RIVERA KR 55 power transformer trouble

[Duchesne Phil]

Hi, I'm french and have a rivera kr55. Power transfo is dead and I had to replace it. I have mailed to Rivera but no answer... Does anybody have the technicals specifications of this Transformer ? It has 4 secondaries : one for HT with CT for 2 EL34, one for bias, one for 6.3v Heather and one with +24v and-24v with CT. Sorry for my bad English, school is so far away now ! Thank's for your help. Phil

[Amp Kat]

Try Mercury Magnetics. They probably could find the specs and send you a replacement that could drop in. Rivera may not deal with International service and the email may have not even reached them.

[Jazz P Bass]

I would think that the + - 24 volt tap is going to be a problem, as far as off the shelf transformers goes.
I could be wrong.
The rest is pretty cut & dried.

[Duchesne Phil]

Greats thanks for your quick answers. I thing so that + and - 24 is THE problem, head amp need that for MIDI and others circuits. May be it's possible to alim with two PT differents, one only for the 48v with middle point ?

[Jazz P Bass]

Yes, another transformer would do the job for the 24 volts.

[Duchesne Phil]

Yes, another transformer would do the job for the 24 volts.

Ok, Thank's for confirmation but I've mailed anyway to Mercury Mag.

[Duchesne Phil]

I'had an answer from Mercury : they have not Spec for Rivera PT.
So, I post again my question. If anybody have the same head amp, may be he could take the exacts voltages (working or idle) and send me this values.
For the 6.3v, it's not necessary, on the +&- 24 either, and the bias is often 50v, but the HT needs more precision, I presume?

[mozwell]

Is the primary still ok ? if so, power it up & measure each secondary (careful with the high voltage ones).
You will see which one has no output.
You can add a second transformer just for that output.

the transformer is probably the same for the knucklehead & the R series
grey wires look to be 18-0-18VAC 0.25A
green wires are 6.3VAC 5A for 55W, 10A for 100W models
orange wires are for bias
red & red/yellow are for the HV supply

If the primary is open, you will need a new transformer.

There are lots of fuses in this amp, pull each one (with power off) and check they are all ok.

Some IEC inlet sockets have an integrated fuse, check to make sure that is not blown.

the bias & grey wires, have polyswitches on them, if one of these was open all the time, it could appear teh transformer was faulty. If you have secondary voltages on all outputs, but (say) no bias output, the polyswitch may be blown. These can be replaced, or you could temporarily install a 4.7 ohm 0.5W resistor for testing.
If you have no bias supply, pull the output tubes when you do the testing & only put them back when all power supplies are ok.

[Duchesne Phil]

Hi Mozwell, All that you say is totally right, but I get back this amp from my young son without the PT ! It was totally burnt and put away to trash can. You understand why I'm a little "blind", without maintenance manual, Tension points and technicals specs to make this head working again... Rivera don't give maintenance book and I'd the schems you've send, better than nothing but a little short for my competence !
But, I'm glad to see that you dont let me alone ! Greats Thanks !

[mozwell]

A quick search comes up with

mains transformers - Transformators from the UK, search for rivera
p/n R5512P rivera p/n 109026 (230 / 240V)
The colours & voltages look ok compared to the rivera sch's i posted

In europe Rivera dealers Dealers - Europe may be able to help.

good luck

After installing the new transformer, take all the tubes out & power the amp up on a light bulb limiter. There may be semiconductor diodes shorted & maybe faulty power supply capacitors.
If you are not "too technical", i suggest taking it to an amplifier tech who is familiar with valve amps.

[Duchesne Phil]

Thank's Mozwell, it seems to be the good one ! I hope I'm goin to finally find the tech book with the tension points to go on to the fix each circuit one by one.

[Prairie Dawg]

I think that if you have some specifications and a footprint of the real estate the transformer occupies your search will be a lot easier. Rivera is not the only amp maker that uses a low voltage tap for the integrated circuits and/or channel switching. I'm quite sure there's something you could use.