18watt trem -> TMB

[martinman]

Hi Everyone,

I got a great deal on a GDS 18watt trem off of ebay. The build wasn't the cleanest in the world - i knew this going into it. Upon plugging in, there (at times) is a very audible tapping noise that lasts for a few seconds, then stops. It's almost as if the amp becomes unstable and then quickly rebalances. Also, there is a rustling noise thought the speaker.

Anyway, i bought it to convert to a TMB. Are there specifications / layouts on this? It's just as easy for me to compare the 2 layouts. One problem... I don't have the GDS layout for the term version. Not sure how difficult this will be? Thoughts?

[George61]

18watt.com has layouts and schematics for several different versions of the 18W. Beware, the input jack wiring is wrong on some of the 18W Tremolo layouts. If you are going to convert the amp it would be easier to start with a new turret board (Watts Tube Audio).

I have built both versions and I do not care for the TMB version. The TMB tone stack seems to kill the character of the amp. The TMB channel does not have as much gain and the amp loses the chime that EL84 amps are known for. The tremolo channel with the tremolo on or off is a great 60's British Invasion sound. The normal channel on a 18W Tremolo, in parallel mode, will out-rock the TMB channel on a TMB. The TMB only has single mode on the normal channel. Just my opinion.

Solder on,
George

[martinman]

Wow George -- thanks for your post. Quite interesting feedback -- I hoped that it would be quite the opposite!

What do you mean by parallel mode? Are you talking about jumpering channels?

Still considering other options. The trem channel is giving me all sorts of problems (but... it *does* sound the best). Everything from the strange audible nuances to a temperamental v3 tube socket.

I'd likely start with a new turret, but would reuse some of the caps and resistors.

[George61]

In parallel mode V1a and V1b are paralleled. A lot of people would refer to it as the High and Low input. Attached is a schematic. On the normal channel the High the input goes to pin 2 and pin 7 of V1 (grids). The plates (pin 1 and pin 6) are tied together. On the normal channel Low, just V1a is used. Parallel mode adds a slight amount of gain and fattens up the sound a bit.

Solder on,
George

[George61]

An 18W that works good. Built by the 18watt.com community.
https://www.youtube.com/watch?v=enc4maI9OV4

[xtian]

I'm very happy with the way my 18-watt TMB turned out. Started with Richie's 36-watt schematic, and trimmed down until I ended up with just one channel, paralleled input triodes, single tone stack, NFB switch, and awesome tone.

http://ampgarage.com/forum/viewtopic.php?t=26052