• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

The all DHT SET Headphone Amp

I got out my quad of 4P1L's, boy they are odd looking tubes. Trying to find a western equivalent, spec wise I think they are sort of a cousin of the 306A/307A ?

No Western equivalents. They were designed by Telefunken for German military. After WW-II repackaged for Soviet military purposes. The majority of special Telefunken military tubes was repackaged in loctal envelopes, except LS-50 that was too big for that.

Soviet 4П1Л = Telefunken 2,4LS1 in Loctal envelope.
 
I received a couple quotes for single-feed 5k:40 output transformers.

For a pair made by the brits its a bit over $400, with guarantee to design for lowest secondary dcr/inductance M6.

For pair made in sin city its about half that price but not guarantee on high dcr, probably M19.

Then there are china elcheapos called BEZ's that are 4k: 32-64-100-200 for only $100 shipped.

No response from the parafeed experts Magnequest, so rule that one out. Cinemag has some interesting mic ouput transformers that could be good for parafeed, but probably too small for orthos's power.

So its either britain, LV-USA, or China. Have no idea which direction to take.
 
Hi everyone...
A bit off-topic but for those of you using the SSHV regulators, what op-amp are you using in the regulator? I understand that some of the high end op-amps that can be used cause oscillation in the SSHV circuit.
One more thing... Wouldnt permalloy cored transformers be better for use as a headphone amp as they are much more sensitive magnetically? Like the UTC LS or HA series of transformers?
Thanks for your time... Daniel
 
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I know enough about output transformers to know that their is potential to do better than an 8 ohm secondary, hopefully if we can all settle on at least the output tube we could catch a winder's interest to really design a nice OPT for headphones.

Is there any benefit to having multiple secondaries off the transformer based on the headphone's impedance? I was looking around and it looks like some high end transformer coupled amps designed by Pete Millet like TTVJ 307a and Apex Pinnacle have multiple secondaries selectable depending on the headphone's impedance.

Frank Cooter has used Electra-Print OPTs for some of his dynamic headphone amps. For this DHT design were you aiming for something higher/lower priced? I agree with Frank that DC coupled is the way to go. And CCS load both stages.
 
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I received a couple quotes for single-feed 5k:40 output transformers.

For a pair made by the brits its a bit over $400, with guarantee to design for lowest secondary dcr/inductance M6.

For pair made in sin city its about half that price but not guarantee on high dcr, probably M19.

Then there are china elcheapos called BEZ's that are 4k: 32-64-100-200 for only $100 shipped.

No response from the parafeed experts Magnequest, so rule that one out. Cinemag has some interesting mic ouput transformers that could be good for parafeed, but probably too small for orthos's power.

So its either britain, LV-USA, or China. Have no idea which direction to take.

I'm not surprised that Sowter are the only company that will actually do exactly what we want - even if we only order one pair.

It's my personal experience that Sowter will deliver what they promise, and with quality that will last for anyone's lifetime. With that in mind, the cost is not high.

My opinion is that it would be better to use a bipolar transistor to make the impedance transformation, that to use a cheap, or compromised transformer.
 
Ah yes - forgot about that. They are PP so for SE use looks like parafeed. Unless, that is, the PP transformers are routinely gapped for 5mA. If that's the case I could use a 26 at 4 or 5 mA.

I was hoping for the PP version because I have a proposal you might like....

You could use the 9+9:1 connection so that for 62 ohms load you get 20K plate-to-plate impedance and go for an ECC40 Class A push-pull!
At 250V/6mA (bias about -5.5V) you would get about 0.7-0.8W at 1% THD. :D
You need no more than 4V RMS drive which you can get from another ECC40 in concertina configuration. This is able to give 30V RMS at 1% THD! At 4V out THD should be a lot less.....It uses the same 250V supply voltage.

The original Class A PP amp in the datasheet uses 30K plate-to-plate and about 5 mA for 0.5W Pout while the single ended version uses 15K at 250V/6mAfor .28W Pout.
 
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