Re: [drakelist] TR7 oscillation
Jim Shorney [EMAIL PROTECTED] made an utterance to the drakelist gang -- On Fri, 11 Jul 2008 23:13:07 -0500, Jim Shorney wrote: You may recall from our previous episode, I was experiencing instability in the 7-10 MHz band of my TR7 when operating at or near full power levels (140-150 watts) with the upgraded transistors. The instability seemed to be related to the setting of the predriver gain pot, so I was guessing that the predriver board was breaking into oscillation. I have been unable to confirm this. I'm wondering if anyone has been down this road before or has any suggestions? The silence is deafening. So, diving in to the problem with wild abandon and a hot soldering iron Googleing the problem turned up two or three references to notes from other hams in various forums that were experiencing the 40 meter oscillation problem. The only fix that was offered was to turn down the power level, along with speculation regarding the PIN diodes as the source of all evil. This was not satisfactory. I also found references to the power output of a properly working TR7 being 140-150 watts on 80/40 meters, gradually decreasing to a little over 100 watts on 10 meters. From my experiments, it seems that the PA deck is easily capable of this, especially with the upgraded transistors. Looking at the schematic of the (version 2) predriver board, it looks like the R2203-RFC2202-C2204 network from collector to base of buffer Q2201 is designed to flatten the gain of the predriver board across the HF range by providing increasing negative feedback as frequency is decreased. I added a 1K resistor across R2203, which should reduce the net resistance to 338 Ohms. This did decrease the gain somewhat, and I am now able to adjust the ALC for 150 watts CW output on 40 meters at the point where the ALC LED *just* comes on. There is no longer any apparent instability or oscillation on 40 meters at this point. Power on 10 meters is now 105 wattts at 28.3, decreasing to 95 watts at 29.8, with ALC action across the entire band. The predriver gain pot was adjusted at 29.8 MHz, as I previously described. This provides plenty of ALC at 28.3, and just enough at the high end of 10 meters. So far, the PA has been rock stable on all bands after this modification. As the manual states, for proper operation under normal operating conditions the carrier level should not be set beyond the point where the ALC LED just comes on. Observing the output on a scope, power does not increase but the carrier does start to garbage up beyond this point. Better yet, back it off so the ALC light just goes out. On SSB, I like to stay out of ALC as much as possible for the reasons cited here: http://www.nitehawk.com/sm5bsz/dynrange/alc.htm So in a nutshell, to cure a TR7 that oscillates at full power on 40 Meters, try this: 1. Decrease the value of R2203, either by adding a 1K in parallel or replacing it with a 330 Ohm resistor, and readjust ALC and predriver pots per service manual spec. 2. If output on 10/15 meters is still low, try the PA board grounding improvements described by DL7MAJ at http://www.dl7maj.de/TR- 7.html. This MAY NOT work for all cases - this is what worked for me, it may not work for you. YMMV. Standard disclaimers apply. It's your responsibility if you let the smoke out. In stereo, where available. Contains no trans-fat. Note: I do not believe this problem to be a reflection on the upgraded transistors suggested by K8AC, VE3EFJ, and others. Rather, the notes I found seemed to indicate that it can happen in a completely stock TR7, and it seems likely that it is related to component and build variations in individual radios. The work these gentlemen have done is excellent, and I humbly thank them once again. Now, to see what other havoc I can wreak in my poor TR7 while the covers are off... 73 -Jim NU0C -- Submissions:drakelist@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 --
Re: [drakelist] TR7 oscillation
Nice work Jim; this one is going into the Drake List Items by E-mail folder ! 73 de W4DL Mike ex AK7P * WA9SWF * WN9SWF
Re: [drakelist] TR7 oscillation
K8AC - k8ac [EMAIL PROTECTED] made an utterance to the drakelist gang -- Jim - Just received this message via email and it appears to have come from the drakelist at zerobeat.net site, but when I go there, your message is not in the forum there. Maybe you can tell me the exact URL of the site where you posted it? My TR7 with the rebuilt PA ran just fine for quite a while, until I erected a new 40 meter vertical. The first time I used that antenna with the TR7 on 40, the final oscillated. Switching back to a dipole antenna - no oscillation. Really odd, since there is virtually no reactance seen on either feedline and the antennas are a ways from the rig. Anyway, dialing back the gain pot in the pre-driver eliminated the oscillation but of course reduced my output on 10 meters again. I'll have to try your change and see if that changes things. 73, Floyd - K8AC - Original Message - From: Jim Shorney [EMAIL PROTECTED] To: drakelist@zerobeat.net Sent: Sunday, July 20, 2008 12:40 PM Subject: Re: [drakelist] TR7 oscillation Jim Shorney [EMAIL PROTECTED] made an utterance to the drakelist gang -- On Fri, 11 Jul 2008 23:13:07 -0500, Jim Shorney wrote: You may recall from our previous episode, I was experiencing instability in the 7-10 MHz band of my TR7 when operating at or near full power levels (140-150 watts) with the upgraded transistors. The instability seemed to be related to the setting of the predriver gain pot, so I was guessing that the predriver board was breaking into oscillation. I have been unable to confirm this. I'm wondering if anyone has been down this road before or has any suggestions? The silence is deafening. So, diving in to the problem with wild abandon and a hot soldering iron Googleing the problem turned up two or three references to notes from other hams in various forums that were experiencing the 40 meter oscillation problem. The only fix that was offered was to turn down the power level, along with speculation regarding the PIN diodes as the source of all evil. This was not satisfactory. I also found references to the power output of a properly working TR7 being 140-150 watts on 80/40 meters, gradually decreasing to a little over 100 watts on 10 meters. From my experiments, it seems that the PA deck is easily capable of this, especially with the upgraded transistors. Looking at the schematic of the (version 2) predriver board, it looks like the R2203-RFC2202-C2204 network from collector to base of buffer Q2201 is designed to flatten the gain of the predriver board across the HF range by providing increasing negative feedback as frequency is decreased. I added a 1K resistor across R2203, which should reduce the net resistance to 338 Ohms. This did decrease the gain somewhat, and I am now able to adjust the ALC for 150 watts CW output on 40 meters at the point where the ALC LED *just* comes on. There is no longer any apparent instability or oscillation on 40 meters at this point. Power on 10 meters is now 105 wattts at 28.3, decreasing to 95 watts at 29.8, with ALC action across the entire band. The predriver gain pot was adjusted at 29.8 MHz, as I previously described. This provides plenty of ALC at 28.3, and just enough at the high end of 10 meters. So far, the PA has been rock stable on all bands after this modification. As the manual states, for proper operation under normal operating conditions the carrier level should not be set beyond the point where the ALC LED just comes on. Observing the output on a scope, power does not increase but the carrier does start to garbage up beyond this point. Better yet, back it off so the ALC light just goes out. On SSB, I like to stay out of ALC as much as possible for the reasons cited here: http://www.nitehawk.com/sm5bsz/dynrange/alc.htm So in a nutshell, to cure a TR7 that oscillates at full power on 40 Meters, try this: 1. Decrease the value of R2203, either by adding a 1K in parallel or replacing it with a 330 Ohm resistor, and readjust ALC and predriver pots per service manual spec. 2. If output on 10/15 meters is still low, try the PA board grounding improvements described by DL7MAJ at http://www.dl7maj.de/TR- 7.html. This MAY NOT work for all cases - this is what worked for me, it may not work for you. YMMV. Standard disclaimers apply. It's your responsibility if you let the smoke out. In stereo, where available. Contains no trans-fat. Note: I do not believe this problem to be a reflection on the upgraded transistors suggested by K8AC, VE3EFJ, and others. Rather, the notes I found seemed to indicate that it can happen in a completely stock TR7, and it seems likely that it is related to component and build variations in individual radios. The work these gentlemen have done is excellent, and I humbly thank them
Re: [drakelist] TR7 oscillation
Back in the day Drake suggested dropping the output to 120 watts and keeping the predriver gain below 1/2 turn. If there is any instability it always seems to be 40 meters. 73, Gary
Re: [drakelist] TR7 oscillation
Jim Shorney [EMAIL PROTECTED] made an utterance to the drakelist gang -- Hi Floyd, On Sun, 20 Jul 2008 14:02:22 -0400, K8AC - k8ac wrote: Jim - Just received this message via email and it appears to have come from the drakelist at zerobeat.net site, but when I go there, your message is not in the forum there. Maybe you can tell me the exact URL of the site where you posted it? I haven't posted it to the online forum yet. I'll get around to that :) My TR7 with the rebuilt PA ran just fine for quite a while, until I erected a new 40 meter vertical. The first time I used that antenna with the TR7 on 40, the final oscillated. Switching back to a dipole antenna - no oscillation. Really odd, since there is virtually no reactance seen on either feedline and the antennas are a ways from the rig. Anyway, dialing back the gain pot in the pre-driver eliminated the oscillation but of course reduced my output on 10 meters again. I'll have to try your change and see if that changes things. IIRC, I was able to achieve a condition where it would or would not oscillate depending on what it was connected to (antenna or dummy load). I don't remember the specifics, but I think that things must be just on the edge at that point. Let me know what you come up with. 73 -Jim NU0C -- Submissions:drakelist@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 --
Re: [drakelist] TR7 oscillation
Jim Shorney [EMAIL PROTECTED] made an utterance to the drakelist gang -- On Sun, 20 Jul 2008 14:50:02 -0400, Gary Poland wrote: Back in the day Drake suggested dropping the output to 120 watts and keeping the predriver gain below 1/2 turn. If there is any instability it always seems to be 40 meters. Yep, that seems to be the case! :) 7 MHz is just evil, that's it. The devil's band. Or was that 6.66 MHz? Maybe I should have tried holy water first. Oh well. 73 -Jim (holy water cooling? Do the overclockers do this?) NU0C -- Submissions:drakelist@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 --
Re: [drakelist] TR7 oscillation
Jim Shorney [EMAIL PROTECTED] made an utterance to the drakelist gang -- On Sun, 20 Jul 2008 14:09:36 -0500, BSugarberg wrote: And if you have the Version 1 predriver board? I've got no expereince with that one, so I can't help there. THe DL7MAJ document covers the version 1 board, give it a look. http://www.dl7maj.de/TR-7.html 73 -Jim NU0C -- Submissions:drakelist@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 --
[drakelist] TR7 oscillation
Jim Shorney [EMAIL PROTECTED] made an utterance to the drakelist gang -- You may recall from our previous episode, I was experiencing instability in the 7-10 MHz band of my TR7 when operating at or near full power levels (140-150 watts) with the upgraded transistors. The instability seemed to be related to the setting of the predriver gain pot, so I was guessing that the predriver board was breaking into oscillation. I have been unable to confirm this. Thinking that improving the high end gain of the PA might result in needing less predriver gain, I performed the grounding improvements described by DL7MAJ in the document he published at http://www.dl7maj.de/TR-7.html. The net result appears to be a wash - although I was able to achieve higher power output on 10/15 meters with somewhat less gain (104 watts @ 29.7), the 40 Meter instability was still there. I ended up right back where I was, with the rig set for about 130 watts out on 40 Meters and dropping to about 88 watts at 29.8 MHz. Above about 140 watts or so, she starts to want to take off. Previously, I had measured the frequency of oscillation at about 9.6 MHz with a frequency counter. Tonight's testing showed that the PO on 30 Meters was slightly higher than on 20 or 40 meters, suggesting a gain peak in the 10 MHz area. Tuning across the bands, it seems that there is a broad but definite peak from about 9.3-9.7 MHz. This matches up nicely with what my frequency counter says. Whether the peak is in the predriver or PA, I can't tell. The problem with testing at high power levels is that RF tends to get into everything, so my scope hasn't been much help. I'm thinking that if the gain were rolled off a little bit more below 20 meters (where there seems to be plenty), this problem would go away. I'm pretty rusty on my power amp theory, so I'm not sure where to start. I'm wondering if anyone has been down this road before or has any suggestions? Or should I just forget it and be happy? This 40 meter instability just *bugs* me 73 -Jim NU0C -- Submissions:drakelist@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 --
Re: [drakelist] tr7 oscillation, predrivers blown.. My drake b-line twins are laughing!!!
Hello Craig and group, I had problems with oscillation on my TR7. Setting the predriver to minimum gain did not help so I removed R2209 which is in parallel with the gain pot of the predriver. (I have board #2 with one MRF476). This further reduced gain and my problem was solved. I am still getting full output power so gain is still enough. Concerning your driver board, I doubt that the two transistors (SRF2281) must be matched because they are not in parallel but one after the other. Check if reducing your driver gain changes something. There might be a similar problem just like described above. 73, Dieter DL5RDO Hello, I remember why I like tubes now.. :) My tr7 failed one night when I turned it on. It had been performing fine with no apparent problems. I noticed that output power was down (all other functions are ok), then as I continued troubleshooting (checking feedlines etc), it went into oscillation even when unkeyed. We have been tinkering with it, and it appears to start oscillating when we key it (and unkey)after replacing the drivers with a set similar to what was in it. Question: Are these supposed to be a matched set (mrf475)? And, will the pin diodes everyone refers to in the high pass filter cause oscillation? The set (predrivers) that was in it, was not a matched set (not mrf475 or drake stock), and they were not high quality (someone had replaced them before, and done it poorly). The rig did work for quite a while (2 years).. so maybe a matching pair wasn't critical. Looking for thoughts. My service manual doesn't do step by step troubleshooting.. thanks, Craig kc5pgz -- Submissions:[EMAIL PROTECTED] Subscribe: [EMAIL PROTECTED] - subscribe drakelist in body Unsubscribe:[EMAIL PROTECTED] - unsubscribe drakelist in body Hopelessly Lost:[EMAIL PROTECTED] - help in body of message Brought to you courtesy of TLCHost.net http://www.tlchost.net/ -- -- Submissions:[EMAIL PROTECTED] Subscribe: [EMAIL PROTECTED] - subscribe drakelist in body Unsubscribe:[EMAIL PROTECTED] - unsubscribe drakelist in body Hopelessly Lost:[EMAIL PROTECTED] - help in body of message Brought to you courtesy of TLCHost.net http://www.tlchost.net/ --
Re: [drakelist] tr7 oscillation, predrivers blown.. My drake b-line twins are laughing!!!
Craig, I am interested to see the responses you get. I am helping a friend with one doing exactly the same thing, except the drivers didn't go out, he had static (or lightning) take out some of the PIN diodes, he replaced them and now has the same oscillation problem. I am going to re-check his work to make sure some or all of the diodes are installed properly or are all good ones. I'll let you know what I find too. 73, Don, WB5HAK -- Submissions:[EMAIL PROTECTED] Subscribe: [EMAIL PROTECTED] - subscribe drakelist in body Unsubscribe:[EMAIL PROTECTED] - unsubscribe drakelist in body Hopelessly Lost:[EMAIL PROTECTED] - help in body of message Brought to you courtesy of TLCHost.net http://www.tlchost.net/ --
