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Old 1st July 2012, 10:53 PM   #1
diyAudio Member
Join Date: Mar 2011
Default power transformer wiring help

I have an amp I'm rebuilding with an original transformer. I think it was an RCA and it's 6bq5 push pull. I thought I kept the wires marked correctly for the heater, secondary, primary, etc. but the heater wires don't have the correct voltage. One side, green/black is 3v+ and the other, green was close to 9v. I've disconnected them and tested all the other wires on it and get this:

green/black: 6v+
green: 11v+
tan: 14v+
green/yellow: 18v+
red/green: 280v
red: 280v
red/yellow: grounded for center tap
black and red/black are used for primaries

Anyone know what two I should use for the heaters? I'm sure the primaries, high voltage secondaries and center tap are correct, but not the others.



Last edited by dscottguitars; 2nd July 2012 at 12:57 AM.
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Old 2nd July 2012, 02:27 PM   #2
Simon B is offline Simon B  United Kingdom
diyAudio Member
Join Date: Dec 2011
Location: North-East England
Originally Posted by dscottguitars View Post
......One side, green/black is 3v+ and the other, green was close to 9v......

green/black: 6v+
green: 11v+
tan: 14v+
green/yellow: 18v+
So is green/black 3v or 6v ? Is green 9v or 11v? What are you measuring these voltages with respect to? Where are you sticking the other pointy thing?
Engineer: One who can do for 10 shillings what any fool can do for 10 pounds.
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Old 2nd July 2012, 02:52 PM   #3
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Join Date: Mar 2011
The 3 and 9v are when it is connected to the tube socket. The other values for the same wires are measured when disconnected. I am measuring with respect to ground in both cases.

I did just test the voltage by connecting the meter to both wires and got 6.8v which seems correct. But I don't know why they would be so different when connected to the socket with respect to ground.

What led me to check this is on my phase splitter tube one plate was around 200 volts, but the other plate was 350v, and after rechecking I don't see anything connected wrong either. I changed tubes also. Maybe that's not the issue with the heaters, but I'm not that experienced.

Thanks for your reply Simon...
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Old 2nd July 2012, 03:36 PM   #4
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Join Date: Mar 2011
Problem solved!!

I don't think it was the heaters now. But maybe someone could tell my why this was the case:

Two things:

First was I did not have a capacitor on the input to the phase splitter directly. I thought the one coming from the preamp tube to the volume was sufficient. I decided to put a 0.01uF on pin 2's grid, and turned on the amp. SQUEAL!!!!

Second: That told me the output transformer wires were backwards. I changed them around and now get correct voltages throughout.

But I am curious as to what made the voltage on that plate associated with the capacitor directly on the grid, be more than 100v different than the other plate?
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