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In Reply to: RE: Octal Triode search posted by Frihed89 on February 01, 2015 at 14:34:47
What's the circuit?
Follow Ups:
Of course that's the right question, but i don't have a schematic and I can't follow the wiring that easily, but here: have a look. It's a deHavilland UV3 preamp (made in Vancouver, WA). The first stage uses a 1/2 6SN7GT, but what you call the connection of the grid of the 6SN7GT to the to the plate of the cathode follower 6AH4, I don't know. There's a cap in between the two.The jpg is 5,000+KB, if you want to save it and blow it up.
Observe, before you think. Think before you open your yap. Act on the basis of experience.
Edits: 02/02/15
Hello, was wondering if the two large copper colored caps were stock and also what brand they are. Thanks.
You mean the plate of the gain stage (1/2 6SN7) is coupled to the grid of the follower (6AH4) and there is no cap there. There is just a wire with clear insulation connecting these points. The large copper-colored caps are output caps, since one end of each is connected directly to the output RCA jacks.
What I don't understand is why the other ends of these caps are not directly connected to the follower cathodes. It looks like there are two resistors in parallel off the cathodes, then a wire runs to a board with some chips on it, then another wire runs back to each output cap. But maybe those resistors aren't in parallel.
Anyway, +1 to the suggestion you contact Kara at DeHavilland for help with the gain issue. Remember, you want to maintain the sound quality you already have, and using a different tube type is not likely to get you there. 6BL7 and 6BX7 have the same pinout as 6SN7, and even big twin triodes like the 6AS7 do too, but the operating parameters are very different.
I already re-wired the trimmer circuit so i have full attentuation control over the gain, but it flattens out the sound.
I have already sent a msg to Kara.
Thanks.
Observe, before you think. Think before you open your yap. Act on the basis of experience.
I'm not so sure that you're going to like the 6BL7 or 6BX7. They do have lower gain, but you'll also need to run a lot more current through them compared to the 6SN7.
What you could do is to lift the wires that connect to the tube socket from the attenuator. Put a 100K resistor between each wire and the tube socket pin it used to connect to, then a 33K resistor between those two tube socket pins and ground (looks like there are some ground terminals nearby.
This will pad down the signal before it gets to the first tube.
Otherwise, if you have sensitive speakers and a sensitive amplifier, adding some padding at the input of the amplifier can be more helpful than actually modifying the preamp.
(You could also talk to Kara, she's generally very helpful)
Some attenuators are hidden under a small board on the rear of the amp. I can attenuate the gain from 0-12 dB, now.
Observe, before you think. Think before you open your yap. Act on the basis of experience.
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