Nathan Quade's 5C1

I have put up this web page so we can look at schematics and compare notes so there are no misunderstandings. If the voltage you measured is from points A and B on the transformer then I would say it is a little too high for 1Kv (bridge) diodes. You should probably use two 1KV diodes in series, each shunted by .01uf 1Kv capacitor in each leg.  I am assuming that the transformer was unloaded when you measured the voltage so loaded the voltage would be somewhat lower. I would suggest that you wire the power cord as shown with a safety ground and get rid of the .05uf “death capacitor”. There are several other items I would like to discuss, but lets figure out your power supply first. Other members on the forum please chime in. I will not suggest anything that I am not willing to provide from my junk box other than tubes or transformers.  My Email address is:                   Denny Allen


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power transformer

this schematic is for reference so that we can talk about it

5C1 power supply showing mods


If a choke of 3hy or greater choke is placed between the cathode of the rectifiers and the first filter cap, the voltages should be OK for your amp. The choke will keep the DC output at or near the AC RMS output of the transformer. A loaded transformer will probably put out less voltage than the 360 that was measured. If you have a 4 pin tube rectifier socket, the amp probably used a type 80 rectifier tube. A 5Y3 is just an 80 with an octal base. Fender used what tubes were available at a good price and in some models an 80 was used long after they were considered obsolete.


Some more thoughts on a 5C1 build. A 6SJ7 is a metal tube which is kind of handy, because metal tubes are self shielding. Pin 1 of most metal tubes is connected to the metal shell, so connect pin 1 to signal ground. There is some anecdotal evidence that grid self biasing a tube ( 5 meg grid resistor ) is not a good idea a conventional cathode resistor and bypass cap is preferred. The volume control, when turned all of the way up, would present the grid of the 6V6 with twice the recommended grid return resistance. Maybe a 500K pot or a 1Meg resistor from wiper to gnd. would be a good idea, but who an I to second guess a Leo design which worked. A resistive center tap on the filament winding returned to the cathode of the 6V6 would reduce hum in the 6SJ7 amp stage. A 250K plate resistor may be hard to find, a 220K resistor would probably work OK.  Check out this link




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