ping musant @ high voltage on 6V6's

[Leo_Gnardo]

Jim Kelley thread on Garage Talk has devolved to WallyMart photos & amps of another brand, so let's see if we can cut, edit, pull to master reel... and re start at a point which (hopefully) will yield some good answers from Jim Kelley.

musant wrote:
Why does no one ever feel sorry for the poor little EL84's that are abused in so many other amps? They're even littler, and more helpless. Cathode bias - oh the agony! Smile


As much as one can feel sorry for a tube, yes EL84 or 6V6 run at elevated B+, OW! I'm more thinking "what were THEY thinking" referring to the designer/manufacturer. There's always some spec-sheet-reading wag who will sound off, "EL84 rated up to 800V plate, as long as you don't draw any current," or "6V6 were used in B&W TV Vertical circuits with voltages up to 850V." But we're concerned with guitar amps & looking for trouble-free operation as well as good tone & power. Now that you're here Jim, what's your solution A) for your current amp design and B) for the older amps. We now have JJ 6V6 which seem to put up with 500V plates, but techs & amp owners who try other brands or NOS 6V6 find themselves with a fireworks show instead of an amp. (And heaven help those who try it with Visseaux or Mazda 6V6 - these have no tolerance at all for B+ beyond 325V.) For the moment I'll select JJ's when re tubing a Kelley or other amp with elevated B+. At times in the past, I've been tempted to substitute a pair of 6L6 for the quad of 6V6, with bias set accordingly.

[ToneMerc]

My opinion of the JJ 6V6 is that it's just a small glass envelope EL34 like tube. I ran a sick experiment of running the JJ with 580V on the plates, with 292 on the screens.

TM

[Blackburn]

My opinion of the JJ 6V6 is that it's just a small glass envelope EL34 like tube. I ran a sick experiment of running the JJ with 580V on the plates, with 292 on the screens.

TM

Maybe I should refer to you as the mad doctor...

[Leo_Gnardo]

My opinion of the JJ 6V6 is that it's just a small glass envelope EL34 like tube. I ran a sick experiment of running the JJ with 580V on the plates, with 292 on the screens.

TM

Yes they are "tough as nails". With practically any power tube you can get away with a lot of B+ as long as screen voltage is much lower, however that's a rare combination in guitar amps - Musicman & Ampeg SVT the only ones I can think of offhand. And EL34 are true pentodes whereas most other power tubes are beam tetrodes. Which explains a tone difference some like, some don't.

Still waiting for musant to fill us in on the care & feeding & preservation of 6V6 at 500 B+. Maybe he's busy making/selling amps... good!

[Colossal]

I've punished JJ6V6S at 440-460V on the plates for years with no failures. Screen voltages were about 40-50V lower. Dissipation was set to about 70-80% of max under these conditions. I agree with TM's comment that JJ's 6V6s are probably more similar to a 6L6/big bottle in a small envelope.

[cbass]

I ran some old blackplate 6v6gt's At around 480 screens about 460 for a year or two.In a Princeton reverb type circuit before I switched it to 7591's no problems.The 7591's do have more headroom in this amp.

[crbowman]

Keep in mind that Deluxe Reverbs typically run with the screens right at, if not higher than the plate voltage, and usually the plate voltage exceeds recommended specs. That said, I've had the same set of JJ6V6s in mine for 3 or 4 years with no problems (knocks on wood).

[Leo_Gnardo]

For those interested, musant - Jim Kelley - has posted some good advice in Garage Talk, "Anybody Else Want A Jim Kelley amp?"

Thanks to those who posted their field experiences with 6V6 here.

I've run across all sorts, good & bad, sometimes 6V6 that sputter & even howl. Some cheap & nasty ones that render good service (blackened glass varieties from Russia & China) in spite of a bad reputation. And occasionally a customer brings in his own deadly expensive NOS shoulder-tube 6V6's that just don't put up with the strain. Metal covered 6V6's that have a connection from the - control grid - !?! - to the metal surface. Bizarre! Also those 50's Visseaux & Mazda that can't take high voltage, but sound terrific in low-voltage low-power application. Takes all kinds don't it...

[musant]

I've punished JJ6V6S at 440-460V on the plates for years with no failures. Screen voltages were about 40-50V lower. Dissipation was set to about 70-80% of max under these conditions. I agree with TM's comment that JJ's 6V6s are probably more similar to a 6L6/big bottle in a small envelope.

One of the principal, unique and defining features of a particular tube type is its Rp. I find the JJ 6V6 performance to be not completely unlike the old Sylvania STR's. They also seem to sound more like 6V6's than any other tube type. The tube which carries the Tung-Sol, Electro-Harmonix, and other brand names is also a fine example of a current production 6V6, in my opinion. And it 'looks' more like a 6V6.

[Gordie]

I ran a set of "International Service Master" 6V6s from China or Russia in my '65 Deluxe Rev. for 15 yrs or so, in spite of their bad reputation.