New 'Phones

[Paul Barker]

Alls well that ends well. Youve built it beautifully as you always do. You’ve still got it.

[Paul Barker]

Langrex are selling Western made 6C5’s fore runner to the 6J5 for £7.50, just saying. Prefer that to Chinese 6sn7 I know you need two but £15 not at all bad for a similar enough valve made properly in the West.

[Cressy Snr]

Langrex are selling Western made 6C5’s fore runner to the 6J5 for £7.50, just saying. Prefer that to Chinese 6sn7 I know you need two but £15 not at all bad for a similar enough valve made properly in the West.

Thanks for that Paul, I'll have a look right away!

[Cressy Snr]

Hold the bus!

I've just found a black T-plate 6SN7 from the 1950s by the Italian firm Fivre. It has a broken spigot on the base but getting it the right way 'round in the socket was easy enough. The base can be repaired with one of these from Hotrox:

Screenshot 2025-05-31 at 16.01.33.jpeg (8.88 KiB) Viewed 41763 times

The prices of these particular 6SN7 in NOS form are tantamount to feckin' daylight robbery 400 to 800 Euros for a NiB matched pair
I'm sure I have another one somewhere without a broken spigot, but I'm damned if I know where it is.

Anyway this valve is a great deal better than any of the Russian or Chinese 6SN7s I have.

I still intend to get in a couple of metal tube 6C5 in though; why wouldn't you at those prices.

[simon]

I don't think it'll embarrass me at Owston in September.

You mean you're not going to try something else between now and September?

If you can use 12V heaters Billington has nos US 12SN7 for £11. Or 7N7 which is the same as 6SN7 with a loctal base, also nos US, for £10. The only problem with Billington is they charge a 50% premium for orders less that £240.

Or something completely different, but the same, a 7A4 which is half a 6SN7 but also in loctal - Jono Noble recommended these in the past.

[Cressy Snr]

You mean you're not going to try something else between now and September?

Probably not. Don't want to tempt fate with the respiratory stuff. Can't be doing with the unpleasantness of the symptoms.
However, I will look at the 7A4 option for when I feel up to doing a bit more.

[Cressy Snr]

OK,
Heres a pic of the headphone setup as it is now:

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Looks like the monitor has air extraction
It’s there to get prevent one posting too much hot air.

[Cressy Snr]

I bought a pair of the General Electric, 6C5, metal tubes Paul mentioned in an earlier post.
At £7.50, you can’t go wrong. I might get around to doing something with them before Owston; we’ll see how things go.

[Cressy Snr]

EL38s have returned to the fold:

EL38.jpeg (60.99 KiB) Viewed 19596 times

This time as a single valve amplifier.
5k output transformer tap on the primary side and the 32 Ohm headphones connected to the 16 Ohm tap. That's as far as the OPTs go.
What impedance that reflects to the primary I don't know. Can't remember the bloody formula.

[Paul Barker]

10k

So less distortion and you hVe plenty of power anyway. I love my el38 se. I cant beat it with el84 pp

[Cressy Snr]

10k

So less distortion and you hVe plenty of power anyway. I love my el38 se. I cant beat it with el84 pp

Cheers Paul,
Yep, the EL38 is a great valve. Out of all the combinations I’ve tried, it sounds the most natural and just gets out of the way of the music. There’s plenty of gain using it as a single valve. Also, single valve operation keeps everything ultra-simple.
Apart from the known problem of power valves being a bit microphonic at milliwatt levels it sounds great. And microphonics aren’t really a problem with headphone amps unless you start banging the valves, which you wouldn’t do anyway.
I suspect 45s 2A3s and 300Bs would suffer the same problems at low levels with cans stuck to your ears.

[Cressy Snr]

Well I tried to put DC heating on the amp and what a disaster! A right bleed'n racket of buzzing.
It all went silent when I touched the top caps of the EL38s.
Looks like the RF field coming from the onboard SMPS DC supply is being picked up by the anode leads.
I can't be arsed with anode stoppers, ferrites or anything else, so I cut off the anode leads and subbed in a pair of KT77.
Not a peep of noise anywhere apart from microphonics, which has happened with every power tube I've tried.

Anyway the plan now is to rebuild the whole thing as a two box system, with the power supply and DC heaters in one box; the last cap and the rest of the amp in another box.
I'm abandoning any idea of using power tubes; they are too microphonic with a speaker right next to one's ears. I've learned the hard way that far more appropriate tubes for HPAs are 6H30P, 6N6P, 6N1P, 5687, ECC88, ECC99, ECL8* or 6EM7. Plenty of perfectly good tubes for the job there.

[Mike H]

Looks like the RF field coming from the onboard SMPS DC supply is being picked up by the anode leads.

This is why I have separate SMPS PSU(s) and low pass LC filters on the supply lines into the amp box.