 that I bought, I had to try four to get one. The 6CA5 IS very similar. Some sources do not even have the 6EH5 and refer you to 6CA5. The tube that originally manifested the problem was a 6CA5 that had been in the radio for many years before these symptoms appeared. Whether the difference in 6EH5 and 6CA5 is important here, I cannot say. I'll stick with 6EH5s in the future, while I can get them. For sources I've seen that have both, the price is the same. 73, Randy WB4SPB - Original Message - *From:*Al Al
Re: [Drakelist] R4B Audio Distortion
Steve, If you haven't, take a look at wgar Rob Sherwood did on the audio for the R-4C. Got rid of all that heat...that also causes some drift. I turn mine on and after a very short time it just stay on freq. 73, Lee -Original Message- From: Steve Wedge w1es1...@earthlink.net To: k4oah k4...@mindspring.com; Mike Bryce proso...@sssnet.com Cc: Randy WB4SPB wb4...@earthlink.net; drakelist drakelist@zerobeat.net Sent: Fri, Mar 9, 2012 11:16 pm Subject: Re: [Drakelist] R4B Audio Distortion I just wound up fixing an R-4C - and one of the things I did was to swap V4 and V6. That single exchange did more to reduce the noise in the receiver than anyting else I could have done. I did go on and convert the third mixer to cathode-feed, and that improved things a bit more, but you're on to something with respect to the audio output. OTOH, I still sit here and wonder. At audio frequencies, is everything as designed by Drake really that critical? It might be a good time to replace components to find out... Yeah - I'm a troublemaker... Steve Wedge, W1ES/4 I can't complain, but sometimes I still do. - Joe Walsh If the above message appears, it came from Steve's Son of Laptop! - Original Message - From: Garey Barrell k4...@mindspring.com To: Mike Bryce proso...@sssnet.com Cc: Randy WB4SPB wb4...@earthlink.net; drakelist@zerobeat.net Sent: Friday, March 09, 2012 10:21 PM Subject: Re: [Drakelist] R4B Audio Distortion Mike - I think the problem is that 'new' tubes are 50 years old.. Even a few molecules of air a day adds up after that long. When Drake assembled the radios, the tubes were _really_ new!! The 6EH5 gets 'really' hot in normal operation, and perhaps the heat/cool cycles are harder on the metal/glass seals at the pins. Some tubes definitely are more prone to 'gas' (grid emission), the 12BA6 comes to mind. That one shows as a 'drifting' S-Meter as the tubes heat up. The 6EJ7 is prone to noise in 3rd Mixer service, probably for a similar reason. The only answer I have come up with is to keep trying tubes until you get a 'good' one. 73, Garey - K4OAH Glen Allen, VA Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line and TR-4/C Service Supplement CDs www.k4oah.com Mike Bryce wrote: I wonder. when drake assembled the radios, did they go through three or fours tubes per radio to get one that worked correctly? dosen't seem logical. And although you can't argue with the fact that the subing out the tube fixed the problem, I wonder if there is something hidden down someplace in the design that causes the problem just a thought Mike, wb8vge On Mar 9, 2012, at 4:25 PM, Randy WB4SPB wrote: Altogether, I bought two 6EH5s and one 6CA5. I already had a spare 6EH5, so, considering those alone, I had to try three to get one. If I count the 6CA5 that I bought, I had to try four to get one. The 6CA5 IS very similar. Some sources do not even have the 6EH5 and refer you to 6CA5. The tube that originally manifested the problem was a 6CA5 that had been in the radio for many years before these symptoms appeared. Whether the difference in 6EH5 and 6CA5 is important here, I cannot say. I'll stick with 6EH5s in the future, while I can get them. For sources I've seen that have both, the price is the same. 73, Randy WB4SPB - Original Message - *From:*Al Al mailto:wenj...@gmail.com Out of curiosity, how many 6EH5 tubes did you have to go through to find a good one? Al, n7ioh Payson, Arizona, USA _ ___ 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] R4B Audio Distortion
Steve - Yes, the tube noise only seems to be a problem in the 3rd Mixer, and 'noisy' tubes can often be used in the IF with no problem. I guess it has something to do with the way the stages are biased, but I've never really investigated it. I'm lazy, I'll just select a good tube, and it usually outlasts the radio. I've had a couple (three?) guys who doubted me on this, and all three replaced every component in the AF Output stage. All three eventually ended up selecting a 6EH5! :-) It's a tough sell, cause 'I put in a NEW tube'.. :-) It's kinda like the IDLE current in a PA. If the supply voltages are there, the PA tubes WILL draw current. The only question is how much, and there you have an adjustable bias to take care of minor differences. Except in this case you don't have 'easily' adjustable bias. If you have the right cathode resistor, and the voltages are present, the tube WILL draw ~30 mA. However, (there's always a however',) when the tube gets _hot_ if the grid starts emitting electrons, or there are gas particles in the 'vacuum', the 'natural order of things' is screwed up and the tube starts drawing a little more current. Which gets a little more grid current, which gets the tube a little hotter, which 73, Garey - K4OAH Glen Allen, VA Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line and TR-4/C Service Supplement CDs www.k4oah.com Steve Wedge wrote: I just wound up fixing an R-4C - and one of the things I did was to swap V4 and V6. That single exchange did more to reduce the noise in the receiver than anyting else I could have done. I did go on and convert the third mixer to cathode-feed, and that improved things a bit more, but you're on to something with respect to the audio output. OTOH, I still sit here and wonder. At audio frequencies, is everything as designed by Drake really that critical? It might be a good time to replace components to find out... Yeah - I'm a troublemaker... Steve Wedge, W1ES/4 I can't complain, but sometimes I still do. - Joe Walsh If the above message appears, it came from Steve's Son of Laptop! - Original Message - From: Garey Barrell k4...@mindspring.com To: Mike Bryce proso...@sssnet.com Cc: Randy WB4SPB wb4...@earthlink.net; drakelist@zerobeat.net Sent: Friday, March 09, 2012 10:21 PM Subject: Re: [Drakelist] R4B Audio Distortion Mike - I think the problem is that 'new' tubes are 50 years old.. Even a few molecules of air a day adds up after that long. When Drake assembled the radios, the tubes were _really_ new!! The 6EH5 gets 'really' hot in normal operation, and perhaps the heat/cool cycles are harder on the metal/glass seals at the pins. Some tubes definitely are more prone to 'gas' (grid emission), the 12BA6 comes to mind. That one shows as a 'drifting' S-Meter as the tubes heat up. The 6EJ7 is prone to noise in 3rd Mixer service, probably for a similar reason. The only answer I have come up with is to keep trying tubes until you get a 'good' one. 73, Garey - K4OAH Glen Allen, VA Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line and TR-4/C Service Supplement CDs www.k4oah.com Mike Bryce wrote: I wonder. when drake assembled the radios, did they go through three or fours tubes per radio to get one that worked correctly? dosen't seem logical. And although you can't argue with the fact that the subing out the tube fixed the problem, I wonder if there is something hidden down someplace in the design that causes the problem just a thought Mike, wb8vge On Mar 9, 2012, at 4:25 PM, Randy WB4SPB wrote: Altogether, I bought two 6EH5s and one 6CA5. I already had a spare 6EH5, so, considering those alone, I had to try three to get one. If I count the 6CA5 that I bought, I had to try four to get one. The 6CA5 IS very similar. Some sources do not even have the 6EH5 and refer you to 6CA5. The tube that originally manifested the problem was a 6CA5 that had been in the radio for many years before these symptoms appeared. Whether the difference in 6EH5 and 6CA5 is important here, I cannot say. I'll stick with 6EH5s in the future, while I can get them. For sources I've seen that have both, the price is the same. 73, Randy WB4SPB - Original Message - *From:*Al Al mailto:wenj...@gmail.com Out of curiosity, how many 6EH5 tubes did you have to go through to find a good one? Al, n7ioh Payson, Arizona, USA ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] R4B Audio Distortion
Update: resolved, and another gold star for Garey In early February, I asked for ideas after finding my R4B audio output stage running hot. Positive bias, climbing slowly to +3, would mysteriously appear on the grid after a few minutes of operation, and the audio became distorted. Cooling the tube with forced air mitigated the problem, reducing but not eliminating the weird grid bias. I could find no defective components (leaking caps, thermally-misbehaving cathode resistor, etc.) and had tried three different tubes that behaved the same way. Richard WB6KBL suggested I look for some way that screen voltage might be leaking to the adjacent grid pin on the socket. I could find nothing by inspection, and cleaning made no difference. I began a half-hearted search through my junk box for a replacement socket, but didn't end up going that way. Garey K4OAH thought the symptoms clearly suggested a gassy tube. I was skeptical, having tried several different tubes, both 6EH5 and 6CA5, all of which tested OK (and not gassy) on a borrowed Hickok 600A tester. Garey pointed out that 6CA5 is not an exact replacement and that in his experience it has sometimes been necessary to go through several 6EH5s to find a good one. So I decided it was cheap enough, at $3 each from most sources, to obtain a couple more tubes and see what happened. I've finally done that, and, lo, it appears Garey was correct. One (and only one) of my new tubes behaves properly. Of course (sigh) the R4B has now gone of the rails for some entirely new reason, but I'll open it up soon and see what's what. 73, and thanks for the help. Randy WB4SPB ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] R4B Audio Distortion
Out of curiosity, how many 6EH5 tubes did you have to go through to find a good one? Al, n7ioh Payson, Arizona, USA On Fri, Mar 9, 2012 at 11:24 AM, Randy WB4SPB wb4...@earthlink.net wrote: Update: resolved, and another gold star for Garey In early February, I asked for ideas after finding my R4B audio output stage running hot. Positive bias, climbing slowly to +3, would mysteriously appear on the grid after a few minutes of operation, and the audio became distorted. Cooling the tube with forced air mitigated the problem, reducing but not eliminating the weird grid bias. I could find no defective components (leaking caps, thermally-misbehaving cathode resistor, etc.) and had tried three different tubes that behaved the same way. Richard WB6KBL suggested I look for some way that screen voltage might be leaking to the adjacent grid pin on the socket. I could find nothing by inspection, and cleaning made no difference. I began a half-hearted search through my junk box for a replacement socket, but didn't end up going that way. Garey K4OAH thought the symptoms clearly suggested a gassy tube. I was skeptical, having tried several different tubes, both 6EH5 and 6CA5, all of which tested OK (and not gassy) on a borrowed Hickok 600A tester. Garey pointed out that 6CA5 is not an exact replacement and that in his experience it has sometimes been necessary to go through several 6EH5s to find a good one. So I decided it was cheap enough, at $3 each from most sources, to obtain a couple more tubes and see what happened. I've finally done that, and, lo, it appears Garey was correct. One (and only one) of my new tubes behaves properly. Of course (sigh) the R4B has now gone of the rails for some entirely new reason, but I'll open it up soon and see what's what. 73, and thanks for the help. Randy WB4SPB __**_ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/**mailman/listinfo/drakelisthttp://mailman.zerobeat.net/mailman/listinfo/drakelist ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] R4B Audio Distortion
Randy, Great news! Glad it is resolved...I'll keep that one in mind for future bugs. One more GOLD star for Garey is right! He is super and If he actually had a gold start for all of the things he has helped us with...it would take a very large wall indeed to display them! 73, Lee -Original Message- From: Randy WB4SPB wb4...@earthlink.net To: drakelist drakelist@zerobeat.net Sent: Fri, Mar 9, 2012 1:33 pm Subject: Re: [Drakelist] R4B Audio Distortion Update: resolved, and another gold star for Garey In early February, I asked for ideas after finding my R4B audio output stage running hot. Positive bias, climbing slowly to +3, would mysteriously appear on the grid after a few minutes of operation, and the audio became distorted. Cooling the tube with forced air mitigated the problem, reducing but not eliminating the weird grid bias. I could find no defective components (leaking caps, thermally-misbehaving cathode resistor, etc.) and had tried three different tubes that behaved the same way. Richard WB6KBL suggested I look for some way that screen voltage might be leaking to the adjacent grid pin on the socket. I could find nothing by inspection, and cleaning made no difference. I began a half-hearted search through my junk box for a replacement socket, but didn't end up going that way. Garey K4OAH thought the symptoms clearly suggested a gassy tube. I was skeptical, having tried several different tubes, both 6EH5 and 6CA5, all of which tested OK (and not gassy) on a borrowed Hickok 600A tester. Garey pointed out that 6CA5 is not an exact replacement and that in his experience it has sometimes been necessary to go through several 6EH5s to find a good one. So I decided it was cheap enough, at $3 each from most sources, to obtain a couple more tubes and see what happened. I've finally done that, and, lo, it appears Garey was correct. One (and only one) of my new tubes behaves properly. Of course (sigh) the R4B has now gone of the rails for some entirely new reason, but I'll open it up soon and see what's what. 73, and thanks for the help. Randy WB4SPB ___ 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] R4B Audio Distortion
Altogether, I bought two 6EH5s and one 6CA5. I already had a spare 6EH5, so, considering those alone, I had to try three to get one. If I count the 6CA5 that I bought, I had to try four to get one. The 6CA5 IS very similar. Some sources do not even have the 6EH5 and refer you to 6CA5. The tube that originally manifested the problem was a 6CA5 that had been in the radio for many years before these symptoms appeared. Whether the difference in 6EH5 and 6CA5 is important here, I cannot say. I'll stick with 6EH5s in the future, while I can get them. For sources I've seen that have both, the price is the same. 73, Randy WB4SPB - Original Message - From: Al Al Out of curiosity, how many 6EH5 tubes did you have to go through to find a good one? Al, n7ioh Payson, Arizona, USA ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] R4B Audio Distortion
I wonder. when drake assembled the radios, did they go through three or fours tubes per radio to get one that worked correctly? dosen't seem logical. And although you can't argue with the fact that the subing out the tube fixed the problem, I wonder if there is something hidden down someplace in the design that causes the problem just a thought Mike, wb8vge On Mar 9, 2012, at 4:25 PM, Randy WB4SPB wrote: Altogether, I bought two 6EH5s and one 6CA5. I already had a spare 6EH5, so, considering those alone, I had to try three to get one. If I count the 6CA5 that I bought, I had to try four to get one. The 6CA5 IS very similar. Some sources do not even have the 6EH5 and refer you to 6CA5. The tube that originally manifested the problem was a 6CA5 that had been in the radio for many years before these symptoms appeared. Whether the difference in 6EH5 and 6CA5 is important here, I cannot say. I'll stick with 6EH5s in the future, while I can get them. For sources I've seen that have both, the price is the same. 73, Randy WB4SPB - Original Message - From: Al Al Out of curiosity, how many 6EH5 tubes did you have to go through to find a good one? Al, n7ioh Payson, Arizona, USA ___ 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] R4B Audio Distortion
Mike - I think the problem is that 'new' tubes are 50 years old.. Even a few molecules of air a day adds up after that long. When Drake assembled the radios, the tubes were _really_ new!! The 6EH5 gets 'really' hot in normal operation, and perhaps the heat/cool cycles are harder on the metal/glass seals at the pins. Some tubes definitely are more prone to 'gas' (grid emission), the 12BA6 comes to mind. That one shows as a 'drifting' S-Meter as the tubes heat up. The 6EJ7 is prone to noise in 3rd Mixer service, probably for a similar reason. The only answer I have come up with is to keep trying tubes until you get a 'good' one. 73, Garey - K4OAH Glen Allen, VA Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line and TR-4/C Service Supplement CDs www.k4oah.com Mike Bryce wrote: I wonder. when drake assembled the radios, did they go through three or fours tubes per radio to get one that worked correctly? dosen't seem logical. And although you can't argue with the fact that the subing out the tube fixed the problem, I wonder if there is something hidden down someplace in the design that causes the problem just a thought Mike, wb8vge On Mar 9, 2012, at 4:25 PM, Randy WB4SPB wrote: Altogether, I bought two 6EH5s and one 6CA5. I already had a spare 6EH5, so, considering those alone, I had to try three to get one. If I count the 6CA5 that I bought, I had to try four to get one. The 6CA5 IS very similar. Some sources do not even have the 6EH5 and refer you to 6CA5. The tube that originally manifested the problem was a 6CA5 that had been in the radio for many years before these symptoms appeared. Whether the difference in 6EH5 and 6CA5 is important here, I cannot say. I'll stick with 6EH5s in the future, while I can get them. For sources I've seen that have both, the price is the same. 73, Randy WB4SPB - Original Message - *From:*Al Al mailto:wenj...@gmail.com Out of curiosity, how many 6EH5 tubes did you have to go through to find a good one? Al, n7ioh Payson, Arizona, USA _ ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] R4B Audio Distortion
I just wound up fixing an R-4C - and one of the things I did was to swap V4 and V6. That single exchange did more to reduce the noise in the receiver than anyting else I could have done. I did go on and convert the third mixer to cathode-feed, and that improved things a bit more, but you're on to something with respect to the audio output. OTOH, I still sit here and wonder. At audio frequencies, is everything as designed by Drake really that critical? It might be a good time to replace components to find out... Yeah - I'm a troublemaker... Steve Wedge, W1ES/4 I can't complain, but sometimes I still do. - Joe Walsh If the above message appears, it came from Steve's Son of Laptop! - Original Message - From: Garey Barrell k4...@mindspring.com To: Mike Bryce proso...@sssnet.com Cc: Randy WB4SPB wb4...@earthlink.net; drakelist@zerobeat.net Sent: Friday, March 09, 2012 10:21 PM Subject: Re: [Drakelist] R4B Audio Distortion Mike - I think the problem is that 'new' tubes are 50 years old.. Even a few molecules of air a day adds up after that long. When Drake assembled the radios, the tubes were _really_ new!! The 6EH5 gets 'really' hot in normal operation, and perhaps the heat/cool cycles are harder on the metal/glass seals at the pins. Some tubes definitely are more prone to 'gas' (grid emission), the 12BA6 comes to mind. That one shows as a 'drifting' S-Meter as the tubes heat up. The 6EJ7 is prone to noise in 3rd Mixer service, probably for a similar reason. The only answer I have come up with is to keep trying tubes until you get a 'good' one. 73, Garey - K4OAH Glen Allen, VA Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line and TR-4/C Service Supplement CDs www.k4oah.com Mike Bryce wrote: I wonder. when drake assembled the radios, did they go through three or fours tubes per radio to get one that worked correctly? dosen't seem logical. And although you can't argue with the fact that the subing out the tube fixed the problem, I wonder if there is something hidden down someplace in the design that causes the problem just a thought Mike, wb8vge On Mar 9, 2012, at 4:25 PM, Randy WB4SPB wrote: Altogether, I bought two 6EH5s and one 6CA5. I already had a spare 6EH5, so, considering those alone, I had to try three to get one. If I count the 6CA5 that I bought, I had to try four to get one. The 6CA5 IS very similar. Some sources do not even have the 6EH5 and refer you to 6CA5. The tube that originally manifested the problem was a 6CA5 that had been in the radio for many years before these symptoms appeared. Whether the difference in 6EH5 and 6CA5 is important here, I cannot say. I'll stick with 6EH5s in the future, while I can get them. For sources I've seen that have both, the price is the same. 73, Randy WB4SPB - Original Message - *From:*Al Al mailto:wenj...@gmail.com Out of curiosity, how many 6EH5 tubes did you have to go through to find a good one? Al, n7ioh Payson, Arizona, USA _ ___ 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] R4B audio distortion
Thanks Richard and Evan. I'll give more thought to the socket itself. 73, Randy WB4SPB - Original Message - From: K9sqg To: 1oldle...@ix.netcom.com ; wb4...@earthlink.net ; drakelist@zerobeat.net Sent: Thursday, February 09, 2012 10:35 PM Subject: Re: [Drakelist] R4B audio distortion Here is where a can of freeze spray can sometimes serve to help with diagnostics. I serviced a Collins 516F2 power supply used with a KWM-2 and found that the molded socket for one of the rectifiers had an internal short that could not be seen from the outside. -Original Message- From: Richard Knoppow 1oldle...@ix.netcom.com To: Randy WB4SPB wb4...@earthlink.net; drakelist drakelist@zerobeat.net Sent: Fri, Feb 10, 2012 12:27 am Subject: Re: [Drakelist] R4B audio distortion A look at the schematic indicates that you have hit all the usual suspects. So, what else could cause the control grid voltage to go positive? I wonder if the tube socket is leaky. Even if the tube is on an extender it might be the socket. It might be something on the surface of the socket between pins. Pin 6 is the screen grid so leakage from that could cause the problem. Check the socket for carbon tracks or anything on the surface. Clean it thoroughly with dry alcohol. Temperature might make a difference if there is either a carbon track or something else there. Perhaps far fetched but easy enough to do and worth a try. If cleaning makes a difference but does not cure the problem a new socket might be in order. -- Richard Knoppow Los Angeles WB6KBL dickb...@ix.netcom.com ...___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] R4B audio distortion
Randy - Sounds like a classic case of a 'gassy' (grid emission) tube. Replace it! 73, Garey - K4OAH Glen Allen, VA Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line and TR-4/C Service Supplement CDs www.k4oah.com Randy WB4SPB wrote: Hi folks, I've owned my beloved R4B since the mid-70's. From about 1985 until 2000, it was stored while I got busy with job/family. I used it again for several months in 2002 and 2003, and I didn't notice anything unusual. Now I am active again and want to use it full time, but I am hearing audio distortion after about 5 minutes of operation. Poking around, I observe the cathode of V7 is at higher voltage than expected, and the grid has more than 2 volts, where 0 is expected. Coupling cap C185? No, lift one side, and no change. R154 has the correct value. Cathode resistor? R44 has the correct value, and I tried a different one anyway, in case it was thermally unstable, with no change. I've replaced C176 (along with the other small electrolytics in the RX), no difference. I haven't tackled replacing the big electrolytic can yet, but voltages and ripple seem pretty much OK on all terminals of that unit (e.g. 7mv at C90A, and 35mv at C90D, 75mv at C90C). At power up, the V7 grid is slightly more than 0V, cathode voltage nominal. As time goes on, these creep slowly upward. After 5-6 minutes, the grid is approaching 3V. 30 seconds after power up: V7 pin 1: 4.8 pin 2,5: .006 pin 6: 134 pin 7: 146 5-6 minutes after power up: V7 pin 1: 6.2 pin 2,5: 2.9 pin 6: 129 pin 7: 139 I note screen and plate voltages have fallen off a little. If they were a little high to begin with, it may be because my line voltage is sometimes a bit high: I measured 122VAC today. I presume the drop in these values reflects increased current through V7. I get the same basic behavior when I have the receiver on a variac and control the line voltage to something less than 120VAC. The audio sounds good for the first several minutes, but it becomes harsh sounding at some point. I don't know what the output waveform looks like. So I could feel better about V7 running hard while I poked around, I put a fan on it, above the chassis ... and lo, the grid/cathode voltages started to drop. The grid stabilizes at about 0.3V with a healthy amount of forced air on the 6EH5, and the audio sounds good. Conductive socket material when hot? I don't think so: I put the tube on a 1.5-inch extender to reduce heat at the socket, with no change in behavior. Bad tube? No, two others behave the same way. I've researched other R4B audio distortion discussions, some on this list. None seem helpful. I'm stumped... any ideas? Thanks and 73, Randy WB4SPB ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] R4B audio distortion
Thanks Garey. I have tried 3 tubes altogether, including my own spare and a second I purchased online. The original is a 6EH5, the spares were 6CA5. I believe (hope) there is no material difference. All behave the same way. The one I ordered turned out not to be a new tube by any stretch of the imagination. Where do you like to buy tubes? 73, Randy WB4SPB - Original Message - From: Garey Barrell k4...@mindspring.com To: Randy WB4SPB wb4...@earthlink.net Cc: drakelist@zerobeat.net Sent: Friday, February 10, 2012 5:30 AM Subject: Re: [Drakelist] R4B audio distortion Randy - Sounds like a classic case of a 'gassy' (grid emission) tube. Replace it! 73, Garey - K4OAH Glen Allen, VA Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line and TR-4/C Service Supplement CDs www.k4oah.com ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] R4B audio distortion
Randy - OK. Well not all 'new' tubes are 'good'. That circuit is very straightforward, and should have 4.5V on the cathode with a 120 ohm cathode resistor. (4.5 / 120 = 37.5 mA) which is the specified operating point for the 6EH5 in Class A service. So if you put 140 VDC on the Plate, slightly less on the Screen, and ground the Grid via ~ 500k ohms, the tube should idle at 37.5 mA. The only external thing that can affect this is if a DC bias is applied to the Grid. One possible source is a leaky coupling capacitor (C185) putting a small DC bias on the grid. The only internal source of trouble is grid emission or gas. Grid emission is when small particles of cathode material flake off and stick to the grid and continue emitting, driving the grid positive. This causes the tube to draw more than it's idle current, heating it up, which heats the grid further, which causes it to emit more, which ... You get the idea. The problem presents as essentially normal operation to start, then the grid heats up and starts emitting, shifting the bias, etc... Since this is a Class A amplifier, the idle current should not change when the stage is driven, so the voltage on the Cathode should stay at 4.5 VDC for the constant 37.5 mA cathode current. The 6CA5 is close, but not an identical tube. It's designed for a slightly lower operating current, but 37.5 is still within it's range. You could try raising R44 to 150 ohms with a 6CA5, but I don't think that's the problem. I know that sometimes I have to go through 3-4 'new' 6EH5s to find a 'good' one. Almost as susceptible to this malady as the 12BA6s. I get tubes wherever I can find them! :-) Antique Electronic Supply is a good reliable source, although a little higher in price. N9TEW is another one. Vacuumtubes.net is good. 73, Garey - K4OAH Glen Allen, VA Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line and TR-4/C Service Supplement CDs www.k4oah.com Randy WB4SPB wrote: Thanks Garey. I have tried 3 tubes altogether, including my own spare and a second I purchased online. The original is a 6EH5, the spares were 6CA5. I believe (hope) there is no material difference. All behave the same way. The one I ordered turned out not to be a new tube by any stretch of the imagination. Where do you like to buy tubes? 73, Randy WB4SPB - Original Message - From: Garey Barrell k4...@mindspring.com To: Randy WB4SPB wb4...@earthlink.net Cc: drakelist@zerobeat.net Sent: Friday, February 10, 2012 5:30 AM Subject: Re: [Drakelist] R4B audio distortion Randy - Sounds like a classic case of a 'gassy' (grid emission) tube. Replace it! 73, Garey - K4OAH Glen Allen, VA Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line and TR-4/C Service Supplement CDs www.k4oah.com ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] R4B audio distortion
Randy, I have had excellent luck with www.radiotubesupply.com/ Roy seems to know his business and has always had prices in line with the market. I have purchased used tubes from him when availability or price was way out of line. I have always been pleased. 73, Ron WD8SBB --- On Fri, 2/10/12, Garey Barrell k4...@mindspring.com wrote: From: Garey Barrell k4...@mindspring.com Subject: Re: [Drakelist] R4B audio distortion To: Randy WB4SPB wb4...@earthlink.net Cc: drakelist@zerobeat.net Date: Friday, February 10, 2012, 2:54 PM Randy - OK. Well not all 'new' tubes are 'good'. That circuit is very straightforward, and should have 4.5V on the cathode with a 120 ohm cathode resistor. (4.5 / 120 = 37.5 mA) which is the specified operating point for the 6EH5 in Class A service. So if you put 140 VDC on the Plate, slightly less on the Screen, and ground the Grid via ~ 500k ohms, the tube should idle at 37.5 mA. The only external thing that can affect this is if a DC bias is applied to the Grid. One possible source is a leaky coupling capacitor (C185) putting a small DC bias on the grid. The only internal source of trouble is grid emission or gas. Grid emission is when small particles of cathode material flake off and stick to the grid and continue emitting, driving the grid positive. This causes the tube to draw more than it's idle current, heating it up, which heats the grid further, which causes it to emit more, which ... You get the idea. The problem presents as essentially normal operation to start, then the grid heats up and starts emitting, shifting the bias, etc... Since this is a Class A amplifier, the idle current should not change when the stage is driven, so the voltage on the Cathode should stay at 4.5 VDC for the constant 37.5 mA cathode current. The 6CA5 is close, but not an identical tube. It's designed for a slightly lower operating current, but 37.5 is still within it's range. You could try raising R44 to 150 ohms with a 6CA5, but I don't think that's the problem. I know that sometimes I have to go through 3-4 'new' 6EH5s to find a 'good' one. Almost as susceptible to this malady as the 12BA6s. I get tubes wherever I can find them! :-) Antique Electronic Supply is a good reliable source, although a little higher in price. N9TEW is another one. Vacuumtubes.net is good. 73, Garey - K4OAH Glen Allen, VA Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line and TR-4/C Service Supplement CDs www.k4oah.com Randy WB4SPB wrote: Thanks Garey. I have tried 3 tubes altogether, including my own spare and a second I purchased online. The original is a 6EH5, the spares were 6CA5. I believe (hope) there is no material difference. All behave the same way. The one I ordered turned out not to be a new tube by any stretch of the imagination. Where do you like to buy tubes? 73, Randy WB4SPB - Original Message - From: Garey Barrell k4...@mindspring.com To: Randy WB4SPB wb4...@earthlink.net Cc: drakelist@zerobeat.net Sent: Friday, February 10, 2012 5:30 AM Subject: Re: [Drakelist] R4B audio distortion Randy - Sounds like a classic case of a 'gassy' (grid emission) tube. Replace it! 73, Garey - K4OAH Glen Allen, VA Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line and TR-4/C Service Supplement CDs www.k4oah.com ___ 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] R4B audio distortion
Thanks Ron and Garey. 73, Randy WB4SPB - Original Message - From: Ron wd8...@yahoo.com To: Randy WB4SPB wb4...@earthlink.net Cc: drakelist@zerobeat.net Sent: Friday, February 10, 2012 3:50 PM Subject: Re: [Drakelist] R4B audio distortion Randy, I have had excellent luck with www.radiotubesupply.com/ Roy seems to know his business and has always had prices in line with the market. I have purchased used tubes from him when availability or price was way out of line. I have always been pleased. 73, Ron WD8SBB --- On Fri, 2/10/12, Garey Barrell k4...@mindspring.com wrote: From: Garey Barrell k4...@mindspring.com Subject: Re: [Drakelist] R4B audio distortion To: Randy WB4SPB wb4...@earthlink.net Cc: drakelist@zerobeat.net Date: Friday, February 10, 2012, 2:54 PM Randy - ... I get tubes wherever I can find them! :-) Antique Electronic Supply is a good reliable source, although a little higher in price. N9TEW is another one. Vacuumtubes.net is good. 73, Garey - K4OAH Glen Allen, VA Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line and TR-4/C Service Supplement CDs www.k4oah.com ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
[Drakelist] R4B audio distortion
Hi folks, I've owned my beloved R4B since the mid-70's. From about 1985 until 2000, it was stored while I got busy with job/family. I used it again for several months in 2002 and 2003, and I didn't notice anything unusual. Now I am active again and want to use it full time, but I am hearing audio distortion after about 5 minutes of operation. Poking around, I observe the cathode of V7 is at higher voltage than expected, and the grid has more than 2 volts, where 0 is expected. Coupling cap C185? No, lift one side, and no change. R154 has the correct value. Cathode resistor? R44 has the correct value, and I tried a different one anyway, in case it was thermally unstable, with no change. I've replaced C176 (along with the other small electrolytics in the RX), no difference. I haven't tackled replacing the big electrolytic can yet, but voltages and ripple seem pretty much OK on all terminals of that unit (e.g. 7mv at C90A, and 35mv at C90D, 75mv at C90C). At power up, the V7 grid is slightly more than 0V, cathode voltage nominal. As time goes on, these creep slowly upward. After 5-6 minutes, the grid is approaching 3V. 30 seconds after power up: V7 pin 1: 4.8 pin 2,5: .006 pin 6: 134 pin 7: 146 5-6 minutes after power up: V7 pin 1: 6.2 pin 2,5: 2.9 pin 6: 129 pin 7: 139 I note screen and plate voltages have fallen off a little. If they were a little high to begin with, it may be because my line voltage is sometimes a bit high: I measured 122VAC today. I presume the drop in these values reflects increased current through V7. I get the same basic behavior when I have the receiver on a variac and control the line voltage to something less than 120VAC. The audio sounds good for the first several minutes, but it becomes harsh sounding at some point. I don't know what the output waveform looks like. So I could feel better about V7 running hard while I poked around, I put a fan on it, above the chassis ... and lo, the grid/cathode voltages started to drop. The grid stabilizes at about 0.3V with a healthy amount of forced air on the 6EH5, and the audio sounds good. Conductive socket material when hot? I don't think so: I put the tube on a 1.5-inch extender to reduce heat at the socket, with no change in behavior. Bad tube? No, two others behave the same way. I've researched other R4B audio distortion discussions, some on this list. None seem helpful. I'm stumped... any ideas? Thanks and 73, Randy WB4SPB ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] R4B audio distortion
A look at the schematic indicates that you have hit all the usual suspects. So, what else could cause the control grid voltage to go positive? I wonder if the tube socket is leaky. Even if the tube is on an extender it might be the socket. It might be something on the surface of the socket between pins. Pin 6 is the screen grid so leakage from that could cause the problem. Check the socket for carbon tracks or anything on the surface. Clean it thoroughly with dry alcohol. Temperature might make a difference if there is either a carbon track or something else there. Perhaps far fetched but easy enough to do and worth a try. If cleaning makes a difference but does not cure the problem a new socket might be in order. -- Richard Knoppow Los Angeles WB6KBL dickb...@ix.netcom.com - Original Message - From: Randy WB4SPB wb4...@earthlink.net To: drakelist@zerobeat.net Sent: Thursday, February 09, 2012 8:53 PM Subject: [Drakelist] R4B audio distortion Hi folks, I've owned my beloved R4B since the mid-70's. From about 1985 until 2000, it was stored while I got busy with job/family. I used it again for several months in 2002 and 2003, and I didn't notice anything unusual. Now I am active again and want to use it full time, but I am hearing audio distortion after about 5 minutes of operation. Poking around, I observe the cathode of V7 is at higher voltage than expected, and the grid has more than 2 volts, where 0 is expected. Coupling cap C185? No, lift one side, and no change. R154 has the correct value. Cathode resistor? R44 has the correct value, and I tried a different one anyway, in case it was thermally unstable, with no change. I've replaced C176 (along with the other small electrolytics in the RX), no difference. I haven't tackled replacing the big electrolytic can yet, but voltages and ripple seem pretty much OK on all terminals of that unit (e.g. 7mv at C90A, and 35mv at C90D, 75mv at C90C). At power up, the V7 grid is slightly more than 0V, cathode voltage nominal. As time goes on, these creep slowly upward. After 5-6 minutes, the grid is approaching 3V. 30 seconds after power up: V7 pin 1: 4.8 pin 2,5: .006 pin 6: 134 pin 7: 146 5-6 minutes after power up: V7 pin 1: 6.2 pin 2,5: 2.9 pin 6: 129 pin 7: 139 I note screen and plate voltages have fallen off a little. If they were a little high to begin with, it may be because my line voltage is sometimes a bit high: I measured 122VAC today. I presume the drop in these values reflects increased current through V7. I get the same basic behavior when I have the receiver on a variac and control the line voltage to something less than 120VAC. The audio sounds good for the first several minutes, but it becomes harsh sounding at some point. I don't know what the output waveform looks like. So I could feel better about V7 running hard while I poked around, I put a fan on it, above the chassis ... and lo, the grid/cathode voltages started to drop. The grid stabilizes at about 0.3V with a healthy amount of forced air on the 6EH5, and the audio sounds good. Conductive socket material when hot? I don't think so: I put the tube on a 1.5-inch extender to reduce heat at the socket, with no change in behavior. Bad tube? No, two others behave the same way. I've researched other R4B audio distortion discussions, some on this list. None seem helpful. I'm stumped... any ideas? Thanks and 73, Randy WB4SPB ___ 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] R4B audio distortion
Here is where a can of freeze spray can sometimes serve to help with diagnostics. I serviced a Collins 516F2 power supply used with a KWM-2 and found that the molded socket for one of the rectifiers had an internal short that could not be seen from the outside. -Original Message- From: Richard Knoppow 1oldle...@ix.netcom.com To: Randy WB4SPB wb4...@earthlink.net; drakelist drakelist@zerobeat.net Sent: Fri, Feb 10, 2012 12:27 am Subject: Re: [Drakelist] R4B audio distortion A look at the schematic indicates that you have hit all the usual suspects. So, what else could cause the control grid voltage to go positive? I wonder if the tube socket is leaky. Even if the tube is on an extender it might be the socket. It might be something on the surface of the socket between pins. Pin 6 is the screen grid so leakage from that could cause the problem. Check the socket for carbon tracks or anything on the surface. Clean it thoroughly with dry alcohol. Temperature might make a difference if there is either a carbon track or something else there. Perhaps far fetched but easy enough to do and worth a try. If cleaning makes a difference but does not cure the problem a new socket might be in order. -- Richard Knoppow Los Angeles WB6KBL dickb...@ix.netcom.com - Original Message - From: Randy WB4SPB wb4...@earthlink.net To: drakelist@zerobeat.net Sent: Thursday, February 09, 2012 8:53 PM Subject: [Drakelist] R4B audio distortion Hi folks, I've owned my beloved R4B since the mid-70's. From about 1985 until 2000, it was stored while I got busy with job/family. I used it again for several months in 2002 and 2003, and I didn't notice anything unusual. Now I am active again and want to use it full time, but I am hearing audio distortion after about 5 minutes of operation. Poking around, I observe the cathode of V7 is at higher voltage than expected, and the grid has more than 2 volts, where 0 is expected. Coupling cap C185? No, lift one side, and no change. R154 has the correct value. Cathode resistor? R44 has the correct value, and I tried a different one anyway, in case it was thermally unstable, with no change. I've replaced C176 (along with the other small electrolytics in the RX), no difference. I haven't tackled replacing the big electrolytic can yet, but voltages and ripple seem pretty much OK on all terminals of that unit (e.g. 7mv at C90A, and 35mv at C90D, 75mv at C90C). At power up, the V7 grid is slightly more than 0V, cathode voltage nominal. As time goes on, these creep slowly upward. After 5-6 minutes, the grid is approaching 3V. 30 seconds after power up: V7 pin 1: 4.8 pin 2,5: .006 pin 6: 134 pin 7: 146 5-6 minutes after power up: V7 pin 1: 6.2 pin 2,5: 2.9 pin 6: 129 pin 7: 139 I note screen and plate voltages have fallen off a little. If they were a little high to begin with, it may be because my line voltage is sometimes a bit high: I measured 122VAC today. I presume the drop in these values reflects increased current through V7. I get the same basic behavior when I have the receiver on a variac and control the line voltage to something less than 120VAC. The audio sounds good for the first several minutes, but it becomes harsh sounding at some point. I don't know what the output waveform looks like. So I could feel better about V7 running hard while I poked around, I put a fan on it, above the chassis ... and lo, the grid/cathode voltages started to drop. The grid stabilizes at about 0.3V with a healthy amount of forced air on the 6EH5, and the audio sounds good. Conductive socket material when hot? I don't think so: I put the tube on a 1.5-inch extender to reduce heat at the socket, with no change in behavior. Bad tube? No, two others behave the same way. I've researched other R4B audio distortion discussions, some on this list. None seem helpful. I'm stumped... any ideas? Thanks and 73, Randy WB4SPB ___ 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
