Another weird 69 SVT Problem

[michael_atw]

I have an AV that is making some funny sounds. She likes to vibrate in places I can't reach...dirty girl..

 

[JimmyM]

Arghhhh..... 6C4....... 6C4WA, whatever.....

That was the single most troublesome tube in the whole SVT-HD run..... maybe the most troublesome PART. They were made to be radio tubes, not audio, and it was heck finding enough "audio-good" ones to get through the run.

Might not be your problem, though, we mostly just had noise issues, not static-noise.

Static-noise can be lots of things..... mostly of interest to techie-types.

Noisy tube

A flickery plate resistor ("Fenderitis")

Ditto but with a plate supply dropping resistor (usually a bit more muffled)

A leaky, but not yet totally "BAD" coupling capacitor.

etc........

These things can be triggered by the voltage applied (signal level) and with coupling capacitors, can be responsive to frequency.

Wow, glad I didn't see this yesterday...would have put a damper on my REDDI high

Well I'm going to hope that it's the noisy tube because it just came out of the shop and the tech said everything seemed fine with the resistors and caps and all that stuff. Have yet to psych myself up for doing it yet, but I will absolutely try to get to it today. Or tomorrow. Or Wednesday...definitely by Wednesday, I hope.

Thank you for the advice everyone!

 

[JimmyM]

Bad 6146b. Very first one I tapped. Had just gotten a spare half set, popped it in, all fixed. Looks matched to me Yay, the best SVT ever made flies again!

 

[will33]

Very cool.

 

[JimmyM]

Ya, who said tube amp maintenance is hard? Took 10 minutes.

 

[will33]

A testament to the reliability, longevity, ruggedness, and just plain awesomeness of what a '69 SVT is.

 

[beans-on-toast]

Good one Jimmy!

Sometimes the metal clip on the plate cap that connects at top of the tube can be loose. Good to check that the contacts with the tubes are tight.

 

[JimmyM]

I did that for sure but good reminder. Thx David. But I'm too cheap to throw a perfectly good tube out without checking for that

Got a huge gig on Friday night outside...could easily do it with a B-15, but if it isn't raining, I think I may take the old horse out just for fun and celebrate my full time return to tubes. Then I'll put it back in the house till the next time I have to supply backline to someone else

 

[Jim C]

Must just be me but there really is only one option for this post unless you are a tech:
Check for bad tubes and if that's not it, take it to a shop.

If is was a SS amp: take it to a shop.

 

[JimmyM]

Ya, I just wanted to make sure it worth the two minutes of unscrewing I had to do. What good is the internet if it can't hold your hand through life?