Svt Cl problem

[johnk_10]

the last time (a year ago) i bought four 12BH7's, on pair of them were NOS RCA's and they ran me $29 ea. , the other pair were NOS Philips that ran me $21 ea.

and yeah, not a 6K11 to be found anywhere in an SVT.


IMO, as stated earlier in the thread, it sounds like the OP's CL has an output tube problem (6550) since even the new ones can, have a pretty high failure rate (common). it's just the luck of the draw, but i've been very lucky with the Sovteks that came stock in my '07 VR.

 

[okcrum]

Interesting choice of words? Even the Ex-SLM engineer on this board says they will get you in a safe bias range if the circuit is working properly, the if was carefully chosen.

No interesting choice of words at all, just stating fact. The bias measuring circuits are window comparators with 1% resistors, referenced from the +-15 volt regulated power supplies, so you'll get worst case 5-8% or so accuracy. If the bias measuring circuit's parts are damaged, there are usually bigger problems to fix elsewhere in the amp. 5-8% is a ma. or two of bias current.

Oh yeah, about those " Biasing Lights " in the back. You can NOT trust them for ANY kind of accuracy. After mine came back from the bench, the light on one bank of P{owertubes was far brighter than the other. I didnt dare mess with it, as it sounded brand new.
They run on a "Push-Me-Pull-You " principle.

The brightness of the LED has nothing to do with the accuracy of the bias measuring circuit.

I realize that. I was referring to Voltage measurement when Biasing.

I must have misunderstood you.

 

[okcrum]

IMO, as stated earlier in the thread, it sounds like the OP's CL has an output tube problem (6550) since even the new ones can, have a pretty high failure rate (common). it's just the luck of the draw, but i've been very lucky with the Sovteks that came stock in my '07 VR.

This. Sovtek used to have QA issues with soft vacuum and secondary emission on new tubes, but they have cleaned that up quite nicely over the last 5-6 years. You can still get the odd dud tho.

 

[B-string]

No interesting choice of words at all, just stating fact. The bias measuring circuits are window comparators with 1% resistors, referenced from the +-15 volt regulated power supplies, so you'll get worst case 5-8% or so accuracy. If the bias measuring circuit's parts are damaged, there are usually bigger problems to fix elsewhere in the amp. 5-8% is a ma. or two of bias current.

If you try biasing with the crossover notch method or dissipation method you will find those "user" controls not accurate. They are general "user" controls not tech controls or the "green light" range would indeed be very much narrower. Thats fact

 

[JimmyM]

the last time (a year ago) i bought four 12BH7's, on pair of them were NOS RCA's and they ran me $29 ea. , the other pair were NOS Philips that ran me $21 ea.

Let's hope my guy has the Philips 12BH7's The tech working on my SVT said the 12BH7's work but are not putting out at a level needed for the SVT. So if he doesn't have a good price, I guess I'll just order a couple EHX's for $12. But he usually does have good prices. Got two Sylvania 6SL7's for $15 ea last week. That was cool.

 

[okcrum]

If you try biasing with the crossover notch method or dissipation method you will find those "user" controls not accurate. They are general "user" controls not tech controls or the "green light" range would indeed be very much narrower. Thats fact

That should have been obvious from what I wrote. The point is, the bias adjustment isn't unusably inaccurate nor is it useless, both claims that have been made in this thread. Capice?

 

[okcrum]

Let's hope my guy has the Philips 12BH7's The tech working on my SVT said the 12BH7's work but are not putting out at a level needed for the SVT. So if he doesn't have a good price, I guess I'll just order a couple EHX's for $12. But he usually does have good prices. Got two Sylvania 6SL7's for $15 ea last week. That was cool.

Jimmy, PM me or give me a call.