813s and over-voltage

[W7SOE]

Here is a random bit of info....

I have amp running 3200V on the plates of two 813s.  It has worked out well so far with careful tuning.  (And a lot of help from folks here.)

I bought two new Penta 813's.  They, as opposed to the older RCA types I have been using, do NOT like the high voltage.  They arc over internally.  It appears that these newer tubes don't have as much headroom built into the spec.

I will save the Pentas for the ART-13....

Rich

[K1JJ]

Here is a random bit of info....

I have amp running 3200V on the plates of two 813s.  It has worked out well so far with careful tuning.  (And a lot of help from folks here.)

I bought two new Penta 813's.  They, as opposed to the older RCA types I have been using, do NOT like the high voltage.  They arc over internally.  It appears that these newer tubes don't have as much headroom built into the spec.

I will save the Pentas for the ART-13....

Rich

Rich,

Hmmm... Internally arcing at only a static 3200 volts, huh?  Assuming there is not another problem, like them taking off or something else, sounds like the physical tolerances of those tube elements are too sloppy inside.  I realize the so called "maximum plate voltage" rating is only 2250 volts, but they also recommend 2000 volts on the plate during plate modulated class C service in the same 1956 Handbook. This equates to at least 4KV peak under 100% modulation and more when hitting 120% positive.

I've run many 813's with 3KV on the plate (class C) giving 6-7KV peak. Never had one arc over yet.

So, I'd request a return on those Penta 813's since you bought them new. They especially should not arc over internally with a "safe" static 3200 volts in your linear.

The problem with manufacturing certain power tubes is holding the close tolerances. That's why some foreign companies don't make the 8877. (3CX-1500A7) (do any?) The distance between the cathode and grid is so tiny they are prone to failure if not closely aligned to spec when built.  That's how these tubes are able to get such a high gain for a GG triode config. (amplification  factor =200 in a small 1500w package) Another example is the 4PR-1000A vs: the 4-1000A. The PR version is simply a 4X1 that has passed stricter tolerance measurements. They are built from the same assembly lines, but some turn out better than others. Thus, some are designated as "pulse" tubes, better able to handle high pulse voltages without arcing over between elements and still achieving the required gain.

The same applies to 813's, in a way. Probability dictates there are a percentage that are at "blueprint" specs and others that are not. You probably got a pair that are not, or maybe Penta had a bad run - OR maybe that's the tolerance Penta makes them in now.


Another thang to consider is maybe they are arcing from grid to filament/cathode  -  or screen to control grid, etc. This would make the plate current react too. I'm not sure how much damage would be done with a direct HV arc from plate to the other elements, but it could be fatal to the tube, not sure.


* Be sure the tubes aren't taking off before you ask for a return.


Later -

T

[N3DRB The Derb]

notice how much news about defective chinese stuff there is lately? 

not to mention the chinese food that put me back in the joint.

[ka3zlr]

Richy,

I'm Not tryen to be pushy,,,Listen to what Tom tells you, Please, at those voltages we don't need a boo boo..Just thinken about ya...

[N3DRB The Derb]

does Svetlana make the 813? I'd take quality Soviet Union manufacturing over China's.....

[KM1H]

With all the USA 813's still out there at decent prices why would anyone buy Chinese?

Carl
KM1H

[WA1GFZ]

with all the people needing jobs why would anyone buy anything from china.

[Opcom]

Because they don't make alot of stuff here any more.

There is alot of careful hand labor to making tubes. If I made 813's here, they would probably have to cost $250 each. Would someone pay that? I would love to be involved in making things here. My employer as of April 1 will close both USA semiconductor plants. Call me greedy and self serving but I can't bring myself to resign in protest. The parts we make in Asia and Europe are excellent, and I have no grounds to object on business ethics or quality. If I could find a good job related to making something here, I'd do it. But they are all taken, or, I would have to move to some crowded, pestilent, liberal-controlled, or high-cost-of-living location, which is not happening. Continental Electronics isn't hiring. There is always TriQuint Semiconductor but at my low pay grade one's senority (vacation days) does not transfer. The place that made CO2 LASER-based cutting machines is gone. The good jobs related to making things here are gone. In their place are crappy slave-wage factories in faraway China. So when you buy a Chinese 813, you don't get the workmanship you would get here.

About Penta - In their online datasheet (copy of Amperex) they show 1600V as max HV for plate modulation. I've had no problems with Chinese (most of Penta) 3-500Z's, 811's, or EL34's, nor with their 4CX250's and 4CX350's (might be Russian).

I might have a few US-made 813 pulls and no need for them - send me a PM if you need some.

[WA1GFZ]

When money was made of silver there was a law about defacing money as skimmers would file a little silver off each coin and pass it on. I wish we could apply that law to the present condition.

[Opcom]

How would that work? What is being skimmed - the quality of the new 813 no doubt! What do penta 813's cost anyway? I was buying $11 EL34's and $13 811's. I guess the price says it.

[W7SOE]

with all the people needing jobs why would anyone buy anything from china.

It is my understand that these Penta tubes are made in the US of A.

[W7SOE]

Richy,

I'm Not tryen to be pushy,,,Listen to what Tom tells you, Please, at those voltages we don't need a boo boo..Just thinken about ya...

I really appreciate it.  It is so easy to get complacent and forget "just that one time".  We can all use a reminder once in a while.

I will be glad when I can button this thing back up in a nice grounded chassis.  ;-)

[W7SOE]

Here is a random bit of info....

I have amp running 3200V on the plates of two 813s.  It has worked out well so far with careful tuning.  (And a lot of help from folks here.)

I bought two new Penta 813's.  They, as opposed to the older RCA types I have been using, do NOT like the high voltage.  They arc over internally.  It appears that these newer tubes don't have as much headroom built into the spec.

I will save the Pentas for the ART-13....

Rich

Rich,

Hmmm... Internally arcing at only a static 3200 volts, huh?  Assuming there is not another problem, like them taking off or something else, sounds like the physical tolerances of those tube elements are too sloppy inside.  I realize the so called "maximum plate voltage" rating is only 2250 volts, but they also recommend 2000 volts on the plate during plate modulated class C service in the same 1956 Handbook. This equates to at least 4KV peak under 100% modulation and more when hitting 120% positive.

I've run many 813's with 3KV on the plate (class C) giving 6-7KV peak. Never had one arc over yet.

So, I'd request a return on those Penta 813's since you bought them new. They especially should not arc over internally with a "safe" static 3200 volts in your linear.

OK Tom,

I suspect you are right.  I purchased them off Ebay and although these tubes do look new there is always the chance that they are rejects of some sort.  I have asked for and received a refund for the one tube that misbehaved.  The other one will live in the ART-13  where the voltage is only 1500V.  Of course the state of that tube is still in question....

Thank you very much for you insight, helpful as usual.

Rich

[N2DTS]

I dont think I ever had much luck with penta tubes of any kind.

I have had the same set of RCA 813's in my rig for 30 years, with the usual tuning and loading into no antenna, and other dumb mistakes, and they still work fine! (Graphite plate versions).

The wife is redoing the kitchen, none of the appliances are made in the US anymore, Sears is Korea, I suspect Bosch is also, the fridge motor looks to be made of plastic and the fridge is about 1/2 the weight of the old (smaller) one!
The best I could see was Amana ASSEMBLED in the us (likely by Mexicans)...

Its all thoise right wingnuts pushing corporate profits that dive business to China..

Brett

[KM1H]

with all the people needing jobs why would anyone buy anything from china.

It is my understand that these Penta tubes are made in the US of A.

Not since the early 70's. The name was revived in the late 80's as one of the first of the Chinese copies.

Carl
KM1H

[W7SOE]

So maybe they are not defective,

maybe they are just crap....

 

[KX5JT]

I had purchased a matched pair of 572B's directly from Hong Kong made by the Shuguang Factory in China.  I put them into my Heathkit SB-200 and they did a strange thing.  After a 12 hour filament burn-in, then 6 hours plate voltage applied, I ran a small carrier into them (5 watts for 40 watts carrier out).  Then I increased the drive to 15 watts for 120 watts out.  They graphite plates (which look as beefy as the made in USA Sylvanias that were in there) would glow BRIGHT orange after 30 seconds.  Scary!  This would also occur after about a minute of SSB @ 600 watts pep.  I figured the tubes were trash. 

I then ordered a NOS matched pair of Svetlana 572B's made in the mid 90's (for RF, not the newer made for AF type).  They also would show orange plates but not as bright or as fast.  After a week, one of the russian tubes shorted and my grid voltage would head negative and the amp stayed keyed if it was on an of course did not work.

The fella I ordered the russian tubes will make it right for me so they are on the way back for replacements.  I said to myself what the heck, I'll put the chinese tubes back because they worked although they showed scary color.  Well guess what?  They are behaving fine now and only barely blushing with 100 to 130 watts carrier through them.  Do these tubes go through an initial period of glowing brightly for some hours then settle?  I'm really new to the tube game so I'm learning and soaking all the knowledge I can.  At anyrate, the Shuguang (Chinese) 572Bs are working great now!

KX5JT

[w3jn]

not to mention the chinese food that put me back in the joint.

First you trade the Cadillac for a microphone, THEN you lie to me about the band, and now you're gonna put me right back in the joint!

[K1JJ]

I said to myself what the heck, I'll put the chinese tubes back because they worked although they showed scary color.  Well guess what?  They are behaving fine now and only barely blushing with 100 to 130 watts carrier through them.  Do these tubes go through an initial period of glowing brightly for some hours then settle?  I'm really new to the tube game so I'm learning and soaking all the knowledge I can.  At anyrate, the Shuguang (Chinese) 572Bs are working great now!

KX5JT

John,

I doubt the tubes need a break-in or anything changed inside to the better to show less color.

Just an idea, but it sounds more like you are loading the amplifier more lightly. (more C2 - loading cap meshed more)  ie, You can get the same power out with less color by meshing C2 more, but the amp will not run as cleanly. (splatter)  Usually we peak C1 and C2 for max, then unmesh C2 for about 7% less power output at full strap. This is called loading the amplifier more heavily.

Do you have the loading knob pointer in the exact same spot as before or maybe the antenna impedance changed cuz of wind stretching, etc?   Same frequency tuned up?  Or maybe this is all into a dummy load?

But, bottom line is if it's working now and reliable, then stick with it..

T

[KX5JT]

John,

I doubt the tubes need a break-in or anything changed inside to the better to show less color.

Just an idea, but it sounds more like you are loading the amplifier more lightly. (more C2 - loading cap meshed more)  ie, You can get the same power out with less color by meshing C2 more, but the amp will not run as cleanly. (splatter)  Usually we peak C1 and C2 for max, then unmesh C2 for about 7% less power output at full strap. This is called loading the amplifier more heavily.

Do you have the loading knob pointer in the exact same spot as before or maybe the antenna impedance changed cuz of wind stretching, etc?   Same frequency tuned up?  Or maybe this is all into a dummy load?

But, bottom line is if it's working now and reliable, then stick with it..

T

Tom, Strangley I do nothing different really.  I made a "chart" with the different frequency/bands I usually hang out on and start my amp and antenna tuner settings there and then make slight adjustments to tweak it.  Always have.  /me shrugs.

KX5jt

[KM1H]

At anyrate, the Shuguang (Chinese) 572Bs are working great now!

Ive had 100% positive results buying 572B's direct from them and that equates to about 100 tubes over the past 3-4 years. Your problem was likely due to incomplete gettering and the orange plate test finished the job.

The SB-200 tends to be a bit unstable at times, especially on the higher bands, even with Cetron USA tubes. Ive yet to find ANY Svetlana 572B's good for anything but audio and low HF without making circuit changes in any brand amp Ive tried them in. The only pair I have left are used as modulators in a Clegg Zeus.

Carl
KM1H

[KX5JT]

Maybe I should just shelf them (the Svetlana's that are due back soon) until that time I decide to homebrew something.  Then maybe I could use those  to plate modulate a pair of Chinese 572B's.. hmmm....  I wonder if anyone built such a beast, pair of 572B's modulating another pair...

[K1JJ]

Your problem was likely due to incomplete gettering and the orange plate test finished the job.

Carl
KM1H

Good deduction, Carl.  I'll have to remember that one.

Before use, it's a good idea to run old tubes that were sitting on the shelf - and possibly new ones too, with an hours-long filament-only burn in. 

The red plate idea could probably be refined to a procedure when in doubt.

T

[KX5JT]

The SB-200 tends to be a bit unstable at times, especially on the higher bands, even with Cetron USA tubes. Ive yet to find ANY Svetlana 572B's good for anything but audio and low HF without making circuit changes in any brand amp Ive tried them in. ..  ........

Carl
KM1H

Hey Carl,

I know you are somewhat an expert on the SB-200.  I've seen your posts in the Heathkit amp groups in Yahoo too...
I'll ask this question here because we were heading that direction.  Besides, my SB-200 amp sees more AM duty these day than anything else.

What changes to the SB-200 do you recommend for more stability on the higher bands?  Are they the same changes needed to stabilize the Svetlana 572B's?  Do you have an actual mod for the SB-200?  That would be awesome!

KX5JT John

[KM1H]

Id say that half of SB-200, or SB-220 for that matter, problems are original builder induced. With well over 250 of them coming thru here for 6M conversion Ive seen more than a few strange ones.

The 572B isnt much different than the 1929 211 from which the 811 was derived. And the 572B is nothing more than an 811 with a graphite plate. On 10-15M the circuit is not fully neutralized and you can wind up with a TPTG oscillator under certain mistuning conditions.

A couple of things can help.

1. Straighten up the input section mess if component leads are excessively long, helter skelter, etc.

2. Add a .01 1KV disc cap from each grid connection to ground.

3. Lift the input RF off the socket pin used as a tie point. There is no internal tube connection but enough RF of some unknown phase is introduced through coupling to a filament pin.

4. Especially with non USA tubes a bit more operating bias works well. Start by making sure that you have a full -125VDC in standby. A leaky C-3 and C-19 can drag this down. In operating mode without RF drive the bias is around -2.5V and this is derived thru the relay coil resistance and R-18. Change the value of R-18 by replacing or paralleling another resistor so you obtain around -4 to -5V.

5. Place a 10-12 pf 1 KV silver mica or 2-5 KV doorknob directly across the 40 and 20M switch contacts. While this isnt neutralization related it will snub the high RF voltages developed during tuning due to the shorted turn effect of the switch. It will help protect switch contacts from vaporizing (and Tune cap arcing) which is not due to junk science VHF parasitics hot air as a few try to make us believe. Since that new cap raises the minimum C of the Tune cap it may be necessary to slightly stretch the 10-15M coil to compensate.

6. Make sure the parasitic suppressor resistor is within 20% of 33 Ohms.

Any particular SB-200 might need some or all of the above.

Carl
KM1H