I was looking at the EH 6V6 max voltages ?

[catnine]

 I see some use these in BF deluxe rev amps. Since the max plate is 450 VDC and the max screen is 350 VDC how can they hold up when the deluxe has over 400VDC on the screens? I am using JJ6V6s in my build now .

[sluckey]

the max screen is 350 VDC

That's just a number, obviously not the MAX max. It's not like when you reach and exceed 350v you'll fall off the edge.

[HotBluePlates]

HBP has left the building.

[catnine]

 I got the EH6V6 rating off the tubestore site . they have a PDF if you select the tube and look at the chart . I'm not saying they are absolute max ratings just going by the PDF . They have them for most of the tubes they sell.

 I'm still trying to figure out what the relationship is between plate voltage and screen current . I have looked everywhere on the internet and can't find much that really applies. All I can find is the screen has an influence on the plate as far as current draw and that the grid has more influence than the screen when biasing . I know the plate current on a fixed bias P-P amp rises as more signal is applied that's where the max 70% figure comes in . What I can't find is how the screen voltage changes , I know it draws much less current than the plate so does this mean that the screens voltage also goes up as the signal goes up yet if the screen draws less current then can the screens voltage climb higher than the plates if both have close to the same idle voltage. Is the screen current limited by the screen dropper and or the screen grid resisters.

 I do find some info but can't quite get through the technical lingo terminology to put it in perspective. 

[duke of earl]

Doug says he put 4 in a twin reverb and they handled the plate volts with no problem.

[PRR]

6V6 is a LOW-cost tube. The JEDEC specs allow good performance without promising anything more.

Second-sources and copy-cats usually just copy the original registration specs; if they build something better they give it a new number. (See 6L6/A/B/C/G versus Tung-Sol 5881.)

In fact most post-1950s 6V6 were made of better stuff than the cheapest 1938 stuff. Just because they had better stuff (for TV tubes) laying around the factory.

Fender knew this, and possibly got private assurances from RCA/GE, that later 6V6 would stand 400+V with musician's reliability (2,000+ hours, and nobody dies when the tube fails).

> relationship is between plate voltage and screen current

It's on the (some) curves. Plate voltage has almost no effect on screen current *until* the plate goes below the knee. Then G2 current soars.

> I know the plate current on a fixed bias P-P amp rises as more signal is applied...
> how the screen voltage changes

Doesn't _have_ to change at all. Put twenty-five car batteries in series. G2 voltage WILL BE 315V no matter what you do to the amp.

> does this mean that the screens voltage also goes up as the signal goes up

Usually we don't use car-batts for G2; we get G2 power from plate supply. No car-batts for plate supply neither. If plate current rises, *usually* plate supply voltage falls, therefore G2 supply voltage falls.

> yet if the screen draws less current

Hardly any less. Much more likely for G2 current to rise.

> can the screens voltage climb higher than the plates

So what if they do?? (Remember, pentodes {"beam tetrodes" are pentodes} are NOT tetrodes.)

Also remember the instant plate voltage falls far below G2 on every half-cycle. Pentodes shift the tetrode problem to much lower plate voltage.

> Is the screen current limited by the screen dropper and or the screen grid resisters.

Of course. If you have a 1K G2 resistor, 400V supply, G2 can not possibly suck more than 400mA. And an electrode's suckage falls when its voltage falls. Screens will closely follow the 3/2 power law.

And why do you care G2 current on 6V6? The whole point of the costly Aligned Grid construction is that G2 current is typically VERY small.

[PRR]

> the max screen is 350 VDC
> G.E. 6V6GT data ..maximum voltage rating of 315v plate and screen.

Design Center *versus* Design Maximum.

If you throw together commercial parts and do not test every radio you build, 315V is a good number. This leaves a lot of slack for sloppy design, sloppy parts, sloppy wall sockets. This is how we designed in the old days. 
 
If you tightly specify parts and either regulate or measure every radio (TV) you build, 350V is a safe number. This is utterly appropriate for DIY/boutique guitar amps.

These ratings give excellent service. It was not uncommon to find tubes with 10,000 hours service working fine.

Sometimes, as in G.E.'s Ham News, makers would suggest much higher operating conditions with the note that tube life would be shorter. If you need a union technician on a dog-sled to replace a tube, you design conservative. If a low-pay musician can buy a tube in the drug-store and change it himself, then more aggressive conditions may be acceptable.

Back in 1957, an output pair might be $10 and if *very* over-worked might quit in 1,000 hours. A penny an hour. Meanwhile the musician should be getting a buck an hour. Today with shrunken money it may be $100 for tubes for 1,000 hours, but $10+/hour thus $10,000 of pay per $100 of tube replacement. Tube cost at Fender/Marshall/etc level of "over rating" is NOT a big deal.

[catnine]

"Of course. If you have a 1K G2 resistor, 400V supply, G2 can not possibly suck more than 400mA"        400mA! that's real assuring.

 I'm not concerned about how long tubes may last they are not that expensive and I do have a few extra pairs here , not NOS or great ones but good enough for me. I'm just not up for surprizes . I didn't/never liked the sound of this one P-P build and then found out about my using such a high value 5K screen dropper that this could create screen sag and produce the raspy OD I was getting so I changed it to a 1K and now the rasp is gone and replaced by more headroom and smooth breakup and 1K is what all P-P princetons used so that's what I went with . Since after two hours of pushing the amp and nothing blew or heated up I guess it's ok . My plates are 2 volts higher than the screens , measured across the 1K .  OT primary which also drops 2 volts but that's 2 volts less at the plates  than the B+ . 
 Now I need to find out what the 3/2 law means .

 I have gone on so many searches and end up with more opinions than facts . I have read or at least come across people talking about their BFDR amps running a choke and having 2 volts higher screen than plate at idle , some tried larger screen grid resisters but didn't change a thing some said 1K screen resisters instead of 470 ohm but the sound will change then you run into talk about 5E3's with the 5K dropper and you then need 1 K G2 resisters if you lower the 5K dropper. I needed a drink to stop my head from spinning.

[smackoj]

I never considered Electro Harm tubes because I thought they were not in the same ballpark for tone as old stock that are readily available. Then I heard an amp one of the managers at Guitar Center had bought called a Swart Atomic Space Tone which runs two EH 6V6 power tubes. That amp sounded real nice and the tremolo is as good as any I've ever heard. So, aside from all the tech talk, maybe trying a pair or quad would be a quick way to decide if they do what you want out of this amp?

 

[catnine]

I already  have a pair of the EH 6V6's . I never used them other than to put one in my champ build , it didn't sound as good as the old RCA 6V6GTA or anything like the JJ6V6s . I also have a matched set of Ruby 6V6GTBC but can't find out if they are 12 watt or 14 watt all I know is they are made in China . I tried one in my champ build and it sounded better than the EH .

[HotBluePlates]

HBP has left the building.

[catnine]

... can't find out if they are 12 watt or 14 watt ...

Assume all 6V6's are 12w and operate them accordingly. Even later american production tubes.

Or, assume they are really 14w and be prepared to ensure that no rating is ever exceeded under any possible condition.

This is what PRR was trying to tell you by explaining "Design Center" and "Design Maximum" ratings.

I already  have a pair of the EH 6V6's . I never used them ... it didn't sound as good as ...

In that case, why bother debating ratings for an EH 6V6??? If you don't like them, use something else.

 I only brought up the EH 6v6 because I have a set and looked up the PDF . I said I didn't like them in my champ build , this is not to say I might not like them in my other build. It's not a debate I just question what I read . You can find specs on just about every single part to build a guitar amp other than the tubes , why do they need to be a guessing game or take a chance deal . I suppose the reason is there are only a few companies making tubes and since this is the case they can do whatever they want or there would be no tubes. Didn't intend to poke a stick in anyones eye , it was just a question .

 I go to other amps sites as I feel others here do  too . I see questions on tubes and most say one brand is crap yet (most) never say what amp or how they are running them .