^^^ Great photo!
> Numbers mean nothing.
Numbers mean everything. Or maybe I should say, they mean different things to different people.
I have one of these old Silvertone amps in the Twin Twelve format. I have never even considered plugging a bass into it.
The amp was designed to be an inexpensive, power-limited and bandwidth-limited guitar amp. It was designed with deliberate compromises in mind. It's one of the last amps that you could buy where PTP wiring was used because it was the cheap way to build an amp. Things have changed a lot since then.
The circuit was built with some deliberate design compromises in mind, to limit the amp's power and bandwidth for the sake of cost control. If you try to circumvent the limits that are imposted by one component, then you're likely to exceed the limits of another component and cause the other component to fail. Trying to beef up one of these little amps for bass use is a lot like building a house of cards.
The power transformer on this amp is small. It has a limited current delivery capacity. The filament load from the rectifier shouldn't be exceeded by changing rectifier tubes. If you do that, the increased current load on the transformer will cause voltage sag on the output, in addition to causing the transformer to run a lot hotter. Voltage sag on the output is bad for the circuit; excessive heat over time will make the transformer fail.
Going downstream in the PSU circuit, the choice of rectifier limits your ability to replace PSU caps. Tube rectifiers have a capacitance limit for the first cap in the power supply. Exceed that limit by adding capacitance to the first position and you're going to kill your rectifier tube. Increasing the rating of the rectifier tube by choosing a beefier tube, or by replacing with a solid-state plug in rectifier, will only serve to transfer the failure point from the rectifier tube to the power transformer. You don't want to do that.
Also, beefing up caps in the supply chain isn't going to help you all that much, as the size of the first filter cap tends to place a practical limitation on the performance of the power supply rail. Adding lots of downstream capacitance won't help you much.
But suppose for a minute that you did do some helpful modifications, and increased the linearity of the amp for reproducting LF signals. Now take a look at that teenie weenie output transformer. It doesn't have the mass that's needed to provide the frequency response that you'll need to get the objective that you're looking for. So you either have to replace the OT or reduce your expectations.
In many respects, trying to beef-up one of these little amps is like playing a game of Whack-A-Mole at a carnival. No matter how many times you whack the mole, he pops-up out of another hole. With the amp, no matter how much you beef-up one area of the amp, you're going to find that another area of the amp is going to limit it's capabilities. So then you work on that area, and then you realize that there's a weak link somewhere else. Lather. Rinse. Repeat.
If you repeat the process often enough, you end up trying to shoehorn a totally different amplifier into the chassis.
These amps have been unloved and unrespected for a long time. The result is that hobbyists would mod them to death for decades as if they had no collectors value. During that time I was sort of a lone voice in the wilderness, asking people not to try to beef-up these little amps because doing so would invariably cause their destruction. That would be a shame, as they're one of the last examples of true PTP wiring. Since Jack White became popular, the amps have increased in market value by multiples of their previous valuations. Now these little Silvertones are starting to have real collectors value.
So my opinion on this is going to be a bit different than most peoples. Here's my take on the situation:
The amp isn't intended for Bass, and won't work well for bass unless you're going to limit it's use to a quiet studio-type application.
The amp has some collectors value now, and should be restored instead of modded.
If you mod the amp, you're going to find out that it's never going to end up being what you want it to be, and you're going to end up investing a lot of effort in trying to make it something that it was never intended to be. To save time and money, you might be better off starting with a different platform that's closer to what you want to achieve in the end. Doing that will result in a lot less expended effort.
Just my two cents.
