Modifying the classic Williamson

[artosalo]

My intention is to try and use the original Williamson design topology and run 6L6 output tubes to obtain 25 Watts of output power.

This means that you can not use the triode connection, which is the original circuit.
UL-version came many years later.

[grungeman91]

Originally Posted by artosalo

This means that you can not use the triode connection, which is the original circuit.
UL-version came many years later.

I don't intend to run them in triode.

[SY]

Originally Posted by grungeman91

As far as "iron" goes, and I'm assuming you mean the transformers, I am using the finest Hammond Transformers.

Getting the amp stable with Hammond transformers may prove a challenge- the Williamson is VERY demanding of the transformer bandwidth.

In any case, to reiterate:

1. Nothing in the driver stages needs to be changed when going to 6L6 except compensation.
2. The output stage operating points will have to be altered.
3. The output stage topology will have to be altered to get to 25 watts. UL is a good option. If your heart is set on triode, accept that you'll have 15 watts instead, and that the perceived volume difference between 15 and 25 watts isn't exactly night and day.

If you want further advice on changing out the output stage, it will help if you mention which transformers you're using.

[artosalo]

Here is a good document of the Williamson UL-version.

http://www.technicalaudio.com/pdf/Go...-8072_xfmr.pdf

[kenpeter]

Not exactly Williamson. But similar open loop voltage gain and pole count.

[kenpeter]

I'm not sure what is "LF instability" in Williamson?

I do note a problem when an overdriven closed loop is asked to fix impossible.
The concertina goes overcenter and no longer splits properly. Output pentodes
well saturated before that ever happens, so not directly heard. But can make
weird charges build on coupling caps that mess with bias and can be heard...

D1 is my fix for that. Prevents concertina from going overcenter.

[coldcathode]

I think there is an acrosound schematic for UL tapped 6L6's out there?

[SY]

Originally Posted by kenpeter

I'm not sure what is "LF instability" in Williamson?

Two of the zeros are too close together. Easy to fix, triple the size of one of the sets of coupling caps, drop the size of the other set by 2-3 times.

[coldcathode]

Here it is,

just what Hammond is similar to TO-300?

[coldcathode]

Looks like a 1620a would drop right in to this schematic.