Bassman output transformer question

[dragonbat13]

I bought a weber tweed bassman output transformer on the cheap. It only has the two ohm load on the secondary. I am assuming, since the amps design calls for it, that the primary is 4k.

I've also got a twin reverb chassis.

What I am thinking about doing is running 4x6v6 output into this transformer with a 4 ohm secondary load.

How would this turn out? Would it work at all, assuming the plates are adjusted to allow the OT to handle the load?

Any other suggestions?

[martin manning]

If it’s 4K to 2 ohm, running a 4 ohm speaker would make the primary 8k, good for 2x 6V6.

[dragonbat13]

So what primary impedance would I need for 4x 6v6?

How does one figure out what load the plates need for a given configuration in the power section? Maybe a tech article somewhere?

I'm gonna do some searching but any help would be appreciated

[martin manning]

So what primary impedance would I need for 4x 6v6?

Half as much, so 4k, which is what you'd get with a 2 ohm speaker load. You need half the impedance to admit twice the current at the same voltage.

How does one figure out what load the plates need for a given configuration in the power section? Maybe a tech article somewhere?

The long way is to use the tube data sheets and plot a load line, but most data sheets have some examples at different voltages showing the appropriate load. Typical load impedances for common tubes at their typical plate voltages in guitar amps are well known, though: 4k for a pair of 6L6's, 8k for a pair of 6V6 or EL84, 3k7 for a pair of EL34. For a quad you just divide by two.

[dragonbat13]

Ok I appreciate the help.

I think I am gonna use this output transformer, do the load line math, have a custom power transformer wound.

I have always wanted to do the quad 6v6 thing, I dont know exactly why, I know its pretty much a waste. But I just want to.

One thing I am going to try is the individual bias adjustment for each tube.

Again, thanks for the help.

[martin manning]

I think I am gonna use this output transformer, do the load line math, have a custom power transformer wound.
I have always wanted to do the quad 6v6 thing, I dont know exactly why, I know its pretty much a waste. But I just want to.

You'll need two 4 ohm or four 8 ohm speakers. Unless you already have them, I would weigh that expense against getting another 50W output transformer with 4k primary and 4,8,16 ohms secondary. A Blackface Bassman OT would be great. Either way, with four octal sockets for the 6V6, you could also run it with 2x 6L6.

One thing I am going to try is the individual bias adjustment for each tube.

That might be overkill; one for each side, or a bias + balance trim is sufficient to match the idle currents through the OT.

[dragonbat13]

Well I do have a 4x12 peavey 5150 cab I can wire to 4 ohms. And as far as the individual bias, I want to have the individual bias points for some mismatch tone experiments also, and I want to try my hand at a small circuit on PCB. This amp is a big giant experiment.

Another question, would a silverface twin reverb chassis fit into a dual showman non reverb head shell? I don't want the tall, Dual showman reverb shell, just a shorter showman/bassman/tremoluxe type. I want to say it will, but I'm just asking to confirm.

[martin manning]

Another question, would a silverface twin reverb chassis fit into a dual showman non reverb head shell? I don't want the tall, Dual showman reverb shell, just a shorter showman/bassman/tremoluxe type. I want to say it will, but I'm just asking to confirm.

It would be best to get the chassis dimensions (width, height, and depth) from the suppliers of the chassis and the head shell to make sure they are compatible.

[Stevem]

The silver face twin reverb chassis is 2 3/4 inches wider then a non reverb silver face showman, so the answer is no, but it seems it would fit in a blackface showman since they are said to be the needed 26 inches in width.