Re: [drakelist] AC3 Bias
Thomas Wright [EMAIL PROTECTED] made an utterance to the drakelist gang -- Garey: I think we're saying the same thing. Using two new tubes and each one of the bad tubes to make the trio, I found that all three of the bad tubes produced the same effect when each was used in combination with the two good tubes. I kept exchanging one of the bad tubes in the trio and each time got the same oscillating. This occurred in both transceivers. The only time it functioned properly was when I combined the two new tubes with an older tube which was weak. Then both radios performed normally. The strange thing is that after I peak the rf tune control for max s-level or noise, when tuning the transmitter I find that the current and output peaks at a completely different spot when I turn the rf tune control to peak current. And current peaks when output peaks, of course, but it won't dip. The xmtr gain control will not reduce output or current once the load and plate controls are maxed. And rotating between sidebands makes no difference after the transmitter is tunes either. Both USB and LSB produce high output. I can't say what I'm looking for, but logic suggests that the PS must have something to do with this. Last night I checked at the PS connector and found normal bias and high voltages (although I get the feeling that the high side is a bit high), and I found less than .6 volts of AC at any of the three sides. I've got three new finals on the way, but I have no expectation that those will act any differently. I did check bias voltages with the transceiver on and found them normal at all three final sockets. I'll keep looking. And thanks for your continued comments. Tom - Original Message - From: Garey Barrell [EMAIL PROTECTED] To: [EMAIL PROTECTED] Sent: Monday, December 03, 2007 10:37 PM Subject: Re: [drakelist] AC3 Bias Garey Barrell [EMAIL PROTECTED] made an utterance to the drakelist gang -- Thomas - OK. I'm not sure you did what I asked. Let me try again... I believe I understood you to say that the 20M thing happens in _both_ transmitters when the good tubes are installed. What I want to try is with two of the good tubes and one of the bad tubes, what happens. If the problem is still there, then leave the two good tubes and put in a _different_ one of the bad tubes. If the problem still exists, again leave the two good tubes and put in the third of the bad tubes. What we're trying to determine is if just ONE of the bad tubes is really bad, or if the situation is that two good tubes with any one of the bad tubes results in the oscillation or whatever we're seeing. You also need to check the neutralization with each tube change. It doesn't have to be perfect, but you should be able to get close enough on 20M pretty easily. The voltages you are seeing are certainly in the ballpark. The HV will go to 700 VDC with no load, and should be around 650V at full load of ~350 mA. There's also the possibility that one of the good tubes is actually the problem, but I can't think what it might be! :-) Do you have one other good 6JB6 that you could rotate through the good trio? I thought Gary might have a clue, but I agree that it's unlikely that both transceivers have a bad capacitor resulting in the same symptoms with one set of tubes and not the other. 73, Garey - K4OAH Glen Allen, VA Drake 2-B, 4-B C-Line Service Supplement CDs www.k4oah.com Thomas Wright wrote: Thomas Wright [EMAIL PROTECTED] made an utterance to the drakelist gang -- Garey: The saga continues. This is getting weird. Back to the unable to control the transmit, and unable to dip the plate current on 20 meters thing. Using your advice I used two new tubes and one of the oscillating tubes on both radios (TR-4 and a TR-4C). The same symptom is there using two new tubes and one of the oscillating tubes. The only way I can get this thing to act normally is if I include one older tube that is only producing about 50% output. Any combination of three strong tubes in either radio causes the problem. Now, the only other thing in common is the power supply I just recapped and redioded. No load bias voltage is approx -45-85, low volt is 257, and high volt is a little over 700. At the PA feedthrough under the chassis when idling the voltage was also around 720. Could too high a voltage on the high section cause these tubes to oscillate on higher frequencies? I can't believe that I've got two transceivers that suddenly caught the same bug. WAY too much of a coincidence. Tonight I plan to open the PS and check everything I did, but if you have any thoughts I'd sure like to hear them. And to Gary P...thanks for the comments. I tried
Re: [drakelist] AC3 Bias
Garey Barrell [EMAIL PROTECTED] made an utterance to the drakelist gang -- Tom - OK. Just wanted to be sure we were on the same page! :-) It sure sounds like an oscillation in the PA stage. The only thing that comes to mind is when you have one of the older tubes in there, the maximum plate current is lower. The fact that the max current and output peak at a different point than the max receive certainly indicates that the final is at a different frequency than the receiver. This is also reinforced by the fact that the Pi-net won't resonate, indicating that the frequency is outside the range of the 20M band position. Have you tried to find the oscillation frequency by listening on a general coverage receiver? Knowing that frequency might give us a clue. The fact that the RF TUNE control loses control of the output indicates that the PA is oscillating without drive, once it is kicked off by some initial drive. This is a weird one. Anyone else has an idea, speak up!! I thought Gary was on to something until we found that the problem follows the tubes in two separate transceivers. It's looking more and more like the problem is with the GOOD tube(s)! 73, Garey - K4OAH Glen Allen, VA Drake 2-B, 4-B C-Line Service Supplement CDs www.k4oah.com Thomas Wright wrote: Thomas Wright [EMAIL PROTECTED] made an utterance to the drakelist gang -- Garey: I think we're saying the same thing. Using two new tubes and each one of the bad tubes to make the trio, I found that all three of the bad tubes produced the same effect when each was used in combination with the two good tubes. I kept exchanging one of the bad tubes in the trio and each time got the same oscillating. This occurred in both transceivers. The only time it functioned properly was when I combined the two new tubes with an older tube which was weak. Then both radios performed normally. The strange thing is that after I peak the rf tune control for max s-level or noise, when tuning the transmitter I find that the current and output peaks at a completely different spot when I turn the rf tune control to peak current. And current peaks when output peaks, of course, but it won't dip. The xmtr gain control will not reduce output or current once the load and plate controls are maxed. And rotating between sidebands makes no difference after the transmitter is tunes either. Both USB and LSB produce high output. I can't say what I'm looking for, but logic suggests that the PS must have something to do with this. Last night I checked at the PS connector and found normal bias and high voltages (although I get the feeling that the high side is a bit high), and I found less than .6 volts of AC at any of the three sides. I've got three new finals on the way, but I have no expectation that those will act any differently. I did check bias voltages with the transceiver on and found them normal at all three final sockets. I'll keep looking. And thanks for your continued comments. Tom - Original Message - From: Garey Barrell [EMAIL PROTECTED] To: [EMAIL PROTECTED] Sent: Monday, December 03, 2007 10:37 PM Subject: Re: [drakelist] AC3 Bias Garey Barrell [EMAIL PROTECTED] made an utterance to the drakelist gang -- Thomas - OK. I'm not sure you did what I asked. Let me try again... I believe I understood you to say that the 20M thing happens in _both_ transmitters when the good tubes are installed. What I want to try is with two of the good tubes and one of the bad tubes, what happens. If the problem is still there, then leave the two good tubes and put in a _different_ one of the bad tubes. If the problem still exists, again leave the two good tubes and put in the third of the bad tubes. What we're trying to determine is if just ONE of the bad tubes is really bad, or if the situation is that two good tubes with any one of the bad tubes results in the oscillation or whatever we're seeing. You also need to check the neutralization with each tube change. It doesn't have to be perfect, but you should be able to get close enough on 20M pretty easily. The voltages you are seeing are certainly in the ballpark. The HV will go to 700 VDC with no load, and should be around 650V at full load of ~350 mA. There's also the possibility that one of the good tubes is actually the problem, but I can't think what it might be! :-) Do you have one other good 6JB6 that you could rotate through the good trio? I thought Gary might have a clue, but I agree that it's unlikely that both transceivers have a bad capacitor resulting in the same symptoms with one set of tubes and not the other. 73, Garey - K4OAH Glen Allen, VA Drake 2-B, 4-B C-Line Service Supplement
[drakelist] Burning in New PA Tubes,
Hello, Just wondering on the thoughts of this group on the best way to burn in a new pair of 6BJ6's for a T-4B transmitter. Have heard several ideas in the past, ranging from applying filament voltage for a few days to increasing filament voltage 20% over for a short time. Any good thoughts, and the reason behind them? Best, DW Holtman WB7SSN
Re: [drakelist] Burning in New PA Tubes,
Al Parker [EMAIL PROTECTED] made an utterance to the drakelist gang -- Hi DW, Just b4 somebody else does (am I late?) 6BJ6's won't work very well ;-) 6JB6's OK. I've never heard anything about burning in sweep tubes, but I suppose it wouldn't hurt to leave the filaments on for 8 hrs or so, I've heard that in old transmitting tubes that sometimes had very slightly leaky seals, like the air cooled ones used in Halli HT-33's (can't remember the #, but do have 2 of those amps a cupla tubes), that putting heat to them for 24+ hrs might help. It didn't for me in one of them. YMMV 73, Al, W8UT New Bern, NC www.boatanchors.org www.hammarlund.info - Original Message - From: DW Holtman [EMAIL PROTECTED] To: [EMAIL PROTECTED] Sent: Tuesday, December 04, 2007 6:24 PM Subject: [drakelist] Burning in New PA Tubes, Hello, Just wondering on the thoughts of this group on the best way to burn in a new pair of 6BJ6's for a T-4B transmitter. Have heard several ideas in the past, ranging from applying filament voltage for a few days to increasing filament voltage 20% over for a short time. Any good thoughts, and the reason behind them? Best, DW Holtman WB7SSN -- Submissions:[EMAIL PROTECTED] 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 --
Re: [drakelist] Burning in New PA Tubes,
Dennis Monticelli [EMAIL PROTECTED] made an utterance to the drakelist gang -- I put a couple of NIB 6146B's in my TS-820 a few years ago. These RCA tubes were purchased new (fresh stock) some 20 years previous. When I applied HV and began the neutralization procedure I heard a brief loud pop. The HV caps had been suddenly and momentarily discharged as evidenced by the lamps doing a deep flicker. The pop happened again later that evening after I had put it back on the op table. It did it once more the next day and then nothing ever since. I think either a plate to cathode or plate to beam-ormer ionization trail was the culprit. Had I run the filaments for a few hours before application of HV, the getter would have had an opportunity to scavenge the out-gassing that had taken place over the 20 years of sitting. Moral: HV tubes should have their getters exercised before application of plate. I wouldn't bother with stair-stepping up the filament. Just let them bake for a few hours to give the getters an opportunity to do their thing. I wouldn't bother with receiving tubes. It wouldn't hurt them either. Denny AE6C On Dec 4, 2007 3:24 PM, DW Holtman [EMAIL PROTECTED] wrote: Hello, Just wondering on the thoughts of this group on the best way to burn in a new pair of 6BJ6's for a T-4B transmitter. Have heard several ideas in the past, ranging from applying filament voltage for a few days to increasing filament voltage 20% over for a short time. Any good thoughts, and the reason behind them? Best, DW Holtman WB7SSN -- Submissions:[EMAIL PROTECTED] 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 --
