Koch Twintone Innards

[-CM-]

I had my Koch Twintone head chassis pulled out last night, and thought that it would be interesting for some to see the insides.

http://www.cmwebsite.com/images/kochtwintonechassis1_sm.jpg

Not much to the bottom - tubes and transformers.

http://www.cmwebsite.com/images/kochtwintonechassis2_sm.jpg
High-res version here (http://www.cmwebsite.com/images/kochtwintonechassis2.jpg)

The inside of the chassis is more interesting. Koch uses a one-sided PCB for the circuits. Everything is very neat and tidy.

Anybody know exactly what the Hum adjustment is for?

[Anders Destium]

The site seems to be down :(

I'd like to see the inside of it! I think that the hum adjustment is some kind of internal noisegate thingy. I don't know if you get issues with your warranty if you mail Koch with your question. They're really friendly at Koch (as most as us dutchies are...at least we think we are :D ), I'm pretty sure they'll explain what it's for and then advise to stay away from it no matter what ;)

[Stratmeister]

Awesome bro, what timing! I'm about to pull my Twintone chassis and this will give me some idea where to start. I just recently picked mine up used and it is quickly becoming my favorite small (50W) amp. Tone to die for. But I need to retube it with some EL-34's, haven't decided what to try, and will probably need to rebias it.

You don't have a schematic do you? Mine came with no paperwork, I found a very limited user guide on the website. But no schematic... :(

Anyway, typically a hum control is nothing more than a pot that you can balance the power tube bias with. This allows you use slightly mismatched power tubes, which in turn reduces the audible hum. The better matched a pair, or quad, of power tubes is, the less hum. Think phase cancelling, since this is push-pull. Just install your EL-34's, and turn the pot until you hear the least amount of noise.

Again, thanks for the great pics. What EL-34's are you using? I've got a sweet pair of Mullards in an old Marshall put I don't think I want to pull those, so I'm in the market.

[-CM-]

Thanks for the explaination of the Hum ocntrol. That make sense.

I just have the original Electro-Harmonix power tubes in it. The preamp tubes are all Sovteks, except for v1, which I switched out for an NOS Mullard 12AT7.

I only have the same manual you can download from the site. No shematic.

If you have the original tubes in it, they'll be marked by Koch, and then you can replace them with the same type, so you won't have to rebias. You can get Ruby or Sovetek tubes from here (http://www.custom-sounds.com/usd/FrameUS.htm).