Help Me (tube issue)?

[gtrfinder]

I think my amp needs new power tubes.
Tell me what this leads you to suspect.

I was playing at pretty high volume the other day with my 65 amps London through my 2x12 with a blue and G12H
Before I shut it down I noticced that the bass frequencies were very weak. Like I had a compressor on or something.
The amp distorts very easily now.
And last night I turrned it onand there was a feedback pitch at any audible level. It went away after awhile, but was there for about the first minute or so. It even occured when nothing was plugged into the amp.

What do you think?

[Blue Strat]

The feedback sounds like a microphonic preamp tube. If there's an EF86 in the amp that's probably it.

The early distortion and lack of bass sounds like weak power tubes or one power tube that isn't working at all.

The only way to find out for sure is to ALWAYS have spare tubes on hand and swap them in when something like this happens.

[gtrfinder]

Thanks Blue Strat

Originally I was worried about my speakers (I thought I might have blown one or both), but after playing last night I noticed that they will pass the bass frequencies fine at lower levels, but when the volume comes up that is where the compression, loss of bass, and distortion artifacts happen. That is what makes me suspect tubes.

The amp does have an EF86 (on 1 of 2 seperate channels), but the feedback occured when I was plugged into the 12ax7 channel, and then not plugged in at all.
Would the EF86 still contribute to this, even if nothing is plugged into it?

[Blue Strat]

Any preamp tube can do this. Doesn't matter if there's anything plugged in or not. Pull the EF86, turn on the amp, and see if the problem goes away. If it does, it's that tube.

This is a very common problem with EF86s in those, and most EF86, amps.

[Hipster Dofus]

The London is a bit hard on power tubes, and the EF86. I play quite a few gigs, and at loud to VERY loud volume. My Power tubes get changed 2-3 times a year at least it seems. I like the GT tested JJ's rated 5. I can tell every time I change them that "it's time".... 30 to 50 hours seems to be the life in this amp before they lose the top, and get a bit too loose. Did I say I get to play loud? My amp works damm hard every gig! My last EF86 from Mike was tested "extra" and is a Dario Miniwatt. If was great, then noisy, and now great again..... Go figure... The EF86 can make all kinds of bad noise, from a bit of rattle, to full on chaos. If you are going to gig the London, and you need the EF86 side, have a spare or two. A slightly bad one is better than the one thats out of control...

I love mine!

[Blue Strat]

If that Dario changes, try cleaning the pins. You might be amazed.

[Hipster Dofus]

What do you recommend to clean with?

[Blue Strat]

What do you recommend to clean with?


Check the FAQ on my website, under Resources. There's a lot of other good information there that no one seems to find.

[Hipster Dofus]

Mike

I must have missed that. I know I looked at all that stuff a while back. Good stuff.

Thanks!:JAM