I think the mojotone uses diodes instead of a rectifier. what about adding a gz34 to create sag for the amp?
The stock Silvertone 1484/1485 amp with the multiple voltage doubler stages creates sag all by itself, even with the silicon diodes. A voltage doubler doesn't have much sag until the current demands get high, like when you have the amp way up loud. When the demands get too high, the doubler circuit will sag even more than many tube rectifiers. In the 1484 and 1485, they used two doublers stacked on top of each other, so you have even more sag than usual when the current demands go up. Add to that a really small output transformer that doesn't have much low or high frequencies in comparison to a larger transformer, and the fact they are using a 6CG7 for the phase inverter in a cathodyne circuit, and preamps with lowish gain, you end up with a unique amp. The fact that the screen voltage is using only a couple of the doubler stages instead of all of them limits the power and makes the tone a bit muted and soft. Moving this to the same tap as the B+ like a Fender does ups the power, but not much. These amps are really only about 30 watts RMS in stock form. Moving the screen tap gets you to about 35 watts, maybe, but it increases the risk to blowing the stock output transformer. That said, an amp I modified for my brother years ago does this along with many other mods, and it is still working on the original transformer.
I'd guess the Mojotone circuit was likely using different phase inverter tubes than the 6CG7 since no one makes it these days. You could sort of duplicate it with a 12AU7 but it doesn't have as much current capability. I couldn't find the kit on Mojotone's site, and their link for their schematics went nowhere also.
Greg
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