Svt cl not basising!

[chris678]

Hey so iv searched a few threads and I haven't found anything similar apart from telling me to take it to a tech, which is what I'll probably end up doing!

But my problem is that one of my tubes kept popping/ flashing when I turned it on, so I bought a quad of new PM 6550c tubes and replace the right hand side with 3 new tubes, the original were Russian made tung sols but then problem im having is that the green light will not come on only the red, is it because they are different tubes on each side? Or is there something more wrong inside?

Thanks once again defiantly us bassists have the best forums!

 

[chris678]

However the amp works! And sounds good. Is it dangerous to use it when it's not biast properly? I have a few gigs coming up which I could do with using my amp!

 

[beans-on-toast]

Yes the amp will not work, how well is dependent on how far off the bias is. If you can't set the bias there is an issue with the tubes.

Since the new tubes are not working, I would do the following. Keep careful track of which tube is which. Reinstall your old tubes except for the one that is flashing. Take your new tubes and try one at a time in place of the flashing tube. See if you can set the amp's bias.

The issue can be a plate, screen, or cathode resistor in the tube circuit for the tube in question. A tech could check this out for you.

 

[B-string]

Never heard of "PM" tube matching/rebrands before? Info on one site alludes to the 6550C being some Chianese tube (Sino maybe)?
The new tubes are most likely the reason for the bias trouble, Beans suggestion should help prove that, or switch triads and see if the trouble fallows the new tube set.