tube amp diagnosis

[agedhorse]

at the price of output tubes today you don't want to buy a set just to try that theory Take it back to your tech.

Absolutely.

 

[TTA]

well non result. brought it back to demo the issue and of course it did not have issues. my bass my pedals my amp his cords and power and cab.

He was cool though, we talked gear and he is happy to look again if it returns.

i plan to sanity check my cabs cables, then rehearse my set.

almost contemplated class d… but not today.

 

[TTA]

AFAIK you have an SVT AV which is a special edition CL.

Bias controls and indicators should look like this.
View attachment 7443325
A red bias indicator indicates one or more tubes is over current.

The output section is push/pull. Push has three 6550 tubes and pull has three 6550 tubes.

Basically the bias indicators have two thresholds.

1. Green uses AND logic. Green turns on when all three tubes in the circuit have >15mA of current.
2. Red us OR logic. Red turns on if one or more tubes in the circuit have >30mA
3. If you get red without green, at least one tube is over current and one tube is under current. Good chance one tube is totally nonop.

When a 6550 arcs it can put on a light show. The screen resistors in SVTs are designed to act as fuses. If you have red without green, there is a good chance that the screen resistor on the tube that arced is blown.

The arcing could have occurred from a worn out tube. Another possibility is the pins in the tube sockets need to be retensioned or the amp has some other sort of intermittent connection.

I think it would be a good idea to take the amp to a qualified tech.

I am still just curious. my ears heard what they heard when i had volume reduction, and the blinking red light turning solid one one side with the green light. the volume reduction was not in my head… even if it seems fine now.

bear with me as i am “new to svt” and i suppose amp diagnosis in general. but i hate not knowing. just trying to identify “normal. “

so at idle (power in, standby off) i see two green lights. bias is fine. when i play i do get blinking of the red lights. they flash with individual notes. immediatly turn off. green alwas solid. of interest low notes (e) seem to blink the left red led. mids (d/a) more the right, highs not at all. not a rule, rather a trend. i assume this is all normal?

playing 30-45min x2 today. only the above. no fuzz, no flashes, no volume reduction. tubes all glowing equally.

when i first got it, once warm it would snap through the speakers now and then. a cold solder joint was identified and fixed. no issues now.

I did swap a patch cable that may have been giving connection issues (could also be the jack on my mim jazz… need to test. dingwall fine tonight).

so i guess is the led pattern normal or not, and has anyone seen such issues with a cable/patch?

the past flashing red to solid red led (always withb” green) followed by volume reduction was real. wonder if an old fan intermittantly doing its job might do it also.

 

[Wasnex]

It's totally normal for the bias indicator LEDs to flash when you play.

 

[TTA]

It's totally normal for the bias indicator LEDs to flash when you play.

appreciate that. flash red with no green is the issue.

pushed it harder today but only in the basement. any master above 30% sounded really harsh in the highs, but it could be suboptimal room position. i will have a larger space in the next month so the paranoia/suspicion will continue later.