Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: plexi50 on January 11, 2011, 05:07:34 pm
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Where can i find a place that sells SS power transformers? I need 50VDC with CT
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Not sure what you mean. Do you want 120VAC in and 50VDC out? Or just a transformer?
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Hammond. Use this guide to pick the one you need. It's probably on page 9.
http://www.hammondmfg.com/pdf/Hammond_Sec_Volt_Sel.pdf
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Yes 120VAC in and 50 VAC per lead with CT to ground. Thanks for the Hammond link
So i would want to order a 100-0-100 to get 50VAC on each of the secondaries leads with CT correct? Brain is drained
I also forgot to ask what the minimum amperage rating could be / This is for an old Gibson Starfire / I have no info on the amperage specs of the old PT
This is an all SS amp with power transistors
Is this what i need or do i need a higher amperage rating?
http://parts.digikey.com/1/parts/997654-transformer-115vac-100vct-1a-167j100.html
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So i would want to order a 100-0-100 to get 50VAC on each of the secondaries leads with CT correct?
No, you'ld want a 50-0-50. Really need to see a schematic.
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Here is the schematic. http://www.triodeamplification.com/files/tr1000rvt.pdf
166M48 117V 50/60 Hz. 48V C.T. 3.0 A 22
http://www.newark.com/hammond/166m48/filament-low-voltage-rectifier/dp/51R4208
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> Here is the schematic. http://www.triodeamplification.com/files/tr1000rvt.pdf
That is a VERY ODD OLD amp, and there are errors on the drawing.
How are you sure it needs a new PT?
If transistors are bad, it will be VERY hard to guess replacement.
(If you'd bought a 100-0-100V PT, you would need ALL new transistors.)
To get to your question: the output is about 35 Watts in 8 ohms (no protection), the PT should be sized for 75VA-100VA, no more. 96VCT (48-0-48) at 0.8A-1.0A. (Confirm that the replacement is nearly the same size/weight as the original.)
I would strongly suspect all electrolytic caps.
I'd have to see the rectifiers, but old designers often under-rated these. And a shorted rectifier will toast a PT quick. And the rectifiers seem to be drawn BACKWARD for the polarity this PNP amp runs at.
Power-up on a lamp-limiter with Q13 Emitter disconnected, verify that you get CORRECT POLARITY and about the indicated voltages (not twice-as-high, not all-the-same).
Replace (temporarily) R62 R63 with 100 ohm 10 Watt parts. Replace R57 with 1K 1 Watt. Put 100 ohms 10W in series with the speaker. In this condition, any fault will not cause instant death to all devices, just slow smoke in temporary resistors. If no fault, it should "play" at the quarter-Watt level. If it won't speak, you got more trouble.
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I ordered the 48-0-48 166m48 Hammond from Newark.
I removed the secondary leads from the diodes and tested the PT with a small 2 amp circuit breaker that i use on in doubt amps
The PT tripped the breaker immediatley under a no load connection
The diodes are not shorted but i will use newer ones with the new PT / They are the very old ones that are grounded to and mounted in the chassis
I do have one cap can that has a bubble rise of goo comming out of the indicator hole so they all will be replaced
The PT is definatley fried. The transistors were replaced by some NASA tech that was helping his friend out
I dont know why he could not get the new transformer other than he was not available to do a complete amp repair under his work schedule
I know there is the possability that i could have stepped into a bee's nest. I pray a lot :angel