So here's my story. A while back I built a Class D amp using a Sure Electronics AA-AB31242 and the gigantic power transformer from a dead Sansui amp. It works great except it doesn't have enough gain for my needs.
So I started a project with a 500VCT @40DCMA Hammond 6K88VG which should give me about a 300vdc B+ under load. I've already mounted a 9 pin socket, and a loctal socket, where I think I was going to use a 6CG7 and a 7W7. I sorta lost interest and just recently pulled it off the shelf where I may have a gig soon.
So I'd really like to use the 7W7 in triode mode, and the 9 pin can be whatever. Any ideas? I don't need any tone controls, I like to keep it simple.
Otherwise I may just do an Alembic F2B clone, which would be fitting for my '95 Alembic Epic.
So I started a project with a 500VCT @40DCMA Hammond 6K88VG which should give me about a 300vdc B+ under load. I've already mounted a 9 pin socket, and a loctal socket, where I think I was going to use a 6CG7 and a 7W7. I sorta lost interest and just recently pulled it off the shelf where I may have a gig soon.
So I'd really like to use the 7W7 in triode mode, and the 9 pin can be whatever. Any ideas? I don't need any tone controls, I like to keep it simple.
Otherwise I may just do an Alembic F2B clone, which would be fitting for my '95 Alembic Epic.
It would be best to know a little more. That Sure amp's spec sheet says 10K input impedance. Did you have anything in your chain to help drive it? Active bass, effects pedals, preamp? Sound should be terrible if you were loading down a passive bass to a 10K impedance.
So a loctal and a 9 pin socket, no need for tone controls...hmmm.
If the answer to above question is "no", I would make sure the last stage was a cathode follower to better drive the Sure's impedance.
If you put a dual triode in the 9 pin socket and your 7W7 in the loctal, you could make something like a 1st stage that was switchable between 1 triode in the 9 pin and the 7W7 as pentode, followed by the 2nd triode as a cathode follower. Gives you nice range of sounds.
Personally I would do something like a 12AX7 and a 7N7 in the loctal socket, and use the loctal triodes as cathode followers, 1 to drive a tone stack and another to drive the output.
So a loctal and a 9 pin socket, no need for tone controls...hmmm.
If the answer to above question is "no", I would make sure the last stage was a cathode follower to better drive the Sure's impedance.
If you put a dual triode in the 9 pin socket and your 7W7 in the loctal, you could make something like a 1st stage that was switchable between 1 triode in the 9 pin and the 7W7 as pentode, followed by the 2nd triode as a cathode follower. Gives you nice range of sounds.
Personally I would do something like a 12AX7 and a 7N7 in the loctal socket, and use the loctal triodes as cathode followers, 1 to drive a tone stack and another to drive the output.
I currently use a Line 6 Sonic Port but it doesn't have enough drive and struggles with the Alembic Epic's active output. It's powered by a TI TLE2022 I think.
A 12AX7 is totally do-able, but I've got a good stockpile of 7W7 that I've been dying to use.
A 12AX7 is totally do-able, but I've got a good stockpile of 7W7 that I've been dying to use.
Don't understand this comment. Your 1st post said the 9 pin tube "can be whatever". What does that have to do with using a 7W7 in the loctal socket?
The hum should go down when you put this in a proper metal case. Until then, try using shielded cables for the volume control. Note that the triode sees a worst case input impedance of 500k+100k = 600k. That makes it susceptible to noise pickup.
No RF problems. Quiet as can be. Not even heater noise which surprised me.
Where is the 500k coming from? I'm not a proper engineer and I've got a lot to learn still. I do know the plate resistance of the 7W7 is 300k: . I can also drop the 6CG7's grid resistor from 100K to 1K which might help. I suppose that's why the curcuit I'm borrowing from also uses a transformer to change the load.
Is there a better alternative to the 6CG7? It seemed like an ideal cathode follower.
Where is the 500k coming from? I'm not a proper engineer and I've got a lot to learn still. I do know the plate resistance of the 7W7 is 300k: . I can also drop the 6CG7's grid resistor from 100K to 1K which might help. I suppose that's why the curcuit I'm borrowing from also uses a transformer to change the load.
Is there a better alternative to the 6CG7? It seemed like an ideal cathode follower.
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Replaced the 100k grid resistor on the 6CG7 with a 1k and added a capacitor on the input. Smoke test was OK. Hooked it up to the Bass and Amp... a massive mountain of gain! Nice. Also seems to add some compression which is much appreciated.
BUT... some wicked strong 60hz buzz. 🙁 Probably heaters. Not sure without having an ocilloscope handy to probe around.
BUT... some wicked strong 60hz buzz. 🙁 Probably heaters. Not sure without having an ocilloscope handy to probe around.
Not yet. I'm going to reverse the polarity of the heater wires on the 6CG7 first and then I'll try the resistors.
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