old thread

[Andy Le Blanc]

dont run the amp without a speaker or some sort of load
get a large wattage resistor, say.... 4 or 8 ohm 20 to 25 watt as a load
in place of a speaker......
I got a couple 300 watt 8 ohm that use to series\parallel
4 8 16 when I need too for 50 and 100 watt amps

with a load attached .... you can check out the amp electrically
you can also feel the PT for excessive heat
if its really loud or hot something is not right

[utervo]

No worries, I took six 47ohm/17w resistors and put them in parallel to make an 8ohm load which I am testing the system with.

[Andy Le Blanc]

good job......

whats the voltage on the plate of your 6AQ5

thats my only real worry...following this discussion

the design-maximums are a bit lower than a 6V6

so I'll be curious of your experience...

[utervo]

Thank for your interest and help, I'll need more...

Seem that nothing is getting to PSU. I'm using 5Y3GT/G, tried 4 of them, no difference. I measured the plates on the 6N1P and I get a small negative voltage. I measured around 650V between pins 4&6 without the rectifier, the heaters showed 5.5V. After having the amp for a while the filter caps had a very slight negative charge, nothing else. Heaters on the 6N1P were 6.8V, all of the tubes were glowing nicely orange. What's puzzling is that it's such simple wiring to the power supply, I have a hard time figuring out how I have managed to mess it up. Nothing weird happening, no funny smell or excessive heat anywhere. I wonder if all my rectifier tubes are busted, I bought them the same time, they are JAN RCA.

[Andy Le Blanc]

check the hook up and schematic of the power tranny

check for the center tap on the H.V. secondary

most rectifier tubes are pretty rugged and if you've tried more

than a couple its not that...... disconnect the rest of the power supply

in case the fault is there.... and check the rectifier with no load

it sounds like something was over looked

[Andy Le Blanc]

Its good to post pictures...

I cant see a center tap to ground

and the power take off.....from a rectifier

is off the 5V filament .....pin 2 or 8 ....5Y3GT

[utervo]

Indeed, I have not connected the secondary center tap (0) from the PT to ground, how very sloppy of me... The power is the white wire from pin8. I'll add the 0 to ground tomorrow, better not do first time powering this late.

[utervo]

Connected the wire and boy do I get voltages. I wonder what effect it has that I measured these without the tubes in.

Heaters: 6,73 vac
6N1P: 438 vdc
6AQ5A: 447 vdc

How much will the tubes drop those?

[utervo]

I wonder if my multimeter is playing tricks with me, it says it's 640VACgoing to the rectifier (without it), makes me wonder how that could be turned into even over 300VDC let alone what I am getting now.

[Andy Le Blanc]

the measured AC across the entire high voltage secondary
is the large number your seeing

with the center tap connected.... the retifier conducts half of that at a time

your running your power supply with no load
so the filter caps charge to their highest voltage
this will drop some what with loading

what was the rating of your PT in ma.

your 6AQ5 is rated upwards to as much as 49 ma. of draw....

[utervo]

It's 0,1A I think

This is what it says.
"230V//300-0-55-300 0,1A / 6,3V 4A / 5V 2A"

My multimeter says max 500V, perhaps it starts acting funny when it gets more.

[Andy Le Blanc]

.1 A........100 ma.

looks like its in the ball park

I've cooked multimeters before...... hopefully its ok

even though the 6V6 and 6AQ5 are rated nearly the same

the smaller size of the 6AQ5's glass envelope it the reason

for the differnt max rateing.... it might run hot ....

it might be an issue......it might not

I messed up the wireing of the powersupply in a fender twin once....

ended up with a voltage doubler..... 700 plus volts DC

toasted the filter caps and a multimeter.... sizzle.....

[utervo]

Tried with the tubes on and a 40W light bulb in series, seemed fine until I got this high pitched sound, like an miniature engine revving up, turned it off and on a couple of times and the sound comes back. Bulb was glowing dim, which I think is what it should.

[Andy Le Blanc]

this happend without a speaker?

recheck the circuit from the power supply

pay attention to how you wired the OPT and how feedback is applied

you may have set up the conditions for it to oscillate

also try a turn on with the preamp tube pulled out

your lead dress might be the culprit

[utervo]

Man it's hard to be a beginner. The sound was caused by running the amp without a load, how the hell did I drop it out of the amp's ass I don't know. Hope I didn't fry anything.

I put the load back in and it seemed to do steady at least for a couple of minutes, at least didn't sound like it's in a pot with an apple in it's mouth.

Do I have something messed up in the circuit or is the transformer and rectifier just pushing that much voltage? How do you calculate what the voltage should be after 5Y3GT/G doing it's job when I have around 650 going in?