stash of vintage 6v6 - what's good here?

Discussion in 'Amp Tech Center' started by AndyPanda, Sep 29, 2019.

  1. AndyPanda

    AndyPanda Tele-Meister

    Age:
    65
    Posts:
    263
    Joined:
    Sep 4, 2019
    Location:
    Bay Area, California
    I'm thinking of building a 6v6 push/pull amp but haven't made up my mind between a 5e3 or 6g2 or something else.

    These are the 6v6 tubes I've got on hand and wondering what I have here. Mostly I have the RCA with a shaded glass and not really sure what's the difference between those and the ones with clear glass (and why). 6v6_Stash.jpg
     
  2. Wally

    Wally Telefied Ad Free Member

    Posts:
    33,469
    Joined:
    Mar 17, 2003
    Location:
    Lubbock, TX
    Well, any of those might be good and usable; or they all could be past their due date. They are UOS, correct....used tubes?
    At any rate, one would have to find out if there is a natch or two there before one would know what to do with them. A little single ended amp is useful in determining what is there.
    I have a couple of handfuls of NOS RCA 6V6GTYs. I thought I might find a pair or two there. No way...there was not a matched pair in the whole group. I found everything from 80-150% of max plate dissipation numbers, and none close enough for a pair.
     
  3. muchxs

    muchxs Doctor of Teleocity

    Posts:
    11,904
    Joined:
    Aug 14, 2004
    Location:
    New England
    First the good news: That's a nice stash of RCA black plates. You stand a chance of getting a matched pair out of those.

    Now the bad news: Those old RCA black plates seem more likely to arc than any other ANOS.

    Now the good news: RCA was a leader in tube technology. Seems they got the memo. Those grey plates with the red lettering work well in guitar amplifiers. Seems to me if you found an old Princeton with original tubes that's what would be in there.

    Now the bad news: You only have one of them.


    I have a pair of those with ancient masking tape vulcanized to their bases. They're marked "New 7-9-69".


    The other goody in there is that lone Sylvania. I see those in old Hammond "M" models. "Only driven on Sunday" as in they've been played at church every Sunday for the last 60 years. If you want the exact opposite of new tubes that burn out like cheap light bulbs, there you go.
     
  4. muchxs

    muchxs Doctor of Teleocity

    Posts:
    11,904
    Joined:
    Aug 14, 2004
    Location:
    New England
    Might as well toss this comment out...

    Black plate RCA 6V6s seem to be the darlings of the tube world. Must be some pocket of demented audiophiles somewhere buyin' 'em all up.

    Must be said audiophiles are able to read and comprehend tube charts. Those old RCAs work fine at the 300v (+/- 20%) specified in pre- 1960 tube charts.

    They're all warm and cuddly if you treat them like EL84s. Do not exceed 360v.


    Anyone who has been around for a while has heard my spiel about 6V6 tubes in Champs, Vibro Champs, Princetons and Princeton Reverbs. They all share the same power transformer Supply voltage tends to be a little over 400v, say 410v. An old black plate RCA 6V6GT will hang in there in a Champ if it's in pristine condition. Bear in mind it's beyond design limits for plate voltage and dissipation.

    Maybe that's why they smoked the glass? That way you can't see the sparks flyin' around in there.
     
    rangercaster and AndyPanda like this.
  5. schmee

    schmee Poster Extraordinaire

    Posts:
    7,901
    Joined:
    Jun 2, 2003
    Location:
    northwest
    People covet those RCA's. I agree though that they can be arc prone. A NOS set of those took out the OT on my 65 BFDR years ago! I think many older amps are way high in voltage for those is the real issue. The smoke glass are more common.
    I'm a real fan of Sylvania 6V6's and 6L6's.
     
    SnidelyWhiplash, AndyPanda and muchxs like this.
  6. Nickfl

    Nickfl Tele-Afflicted

    Posts:
    1,645
    Joined:
    May 24, 2016
    Location:
    Florida
    In my experience, old radio pull tubes (which is what I assume these are) are almost always in great working condition. Unlike many guitar amps (especially BF fenders) radios tend to have been designed to run tubes well below the design limits and the tubes therefore lasted basically forever.

    It should also be pointed out that while Muchxs is spot on (as per usual), the two circuits you mentioned in your post are well within the tolerance of those black plate tubes when run at vintage voltages. 315v plate to cathode on a 6g2 and 340v or so on a 5e3. Bear in mind though, that a lot of 5e3 kit builds run much higher plate voltages due to using a power transformer more appropriate to a deluxe reverb and/or using modern production 5y3 rectifiers that aren't actually a 5y3 and produce a higher B+. Vintage amps may also run at a higher voltage because modern wall voltage is higher than what they were built to use.

    So, I'd use those RCAs in a true to spec 5e3 or 6g2, but be wary of subjecting them to something harsher.
     
  7. AndyPanda

    AndyPanda Tele-Meister

    Age:
    65
    Posts:
    263
    Joined:
    Sep 4, 2019
    Location:
    Bay Area, California
    I have a vintage (late 40's I believe) amp that I run a pair of Russian tubes (they say Ruby 6v6GTA-R but Google search hasn't been able to bring up a spec sheet for them so I'm not sure what their max ratings are - but they seem to run fine). If I use a variac or bucking transformer to get my line voltage down to 110, then it puts 360v plate to cathode on the cathode biased pair (shared 400 ohm cathode resistor dropping 25-26 volts). So I'm guessing those old smoked glass RCA 6v6 would not enjoy life in that amp? But if I had matching mates for the Sylvania or Red label RCA, those would be OK?

    (If I'm not using a variac or bucking transformer, I use 6L6GC output tubes and get the exact same wattage output (about 9.8v RMS) but they are running at 40-50% vs the 6v6 running about 80-85% of max. I prefer the sound of the 6v6 but feel safer running the 6L6.

    Can someone please walk me thru a method of matching tubes in a cathode biased amp? What I have done in the past is to measure the Plate to Cathode voltage and pick two tubes that match (and look at the waveform on a scope) but what are some better methods? (adding a 1 ohm resistor between each cathode and the shared cathode resistor to measure current across the 1 ohm? I see diodes across the 1 ohm resistor in many schematics, what is the purpose of that diode?)

    thanks in advance for giving me some edumacation here :D
     
  8. AndyPanda

    AndyPanda Tele-Meister

    Age:
    65
    Posts:
    263
    Joined:
    Sep 4, 2019
    Location:
    Bay Area, California
    Here is a picture of the Ruby tubes in case anyone knows if they have same specs as 6v6gt or if they are rated for higher plate voltage etc. I've been running these just because I didn't want to risk damaging the vintage ones with the higher voltage in that vintage amp.
    RubyTube.jpg
     
    Last edited: Sep 29, 2019
  9. muchxs

    muchxs Doctor of Teleocity

    Posts:
    11,904
    Joined:
    Aug 14, 2004
    Location:
    New England
    For years I used aftermarket PTs intended for any old Deluxe be it Deluxe Reverb or tweed Deluxe. I assumed the '60s Deluxe whacked its tubes with more voltage than a tweed.

    Turns out a tweed Deluxe is around 355-0-355 while a Deluxe Reverb is 330-0-330.

    Multiply the voltage on either side of the CT by a fudge factor of 1.15 to guesstimate loaded B+ with a 5Y3 rectifier.
     
    AndyPanda likes this.
  10. AndyPanda

    AndyPanda Tele-Meister

    Age:
    65
    Posts:
    263
    Joined:
    Sep 4, 2019
    Location:
    Bay Area, California
    I've been testing them by measuring the voltage across the cathode resistor to calculate the plate current. What other things would you look for when using a SE amp to check out your tubes?
     
  11. VintageSG

    VintageSG Friend of Leo's Ad Free Member

    Posts:
    3,342
    Joined:
    Mar 31, 2016
    Location:
    Yorkshire
    That looks remarkably similar to the 6p6s. A fine sounding valve indeed. An almost direct replacement for a 6V6GT, but, sometimes they don't play nicely when run outside the design voltages. They are rated to a maximum of 350V. Some will start showing signs of stress at that voltage, especially if run 'hot'. Some won't. For every post you find with positive comments about them, someone else will say they turned into Soviet lightbulbs with a penchant for snacking on transformers. In a Champ, they're fine. They have all the characteristics of an old 6V6 because that's what they are. If they redplate, thanks to the opaque coating, you won't see it.
    As far as Ruby labelling goes, they at least test the valves, but at what voltage, I wouldn't know.

    The 6p6s is, or at least was, an inexpensive valve on Ebay and other sites. If I was building an amplifier that ran the valves at voltages that exceeded the max on the datasheet, I wouldn't use them for anything other than startup. In my Champ-a-like, I can't tell the difference between a 6p6s and a 1940s 6V6. Guess what they are clones of. I like them, but then again, I don't run them over design specs.

    Compare and contrast.

    http://rutubes.com/product/6p6s-6v6-6ay5-587-tube/
     
    AndyPanda likes this.
  12. AndyPanda

    AndyPanda Tele-Meister

    Age:
    65
    Posts:
    263
    Joined:
    Sep 4, 2019
    Location:
    Bay Area, California
    If I set my variac for 107v, the RCA tubes (push pull pair) run with 350v between plate and cathode and I read 22v across a 400 ohm shared cathode resistor (a little more than 9 watts plate dissipation per tube). Do you think those RCA tubes are OK at 350v? Or would I be advised to run them on an amp with voltages closer to 300-315v?
     
  13. AndyPanda

    AndyPanda Tele-Meister

    Age:
    65
    Posts:
    263
    Joined:
    Sep 4, 2019
    Location:
    Bay Area, California
    Thanks so much! Yes those pictures look exactly like this tube. Reading the specs (350v max plate) have me glad I haven't run them for very long at the higher voltages. I haven't seen any fireworks nor any trouble at all with them, I've probably only run them a dozen times and only for 10-15 minutes but they were run with about 380v on the plates. They came to me with a strange soviet rectifier tube that has no markings but looks like a 5C4S.
     
  14. Nickfl

    Nickfl Tele-Afflicted

    Posts:
    1,645
    Joined:
    May 24, 2016
    Location:
    Florida
    Just so I'm sure I understand, you're saying the correct plate to cathode voltage for a 5e3 should be something like 385v? I had the impression the consensus was more like 340-360v, though it is obviously kind of uncertain since Fender didn't note voltages on the layout or schematic for that circuit.

    Its kind of a moot point for me anyway, I've run my 5e3 clone near both ends of that voltage spectrum before I started really changing the circuit into something completely different and I was never all that happy with it either way.
     
  15. muchxs

    muchxs Doctor of Teleocity

    Posts:
    11,904
    Joined:
    Aug 14, 2004
    Location:
    New England
    Class AB1 is like passing a hot potato hand to hand. It gives the tubes a chance to rest.

    Class A is like a grenade by comparison. One 6V6 does all the work in a SE amp. No breaks and no sittin' down on the job!

    Setting supply voltage with a Variac in only a good idea if you have a separate filament transformer. Filament voltage shouldn't be below 6V.

    If your old RCA 6V6s don't arc with a 350v supply they'll be o.k..
     
    AndyPanda and Wally like this.
  16. AndyPanda

    AndyPanda Tele-Meister

    Age:
    65
    Posts:
    263
    Joined:
    Sep 4, 2019
    Location:
    Bay Area, California
    If I don't use the variac, my filament voltage is 6.9 on this particular amp (1940's era) ... I'm only lowering the variac to about 107-110v ac and filament voltage is about 6.1-6.3
     
    Last edited: Sep 30, 2019
    muchxs and Wally like this.
  17. Silverface

    Silverface Poster Extraordinaire Ad Free Member

    Age:
    67
    Posts:
    9,431
    Joined:
    Mar 2, 2003
    Location:
    Lawndale CA
    I do preliminary tests on a calibrated Hickok 6000A tube tester. That handles all the basics (the hassle is calibrating the thing every 5 years). But because none of the common vintage tube testers supply over 185 volts on power tube plates (much less on preamp tubes) final voltage and matching tests are done in an amp with a balanced PI (I set up one of my Holland Little Jimis, which can run 6V6's to 6550's for tube testing when needed).
     
    AndyPanda and Wally like this.
  18. Guitarteach

    Guitarteach Poster Extraordinaire

    Posts:
    8,720
    Joined:
    Aug 6, 2014
    Location:
    UK
    Nice.. I’d love trying all those.

    I have 50’s NOS RCA with the smoked glass in a champ type build.

    It’s the sweetest tube.
     
    AndyPanda likes this.
IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.


  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.