2. amps-preamps
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EL 34 question

I have a VAC PA 35.35 EL 34 push-pull amp, that has had factory upgrades. I was quite happy with it, until I started using a modified SET 300B amp, which has blown the VAC completely out of the water.

I am actually giving thought to selling it, but decided to see if tube rolling might bring it closer in performance to the SET amp.

I have two sets of output tubes that are used, a matched quad of reissue Genelex KT 77, and a matched quad of reissued Mullard EL 34's.

The small tubes are NOS Telefunken 12AU7 and 12AT7, all aound three years in use.

I'm just hoping I can get some insight as to whether better performance can be gleaned from this old amp.

My experience with tubes is recent, lots I don't know, so any old salts that care to help with suggestions would be great.

By the way, the speakers are 94db sensitive custom Tannoy HPD's.

Best regards,
Dan
Ag insider logo xs@2xislandmandan

Showing 2 responses by jjrenman

jjrenman
279 posts
 
I used to have a pair Dynaco MKIV's which is basically a mono block versions of a stereo 70. Besides extensive tube rolling I had converted them from fixed bias to cathode bias, from pentode to triode operation as well as lowering the negative feedback. Each was an improvement in sound quality. Each was a step toward a SET "type" of amplification but in the end it does not come close to what my current 300b SET does.

In the end only you will be able to decide if you can get your VAC close enough to suit your needs.
jjrenman
279 posts
 
"Jjrenman was on the right path when he changed his pentode amp to a triode configuration"

Yes, changing my amp from pentode to triode was an improvement, easy to do and you only give up 3db of output. However IMO, changing from fixed bias to cathode bias was a bigger improvement. You give up even more output when you do this however the amp handled dynamics better! Must have something to do with how a cathode biased amp recovers from very demanding dynamic peak output. IMO, it is why SET amps seem to play and handle dynamics much better than their low wattage output would have you believe.
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