Working on a better 6AT6 Matchless Clubman schematic

[redplate]

Hi all,
I've been trying to map out a more accurate schematic of the first version of the Matchless Clubman (6AT6 -> 6SH7 preamp). There's a popular schematic at http://www.prowessamplifiers.com/schematics/post/matchless_clubman.pdf of a 12AX7 -> 6SH7 version but apart from the obvious differences, it seems to be off in a few places. I've mostly been working off of chassis pictures I've found around the web which I've collected here: https://imgur.com/gallery/mZ7Jr.

The main differences I've noticed so far are that the resistors in the bass control appear to be 150K not 100K (which makes sense as the 6AT6 wouldn't drive the tone stack as hard as dual 12AX7s), and that the .01 capacitor in the treble control comes after the pot, not before it as in the schematic. I'm running into difficulty in three spots which I've highlighted in the last picture in the album above:

1. I believe this is part of the circuit just before the effect loop send jack. It sort of matches up with what's in the existing schematic albeit the 25uf is really a .01uf and the 470K is a 47K. Also confusing is that it appears there's a shielded cable directly from the volume pot to the effect loop send jack.

2. These two occluded resistors. One is the supposedly 10K resistor in the schematic connecting the bass and treble controls. In one of the pictures you can clearly see the orange band and what looks like a flash of green so it could be 15K. This would make sense if the whole tone section was scaled down for the 12AX7 version. The other I believe is the 150K in the schematic leading to the effects send jack though it's impossible to tell from these pictures.

3. I have no idea what's going on here. This network of two 480R and two small-ish capacitors seems to be connected to the heater supply and then to a small purple wire that heads towards the preamp but disappears into the fray.

If anyone has (or has had) access to one of these amps or if you have different pictures that would be a huge help in figuring this out. Some times it just takes another set of eyes. I will of course post the revised schematic when it's complete.

Cheers,
Dani

[sluckey]

3. I have no idea what's going on here. This network of two 480R and two small-ish capacitors seems to be connected to the heater supply and then to a small purple wire that heads towards the preamp but disappears into the fray.

480Ω is not a common value for carbon comp resistors. The resistors inside your green area 3 box are 47Ω (yellow-violet-black).

With the wire bundles laced up neatly you will probably never figure out the schematic from those few pics. I would need that amp on a bench and use an ohmmeter to reverse engineer an accurate schematic.

[redplate]

Nice catch, thanks.

With the wire bundles laced up neatly you will probably never figure out the schematic from those few pics. I would need that amp on a bench and use an ohmmeter to reverse engineer an accurate schematic.

Agreed, but if I had access to an early Clubman I wouldn't need to build my own :)

I was hoping someone here might have worked with one before.

[sluckey]

Agreed, but if I had access to an early Clubman I wouldn't need to build my own :)

I guess so. If you had access to one you may not want to build one, but you could figure out how it's wired.

I was hoping someone here might have worked with one before.

I've never seen one or a schematic either. If you start this thread in the "Tube Amp Building" forum, a lot more people will see it. It's possible someone may be familiar with that amp. I don't recall ever reading a discussion about that amp.

Is this supposed to be a more special amp than the version that has a readily available schematic?

[redplate]

If you start this thread in the "Tube Amp Building" forum, a lot more people will see it.

I'll try this, thanks.

Is this supposed to be a more special amp than the version that has a readily available schematic?

I think so. Matchless was (and is?) famously uncompromising when it came to production so I assume that any small deviations exist for a good reason.

Apart from that, I just like my clone projects to be as accurate as possible, at least at first. I'm planning to make the amp easily modifiable between the two circuits.

[sluckey]

From what I read the 6AT6 version came first and only lasted less than a year before being replaced. Don't know why but usually when an amp is replaced that quickly the next generation is usually a 'fix' for something. Supposedly the creator was bored with so many 12AX7 amps and wanted to do something different. Didn't take long to get back on the familiar path. 

[DummyLoad]

i have read elsewhere that the 6SH7 was replaced with 6SJ7 due to issues with 6SH7 being not suitable for audio use and reported reliability issues. the current version is equipped with 12AX7 and EF86.


use a 6AV6 if you are going to use 12AX7 values for that amp and use an EF86 or 6SJ7/5693. likely there were many changes to the production line over time and trying to nail down what was done without actually reverse engineering ONE particular unit, then it's just a best guess as to what to build. build it following the documentation that is available then perhaps tweak it to your own taste.


--pete