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Dug out the Egmont variant I made a while back and reinstalled the original 6BL7 outputs (I was using triode connected 7591's) and changed the the cathode bias to fixed bias. Preferred the 7591's by a small amount (an NOS quad will run $300.00 compared to $30.00 for a pair of 6BL7). Changing the bias scheme, although I can't measure the results, resulted in a signifigant subjective improvement. The amp seems punchier, more defined, and tighter in the bottom than with cathode bias. Definitely worth the small additional complexity.

I used a battery stack as a neg. supply to get things started, but as a permanent solution (assuming you are building your own supply) I'll simply use a tapped voltage doubler off the neg. rail ( basically a mirrored image of the headphone bias supply).

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Fixed bias is indeed a much better way to do this. For the extra negative supply I'd just make small, fully floating, regulated supply but pretty much anything works. Batteries are a fun way to do it especially with a large sign saying not to touch... grin.gif One of my friends got a bit too close to the ES-1 when I was testing it's revised output stage but one mention of the batteries floating at -460V was enough for him to back off.

While we are on the subject, I'm making slow but steady progress on my B-10 (improved A-10):


Trying to keep this as small as is possible so 1U for the amp and same size 2U chassis for the PSU.

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  • 3 weeks later...

Time for an update on the B-10 as it is now called. smile.png I decided it was just best to stick with Rays fubar amp design but improve on it where possible so the volume control was moved to the front of the circuitry (not in the middle as on the A-10), grounded DC heaters used for the input tubes and AC heaters used for the output tubes (hungry at 4A). Now using a SRPP setup in a single tube is rather stupid since it means there is too much voltage on the cathodes for the cathode/heater gap. Best way to mitigate this is to use a center tapped heater winding and float it on +300V so this only becomes an issue with the amp swinging 500V or more. Other than that the amp is pretty much stock and here are a couple of pics:



The psu will be in a same size chassis but 2U in height. I designed a new PCB for it loosely based on the old GES supply which should arrive soon.

Edited by spritzer
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Any expectation of te sound?

I cobbled together a version of this circuit when the A-10 first came out so I have a good idea how this one will sound. Thick with distortion and no output power what so ever. There are some tricks here though to try and make the SRPP circuit behave as it should (it only really works into a fixed impedance) so there should be a marginal improvement. For me the enjoyment is building this stuff even if it will sound sucky and with these tube amps it's a lot of fun to dig through my castoff bins to find the parts I need. All the terminal strips in this amp are from the ES-1, the plate resistors for the ECC83's are the brilliant TKD CM2's pulled from a SRM-T1 and the coupling caps are from my first ES-1 repair attempts. I never throw anything away... laugh.png

Birgir, I've made a bunch of adapter pcbs for the alpha pot and ended up with some extras. Do you want them?

Sure, I still have a pile of the Alpha pots left. :)

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