Low plate voltage on an 813

[ka1tdq]

How well will an 813 behave if I were to build a low power rf deck with a plate voltage of 800 volts?  The numbers for a 75 watt deck work out nicely for the parts that I have.  I-plate works out to 130 mills and a plate impedence of 3000 ohms.

Jon KA1TDQ

[W3RSW]

I don't see any problem other than somewhat reduced efficiency, after all it is a beam focused tube similar to a 6L6, 6V6, 6AQ5, etc., just has spacings large enough to handle higher voltages.

Can you cobble up a voltage doubler with your existing transformer and get, say 1600 volts?  It might sag a little under load, but, hey, try it.  You can always load it up lighter.  Or are you saying your RF components are not rated for 2kv or so but are more likely rated for 1kv? 

[ka1tdq]

I could try a voltage doubler but my transformer current is only 200 mA total.  I'd have to run low power and that would drive the plate impedence through the roof.  Q would be higher, dogs and cats living together... mass hysteria! 

I think I'm going to do this and I have a really cool layout in mind for it.  Thanks for the info! 

[KM1H]

The ART-13 works fine at 1000V so I doubt if 800 will be a problem. You might have to play with the screen voltage and keep an eye on its current.

Carl
KM1H

[W3RSW]

It just seems like such a waste to run an 813 with the filament requiring 50 watts just to get 75 RF.
At 800 volts, you'd be far better off with a 4D32, or pair of 6146's.

But, hey, it will look cool and not too out-of-scale with the 813 sunken below the deck to say to top of the metal sleeve.  Some one inch spacers to the socket ought to do it.

I talked with a guy who had a pair of 4d32's modulated by a pair and was quite happy with the lower plate voltages.  N2DTS, Brett, I believe.  Now I think he actually has three 4D32's for RF.

[WBear2GCR]

I wouldn't worry about "efficiency"...

But for 75 watts, why not just a 6146 or two?

The 4D32 = 2 x 6146 in a single package. Nice tube.

Even a pair of 807s or 1625s ought to do 75 watts at a loaf... cheaper too. Nice plate caps!

If ur gonna build to an 813, perhaps the thing to do is to build the RF deck up to full bore level, use higher voltage and current RF and DC parts so that you can use a different B+ supply later and go for the higher power?? Just a thought.

              _-_-WBear2GCR

[ka1tdq]

4D32, eh?  Looks pretty good!  Plus I won't have to get a 10 volt filament transformer and can use the 6.3 I already have.  I've never heard of this tube before so, thanks! 

[W3RSW]

Well !
It is the workhorse of the Collins 32V's 1, 2, and 3 series of 100 watts carrier output transmitters and an early Johnson.  It has a low profile compared to an 813, and, and...    it's a wonder tube.  Many kind comments as to its life span too. If you run it at, say 6.1 volts filament and 600 to 750 on the plate it will give you years of service.  Several threads discussing it on the AM.fone net and the AM Window.  Just enter 4D32 in search.  Google will give you neat stuff too including the spec. sheets if you haven't already found such.

[ka1tdq]

Yeah, I looked at some pictures of it on the internet and it looks like a really neat tube!  Exotic...

Anyway, I've cranked the numbers for an RF deck of 90 watts which will be driven by my rice box (like my 75 meter RF deck) and I'll use my existing solid state audio modulator (just install a switch for changing between the 75 and 40 meter decks).

This will fit the profile of my shack anyway of using odd tubes.  My 75 meter deck uses a pair of 7984's. 

 

[W3SLK]

Rick said:

I talked with a guy who had a pair of 4d32's modulated by a pair and was quite happy with the lower plate voltages.  N2DTS, Brett, I believe.  Now I think he actually has three 4D32's for RF.

Yep, Brett is the man. He has done quite a bit of work with the 4D32 and from what he has written, it seems to be a hearty bottle. The price has come down quite a bit on them since the government cut loose on their surplus. Last I saw, (un)Fair Raido was hawking them for about ~$20.

[KM1H]

The 4D32 price has been going up slowly after everybody stocked up when the USAF dumped thousands. I and many others stocked up at around $5-6 a pop. Maybe the audioholes have found it.

It has a 6.3/12.6V filament and its 4D22 twin is 12.6/25.2

Its one of my favorite tubes since my first Viking I in 1957. Even had a pair on 6M AM running 250W out around 1962.

Carl
KM1H

[Opcom]

Does the 4D32 take the same 7-pin Septar socket as the 3C33, 3E29, 4-65A 829B, 832A, 5894, 6524, 6850, 7094, 7270, 7271, and 8877?

[KE6DF]

Back on the original topic of low plate voltage on the 813.

The ART-13 transmitter uses and 813 modulated by a pair of 811's.

The dynamotor has a barometric switch which drops the voltage from the normal 1150 volts to 750 volts when the aircraft goes above 20000 feet.

The output power goes down of course, but Collins obviously felt that it was OK to run an 813 at lower plate voltage.

Dave

[KM1H]

Yes to the socket. In fact when the USAF cut off Raytheon from selling to the civilian market they used the 829B in the Viking I. I guess Collins had more clout.

Carl
KM1H

[N2DTS]

Running an 813 at 800 volts has the advantage of being able to turn it up to 2000 at some future time, if the rig is built for it.

The 4D32 is a good tube, think two 6146 tubes in one bottle.
Collins ran one at 600 or 700 volts in the 32v series rigs, the higher the votage, the better they work it seems.

I run three 4D32's at 1200 volts modulated by a pair of 811a tubes, 300 watts of carrier out.
Been working years that way.
have had the same 4D32 in the 32V3 for the last 30 years.
I got a batch for $20.00 each many years ago, plus many hamfest specials that seem to work fine.

Brett
N2DTS