Jim Kelley Amps Info wanted

[Andy Le Blanc]

dont forget that there are differnt definitions for "maximum"
what are the "limiting values" presented in the JJ publication?.....
are they "design center"....."design maximum"..... or are they "absolute maximum"?......
there are benifits to "push" the voltage if modifications are made to keep the
rest of the tube limiting values in line...

[Tavda3172]

Hi guys,

are they "design center"....."design maximum"..... or are they "absolute maximum"?......

Either way we would be OK. Design Center ratings are more conservative ratings than Design Maximum so we definitely would be OK. If it was Design Maximum and only accounted for manufacturing tolerances we would still be fine. In the Kelly circuit we are going to operate the tube below this value by a minimum of 15v and under full load we won't be close to the maximums. In my experience the JJ's will handle up to 495v (I have not tried higher than this) unless QC took the day off. I've had them fail out of the box with 300v B+ but this is a QC issue and is not indicative of the performance of the tube.
-Kevin

[tictac]

Look at the peak voltage of NOS 6V6GT's; it's 1200V. That's why Kelly knew he could use them at those higher voltages.

Another interesting point I've never heard anyone mention is that the Kelly circuit is almost EXACTLY the same as an Ampeg model SB127868. (the 7868 is a 7591 with different pinout)

If you're paranoid about using 6V6's why not try 7591's they're a great sounding tube, as good or better than the 6V6 IMO.

TT

[jelle]

JJ 6V6 can handle 450V plate and screen voltage. This is personal experience...This is a VERY sturdy tube. IMHO a current production tube that is better than the original.

Have fun!

Jelle

[CaseyJones]

We probably should use solid state if we want an amp that passes the stone hammer test. Tubes are made of glass after all and easily mechanically upset especially when hot. We all make compromises we can live with.

(cue choking, retching and coughing noises)

Heretic! Infidel! "Compromises we can live with"?

My experience is that unless you step up to the line and pay top dollar for ultra professional quality gear solid state is less reliable on the road than old tube stuff, that doesn't begin to address the gag factor of solid state tone.

Vintage tube amps are wired to a standard somewhere between full mil-spec (old HiWatts) and pseudo mil spec (old Fenders). Any issues they may have can be worked out short of the fact that if you whack the thing really hard you'll waste the tubes. You gotta whack it really hard to hurt it.

I've had more hassles with solid state goin' belly-up due to dirty power, brownouts and spikes on the road than I care to admit. I've had mpre printed circuit crap lift traces or burn holes though the boards on the road than I care to admit. When I say, "stone hammer simple" that means I want to be able to easily repair it on a dark stage. With a stone hammer!

If you're paranoid about using 6V6's why not try 7591's they're a great sounding tube, as good or better than the 6V6 IMO.

I like 7591s. I don't like 7868s. The pins go straight through the glass w/ '68s, I've had 'em go gassy due to bent pins. Either way, 7868s or 7591s are expensive in NOS. Must be every Reverberocket owner is willing to pay a premium for them.

Ya makes yer bets and ya lays yer money down. My money goes towards reliability, availability and tone.

I'm surprised no one has piped in with "Try Red Bank 5992s!"

[Tavda3172]

Hey guys,
Yeah, i don't use any solid state gear as far as amps go, so no heresy here. I haven't found one SS amp that had good tone either. I just figured if you did build it well (mil or NASA spec) you could probably drop it off your house several times and still go play a show. The compromise would be the extra reliability versus tone. That's not a compromise I can live with either, but I suppose it may be an option for someone who absolutely can't have their amp break down or tuned up while on the road. I figured you could hit an amp like this with a stone hammer, and the amp would still work without having to replace the BJTs or MOFETS, where we would definitely have to replace our tubes.
-Kevin

[CaseyJones]

I figured you could hit an amp like this with a stone hammer, and the amp would still work without having to replace the BJTs or MOFETS, where we would definitely have to replace our tubes.

That's why I bring up the Bendix/Cetron "Red Bank" tubes. No, I'm not gonna pay the zillion dollars each a lot of vendors want but I respect what they are. Those tubes are literally built so you can hit the amp with a hammer.

Way off topic but I'd really be interested in how much NASA relied on tubes for the Apollo missions.

[drz400]

Hi guys,

My only point is: has anybody tried JJ 6V6's in an amp with these voltages? Have they personally experienced a cloud of electrical smoke with these tubes?
-Kevin

Not JJ's but I tried every NOS RCA etc type tube I could get my hands on and when the amp went into clipping and hard use nothing lasted in my amps.

[tictac]

[quote]I like 7591s. I don't like 7868s. The pins go straight through the glass w/ '68s, I've had 'em go gassy due to bent pins. Either way, 7868s or 7591s are expensive in NOS. Must be every Reverberocket owner is willing to pay a premium for them.

Ya makes yer bets and ya lays yer money down. My money goes towards reliability, availability and tone.[/quote]

JJ's makes 7591's that are reasonably priced and sound good; check them out

[km6xz]

There seems to be a general misunderstanding of specs and what they really represent.
A "real" 6V6 or even 6V6GT is not going to survive when operated in a real circuit at levels mentioned in this thread. There are no 6V6 in production now and haven't been since 1970. There are a lot of tubes marked 6V6 or 6L6, or whatever but are not and never were designed as those tubes. The market is just too small for any current manufacture to develop new designs. A good example is the very popular US brand Sovtec 6V6GT, still in production. Why does it sound so different from a RCA or Tunsol NOS? Because it is was never a 6V6 and does not spec as one. It was a tube designed for the Russian market(and their trading partners in the 50s and 60s) as a completely different tube "6P6S" which had a different characteristic and different base. Electrically, it is still a 6P6S but for export New Sensor(owner of the Sovtec brand name) ordered them remarked as 6V6 and 8 pin base installed. That is the case throughout the regions of the world where vacuum tubes are still produced. All the talk and rumor is not going to stand up to actually measuring the tubes. How many here have a Tek 570 tube curve tracer? I do not have one now for had one until I moved to Russia a few years ago. Every tube I measured of the new production from the old Soviet block counties and China, all of whom had large electronic component manufacturing industries for their internal consumption that were parallel universes to the US industry but with little cross pollination.
What is left for guitar amp fans are remarked designs that are not equivalent to old US or even western European or Japanese models. Some are better for our application but most are not. If we know what they really are in terms of characteristics we can build anything and get it to sound good but popping tubes into old designs will produce results different than the original tubes produced. People looking up specs in the RCA Handbook will be misinformed if they are assuming the printed charts are describing the new tubes in their hand. As long as new designs conform to the reality of these currently produced devices instead of the reality as it was before 1970, all is fine.
All this is a preface to the discussion about outrageously high anode potentials on 6V6's. Notice I made my comments by specifying "real 6V6's" in my first post. Others said "no, xx 6v6 handles 500volts and 14 watts" or something to that effect. That is apples and oranges. Whatever it really is and what its real characteristics are is another point, regardless, a 500+volt "6V6" is not a 6V6. If for example, someone is confident that their amp with "JJ6V6", that is fine, but don't assume it is really a 6V6, it is something else that has an ink stencil on it of anything they want to sell it as.
I know one company tried to produce a modern copy of the famous GZ34 rectifier although many companies sell a "GZ34/5AR4" , two tubes that have quite different natural characteristics. First it required fully modeling the original GZ34, which I did and soon realized, as I had assumed based on the differences in in-circuit performance, that it was radically different than the current units marked with the GZ34 label. Working with the Chinese factory which was making the new tube, will lots of revisions trying to steer their manufacturing techniques towards the desired spec, and 6 months of frustration resulted in a new manufactured tube that was within 5% of the original in all significant specs. That is the only new tube I have seen that is like an old long out of production tube.
I spec'd a exterior anode power tube for a liquid cooled power amp, the 3CX300AE, that was produced by Svetlana. 300watts of plate dissipation in a tube 1/2 the size of a 6L6 was quite attractive for a PP design. The tube was similar to the Eimac series of very familiar RF and high power tubes, even the same numbering series. I found out that the tube was originally designed as a transmitter tube used in Soviet era tanks so assumed it to be very ruggedized. But the original tube was a "G5M" with only a minor difference in the base pin out and socket. Here in Russia the G5M is cheap on the NOS surplus market for $3-5 each and the new stock Svetlana branded version called 3CX300 was $59 in manufacturer lot sizes and $112 retail. The true specs are exactly as the spec sheet say a G5M should measure, and nothing like the 3CXxxx series it was being sold as in the West. It made no difference as long as the designer knows the actual specs of the device being used. If I had assumed it was the same as the other 3CX300s in the west, my circuit when prototyped, would have produced quite different results if I had assumed the tubes were the same as their markings suggested.

So, a long post, just to say that I stand by my original post that a real 6V6 is not going to survive in the operating conditions mentioned in this thread. No one who knows the engineering and historical aspects of this discussion would disagree.

[Andy Le Blanc]

the last post sent me scambleing for a back issue of audioxpress....
a reprinted article from 'MJ audio technology' by Satoru Kobayashi useing
3cx300a........

so...... we are once again the victim....... the next time a project flames
with Sovtek tubes......and everybody re-stamps the sovtek product.....
you can take them to small claims for they're deceptive product....

[Andy Le Blanc]

the 6p6s has a lower dissapation rateing than the 6v6...... 13.2 W
and what looks to be a lower max volt too... but it does have vibrational
acceleration rateing of 2.5 G....... is there a complete data sheet available?....

[Wayne]

On a *nearly* related note, if a smart bunch of folks (like us, ferinstance) looked hard enough at the specs of our favorite tubes vs today's rebranded offerings from the East, I wonder if we couldn't make some subtle changes in our circuit designs that would produce results more like the results obtainable with the (usually) more expen$ive NOS products?

W

[km6xz]

On a *nearly* related note, if a smart bunch of folks (like us, ferinstance) looked hard enough at the specs of our favorite tubes vs today's rebranded offerings from the East, I wonder if we couldn't make some subtle changes in our circuit designs that would produce results more like the results obtainable with the (usually) more expen$ive NOS products?

W

Using the actual parameters of the tube at hand to design its support circuit for what "is" instead of "what we assume", just about any transfer function can be reproduced. I have heard terrible sounding amps with all the "right" parts, and great sounding amps using the most discredited parts. There is no reason a very good amp can't be made from any of the tubes available to us currently. There is nothing "magical" about highly praised components.
By the way, the 3CX300 amp projects I've built were designed on the spec sheet from Svetlana and they proved to be quite consistent with what I had in had but quite different than the 3CXxxx units that are better known in the west. I've attached a photo of one such amp before the face place was fitted.

[Runaway J]

Thanks again guys for your input.
I come to think a Kelley clone would definitely be a candidate for VVR .
So ... just an idea ... if I'd build the FACS version, instead of the attenuator I could make the VVR switchable.
Anyone tried this?