Hum problem with SWR Bass 350

[Gerhard Grass]

Hi,

with the wiring diagram from slawkowski (thanks) I will check the wiring.
A wrong wiring would really explain the symptoms.

Gehard

[Gerhard Grass]

Hi to all of you,

at last I fixed the problem. The PT was bad. I relaced it and now the rail-voltages are about 77V.
Just as they should be. The only thing that worries me a bit, is the fact, that the Mercury transformer
was bad. Why? It is built like a tank.

Now that the amp seems to work properly again, all I have to say is

Thanks to all of you here!

Gerhard

[MarkusBass]

So the primary winding was shorted (partly). It happens. Did you buy the transformer from Mercury? If yes, how much was it? I sometimes get requests to replace "domestic" version of the transformer with "export" one. The easiest way would be to order the transformer from Mercury. But do they still sell transformers for old SWR amps?

Mark

[Gerhard Grass]

Hi Markus,

no, i didn't buy directly from Mercury. The guys at mecrury told me to contact irving.blacker@tonehenge.de. tonehenge is a mercury part supplier in germany.
Buying from them and not fron USA saved shipping costs. The PT was €201,- including tax (19%) and shipping.

For other transformers take a look at Tonehenge Amplification. To me it seems they have a very interesting catalog.
I think you can fond there the PTs you need.
Irving as well as their technicians are very friendly and competent guys. Can only recommend them.

Gerhard

[MarkusBass]

Thanks for the link. They have nice catalog but this is quite expensive. The price for power transformer is almost half of the price of the whole amp. If I had to additionally fix the amp, the customer should pay more than for a new amp. I have to calculate it carefully :-).

Mark

[J M Fahey]

The only thing that worries me a bit, is the fact, that the Mercury transformer
was bad. Why? It is built like a tank.

Sh*t happens, even for tanks , or the replacement transformer market wouldn't exist.

@ markusbass: I'm sure you must have a lot of high quality winders in Poland .
Plus high quality wire and steel.
I understand the reason to replace a tube OT with the exact same one, but on SS power ones, they don't have much direct influence on sound (if any), all that's required is that they supply rated voltage and current without overheating, which simplifies substitution a lot.
Good luck.

[slawkowski]

hey Mark
edis ogonowski.net.pl

this guy made custom (pictured) transformer for my friend for less than 300 zl

slaw

[Enzo]

Sh*t happens, even for tanks

Or as we say in our shop, even the Rolls Royce dealer has a service department.