Throwing metal film resistors in Fender amps

[tubeswell]

If your DMM has crapped out like JM Fahey has suggested, then the measurements you are seeing could be wrong. Typically red-plating occurs when there is waaaayy too much plate current. The lowish -ve grid voltage is a clue here (like JM says)

Also if its bias-vary trem wiggling the output stages, that won't work very well if the bias wiggle voltage is 'fighting' too much tube current. You need to have the lowest optimal tube current in order to get bias-wiggle trem to 'kick in' properly. (Which could also help validate why it definitely appears to be red-plating even though your DMM reading is telling to otherwise). You got another meter?

[soundguruman]

This thread has been going on too long. I declare it's fossilized.
164 e mails i have received for replies to this thread.
This is not a thread, it's a rope.

[tubeswell]

This is not a thread, it's a rope.

A steadily lengthening rope.

[kg]

a thought: what's the tolerance on those 1r cathode sense resistors?

when dealing with such low resistances a little bit of drift can make a huge difference.

any possibility of switching to 10r resistors just for better resolution?

[Wil]

They are 5W 5% wirewound if I remember correctly.
Now the reverb is making a lot of noise (mainly "high" pitch buzz) and I got some sort of parastatic noises since I brang the amp to jam with a friend.
The thing sounds great but is noisy has hell and has no tremolo.
I'll reflow everything and see if nothing shorts to ground.

Thanks for your help, guys.

[Wil]

Well, after some new tries at debugging, the thing is now out of control. Tried to cure the hiss, the non-working tremolo, etc... I failed at this.
The more i solder/desolder, the more problems I get. I don't have enough money to deal with such a capricious amp. So tommorow, I'll start playing the banjo.
Thank you for your help everybody.

[Jazz P Bass]

Bummer.

[Leo_Gnardo]

tommorow, I'll start playing the banjo.

Belgium needs more banjos! Now we know where to send them.

[Wil]

Giving up just plain sucks but maybe I'm not ready to build amps yet...
I don't understand how soldering/desoldering can make an amp go crazy.
It's as it was when I finished the build now and it has plenty of problems.
Not knowing what was going on, I measured the bias at got 77mA at the tubes... Those tubes are gone gone gone haha.
Silly thing is that I ordered a 5u4GB with my banjo...

[Wil]

Well after whining I fired up the amp again. The JJ 6V6 are still alive... after being at 77mA, that's a achievement.
I made a video so you can hear how it sound. I wanted to show you also, that the vibrato is "working" even with no footswitch plugged in and that the speaker is moving (as you'll see in the video) so it oscillates. But it goes up and down the idle bias setting and I believe it should rather go down and then come back to the idle setting (which is 22mA). At the end of the video you can also hear the parasitic noises that make me go crazy.
Please excuse the "dry" picking which, I agree, can be annoying but playing that way reveals there's no distortion when I strum a bit harder.

If you were wondering, Yes the speaker is sitting on top of a wooden box full of pcbs

[g1]

Here's a thought, all your problems seem to be related to bias/tremolo and the trem is a bias modulating type.
How about disconnecting the trem where it connects to the bias circuit, set it up like a standard non trem bias type.
Get it running right, then worry about the trem circuit later.

[Wil]

Can't wait to receive it !
I tried to disconnect the tremolo as I used to do with my DRRI (simply cutting a wiring that goes to the intensity pot). Cutting lug 1 makes the intensity all the way up, no more control on the intensity (logical). Cutting lug 2 kills the amp and make the bias go up to 70mA...
I don't really understand the 6g16 tremolo, I didn't study it actually. But the current things that aren't normal are :
-It "works" with no footswitch plugged in
-It oscillates but makes the bias goes up and down instead of idle down idle (bias idle is set at 22mA)

[Jazz P Bass]

VibroVerb 6g16 Schematic

I tried to disconnect the tremolo as I used to do with my DRRI (simply cutting a wiring that goes to the intensity pot). Cutting lug 1 makes the intensity all the way up, no more control on the intensity (logical). Cutting lug 2 kills the amp and make the bias go up to 70mA...
I don't really understand the 6g16 tremolo, I didn't study it actually. But the current things that aren't normal are :
-It "works" with no footswitch plugged in
-It oscillates but makes the bias goes up and down instead of idle down idle (bias idle is set at 22mA)

Lifting the center lug connection on the Intensity control removes all bias voltage from the output tubes.

Can you say "Red Plate"?

The 6g16 Tremolo modulates the bias voltage. (not simply the idle)
That is how it functions.

[g1]

Lifting the center lug connection on the Intensity control removes all bias voltage from the output tubes.

Can you say "Red Plate"?

Romoving a connection that "makes the intensity all the way up" should have also made the bias go way high and red plate the power tubes. Seems something is wired up wrong at the intensity pot.
Try connecting the wiper of the bias pot directly to the wiper of the intensity pot, remove the other connections on the intensity pot, then check/reset bias. Make sure the 47uf cap is still connected to the bias pot wiper, and the intensity pot wiper is still connected to the two 220K resistors.

[Wil]

Ladies and gentlemen, I just realised how dumb I am.
See those 1ohm resistor going to ground from 1-8 on each power tubes. I did not realised they were used to set the bias !! I already had them bolt on the chassis so I was biasing my tubes twice as hot as I believed they were!! Just put the Tung Sol 6V6 and they're not red plating !
At least now it's one problem less. The vibrato is now working (a bit weak to my taste be I think there are mods for this)
I still have what I think is too much hiss and since this afternoon I have a big volume drop (4 is like 0.5). I might have fried one of the filter caps or the rectifier.
I remember when I disconnected, I believed it's the center lug of the intensity pot I had a lot of volume, like it's supposed to be I think. But then, the tubes obviously went out of breath and got no sound for 1-2 minutes.