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/ ----------------------------------------------------------------------
