audio-talk

Yes, sorry to hear that Phil condolences to Jean and yourself.

It's wrong on so many levels but I might leave it in.

This has to be the daftest thing I've ever done with a headphone amp :lol: :lol:
I fitted my 4V heater transformer and have been using a classic UU4, Art-Deco styled rectifier to good effect,
However, a long time ago now, Paul gave me a few GEC and Marconi U19 half-wave rectifiers, so naturally I ...

Got the TAD Redbase EL84s this morning...nice! Great bass, excellent dynamics and a sweet top-end. That they have a lovely midrange doesn't need saying; they are EL84s after all.
They draw more current than the Russian 6P14Ps, which seem to have slightly higher gain so I've had to revert to the ...

Slight mod to the power supply:
I changed the first cap to a 4uF motor-run, which lowered the HT somewhat, so a GZ32 was used as the rectifier.
This brought the HT back to 308V. I've got a pair of TAD, Redbase, EL84 coming tomorrow, so that will throw the 6P14Ps spare.

I'd be very happy to have that quad of el84s back. Ant put out a story long ago of a military mate who wanted a valve amp and he was putting such together. I sent a quad of these russian valves. Never heard nowt then. But maybe the military mate never happened!

That'd be Andrew Spooner. Was in ...

Indeed they are.

EL84_Audiocct.png
Above is the Audio circuit and power supply.
The thing is completely silent on AC heaters, so I'm wondering whether the 6EM7 HPA might benefit in a similar manner. It'll certainly be a lot simpler.
We'll see. Screenshot 2025-04-12 at 22.24.45.png

EDIT
Wrong diagram of PSU now ...

This is getting silly now, but I couldn't resist it.
During his house move, our Ant has been unearthing one or two long forgotten about valves. The other day he found a quad of Russian 6P14P (EL84) valves and gave them to me. To cut a long story short, after getting good results with the 6EM7 HPA, I ...

Audio circuit:

As I promised Paul I would do, I've just lashed up a 6EM7 headphone amp, using the power valve section of the two dissimilar triodes as a single gain stage. I've used my other headphone amp as the test bed for the job:
IMG_0638.jpeg IMG_0637.jpeg
In the bottom picture, a Meanwell, 12V switch mode ...

I've bypassed the cathode resistor on the 12B4A.
There was a bit of residual hum between tracks with the cathode un-bypassed. That sort of noise drives me up the wall after a while with headphone amps. Some people will put up with it but it gets on my bleed'n wick!
A completely silent background ...

I've ramped up the HT by fitting a higher voltage, 150VA mains transformer.
So now we have more realistic voltages for the EL38s and the 12B4As.

Power supply and audio circuits below:

I now have single-triode, RCA 12B4As running at 11mA as the input stages: It was still slightly too loud with the ECC82s, but with the 12B4As, the gain is now just about spot-on.

Ouch!