too many questions...... power transformer testing.

[michael_krell]

I have posted many questions before about my ampeg V4. I took the power transformer out completey and i am trying to make sure it is working correctly. This is what I did. ....

I hooked up my wave generator and applied a 60 HZ wave to the primarys. when i test the red (HV) wires i get some strange results. When i touch the scope to one of the red wires i get a signal almost identical to what i am applying to the black primary wire. on the other red wire I am getting a much larger signal.


I am not sure if my testing is even usefull, but maybe someone can help me with a better way to test this power transformer.

[michael_krell]

Ok forget that one, heres the situation. I am getting 400 VDC across the standby switch. when i turn on the switch i get burnt rectifier diodes. even with no tubes in the 400V's is still there. should this be?? im thinking no, but i could certainly be wrong. someone help.

[toneman]

U can't use a function gen to test a power transformer.
U need 2 use an ohmmeter then a voltmeter.
U first ohm out primarys/secondarys, looking for obvious shorts.
*then* U plug it into AC and look for (proper)AC on the secondaries.
if U R inexperienced in working with AC voltages, i suggest U find someone
to help U.   All of your checks could have been done in the chassis,
by just removing the rectifier tube.CAUTION: All tube amps contain lethal voltages.  
As Elmer says:  "B Vwerry Vwerry carrful"!!
also, this is a stompbox forum. not a tube amp forum.
there are *many* amp forums which might provide better help.
staysafe
tone

[R.G.]

There's a whole other section of GEO that doesn't get much play here - the tube amp technology section.

What you need is the "Tube Amp Debugging Page". It will lead you through finding this one.

Going only on your description, it's likely a shorted inductor or filter cap, not the transformer at all. But don't just go messing about on that diagnosis. Go read the Debugging Page and follow it. Just building the light-bulb power limiter will save  you a fortune in fuses.

There's more there, including how to tell from the outside if a transformer is shorted inside. That's a toughie.

[nightingale]

I 2nd the Geofex page,
I was able to get enough info from that page to discover that i a friend had a dead PT in his 70's SVT.
hope this helps,