help using ECC82 as output tube

[HTH]

I have a Hughes & Kettner Cream Machine 1/2 rack amp that uses an ECC81 preamp stage into an ECC82 run SE to produce around 1w.

It sounds really nice and the output stage cranks nicely at full volume.

Anyway, I'm wanting to add a 1w option to some of my homebrew amps and want to know the primary Z I should be looking at for a SE ECC82 OT (10k was suggested to me)

Also, if I wanted to use both triodes of the ECC82 for a push/pull arrangement, would I be looking at a Primary Z of around 5k? Has anyone tried this and/or could point me to a schematic? I'm assuming it could be wired up much like a typical two-tube output stage with a LTP driving it ???

Any help appreciated, I'm looking to give myself cranked tones at (loudish) bedroom levels and the Cream Machine is fine for that, it would just be cool to add this to my other amps as an option.

[Chuck H]

Well I can't say what the primary Z for the Cream Machine is. But all the info you need will be in the tube data. Just pretend your looking at specs for a power tube.

Chuck

[zhyla]

The ax84 Firefly uses a ECC82 as an output tube. They say it is "self-split" and I'm not quite sure what that is, but I'm pretty sure it's a push-pull configuration.

[Robert M. Martinelli]

Hi HTH,
very nice idea, it would be a great option for all modern tube amps to have!

As already stated, all you need is in the datasheets, my additional advice is to take a look to the Vox valvetronix AD60 / AD120 schematics to see a practical application of this concept, as they both use a double triode ( or two, being the AD120 a stereo amp ) in a push pull "output" configuration ( I used the two "" because actually that stage does not directly drive a speaker, but an ultra-linear output stage ).

Hope this helps

Best regards

Bob

[Steve Conner]

I've used an ECC82 in self-split push-pull before, with the Oxford Electronic Products universal OT from RS. (http://rswww.com part # 210-6475 - also search here for previous threads on it)

It seemed to work pretty well, and actually sounded OK driving a 12", although the clipping was asymmetrical and output just less than 1w. I imagine with proper drive from a PI tube, it would give more power, but I didn't bother, as it was already more than enough to drive the reverb tank. I connected it using the whole primary to give 10k a-a to 8 ohms.

Failing that, I imagine a Fender reverb driver transformer would work in SE. An OT from a SE EL84 amp would probably sort of work too, with a speaker load of twice the design value, although it would probably lack bottom end, due to the transformer being designed for a lower impedance.

[HTH]

I've used an ECC82 in self-split push-pull before, with the Oxford Electronic Products universal OT from RS. (http://rswww.com part # 210-6475 - also search here for previous threads on it)

It seemed to work pretty well, and actually sounded OK driving a 12", although the clipping was asymmetrical and output just less than 1w. I imagine with proper drive from a PI tube, it would give more power, but I didn't bother, as it was already more than enough to drive the reverb tank. I connected it using the whole primary to give 10k a-a to 8 ohms.

Failing that, I imagine a Fender reverb driver transformer would work in SE. An OT from a SE EL84 amp would probably sort of work too, with a speaker load of twice the design value, although it would probably lack bottom end, due to the transformer being designed for a lower impedance.

Thanks for all the replies so far, much appreciated.

Steve, nice one on the link to the OT on the RS site. Good price too at under £10.00

I've found some Hammond OT's that will work too - the 125A will work SE or push/pull (around $30.00) and then there is the 125ASE which has larger air-gap and is physically bigger for improved SE operation ($43.00)

I'll try them both - hopefully there is a Hammond outlet in the UK that stocks them (anyone know?)

[Steve Conner]

The only Hammond outlet here I can think of is Bluebell Audio in Dundee.
http://www.bluebellaudio.com/

[HTH]

The only Hammond outlet here I can think of is Bluebell Audio in Dundee.
http://www.bluebellaudio.com/

thanks for that Steve, their prices are good too - certainly comparable to the US prices that Angela.com list (makes a change, we usually get stiffed for US imports here in the UK).

gonna order the 125ASE and the 125A.

[6267]

Self-split is a pretty neat topology for lower output stages, although you may get more power running them in a more standard arrangement (fixed bias might be neat!). The self-split arrangement is so simple that it's almost a surprise when it works. No PI. Shared, unbypassed cathode resistor (1/2 R of a single triode half). Signal to first grid, the other grid goes to ground. Signal gets coupled through the cathodes. I can't say I entirely understand the theory of it, but it does work--I did a 6bm8 p-p reverb driver this way, and it shakes the springs good.
Another option would be to tap the out of phase signal off of one side of the p-p's anode and run it to the other grid with appropriate attenuation, a sort-of self-split paraphrase (hifi nuts may hate the paraphrase but it can sound great in music amps)...lotsa 2nd harmonic and crunch when overdriven.