excellent elimination fella.
a small choke around 50mA/4H would be fine. lots of 50's single ended 6v6 powered radios used a choke input PS, so any out of those would be fine.
the fact that the hum doesn't change with speaker swap suggests to me that it's not filament noise, so must be power supply. the choke should help.
the input lead to the 6V6 runs from the volume pot wiper to pin 5, the screen for this wire should connect to the earthed leg of the volume pot, and not to anything at the valve end. is this how you wired it?
to drop the filament voltage i would not use the divider as you've drawn given the AC heater supply. if you want to go the diode route that should work, provided you run two in opposite polarity on a given AC line. check the system on the valve wizards page i gave you the link to earlier. he uses 2 diodes on one leg for 0.7 volts drop, but if you repeated the circuit on the other AC leg with another 2 diodes you would have 1.4 vac drop. (or in the case of your 0.6v...1.2v)
you need the diodes parallel and opposite to keep the AC as that, and not half wave rectified.
you could also just put a resistor in each supply line. heater total current = .750A, for 1v drop R=1.3ohms. split this between the 2 resistors (to keep the supply balanced) =0.67ohms each.
power through each resistor is about 375 mW, 1/2 watt resistors would probably be fine, though getting low value resistors can be hard. should be able to get 1w/1ohm, so 2 would drop your voltage by 1.5v. (W would be up around .5 each with those values)
all in all i think go with a double version of the wizards plan.
very insteresting problems and possible solutions you are bringing to us all hermit.
I'M AN IDIOT,
it was'nt the wire from pin 5 on the 6V6 to the vol pot, but the wire from pin 3 on the 6V6 to the OT that is causing all the hum/squealing,
anyway, i swapped the valve's, still squealing, swapped the OT, still squealing, reversed the OT wire's, still squealing,
in the meantime the original OT decided to short out and also fried the 500 ohm/5 watt ceramic resistor that goes across the first two cap's, replaced the OT and the resistor, still hum/squealing,
not really sure what to do next, unsolder everything and start again,?? or fling it all in the bin and take up gardening,
thank's for that detailed explination about the voltage dropping,
squealing as well as humming!
can you post a schem with the voltages measured everywhere, measure for both AC and DC. is your rectifier OK?
that 1st resistor in the power supply should only be seeing about 3/4W, in fact, i generally use only 1W resistors in the powersupply of champs (though i do use a choke at the front). what happened to fry a 5w one and the OT?
BTW, as a single ended amp with no negative feedback, swapping the wires on the B+ side of the OT shouldn't make a difference to any noise issues. the speaker side only transfers the low voltage signal, so i don't think it should matter which leg is earthed either.
apart from something wrong in the wiring somewhere hiding, i'm not sure.
the grid leak bias design doesn't like hot inputs though. apparently it's not a good idea to hit these amps with a tube screamer or such.
did the amp squeal with nothing plugged in and the volume right up?
did the amp squeal with the volume on the guitar on zero and the volume on the amp right up?
with the volume on the amp starting down, and the volume on the guitar on 10, did the amp squeal sooner as you turn up the amp than with the guitar on 5?
just trying to think of ways to find where you problem might be.
i've only had 1 squeally champ, which was a vibrochamp running quite high voltages - i had the negative feedback on the wrong leg of the speaker winding so it was positive feedback - and it did.
thank's eric, i'll measure the voltage's etc as soon as i can, weather's quite nice here for a change, so i've been out on my motorbike a lot lately, plus helping my brother rebuild his,
that's it. still check your actual voltages once it's in the amp of course.
haven't had a chance to look at your latest voltages yet, but the voltage from your rect is because you built a bridge rectifier.
if the transformer is centre tapped, don't use a bridge rectifier, just use 2 diodes as a full wave rectifier where the valve rectifier would go. as you have labeled the AC 350/350 and not 350/0, i would assume you still have a centre tap.
full-wave rect will product lower voltageDC but can take a higher DC current for the current rating of the transformer. conversl, bridge rect will produce higher voltageDC but cannot pull as much currentDC from the same AC rated trans.