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,
Try some 6ca7 Fatboy tubes from the 60's.......
Try some 6ca7 Fatboy tubes from the 60's.......I owned a pair of these amps, no way you will get SET sound.....I should of kept them, sorri sold them
Thanks Ryriken,

I checked last night, thinking I had the Mullard reissue EL 34's in but, instead, the EH EL 34's were in. I quickly swapped the Mullards back, and the amp sounded a bit better, but still no match for the SET 300B mesh plates.

I'll see if some 6CA7 Fatboys can be found and give them a try.

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.
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Thanks guys, for your responses. I have been more than mildly surprised by the improvement wrought by the modest Assemblge SET 300B, however, it does have fresh factory upgrades w/new carbon film reisitors, Jupitor foil and paper beeswax capacitors, and it just seems to keep getting better and better.

I won't give up on the VAC yet though, until I do a bit more tube rolling. It's still a very good amp, with high current output. I'll see how it goes.

Thanks again,
Hello Dan

Derrick here, I purchased your Plinius. I was a strong EL-34 guy , until I tried the Plinius.

How many El34s do your VACs use?

I have some Fat Boys and you are welcome to try them out if you'd like.

Shoot me a message if interested
I use two different el 34 based amps and depending on the rest of the system if you use real Mullard XF 2 dual halo el 34's, not the reissues, you will get a huge performance boost in areas of midrange depth and image density or riichness. Also with the right input tubes- long plate square halo Mullards from the 1950's-your bass impact and neutrality will also improve markedly. What you will not get is the liquid immediacy of a 300b but again this also comes at a price. To put it another way, if you voice the system around an el 34, much gains are possible with tubes, cables and pc cords , and cartridges, etc
With the 300 b, you have an entirely different blueprint that requires in most cases a different compliment of accessories.
If the set 300 b has enough power it may be the ideal path.
6ca7 Fatboys are very expensive, take alook at e-bay and you will see.
I've got a line on some 6ca7 Fatboys, I'm going to give them a try.

There's no question, the SET 300B is my go-to amp (system sounds its best in forty five years of trying).

I like having an alternative to turn to, for variation, and for back-up. The VAC is a very different beast (about 80lbs; mostly in iron), and has some advantahes for highly dynamic music.

Thanks to all for your contributions. Regards,
>>>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.
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.
Ryriken- Expensive but hopefully worth the price of admission. I have heard a of a few LM owners gaining a nice improvement changing factory tubes. Very nice amp as is for the money though. I assume you like the Amperex Hollands?
I have 5 NOS Mullard Holland that test very good, don't use them yet, i dig those Fatboys in my VTL ST 85 amp.Come to think of it they may be Amperex but i think Mullard.