audio-talk

Beefed up the heatsink on the heater reg. The sink runs a bit cooler.

Everything squoze in Pin 1 needs strapping to pin 8 to use EL34s. I haven't got 'round to that yet. Just keeping an eye on the heat being put out by the reg before I go any further. It's not too bad after an hour. About 60 deg C

OK,
I changed the resistor on the reg board and using a couple of KT77, which have 1.4A heaters, they came up nicely to 6.3V after a bit of twiddling of the variable pot that sets the current through the reg.
In triode mode the KT77 has a mu of 11.5. This has given a useful boost to the gain, so ...

Hi Paul,
There’s no room in the case for EL34s. I did try a couple by loosening the bracket so they could be lashed up. Unfortunately the Rob Coleman regulator proved not to be set up for the heater current demanded by a pair of EL34 (3A) and it simply sulked when the amp was fired up with them in ...

I have a couple more octal sockets, so I'll make up a module using triode No2 in the 6DN7 over the weekend, slot that in and see how it sounds.

simon wrote: Thu Feb 06, 2025 1:12 pm I've got a couple of 6DN7s if you want to swap them for the 6EM7s Steve

Hi Simon
You loaned me both types.

I think the only problem for a headphone amp with the 6EM7 is the amplification factor of 5.4 on the low mu triode.
You'd be back to 2 stages with that.
OTOH the amplification factor of the low mu triode in the 6DN7 is 15.4. The gain will be knocked down a bit by the loadline so that might work ...

Cheers Paul.

6V6 amplification factor in triode mode is around 9.8 So gain might be around 7.
That’s OK for a headphone amp.

The others I’ve built have had far too much gain, with all the dangers to hearing that the high gain represents. With the single 6V6, it’s loud enough, but not so loud that I put what’s ...

Been having a bit of fun with the headphone amps and have built a nice little single valve headphone amp using one triode connected 6V6GT per channel:
6V6HPA.jpeg
I decided to do this after I acquired a 240V - 2x120V toroidal transformer from Mouser UK last week. Using the two 120V windings in ...

Thanks for all that info Paul.
The bottom end sounds a bit more punchy than with the previous 470uF cap. Whether that has anything to do with Nicks information, I don't know, but it seems probable.
The bypass cap change was born out of expediency as the 470uF caps simply would not fit under the ...

The sound quality has taken another step up. Nice.
All bodes well for the 45 HPA.

Another week and another mod. The input stage is now choke loaded, using one Hammond 156C, 150H choke per channel:
IMG_0607.jpeg
This necessitated making a new board from black perspex to mount the chokes on and cutting a hole in the bottom of the cabinet to provide access to the electronics for ...

Larry Coryell - Cedars of Avalon. (2002)

Focus - Hamburger Concerto (1974.)