Einstein pre problem

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RG955TT

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I am kind of stumped and before I pack it up and send it off to be beaten by UPS I thought I'd ask for any opinions on what my issue could be. I had a power tube glowing bright orange and hum went up so I replaced the outer 2 tubes with almost new known good EL34 Mullards bought from Doug's Tubes. Rebiased amp to 74mv (tubes are rated for plate current at 37.5 each) and checked bias on inner 2 at 65 mv. So far so good. Sounds fine. Then I get the idea of seeing what pre-amp tubes are in this amp. I bought the amp used (early serial number 008) and found a mix of several different types. So I tried some new JJ's and Tung Sol mix, a NOS Jan 12ax7wa, several others. I must admit I changed out the first three tubes quite a number of times, settling on the Jan and 2 JJ's 83S for a sweeter overdrive. Then I wanted to try one more different one in V1 and put a JJ there and ...no output, or very low. Changed to a different tube in V1, sounds like only 1/2 of the tube is working, low output, no drive. Changed back to the Jan, drive is OK but as the amp warms up the tone becomes more brittle and harsher on the top end. I know it seems I have an issue w/V1, either the socket or solder joint. I'll pull the amp from the case tomorow, any advise on what I should be looking for? Thanks in advance for any ideas....also, does anyone know of a good amp tech in the Chicagoland area just in case, I'm in the north west burbs. Otherwise I'll have to send to NY to my tech or to Diezel US service (who can I contact and where to ship) Thanks
 
Unplug the amp readjust the small clambs
in the tube socket.

I would go with following tubes:

V1, V2: E83CC
V3 to V6: 12AX7A-C
KT77-JJ: power tubes

Thanks,

Peter
 
Thanks Peter. You're suggesting that the pins from the tube are not making full contact with receivers in the socket?
I see you suggest the EC83CC for one and two and 12ax7-C for the rest but these number by themselves don't mean anything different to me (sorry if I just don't get it, perhaps a brand suggestion etc) JJKT77's for the power tubes ehh? I like the amp a little more on the vintage side, will these help in that regard? What did you like about the KT77's vs the EL34L for example? Thanks again for the response!
 
Yes, get contact with the recievers-

E83CC is from JJ, 12AX7-C is from Shuguang.

There are sold with different names by the distributors.

The KT77-JJ is more reliable than the E34L-JJ for my
experience.
 
Excellent! Ich verstanden....danke schon. (my lame attempt at what little German I remember from school) Thanks again!
 
I replaced all of my tubes about a month ago and then the other day I had both outer KT77's turn bright orange and the hum level went up significantly. I re-checked the bias when it cooled off and it was a little high at 69mv so I dropped it down to 60 or so (it fluctuates a bit) and I haven't noticed the problem since. My question is the orange glow or red plating, is this specifically a tube problem or is it an amp problem. Both times now it's been the outer two tubes with two very different tubes in it.

BTW after trying a ton of preamp tubes believe it or not I settled on V1 and V2 are the cheaper silver box 12ax7-C and V2 is a Jan Phillips 12ax7WA. I tried about everything and this combo is fat and creamy and hamonically very pleasing to the ears. Just thought it moght help someone else out who is looking to go thru 15 differnt pre tubes like I did. Thanks
 
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