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Gibson GA4RE


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Hi I recently purchased A Gibson GA4RE amplifier with oil can echo and am a bit of a novice when it comes to electronic repairs. It's not in that bad a condition it powers up and produces a somewhat muffled echo which probably needs attention but the main problem is the amplifier hum and somewhat weak pre amp signal. My attention is brought to the transformer as this is the most likely cause of the hum, The Schematic is somewhat vague and confusing so that's not much help. I found some info on the transformer on the Oil can addicts site explainng the caps to replace etc but it's old posts and their no longer responding to questions, I've reproduced part of the article here: On the secondary side of the power transformer, the AC is converted to DC with 2 diodes and two capacitors; these are the 'first caps'; two each at 20uf @ 450V. These caps are followed by two resistors and then two more caps 40uf @ 450V.


Taken together; the diodes, caps, and resistors make up the power supply. Except possibly the 25K / 5 watt resistor, all these pieces and parts are easily found on the web.


If you are hum-hunting, you need to refurbish the power supply first. O.K. that's all the info i could get from the Tel Ray site. The previous owner told me the first inline is the Black cap marked 160P. So i guess that's the one to start with, I purchased a 20 UF 40v cap but am unsure on the info given to me and want to double check before blowing myself up or destroying my Gibson. Thanks any help would be greatly appreciated.

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