Blackface Bassman AB165 - what transformer?

[IgorBFB]

Hey guys!

I'm building a Bassman ab165 (with a different preamp etc.), but I'm using the original power stage.

I have the factory schem and transformer codes, but can't seem to find the specs for them..

Can anyone please help me out - watts, voltages, impedances, frequency etc.?
I'm from Croatia and it's really hard to find that stuff around here, so I have to give the correct specs to a local company that also makes transformers for guitar amps.

This is what is written on the schem:

power transformer - 125P7DX
output transformer - 125A13A
inductor - 125C1A

Thanks!!
Igor

[tubeswell]

Well for the secondaries the AB165 scheme shows 320-0-320 on the HT, and with 2 x 6L6GC and 3 & 1/2 (lets say 4) preamp tubes, I guess the plate current rating on the HT would be (66mA max Plate current and 7mA max screen current per 6L6GC, and 8mA max per pre-amp tube, so) about 200mA to be on the safe side. Someone will correct me if I'm wrong.

The heater current on each 6L6GC is 900mA and on each preamp bottle is 300mA, (which adds up to exactly 3A) so I would go with 4A rating on the 6.3-0-6.3 heater winding to be on the safe side.

Diode rectified so no recto winding required.

Get someone local to make one up for ya.

[tubeswell]

On the OT the load resistance I get for Class AB1 off the Svetlana datasheet for the 6L6GC says 5.6k plate to plate for the primary (assuming two tubes), and 55W max signal power output, so get someone to wind you up a 55W Push-pull OT with a 5.6k Primary accordingly. Get 4R-8R-16R taps on the secondary.

For the choke, I guess a little 4 Henry choke is okay for the screen supply:

http://store.triodestore.com/22707.html

Someone else'll jump in if they have a different opinion

[IgorBFB]

Thanks for the info!

This is the part I was wondering about:



Is that 320-0-0-320, like two 320-0 windings put together, so the wire going to the 470 ohm resistor has 0V?

[MattT]

That wire going to the 470/1W is the bias tap and is lower voltage than the 320s. It is a special tap on the secondary. You don't have to have that bias tap...you could just tap off of the 320s and use a bigger resistor (like around 220k)...lots of amps do that.

That choke is a standard choke on lots of Fenders...you should be able to get an exact replacement or info for it.

The PT has been covered...I would think 200mA would be a minimum...250mA or 300mA might be better.

Most Fender OTs for 2x6L6 had a 4k primary impedance. The original Bassman AB165 had only a 4 ohm secondary.

[IgorBFB]

Great, this pretty much solves all my problems!

The two 6L6 I have are JJ/Tesla 6L6GC and they're around 30W each, so I guess I'll have to adjust the OT accordingly..

Has anyone ever used a toroidal transformer for the OT?

[tubeswell]

I forgot about the bias tap on the PT.(Oooops) If you're getting a PT made up, you could either get them to chuck in a 50-0 secondary winding for bias supply, or build the HT winding with a 50Vtap off on of the 320 windings, (or simply tap straight off one of the 320 windings with a bigger resistor as MattT said).