6C33C OTL DC schematic needed

[banat]

I find the second circuit very interesting. I guess each tube shown in the schematic is one of the two pairs inside the 6as7, so I need two 150ohm resistors for each tube and a total of 3 tubes (6 tube sections) per channel, am I getting that right?

Two modifications to propose:

1. One could throw away the semiconductor section and build a tube driver connected through the 150ohm resistors to the grids of the final tubes.

2. One could make a tube driver using ECC86 tubes for a full 26V operated amplifier


And two questions:

1. Will this 82uF and 3.3k still be needed for the cathode bias if using a custom tube driver instead of the solid state one?

2. Can I use more tubes on this schematic, say 5 in parallel for greater output and lower impedance?

Modification is always posiblle, think well need long time experimentation and probes(there is no guaranty for final succes).Driwer section with SS 2sc3421 cood be replaced with tube 6c45p (triode), but to substitute input diff OP Amp NJM 2147D with the ECC86 Tube diferencial amp(gain stage) is `tricki` one.This 82uf elko and 3k3 res. together with this 33k res. is the integral part of output stage Bias and NFB net(loop) and well be NOT a part of bias of input ECC86 Tube differencial gain stage.Here in Mr Ikeda schematic bipolar PSU is limited to +- 26V only beacose of Psu limitation of NJM2147D IC`s(see the datasheet of NJM2147D IC).Think this original Mr Ikeda shematic is 100% OK and dont need mods.Four 6as7 with good sensitive 16 ohm speaker well owerperformed any SE Opt 10 W amp for sure.Good Luck

 

[banat]

BTW You allready have this 6c33c-b tube so you cood replace four 6as7 with two 6c33c.In that case you have to find right value of r3/r5 resistor(I well be replace that r3/r5 with 47k trimpot).Good Luck

 

[neazoi]

BTW You allready have this 6c33c-b tube so you cood replace four 6as7 with two 6c33c.In that case you have to find right value of r3/r5 resistor(I well be replace that r3/r5 with 47k trimpot).Good Luck

Thank you very much for your help. Since I like simpler designs, it is more clear to me how I can bias this tor class-A operation (of not already), by varying the resistor values and make measurements on the oscilloscope.

P-P designs are more tricky and matched tubes may be needed.

 

[banat]

Thank you very much for your help. Since I like simpler designs, it is more clear to me how I can bias this tor class-A operation (of not already), by varying the resistor values and make measurements on the oscilloscope.

P-P designs are more tricky and matched tubes may be needed.

Yes agree with You to made some `scope`probe but right sound You well be found with Your Ears during play Your favorite music track and adjusting that trimpot,and listen that over asociated(16-24 ohm) loadspeaker(lets say-line aray speaker box).PP design are not so `tricky` if You use balanced bridge topology(OTL circlotron),and matched output tubes are NOT isue if You use OTL MULTIPHASE BALANCED BRIDGE Concept.Salute

 

[banat]

Actually this hybrid SE OTL cood be powered with wery`Exotic`PSU,two truck bateries(acumulator)24V each(26-27V when is fool charged)conected in series.Or four Automobile/Motorcycle acumulator- 12V/45Ah- each conected in series.remain only filament trafo 6,3v/12A with center tap conectet to earth star point

 

[neazoi]

And if properly manage to achieve the gain of the opamp using ECC86 tubes these can also be powered with 26V, which is about their maximum voltage

 

[banat]

Worth to try for sure

 

[analog_sa]

Think this original Mr Ikeda shematic is 100% OK and dont need mods.

Before everyone starts drooling at the idea of having an OTL for the price of a chip amp let's get a bit realistic. The proposed opamp has an atrocious audio performance and the resulting OTL will likely sound a lot worse than a decent chip amp. Not sure if any opamps with rail voltages above 22v are acceptable for audio but choosing a good opamp may be worth losing a few output watts. And with a good opamp the emitter follower will likely become unnecessary. Another possible improvement will be to replace the cathode follower loads with CCSs.

 

[neazoi]

CCS?

some op-amps have really good performance indeed. My favourite audio equipment up to time is the Le Monstre , fully solid state direct coupled but... tubes are tubes

BTW 2.5A@6.3v for each 6080 tube makes 20A@6.3v for both channels if using 4 tubes per channel and 25A if using 5. Now I wouldn't short circuit this filament transformer....

 

[analog_sa]

CCS?

It will hopefully improve the voltage headroom of the followers and the dc stability. Chokes will arguably be better; i just don't have plate chokes rated for such current and good ones are not exactly abundant.