Another express rewire

[KGW]

http://beggingdogrecords.tripod.com/TWEX.html

Obsessive as I am, I did another rewire (I've done at least 3) on my express clone to try to further reduce the hum and fix a "sound" that I was getting during sustained notes (note rings, low end fades out and back in). I have not had much time to play the amp, but the hum seems to have gone way down and the "sound" is mostly cured.

details are on the link above.

[Tubetwang]

I like it Kevin!

Nice and clean...

Hey i also built a few Bottleheads in my days...

I did the Champ with Solen instead of eletrolytics...and auricaps ...

[Fischerman]

So did you orig wire it using Alan's suggested ground scheme or did you just change it to that? What was it before and what is it now?

Nice looking build. There appears to be at least one OD near the fuse holder...what's that for? Why did you mount the bias resistors on the socket? Always curious!

[KGW]

So did you orig wire it using Alan's suggested ground scheme or did you just change it to that? What was it before and what is it now?

Nice looking build. There appears to be at least one OD near the fuse holder...what's that for? Why did you mount the bias resistors on the socket? Always curious!

I've tried a few grounding schemes. The last was using 12AWG ground busses - one for the pre and one for the power amp. It worked pretty good, but I'm thinking that Allan's is better. And yes, I was skeptical that it would cause more ground loops. However, you can't be sure until you try, right?

The OD near the fuse is a line filter. It helps the sound of the air conditioner/heater going on/off from getting into the amp.

Bias resistors - I tried this (the "Traynor" mod) on my 1987 (see photo - sorry about the flux) and liked it. The raw bias voltage goes to pin 1 (G3 on an EL34, n/c on a 5881). This is purported to give more life to EL34 tubes (BTW, I have the Mullard reissues). My 1987 has a 10 turn pot with a turns counting dial (like the Komets) and has enough range to accommodate both EL34s and 5881s.

Mounting the bias resistors this way is suggested in Gar Gilles' book as well - a bit more convenient to wire IMHO.

[rooster]

Kevin - Yeah, it looks good. However one thing you have avoided, and maybe not on purpose, is the *proper* 9 pin sockets? I did this, too, on the first build and realized that the ones KF used are actually about 15 degrees different than what you ended up with. I now use the ones made by 'Cynch' [sic], not too sure how it is spelled. Whether this made an actual improvement to the character/noise floor of the amp, I can't blind test tell you because I have no intention of going backwards to find out. However I have to say that my impression is that it did/does - my Express is very quiet now and it wasn't quite there before.

Using these *proper* sockets just makes way more sense of the KF layout. V2 for example, using your socket, its probably a better layout to use pins 1-3, and not 6-8. Do you see this? Your pin 8 is crossing the filament wire, for example, probably not the best layout. Too, the phase inverter is a tangle of crossed wires compared KF's build. Go back and look at Francesca maybe, you will see this.

I have read here that someone thought that KF used pins 6-8 because this section of the tube was actually quieter? Sorry to laugh, but its plain to see that his logic was simply the proximity of the pins.

Oh well. If this is old news and you knew this, cool. I know I sure missed this at first so I am pointing it out just in case. And yes, sorry to throw some rain, but if you are rewiring this amp now for the 3rd time, it might be something as simple as the sockets. Check in with the other guys, Allyn Meyers or Ritchie, for example. You will see that they wouldn't dream of building a TW clone without the *proper* sockets.

[rooster]

Kevin - Oh. Please don't shoot me, BTW!!!!!!!!!! I am really trying to help.

[Bob-I]

I have read here that someone thought that KF used pins 6-8 because this section of the tube was actually quieter?

Don't laugh at that. Soldano uses 6-8 for the first stages because it's quieter too. I've tested and they're right, the second triode is quieter than the first.

[Bob-I]

I looked over your pics. I don't see any cold solder joints, but I see a lot of splatter and excess solder. I'd spend some time with the solder wick and compressed air and clean it up. Get the joints down to min solder and remove any splatter. JMO

[KGW]

I did notice the orientation. I drilled the holes like on Francesca and then noticed that the sockets that I had on hand were 90˚ off from the ones that Ken used. I guess I could drill more holes, but I didn't.

Another thing about the original sockets is that they look to be almost flush with the chassis. That would allow more of the wires to lay against the chassis. So, I can see that there may be a point to rooster's comment. Worth a try.

What is a good source for the "proper" sockets?

Thanks for the comments.

[jjman]

I have read here that someone thought that KF used pins 6-8 because this section of the tube was actually quieter?

Don't laugh at that. Soldano uses 6-8 for the first stages because it's quieter too. I've tested and they're right, the second triode is quieter than the first.

What is the technical explanation for this? Location of the heater connections to the base?

[rooster]

CEDist or Antique Radio Supply - same company. Also Allyn has them.

As to one triod being quieter than the other? Hm, no buy-in here. Especially when you consider that either triod may have more output than the other given the batch. Did Soldano actually express this thought somewhere in print? Did KF, for that matter? If he/they did I would like to read that. You can cover all of O'Connor's work and not find a reference to this behavior, also Aikens, as well - and these guys are fanatic in their way, like them or not. Frankly, I think someone has just jumped to a conclusion - and - as is the case with KF's wiring on V2, missed the simplicity of his thinking. Its beautiful, yes, but surely because its so simple, and pure as a result - follow the shortest and straightest path.

In fact, if you read Aikens, he says that joining BOTH triods, (and readjust the cathode when you do), will give you the quietest result. Yes, quieter than running a single triod. ?? You have to wonder why KF didn't give this a go, but he was probably happy with his results.

On the other hand, fast forward to Mark Sampson of Matchless, and you will see that he nicks the TW circuit, but instead makes V1 home of the doubled triod (at input) and then moves on to make V2 a combination of KF's V1 and V2, each triod getting the duty that was split over two different tubes. Clever, of course, and since he also skips the cathode cap at V1, he gets a VERY quiet input stage, something very desirable in any amp.

OK, show me something in print. I would really get a laugh if it could be shown that Soldano - or whoever - had really done a backflip to get to pins 6-8 instead of 1-3!! To the point of crossing wires, etc.. Then, even without printed word, I might consider such a thought. Do you have a picture of a stock Soldano amp showing such a thing? That would be really interesting, you know?

[KGW]

In fact, if you read Aikens, he says that joining BOTH triods, (and readjust the cathode when you do), will give you the quietest result. Yes, quieter than running a single triod. ?? You have to wonder why KF didn't give this a go, but he was probably happy with his results.

Do you mean wiring them in parallel? If so, that would increase the gain.
A better way to reduce any noise from the unused triode would be to wire it to ground.

BTW, I was considering using the other half for a fast/gradual mod.

[rooster]

Kevin - If you correct the cathode bias, you will not increase the gain. Its a matter of using a common cathode resitive load, a 1:2 ratio. Fender uses this on BF reverb circuits, BTW, nothing new. Fender, since you brought them up, also uses a grounding of the non-used pins in their BJr amp. Does this make things quieter? I don't think so but I can't say with any scientific accuracy. I can add that in the BF Bassman, they used only 1/2 of a triod and DID NOT ground the unused pins. ??? Did they get smarter? BF Bassman fans will disagree of course.

[KGW]

Kevin - If you correct the cathode bias, you will not increase the gain.

Of course you are correct about that, however grounding the unused pins may do the same thing - maybe even better - would have to try.

An earlier version of one of my hifi (SE 2A3) amps used half a tube and grounded the unused half. That's where I learned this. Since going from the DIY hifi world to the DIY amp world, one of the major things that I learned is that guitar amps are MUCH different that hifi amps - especially in terms of grounding.

As for me, I build different kids of amps to learn about different styles. I'm that way about guitar playing too. In other words, I don't try to learn other players music unless it is something new and different to my ears.

So I think one should always experiment and keep an open mind. From what I read about KF, I think he would agree.

blah blah blah ... sorry

[Deric]

...a stock Soldano amp showing such a thing...