811 insanity

[6G6]

Last year I inherited a transmitter that uses a pair of 811s.
OK, they are actually marked VT217, but I think they are the same thing.
So, I'm thinking; there is a chassis, a power supply, a pair of tubes and sockets...

Yeah, I know, HIGH voltage!
Plate connectors on top (you'd think they would've at least insulated them!?) 

Aside from the obvious danger, is there any reason this couldn't become a
fairly powerful push/pull dual triode amp?

Anyone have any experience with these?

So far, I'm just wondering.

PS, it must be good, it has an inspection tag stating that it has passed all tests
and is cleared to be reissued...
dated Jan. 1955. 

[HotBluePlates]

Last year I inherited a transmitter that uses a pair of 811s.
...
Aside from the obvious danger, is there any reason this couldn't become a
fairly powerful push/pull dual triode amp? ...

PRR talked some sense into me when I bantered around the idea of turning the 803 I have into a giant Champ.

Did you notice the 811 only has a plate dissipation rating of 45w in continuous service? Yeah, you & I can push that to the 65w intermittent rating, but...

These tubes deliver large powers in class B2 and class C operation, but especially in class C where they operate into a tank circuit that's like a large electrical flywheel. The tube only has to output a portion of the total transmitted power because the output circuit is tuned to resonate at the single-frequency transmitted RF.

The class AB2 number may get you jazzed, but keep in mind the data sheet shows "Driver Power Output" for these conditions in the neighborhood of 8-9w, which means you'll need something like a 6L6 (SE or push-pull) driving a transformer that has a center-tapped secondary to deliver the push-pull driving power needed to swing the 811 grids positive.

The 4A per 6.3v heater also kind of sucks when you realize you'll have a ~50w space heater lighting up the pair of tubes (not as bad as the 803's 50w of heater power per tube though).

Also, unless your current rig was intended for AF output, you may need to buy a very large (and probably expensive) custom OT as common off-the-shelf audio OT's aren't going to withstand the high voltage of the supply.

But if all that hasn't scared you off, it can be done. It's just money standing between you and the completed amp.

[kagliostro]

Some years ago I had the chance to get a pair of NOS 813 on the cheap

having seen the 1000W amp by John Chambers I was enthusiast about that tube

and would like to build a BIG Champ, I didn't remember in detail the reasons

but PRR explained to me why it wasn't a good idea

I think the first was the price for an SE OT with a high primary Z

If you want see, here the Chambers amp

http://www.chambonino.com/construct/const9.html

http://www.chambonino.com/construct/constwire2.html

also Kevin O'Connor in The Ultimate Tone n. 5 chapter 19 discuss about the use of SV572 - SV811

for a Super Scaler (a Booster) to increase the power of an amp

http://www.londonpower.com/super-scaling

Pete Millet conversely used an 813 as to build a "small" HiFi SE amp

http://www.pmillett.com/813_se_triode_amps.htm

My interest swapped to 4CX250 when a friend give me a pair

this tubes were used by Kevin O'Connor in Super Scaler configuration, 700W with a pair

but they required an insane 2000-2500v B+ and a special OT to be used

so I thanked him and returned the gift  not having the chance to use it 

K

[6G6]

The OT already had me concerned.
I guess I am just trying to find a better use for an intact,
but obsolete transmitter than rendering it down to a pile of copper and iron.
I have always admired the build quality of most anything that was 'milspec'.

Also, this is jsut the tip of the iceberg, in that I need to empty a ham shack
with 50+ years of accumulated stuff.
It has taken me several months to reach the floor at all. 
I did find a big variac and a very old all tube o scope. 

The few references I found for 811 amps were big, high dollar monoblocks,
with mention of detailed response.

[eleventeen]

Sometimes the cure is worse than the disease.

[kagliostro]

6G6 you've a message to read

K

[sluckey]

...I guess I am just trying to find a better use for an intact but obsolete transmitter than rendering it down to a pile of copper and iron.

...I need to empty a ham shack with 50+ years of accumulated stuff.

I'd take it to a hamfest and put it in the hands of someone that will appreciate it as it is. Same with the other stuff in the shack that you cannot use.

[kagliostro]

Here in Italy there are many Hamfest Flea Market and you can swap materials

you don't need with other that you can use, I think in your country is the same

K

[eleventeen]

**excellent idea**. Hamfests are rare, but I got a load of 9 pin sockets and several nice Pomona test lead thingys (for $2, they are usualy $20) at the last one I went to. And my Fluke 407 supply for $25 which was a flaming steal. 

[6G6]

There is a hamfest coming up.
Trouble is, some of the stuff I have is too freakin' heavy to load up by myself.

[HotBluePlates]

Trouble is, some of the stuff I have is too freakin' heavy to load up by myself.

Look again at the links Kagliostro posted; those transformers are HUGE next to REALLY BIG tubes like the 813. If you think your stuff is heavy now, the resulting audio amp for any circuit worthwhile with these tubes will probably be bigger and heavier.

And if you didn't read through to the 500w amp also found in those pages, you might not realize the guy posting those pictures also made his transformers himself (likely because you just can't buy them).

[PRR]

> operate into a tank circuit that's like a large electrical flywheel.

As you go on to say: it is the INPUT that really sucks.

Look at the picture.

For easy driving we must stay under the zero grid-volts line (highlighted red). To make the best use of the monster bottle we want to push the Pdiss rating (50W hilited blue).

But the zero-grid line is FAR-FAR below the Pdiss line.

The tube won't pass ANY (useful) current unless we *force* the grid positive or use insane high B+ and load impedance.

In RF duty we can use an INput tank to flywheel energy over the peak grid swing. In audio they suggest a two-2A3 amp, which used to be a "theater" size amplifier.

______________________________

> some of the stuff I have is too freakin' heavy to load up

Load the little stuff and bring pictures of the big stuff.

If the right person comes along and sees a picture of the 300-pound iron or amp-rack of his dreams, he'll bring his buddies and truck to your place.