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
islandmandan
>>>I like having an alternative to turn to, for variation, and for back-up<<<

We share similar tastes. 300b SET's have been at the top of my list of favorite amps for many years now...and... I use a Marantz 8b (pp el34) in a separate vintage system (with a 7c and 10b) and can listen all day to it. It has some of that "dark matter" magic stuff that does that kind of thing that is hard to describe or measure...it just sounds great.

It is nice to have an "alternative". Looks like you have some tubes on the way but will mention that I have liked the SED winged C and Siemens el34 tubes in the 8b.

If you can't find the magic with the VAC, you could try the pp 300b route. I have one and it works for me. It has that kick that pp has and with the 300b tone.

I have Amperex BB EL34's on the way for my LM integrated. I will chime in next week to give my opinion on them. I was told Mullard tend to be warmer than Amperex, while the latter is warmer than the Siemans. It should be interesting anyway. My guess is they will kill my stock chinese tubes, which aren't too shabby. These cost like 1/4 of what the amp cost, so expectations are high.
Dan,
IMHO the issue you are facing is fundamental one in that you are hearing the difference in amplifier topology - the EL34 amp is a push-pull probably configured as a pentode amp while the 300B is a single-ended (as you wrote) amp. The EL34 is a pentode tube but it can be configured as a pentode or as a triode. The pentode configuration gives more output power but at higher distortion. The triode configuration gives lower power but with lower distortion. I used to own a Cary/AES Sixpac that used EL34 in triode configuration & the sonics were really very good. (Too bad for me that I bought a 1-ohm version Apogee Scintilla that the Sixpac just could not drive!).
The push-pull amp will have more distortion (pentode config) & maybe even cross-over distortion since one/one set of tubes will be used to push & the other/other set will be used to pull. The matching of the push-pull pair is critical & it will never be perfect.
The SET amp uses just 1 300B tube to push & pull. so, by design the push pull ckts are perfectly matched - it's the same tube doing both! The distortion is (way) less.
Plus, reading other tube users' comments, it seems that the 300B has some sonic attributes that the EL34 simply does not have.
IMHO, Jjrenman was on the right path when he changed his pentode amp to a triode configuration (it is also why I chose the Sixpac as I, too, want a the pentode EL34 configured as a triode).
BTW, the 300B is a triode tube (& it sounds awesome) - there's a correlation here......
Did you get a good deal on the Fatboy tubes. Hope they from the 60,s. Sylvania or RCA.I have 3 quads NOS. Got lucky bought them years ago when not so expensive.
"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.