### 2A3 get*set*go docs

Posted:

**Sun Aug 05, 2012 6:44 am**Here's a stab at a 2A3 get*set*go. I've been getting more and more requests for a 45 & 2A3 compatible amp over the last year, which I attribute to 6B4Gs getting more expensive and modern 2A3s - particularly Chinese ones - are much more abundant. I also guess people want to use part of their tube stash, which I can't blame one for that. But the get*set*go was very much designed around the 6B4G. It uses a just two filament taps from a single power transformer, whereas a 2A3 amp usually requires four.

Anyhow, I think I have a nifty scheme using a regular GSG PCB. The filaments will be AC and the DC circuit gone. The power transformer will be an Edcor XPWR067-100/120. Three small socket jumpers on V2 turn our rectifier into a 5U4/5V4/5Y3. And a voltage divider and jumper wire is added for the 6SL7 AC heater reference (using D2 & D4 footprints, so it doesn't get messy).

get*set*go 2A3 manual

Mouser Parts BOM

Notes:

1) I haven't built this, so there could be some documentation errors. If anyone sees something goofy, let me know.

2) B+ voltage will probably be different than the 6B4G design due to the new power transformer (640VCT instead of 660VCT). The 5V rectifiers allow some adjustment due to their different voltage drops. The Hammond 302AX is a second source for those that can't wait 6 or 7 weeks for Edcor, but it is double the price and only 600VCT. But hopefully the 5V4 will accommodate that.

3) The voltage divider resistors are now all 24 ohms across the 2.5V filaments. Since we have a perfect sine wave, we want a perfect voltage divider. You can even match your four resistors up. The 6B4G scheme is 47 and 51 ohms to compensate for the 120Hz ripple in the rectified filament supply.

4) I assume that using 45s would mean a slightly higher filament voltage due to the lower current requirements. You might want to have some 0R1 power resistors on hand to drop extra voltage if needed. This might even be needed on the 2A3s. Symmetry won't matter, I think. Just put them in series with the filament.

Shannon

Anyhow, I think I have a nifty scheme using a regular GSG PCB. The filaments will be AC and the DC circuit gone. The power transformer will be an Edcor XPWR067-100/120. Three small socket jumpers on V2 turn our rectifier into a 5U4/5V4/5Y3. And a voltage divider and jumper wire is added for the 6SL7 AC heater reference (using D2 & D4 footprints, so it doesn't get messy).

get*set*go 2A3 manual

Mouser Parts BOM

Notes:

1) I haven't built this, so there could be some documentation errors. If anyone sees something goofy, let me know.

2) B+ voltage will probably be different than the 6B4G design due to the new power transformer (640VCT instead of 660VCT). The 5V rectifiers allow some adjustment due to their different voltage drops. The Hammond 302AX is a second source for those that can't wait 6 or 7 weeks for Edcor, but it is double the price and only 600VCT. But hopefully the 5V4 will accommodate that.

3) The voltage divider resistors are now all 24 ohms across the 2.5V filaments. Since we have a perfect sine wave, we want a perfect voltage divider. You can even match your four resistors up. The 6B4G scheme is 47 and 51 ohms to compensate for the 120Hz ripple in the rectified filament supply.

4) I assume that using 45s would mean a slightly higher filament voltage due to the lower current requirements. You might want to have some 0R1 power resistors on hand to drop extra voltage if needed. This might even be needed on the 2A3s. Symmetry won't matter, I think. Just put them in series with the filament.

Shannon