Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: TIMBO on October 22, 2013, 02:06:31 pm
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Hi guys, Dusted off a project that didn't quite fly :sad2:
The PT is out of an old radio/record player, with an output of around 305v per leg and with a SS rectifier about 425v. :icon_biggrin: unloaded.
I have a choice of Tung Sol and Groove Tubes.
The Tung Sol data says that max plate voltage is 315v
The power amp circuit is from the Garnet LIL ROCK B90L amp and has the 6V6s running on 435v.
I know that a lot of tubes will handle higher voltages but how much more???
The chassis has a 8pin rect socket that I could put in a SS plug OR I have a 5U4GB and a 5Y3GT rect tubes if these are a better option.
Just need a little guidance. Thanks
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... around 305v per leg and with a SS rectifier about 425v. :icon_biggrin: unloaded. ...
Look at a blackface Princeton Reverb (http://www.el34world.com/charts/Schematics/files/fender/PRINCETON_REVERB_AA1164.pdf).
Its B+ is 420v. Loaded. With a tube rectifier. And lower wall voltage in the 60's.
I had one of those amps and played it for years with the same pair of 6V6's, with higher B+ due to higher wall voltage. I also never had any issues with any 6V6, regardless of maker (US, Russian, etc).
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I converted a Bogen into a tube amp for my son in law yrs ago. It has had 476 volts on the plates of JJ 6V6's which I understand are rated for 500v. So that could another option if you don't want to risk the Tung Sol or Groove Tubes.
with respect, Tubenit
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Thanks guys, I did look at the fender schems and the deluxe models all were running the 6V6s at high voltages. So I think that i'll start with the 5U4GB and see what happens. :icon_biggrin:
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So I think that i'll start with the 5U4GB and see what happens. :icon_biggrin:
Make sure the 5V winding is rated for 3A in that case.
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In the 6V6's power class, you'd be "insane" to want to work with more than about 300V.
So even if the tube could stand more, there was no profit in listing higher ratings.
Like those 1980s cars where the speedometer only went to 85. We knew that even the lame smog-350 Camaro would touch 100, but under a national 55 limit the car-makers didn't want to say the real speed, or even hint it.
All the "sane" users of 6V6 quit using them in 1963. (Transistors took the smaller jobs, and EL84/6BQ5 was more convenient while waiting for transistors to rule the world.)
So for the last _50_ years, there's only been "insane" users. Supposedly Fender was THE main customer for years. 6V6 has never quite gone out of production. All those tubes are made knowing that they will go into "insane" uses like the over-Volted Fenders and their imitators.
So any modern "good" 6V6 will stand much more than 300V.
For what it's worth, the last datasheets showed 350V Absolute Maximum. The 315V rating gives a lot of slop for production tolerances. AbMax numbers assume _you_ know what you are doing and accept it is "your" problem if it ever goes over 350V. Even that surely has significant headroom. And also: mild over-voltage is a wear-out problem. The tube won't go FWOOMPH, it fades-out in 2,000 hours instead of 5,000 hours. In stage-amp use, 2,000 hours is a long time. In that time you will replace a lot of picks, strings, shirts, and beers, so what's another bottle or two?
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A BIG pat on the back for tubeswell, PT only has 5v@2A :thumbsup: PRR :thumbsup: :thumbsup:
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I have an Ampeg B25B with Winged "C" 6L6GC with plate voltage at 525 Volts
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If they're the new production (New Sensor) Tung Sols, then I'd probably be inclined to keep the plates below about 380.
On the other hand JJ6V6S can go to 460 on the plates no-sweat, so they're ideal for those Fender PR and DR type amps
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I can't swear to the absolute max plate voltage on the old or new 6V6 tubes but I'm running a RCA 6V6GT in my single ended modified Crate/Champ/JMP at 425Vdc . I can't swear to anything in regard's to any JJ tubes all that I have bought for the past 2 years have been bad ( from 3 different vendors) .
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So I think that i'll start with the 5U4GB and see what happens. :icon_biggrin:
Make sure the 5V winding is rated for 3A in that case.
5V4 will give similar results with a 2A draw....still fairly affordable NOS. My favorite recto tube
G
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I can't swear to the absolute max plate voltage on the old or new 6V6 tubes but I'm running a RCA 6V6GT in my single ended modified Crate/Champ/JMP at 425Vdc . I can't swear to anything in regard's to any JJ tubes all that I have bought for the past 2 years have been bad ( from 3 different vendors) .
Old RCA will run quite comfortably at that voltage - but they're a far cry from New Sensor RI
I've never had any problems with JJ6V6S and I've used tons of them since they brought them out, and continue to do so. Some of their other tubes (5U4, 6L6GC) I wouldn't touch with a bargepole
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The most "insane" use of the 6V6 I can think of is the Jim Kelley FACS amp from the early '80s. 4x6V6 for 60W, 495V plate. He specified Sylvanias only, I think GTA or GTB. I don't recall if it runs in AB2 but it wouldn't surprise me.
No idea how long they last at that voltage but you can bet the cathode draw is very low, probably about 20mA or so.
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Hi guys, Got the groove tubes in and with a SS plug. I'm getting 355v on the plates and 24mA on the cathodes and all seems good, so I guess only time will tell. I've got a GZ34 so i'll give it a try as well.Thanks :icon_biggrin: