EL84/6P14P Headphone Amp

[Cressy Snr]

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 thought I'd try out the 6P14P as a single gain stage headphone amp.

IMG_0640.jpeg (102.93 KiB) Viewed 9437 times

IMG_0639.jpeg (144.54 KiB) Viewed 9423 times

I've ditched the EL38 for now, as I want to build something that will do the valve justice. I'm considering a pair of JBL Control 1 speakers for the study system and at 89dB efficient they should cope with a 4W amp, as the room is only half the size of the living room and I will be listening in the near field.
This little amp sounds excellent on my headphones and as a single valve, the gain is just right.

[Cressy Snr]

EL84_Audiocct.png (27.34 KiB) Viewed 9425 times

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 (50.75 KiB) Viewed 9331 times

EDIT
Wrong diagram of PSU now corrected.

[Ant]

Thought the 84 would make a good hpa valve, gain is about right

[izzy wizzy]

I have AC heaters in my line stage. Wouldn't even know if it's on. It is differential not SE. Don't know if that would make a difference.

[Paul Barker]

Back in the day when those Russian equivalents to the EL84 were cheap as chips, I preferred them to Mullard EL 84’s. Also the Russian version of the ECC83 but with a different heater supply and so different pin out sounded better to me to the Mullard ECC83. I put them in my various riaa stages which called for Mullard such as the WAD phono stage and one from Glass audio called “True Realism”.

True Realism was the better of the two. The OEM EAR phono stage was a bag of shyte even after I applied the Thorsten mods. So I sold it, there were always people that wanted to buy an oem phono stage. Now I am not besmurching the Late Tim de Paravachini Im only criticising one of his products, nothing else. We can all have a bad day. RCA phono stage was also shyte.

The Oz Lurch Phono stage was the first to use a fet. But sadly the schematic dissapeared of the web over 20 years ago and its not even found on the way back machine. Actually I dont thing it ever appeared on any of the forums. It was recommended by my friends on the private email group with Steve Bench and other seniors at that time who were also on the Jo list. If you lost those emails you losst all those schematics. Whish I had the oz Learch schematic.
But anyway those el84’s are great!

[Cressy Snr]

Indeed they are.

[andrew Ivimey]

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!

[Cressy Snr]

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 the army, in Afghanistan, Helmand Province at the time. He left the army at the end of the tour, worked for a while as an inspector of water and aircon facilities, Legionella and all that, but Ant lost contact with him quite a while ago, so the amp never got built.
PM me your address and I'll get the valves back to you.

[Cressy Snr]

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.

EL84_HPA_PSU_4uF.png (44.68 KiB) Viewed 5285 times

I've got a pair of TAD, Redbase, EL84 coming tomorrow, so that will throw the 6P14Ps spare.

[Cressy Snr]

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 5R4GY in order to avoid over-dissipating the TADs.
With the 5R4GY rectifier, the TADs run at 10.5W of anode dissipation, 1.5W below maximum. They seem happy with that.

[Cressy Snr]

This has to be the daftest thing I've ever done with a headphone amp
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 thought, why not try one out after a solid state bridge, you know, like you do.

It looks ridiculous, louring menacingly behind the output transformers like something out of Quatermass. And it's only feeding a pair of EL84. But it's nothing if not fun.

IMG_0648.jpeg (73 KiB) Viewed 762 times

IMG_0647.jpeg (60.86 KiB) Viewed 747 times

And the fecking bass is riciculously good! The 120mA UU4 will be put back, as the GEC giant is complete, utter overkill but the U19 does sound rather fab.

[Paul Barker]

Well thats great.

[Ant]

Leave it in there, why not?

[Cressy Snr]

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

[Paul Barker]

Its a Harlem Globe Trotter standing tall over the Shire.