Audio Innovations 500 amp valves ?

[Audio Al]

Trouble at mill , Yesterday one of my Harma E34L Superior Grade valves lit up like a candle

Time for a new set , any recommendations ?

[Mr.Ian]

I was running one of these many many many years back and it was a regular problem for me, my local valve guru, John Turrell (RIP) diagnosed problem as a shared resistor on the output valves somewhere, i cant remember what/where exactly but he replaced it with individual resistors on each channel and the problem went away.

I used 5881 sounded as good as el34 to me and at the time far cheaper

[tapid]

David Wright always recommended 5881 sovtek over the 34 s. On my 500 A/I amp I've been running 5881 Edicrons the past 4 years really nice sound in my view, no issues at all but like yours will soon need replacing.
People also seem to be trying KT77 a very good output valve by all accounts and one to seriously consider me thinks.

[AD Audio]

Kt77 or Sovtek 5881s are my faves for this amp. I've serviced /restored 7 or 8 of these in 2018 and apart from old age popping valves hasn't been a problem. I can see that adding a second resistor could help, and certainly won't do any harm. It's the output valves cathode resistor that's shared.
David

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[Audio Al]

Thanks all , just ordered KT77-JJ TESLA Matched in quads

[tapid]

Kt77 or Sovtek 5881s are my faves for this amp. I've serviced /restored 7 or 8 of these in 2018 and apart from old age popping valves hasn't been a problem. I can see that adding a second resistor could help, and certainly won't do any harm. It's the output valves cathode resistor that's shared.
David

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. For those interested David has some brilliant upgrades for this amplifier and improvement is huge and very well
worth the outlay. Let us know how the KT s go Al. Good luck

[AD Audio]

Hi Brian, thanks for the mention! Have a great New year!
David

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[Spectral Morn]

5881s would be my recommendation, they run well on the amp and as such the amp doesn't need adjusted to run them.

One small issue is that an EL34 going off like that on a AI500 often damages a resistor under the valve, that might need replaced.

[Audio Al]

My AI 500 is now with AD audio for a fix and some upgrades

[tapid]

Good things await Al... Good things await !.