RFT EL34 usable in Modern Classic ?

[thegame]

I'll start the Wizard tech questions

So, I have some unused, matched RFT (Siemens) EL34s sitting around doing nothing. Besides a re-biasing and probably changing the bias section to accommodate EL34s (the amp currently is setup for 6L6), can the RFTs withstand the Modern Classic's screen voltage ?

I believe the RFTs can handle higher plate voltage, but are happiest with only 450 V or so on the screens.

I'm very satisfied with the Sylvania 6L6s in there right now, but I'm in the mood for the classic EL34 crunch.
Thanks !

 

[glip22]

I have a fair amount of NOS knowledge. I am definitely not an expert by any means. I bought and sold hundreds of desireable tubes. I personally would not use them in the Wizard. If I remember correctly when I checked the MC's plate voltage it was around 500. The RFT does not do a good job with plate voltages above 450. Those tubes sound great at lower volumes and gain, but I do remember I wound up removing them from another amp I had them in(Engl Invader 100) because they became unstable at higher volumes. They also lost their character. I would not chance it.

 

[novosibir]

Unfortunately (or fortunately) it's not that simple, to judge about RFT's

First you have to differ between 60's production, 70's production and 80's production (production has ended in spring 1989)!
Second you must know, that 60's production is superior to 70's production, but 70's production is superior to 80's production!

But how to differ?

50's and 60's RFT's do have a pretty flat tube's base.

70's RFT's have printed additional to the 6-digit production code "TGL9649" and most of them additional do have a triangle printed on, where inside is either a "S" or a "1" or a "2" or it's empty.
- S is the best choice and means "Sonderklasse" - translated ~about~ best selection
- 1 means, that the tube was tested and is of an excellent quality, most of them went into export
- 2 means, that the tube was tested, but parameters weren't absolutely convincingly. These tubes went uinto the national supply.
- empty means, this tube wasn't tested for purpose, but has easily withstand a quick test.

I've attached a sheet, but describtion is in German

80's RFT's only wear the RFT logo and a 6-didgit production code - nothing else.

But keep in mind, that many of the 'Siemens' or some misspell it 'Seimens' labelled RFT tubes went over the pond in the early 90's and are from late 80's production. Often you can't verify this, because the tubes became relabelled 'Ultron' or 'RCA' or 'Mesa/Boogie' or, or, or.....

... but then watch the tube's top! Is there a smooth dimple, then it's presumably from the 70's or from the very early 80's
is there a not so nice spot, what rather looks like a welding spot from automotive production, then it's presumably mid to late 80's

Ok, this was the lesson of today
But now to my (over 20 years) experience with RFT's:

I've never had failing a 60's RFT in any amp. They all were strong, constant and have had a remarkable life span.
With only a hand ful exceptions the same is valid for all the 70's RFT's, which already went through my hands.
I've built 70's RFT's into earl 70's Marshall Super Lead's with a B+ of 530V (!) w/o any problems!
I've built in 70's RFT's in Marshalls of customers with 150+ gigs every year - and after 3 years the tubes still were working well.
But I've had troubles and headache with 80's RFT's, especially with mid to late 80's and especially in amps with a B+ close to 500V or beyond.

But in amps with a B+ up to 470V they're nonetheless working fine.

And there's only one EL34 type, what IMO nails the RFT soundwise, in reliability and longevity - it's the 'real' Mullard, NOT made in Russia!

Larry


BTW: The output tubes I'm using in my DINO amps and what I will be using also in my forthcoming 'Jon Schaffer Signature Head' are RFT EL34's from 73's production - standard, no extra charge.

 

[glip22]

That was some great info. A Larry amps section would be great for this forum. I'm sure Brad would happily welcome you if you were interested. Your knowledge would be an awesome addition to Rig Talk.

 

[novosibir]

That was some great info. A Larry amps section would be great for this forum. I'm sure Brad would happily welcome you if you were interested. Your knowledge would be an awesome addition to Rig Talk.

Thanks! Yes, w/o a 'red face' I proudly can say, that with RFT's my experience really is extensive. It's already been a few thousands of RFT's, which went through my hands during my service tech & amp builder's career - and it's been far over one thousand, which I've put myself into amps.

Concerning a Larry section here it would be a huge honor for me and you can propose this to rareguitar - but I think, that this section wouldn't be frequented very much, because there are too less Larry amps out there. I'm a one-man-company, just hand building about 15-20 amp every years and most of my customers aren't hanging too much in amp forums. And probably 5-10 posts a week is fairly low

Larry

 

[thegame]

Thanks Larry, you're the best

My RFTs are indeed rebranded Mesa Boogie ones. Dimple looks fairly smooth, but I find it hard to tell. Oh well, the Schaffer preamp will probably retire my Wiz next year anyway

You're right, your own forum here wouldn't be that busy, but would still be an invaluable technical resource. Your explanations are worth their weight in gold !

 

[novosibir]

Just an example:

Left you can see a 'short base' RFT, what indicates a late 50' or a 60' production.
Right you can see a RFT with the regular base, but stamped among others with the "TGL9649", what indicates 70' production.

There's no triangle stamped on the tubes, what means the same as an empty triangle as described above.

Larry