i'm trying to make something useful out of a butchered hohner orgaphon keyboard amp. It has a PP PL84 output stage, ecc808 PI (needs new expensive tube), 12ax7 tremolo oscillator, ecl86 reverb, and a really crappy solid state preamp. I would like to use the ecc808 and 12ax7 tube for a nice tube preamp for guitar.
I already found a way to make the tremolo with some irf820 mosfets.
The phase splitter could also be done in FET. I don't like PI clipping, I want a clean one so why not try a FET. I've looked on the web but I didn't find any examples. I would like to see some opinions on different topologies.
Why aren't more people using solid state phase invertors? Is it just because of the added complexity?
I already found a way to make the tremolo with some irf820 mosfets.
The phase splitter could also be done in FET. I don't like PI clipping, I want a clean one so why not try a FET. I've looked on the web but I didn't find any examples. I would like to see some opinions on different topologies.
Why aren't more people using solid state phase invertors? Is it just because of the added complexity?
I dont see any reason to use solid state for phase invertors or any other stage, what are the problems you see with tube based splitters that could be solved using solid state?
Do you think that a FET based PI gives lower distorsion then a tube based? I dont think so, not with the same number of active elements anyway.
I always use the split load or concertina phase splitter, it is very good but maybe a bit misunderstood, the only disadvantage I see is that you need very high B+ in order to get high output swing and that can get you into problems to select suitable phas splitter tubes but otherwise the split load is very good.
Regards Hans
I quite like the long tailed pair. IIRC, EL84s are easy to drive, and 1/2 12AX7 driving each EL84 should give it heaps of drive without too much distortion.
In this case however, you probably want to use the cathodyne option as it only uses 1/2 a 12AX7 for both tubes. You can then cascade all the remaining sections in front of the phase inverter and get heaps of really crunchy distortion.
Get rid of the ECC808, too obscure. Unless it tests as new, ECC83/12AX7 is close enough... Different pinout tho.
Get rid of that SS preamp tho
In this case however, you probably want to use the cathodyne option as it only uses 1/2 a 12AX7 for both tubes. You can then cascade all the remaining sections in front of the phase inverter and get heaps of really crunchy distortion.
Get rid of the ECC808, too obscure. Unless it tests as new, ECC83/12AX7 is close enough... Different pinout tho.
Get rid of that SS preamp tho
Here I need the tube for the preamp. Then I have two tubes for the two channel preamp. If there was any room for extra heater current I would just use a long tail pair splitter.
In a guitar amp a bit of distortion isn't that bad and tube distortion sounds better to my ears. But I need the tube for a preamp. My thought is to make it solid state, as it doesn't get overdriven in this amp. If the PI isn’t overdriven it doesn't contribute much to the "tubey" guitar sound. That's also why I'll probably use an IRF820 cathode follower in the preamp.
I'll do that as the ecc808 is way too expensive for the small performance upgrade.
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