Fender Twin Reverb Silverface power transformer voltage selector switch wiring

[beatnik]

Hello everybody,

I am trying to bring back to life a vintage Twin Reverb i bought on ebay for really good price.

It's an international export model so has selector for input voltage. That selector has been sawed. I read that they used to do that to avoid changing the selector by mistake and damaging the amp.

I would be sure it is in the 220 or 240V position, but also the power cord plug is missing. So i don't really know if the amp is currently set up for US voltage or UK voltage.

I tried to google in all possible ways for transformer wires colour coding for twin reverb power transformer, but couldn't find anything.

Neither I could find any info on that particular rotary switch, to know pin and switching configuration.

I am asking if anybody can help with this. I opened the amp up, made some pictures and made a drawing of how the primary wires are connected to the voltage selector.

Twin Reverb Photos by sad_1024 | Photobucket

[potatofarmer]

I'm guessing by that 10W resistor in picture 2 and the bridge rectifier in picture 3 that you have a 135W twin. Is that correct? Lot of these popping up lately.

If so, here's a link to the schematic, which has the export primary wiring: http://www.thevintagesound.com/ffg/s..._135_schem.jpg

You can see where the switch is currently set by using a multimeter and checking for continuity between the center terminal and each of the six outer terminals.

[beatnik]

thanks, that's exactly what i needed.

today i'll try to fire the amp up.

would you suggest to change the electrolytic capacitors? they don't look too bad

[potatofarmer]

Yeah, I would suggest replacing them. They're 30 years old and who knows when the last time the amp was fired up, given that it's missing the power cord.

[g1]

I would suggest you verify the transformer is ok before spending any other money on replacement parts.
Sorry to be the pessimist, but cutting off an AC cord is sometimes done to indicate "beyond economical repair". The fact that it was got for cheap on ebay makes me even more suspicious.

[beatnik]

i've been lucky! the selector was already in 240V position, i just wired an ac plug and fired the amp up and it's sounding!

it will definitely benefit from a fresh set of tubes and capacitors but with such a simple fix i got this beautiful amp for a bargain!

thanks everybody!

[g1]

Times like these are when I really enjoy being wrong .

[Enzo]

How do you do that? My wife tells me I am wrong all the time, I might as well make it enjoyable.

[gui_tarzan]

127v? I saw that on my DuKane PT schematic but haven't seen it anywhere else outside of this realm. When did that become an option? My house voltage consistently reads 122-124v. Should I be using that 127v tap instead of the 110v tap?

[Enzo]

That is what it is there for, but SHOULD you? It is just an amplifier, not precision lab equipment, so if it works OK on 110, leave it.

[gui_tarzan]

I was just thinking since it's closer to my actual voltage... would that have the effect of dropping my B+ slightly or wouldn't it change that?

[g1]

Yes, it would drop the B+, also the heater voltage. If your choice is 110 or 127, running it on 110 may put the heaters a bit high, and the B+ may be too close to the voltage rating of the filter caps. I would look at those 2 measurements and adjust the tap accordingly.
If the choice were 120 or 127 it would not be much of an issue, but 110 tap could be a bit iffy. See what you measure.

[gui_tarzan]

It actually did drop the voltage to acceptable levels when I hooked it up to the 127v tap. Heater voltage is still 6.0 so I'm going to run with that and see what happens. I took the transformer out completely and checked all the voltages again and they're all the same as the first time I checked it, so my circuit must have a glitch.

[g1]

I took the transformer out completely and checked all the voltages again and they're all the same as the first time I checked it, so my circuit must have a glitch.

Best not to confuse this thread by talking about another amp, as far as I know this one is all wrapped up and working.
The one you are referring to can be found here: http://music-electronics-forum.com/t35809/