Tweedle Dee OT question

[Oddvar R]

I am thinking about changing the PT as well, any suggestions?

[Colossal]

Thx Colossal. This is of interest for people willing to build a tweed as well, I guess. At least, that seems to me.

About the bus bar, also:

- I suppose that the best solution is to have its "non chassis-connected" side held by the physical connections (bits of solid wire) between the pots and the ground?

Yes, if I follow your meaning, the preamp ground bus wire can run along the "back" side of the turret board and ground connections from pots are run down to the bar via a length of wire. Lead lengths should be kept as short as possible

[Oddvar R]

Thanks.

[Colossal]

I am thinking about changing the PT as well, any suggestions?

If you are aiming for low plate voltages, which will work well with the 8k single ended output transformer, I would use an NOS 5Y3GT. They aren't too expensive and pretty readily available. The rectification factor, under load is about 1.0 to 1.05. You will also want a lower primary with modest current handling. You are only running the one 6V6 at at about 40mA, give or take. So, Secondary AC x Rectification Factor = Rectified DC voltage under load. Rectified voltage target might be 315-320VDC.

320VDC / 1.05 = 304VAC

So we might look for a secondary of about 300VAC. Some of the ClassicTone data sheets call out the sag for a given current. For example, 40-18019 shows with a 5Y3GT rectifier and a current draw of 45mA, the approximate load of a Champ amp with one 6V6 and one 12AX7, the rectified voltage is 415VDC. This is too hot. If current is increased to 70mA, this sags down to 391VDC, still too hot.
http://www.classictone.net/40-18019.pdf

So a different transformer would be better.

Using the 275-0-275VAC tap on this transformer with a 100mA load and a 5Y3GT rectifier gave a 315VDC voltage, so definitely a better fit. Your voltage might be slightly higher with the reduced load.

http://www.classictone.net/40-18027.pdf

[Oddvar R]

Thanks for the advice there, I'll buy the 18027 then.