5E3 build

[Twin]

5K(2watt) metal oxide resistors burnt after 20 seconds off standby.

Measuring 385V on positive side of first main filter cap.

Thanks for any help in advance!

[soundguruman]

What?
We are not the psychic friends network.
You have to give DETAILS. AND pictures, lots of them, clear, with plenty of light.
Otherwise we would not have a clue what you are talking about.

[Bruce / Mission Amps]

Bad power tubes, a dead short at the second filter cap or the actual screen node wire to the 6V6 tube sockets is grounded... etc... nothing in the preamp stage past the 22K can draw enough current to blow up the 4k7.

[Twin]

Bad power tubes, a dead short at the second filter cap or the actual screen node wire to the 6V6 tube sockets is grounded... etc... nothing in the preamp stage past the 22K can draw enough current to blow up the 4k7.

Thanks Bruce, very helpful info indeed! Tried swapping 6V6's with another fresh set of matched JJ 6V6's & still encountered the same issue... Also did the same with the 5Y3 rectifier tube just to be sure there wasn't a short there but still had same result(burnt 4.7K resistor between 1st & 2nd filter caps), so then I did as you said & traced the screen node to the tube socket - solid solder connection there too... MUST be a bad filter cap - the weird thing is they are also brand new Mojotone 16uf's & I took my time on dialing up the variac to avoid any shorts, but it does happen sometimes(darn bad components!). Thanks again for your wisdom!

[Bruce / Mission Amps]

I haven't used many of the TAD 16uF-475v caps but I use the heck out of the 22uF-500v ones and the F&T 22uF-500v caps... after many many hundreds of them, I honestly don't think I have had a bad one of either.... can not say that about the Sprague 16uF and 20Uf caps.

[Twin]

Thanks for the tip. I have used F&T's before & they all worked great, but this small parts kit came with the TAD's so I thought I'd give 'em a shot... Can I up the caps to 22uf 500v without any issues or should I just get 16uf 475v F&T's?

[Bruce / Mission Amps]

Sure, all 22uF-500v caps is the way I sell my 5E3 kits.
You can go up 33uF on the first, main filter cap and 22uF straight across the rest if you want.
I have never heard much, if any at all, difference with that combo compared to all 16uF caps, except there is a little less AC ripple noise with the larger caps.

[Twin]

Sweet, thanks Bruce!

[Twin]

OK, so I replaced all of the main filter caps with a few I had on hand(1x 22uf 450v & 2x 20uf 450v) Still burning 4.7k/2watt resistor within 20 seconds(or less) off standby... 2 brand new JJ 6V6 S in the output. Double checked the screen node for continuity to pin 4 of both 6V6's - both good...? Any other ideas how I'm roaching these resistors?

Just FYI, I Took a few voltages & here's what I came up with:

5Y3GT Recifier - 385vdc at pins 2 & 8

Right lug of standby switch(on standby) - 385vdc

When turn the standby off & quickly measure the B+ at the 1st filter cap I am getting 496vdc...!

All filaments around 6.5vac(including pilot lamp) / 116vac at power on/off switch

[soundguruman]

OK, so I replaced all of the main filter caps with a few I had on hand(1x 22uf 450v & 2x 20uf 450v) Still burning 4.7k/2watt resistor within 20 seconds(or less) off standby... 2 brand new JJ 6V6 S in the output. Double checked the screen node for continuity to pin 4 of both 6V6's - both good...? Any other ideas how I'm roaching these resistors?

Just FYI, I Took a few voltages & here's what I came up with:

5Y3GT Recifier - 385vdc at pins 2 & 8

Right lug of standby switch(on standby) - 385vdc

When turn the standby off & quickly measure the B+ at the 1st filter cap I am getting 496vdc...!

All filaments around 6.5vac(including pilot lamp) / 116vac at power on/off switch

Like I said before, no clue without pictures. If you can't see it, it's guessing.
I, however hypothesize that there is a mistake somewhere...don't feel bad, happens to everybody.

Looks like the output transformer might be hooked wrong.

[Twin]

Here are some pics I just took, thanks for the support!
Bill

[soundguruman]

Lets see more of the output transformer...looks like something funky.
Is that pin 3 of the output tube, that is hooked to the (green) transformer secondary?
anyhow until you find the mistake DO NOT power it up anymore.

[Twin]

The OT is a Classic Tone & has only one tap from the secondary(black wire) the other is grounded to the OT frame... but you're right it certainly doesn't look like a Fender OT. The green & yellow wires are part of the primary & go to 6V6's & the red wire goes to the rectifier via the standby switch.

[Twin]

Classic Tone Tweed Deluxe OT 40-18022.pdf

[soundguruman]

Have you verified that?
Green is usually secondary.

Lets see the other side, where the wires are coming out of the OT.