derrickdj1 Posted April 29, 2018 Share Posted April 29, 2018 Last night I changed my preamp and power tubes. Three of the power tubes biased with no problem, one did not. I tried the bad in other spots to make sure that amp socket was not bad. The bad tube did not bias in the 3 other slot. I can't detect no broken parts, loose part, tube color change or discoloration? Can I get by with replacing only the two tubes on the one side of the amp or do I need to do all 4 power tubes(V1-V4). Quote Link to comment Share on other sites More sharing options...
MerkinMuffley Posted April 29, 2018 Share Posted April 29, 2018 How much off was it from biasing? A few mills will make little difference. 1 Quote Link to comment Share on other sites More sharing options...
Schu Posted April 29, 2018 Share Posted April 29, 2018 Get by... you can probably "get by" with only replacing the bad tube instead of the set on that side. 1 Quote Link to comment Share on other sites More sharing options...
derrickdj1 Posted April 29, 2018 Author Share Posted April 29, 2018 The bias range is 0.35-4,0. The meter is at 0.0 no matter which of the 4 sockets the bad tube is in? Quote Link to comment Share on other sites More sharing options...
MerkinMuffley Posted April 29, 2018 Share Posted April 29, 2018 Probably do just fine by replacing the one bad tube. (Always have a spare!) 1 Quote Link to comment Share on other sites More sharing options...
derrickdj1 Posted April 29, 2018 Author Share Posted April 29, 2018 I just pulled the other three 6CA7 and putTung-Sol EL34B's in and all 4 biased. It took about 1 1/2 min. to bias the 4 tubes. This is just strange that I can't find a tube defect. Maybe I will look into a tube tester, not like I need more things to monkey around with, lol. 1 Quote Link to comment Share on other sites More sharing options...
jimjimbo Posted April 29, 2018 Share Posted April 29, 2018 For now, I think you did the right thing and replaced the quad. That single tube is obviously bad. You can now look for a tube to replace that one. I have a couple of tube testers that I can make available (I have 4, and only need one.....) PM me if interested. Quote Link to comment Share on other sites More sharing options...
Schu Posted April 29, 2018 Share Posted April 29, 2018 Was there sound coming from that "bad tube"socket? 1 Quote Link to comment Share on other sites More sharing options...
derrickdj1 Posted April 29, 2018 Author Share Posted April 29, 2018 1 hour ago, Schu said: Was there sound coming from that "bad tube"socket? No, the speakers sounded the same. I think it would be just a matter of time before some visible form of tube failure. Then the amp may be damaged. Tubes are cheaper than amp repair, lol. Quote Link to comment Share on other sites More sharing options...
Schu Posted April 30, 2018 Share Posted April 30, 2018 I had a similar situation with a non bias tube... the socket itself was grounding in some manner and the mono sounded fine and was actually running fine, but I just could not get a reading at that bias point... but it also didn't move from socket to socket when I moved the drivers around. 1 Quote Link to comment Share on other sites More sharing options...
derrickdj1 Posted May 3, 2018 Author Share Posted May 3, 2018 I talked to the people at Tube Depot and they said the tube was bad. They also said there was no need to buy 4 matched tubes since they will get a good match to the old tube they sold me. They keep good records. The new tube arrived today and all 4 tubes had no problem biasing them. 2 Quote Link to comment Share on other sites More sharing options...
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