My Tabor clone has a dual supply with the front end hanging off the bottom rail at -400V. This is generated off the main power supply and the grids are referenced via the center tap of the input transformer. So the Answer is to generate a silicone bottom rail and then put a huge Tail resistor in the front end. Place a pot in the tail (240K) and then you can fine tune it to the right voltage. Unfortunately the Garter bias will not work with direct coupling, so you would need to put CCS's in the tails of the outputs. That will do it. The neg raail only draws about 2mA so is a cinch to build an absolutely quiet supply.
Dave I was looking for information on some Isophon drivers, do you have any Theile small parameters for the 70's vintage Alnico Isophons with cloth surrounds. Planning my reverse taper TL's.
Shoog
Dave I was looking for information on some Isophon drivers, do you have any Theile small parameters for the 70's vintage Alnico Isophons with cloth surrounds. Planning my reverse taper TL's.
Shoog
Hi!
Well, I did not become cleverer one....
1, I didn't want to kill the Baby Huey.
2, I just want to use my 4 pieces of ECL82 tubes, the LL1517 transformers and the 250Vdc PSU what I have already.
3, I am looking for a simple but good amp with only two ECL82 tubes/channel and input transformer.
Something similar arrangement like Revintage' s ECL82noc (but with caps)
So could somebody help me?
Tyimo
Well, I did not become cleverer one....
1, I didn't want to kill the Baby Huey.
2, I just want to use my 4 pieces of ECL82 tubes, the LL1517 transformers and the 250Vdc PSU what I have already.
3, I am looking for a simple but good amp with only two ECL82 tubes/channel and input transformer.
Something similar arrangement like Revintage' s ECL82noc (but with caps)
So could somebody help me?
Tyimo
Tyimo said:Hi!
Well, I did not become cleverer one....
1, I didn't want to kill the Baby Huey.
2, I just want to use my 4 pieces of ECL82 tubes, the LL1517 transformers and the 250Vdc PSU what I have already.
3, I am looking for a simple but good amp with only two ECL82 tubes/channel and input transformer.
Something similar arrangement like Revintage' s ECL82noc (but with caps)
So could somebody help me?
Tyimo
see post no 169 in this thread
I was the source of those dodgy LL1517's - sorry about that. If its any consolation I still haven't found a use for mine. I was thinking of trying to build this design with MOSFETS and an output transformer - running things at valve voltages. I would have to put a OPA627 at the front to drive the LL1517. So many projects and so little time.
I recommend building as originally proposed but with a better ratio output transformer, or building as modified by Jaap. Either will sound good.
Shoog
I recommend building as originally proposed but with a better ratio output transformer, or building as modified by Jaap. Either will sound good.
Shoog
I think mine is elegantly simple - it belies all the interesting ideas it contains. I am not averse to using silicone in the right place, but this design was an exercise in what could be achieved without silicone. The garter bias works particularly well, and allows a differential output stage without CCS's and with zero DC offset - as far as I'm concerned its a miracle and I would do it again where ever appropriate. The grid leak bias works very well and sounds very clean ( there is plenty of input headroom because of the step down), though it does hiss a bit as the valves age and draw a bit more grid current.
But those transformers wont hack it, its fairly important to step down the input. The triodes bias up so low and have so much gain that almost all modern signals will overload the grid. Applying anything but cathode feedback to the triodes just will not help. The partial feedback only effects the plate signal and not the grid to cathode signal.
Shoog
But those transformers wont hack it, its fairly important to step down the input. The triodes bias up so low and have so much gain that almost all modern signals will overload the grid. Applying anything but cathode feedback to the triodes just will not help. The partial feedback only effects the plate signal and not the grid to cathode signal.
Shoog
The final schematic is slightly different to that one so don't all rush out and build it. I think the 66R is now a 47R - with 66R the grids of the 807's ride up at about 90V's which puts the CCS's under a bit of strain. The screens of the 807's are tied to the +B as per Gary Pimms recommendation. Finally there is no screen adjustment for the 6AU6, the output CCS's take up the slack.
You could build it now.
Shoog
You could build it now.
Shoog
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