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Discussion in 'Amp Central Station' started by RustySterling, Apr 16, 2020.
Sorry to hear this! Will be throwing good thoughts your way! Hope she recovers quickly!
Thanks everyone for their well wishes. Turns out she has a bacterial infection that leached into her blood stream. They are testing her for Covid-19 but the prognosis so far is very good.
Meantime, I've done a lot of tube rolling and still conclude that it's the speakers.
After the good news about my wife, I did some tube rolling. This had all the original Fender Groove Tube valves. I tried JJs in power, never really like them. I also have a pair of RCA black plate with some life left so I settled on them. Put a E-H 12AY7 in V1, Tung-Sol 5751 in V2, EH 12AT7 in V3, 12AX7s in V4 & 5, and (I played with a lot of tubes) settle on a Tung Sol 5751 in V6. Sounds better, closer to being articulate but still quite ice-picky. I can tame it some with tone controls on amp and guitar. Leaning more toward Webers for speakers, with Warehouse running second. Still a lot to consider.
Rusty, ime, one thing these amps can use is a bias voltage adjustment. Fwiw, there is a hole in the back of the chassis that is ready made for such an application. It is covered up by the rear panel plate, but one can drill that out. Note: the bias vary trem is affected by that bias point. I did one CVR that would cease Trem function above 62% of max plate dissipation. Another one would run 68% with trem function but not above that. This point seemed to be particular to the certain power tubes.
I also like to create a different sounding channel on the left and install a negative feedback loop with an adjustment pot in it. Fwiw, the Reverb being applied to the left channel is NOT what causes the noise that some folks object to.....that comes from the lack of a NFB loop. I like the reverb on both channels.
I’m glad about the good news about your wife’s health concern!! Scary times...
Glad to hear she's alright.
Whenever those RCA tubes are spent, I highly recommend current production Tung Sol 7581A's. They're beefier and have a wider range than typical 6l6's. Kinda in the same family as KT66. They sound beautiful and would have a long lifespan. I also agree with Wally about getting a bias pot in there sometime, since the 7581A's like to be run hotter.
glad things are progressing nicely.
First, update on my wife: No coronavirus. She's leaving the hospital today. Just glad it wasn't more serious.
I agree with all about a bias pot. I got a footswitch yesterday and now I've discovered the reverb doesn't work. So, I'll have to drop this puppy and do the chopstick dance with the reverb section but I'll just check connections first. I have a EH 12AT7 in the reverb section, which should be a good valve for that. I've always found EH tubes to be very musical, which is what I'd want in the reverb section.
V3, a 12AT7, is the reverb driver. V4A is the reverb return. Sub tubes in those spots one at a time to see if it is simply a tube problem. If that is not a cure, unplug the cables from the amp and measure the resistance at the end of each cable. You should see 2ohms or a bit less 9n one cable and 175-200 ohms on the other. If you see those numbers, the problem is inside. If you don’t see those numbers, pull the tank and take measurements at the jacks’ connections to the inductors in the tank. This will well you if you have a bad tank or a bad cable.
@Wally Thanks. That's all helpful. I put in a new Tung Sol 12AX7 in V4, but I'll find the old tube and try it. Previous owner said he didn't use the reverb because it was noisy. We shall see.
So sorry to hear. Hang in there. I will keep her in my thoughts.
@frank a Thanks. At least, as it turns out, it wasn't the coronavirus. She tested negative but had a lot of the symptoms. Turns out to be a bacteria infection that got into her blood stream. She's home now.
Will keep on sending good juju y'all's way! But, glad to hear she's home.
I have rarely had a reverb issue be something inside the amp... As @Wally gave you the order to check, I have found tubes, tank, cables (in that order) be 90% of the reverb issues I've personally seen.
But, once you get it working, the reverb on these amps is nice and warm and luscious! Enjoy!