803 as an RF Final

[KB3DKS]

 Awhile back there was a thread on using the 803s for modulators that presented quite a few options for configuring the suppressor grid.
 The tube seems to have been originally designed for suppressor modulation in mostly Westinghouse mfg Mil transmitters like the TBW series, etc.
  It appears from the RCA data that it is similiar to the 813 in application and performance except for the upper frequencies.
 
 These tubes seem to hold vacuum over time better than the 813 and 814 which I have seen several loose the getter flash and light up real pretty when HV is applied in the test set. They are also now priced lower than the 813 since the audio builders have yet to figure out what to do with the extra grid. 

  So, does anyone have experience or is using a pair or single in a Class C Plate
modded RF final and how was the suppressor grid configured? Voltages used, etc.
  I have a TBW to set-up someday.

 Bill,
KB3DKS

[W7TFO]

The USN type TBL used two of them in the final, parallel @ 2kV.

400W+ in A1 as pentode RF amps.

50W+ in A3 supressor modulated.

I have the complete book on the TBL, let me know if I can scan a bit of it for you.

73DG

[KE6DF]

There is an 803 based transmitter article in QST Nov 1935.

It's a supressor modulated design.

There is operating info in the RCA tube manual for using 803's in plate modulated service.

One question I would have is do you need to modulate the supressor and the screen in a plate modulated design?

[KB3DKS]

There is an 803 based transmitter article in QST Nov 1935.

It's a supressor modulated design.

Think I saw that one. All I have seen so far are suppressor mod.

There is operating info in the RCA tube manual for using 803's in plate modulated service.

Been looking at that data and comparing it to the 813.

One question I would have is do you need to modulate the supressor and the screen in a plate modulated design?

That's my quandary. I would like to plate mod the TBW and not sure just what to do with the Suppressor grid.

Bill,
KB3DKS

[W7TFO]

One big difference is the 815 is a 'beam tetrode' by design, whereas the 803 is a power pentode.  Think of the 813 as a big 6V6, the 803 as a big 6F6.

Running an 803 in high-level class "C" plate modulated service can be done in two ways:  As a pentode or as a tetrode, with grids 2 & 3 tied together functioning as the screen.  As a tetrode, it would need more drive.

RCA recommends not modulating the 803 screen in tetrode service, do modulate the screen in pentode service.  There is the trade-off...

73DG

[KB3DKS]

 You make a good point there !
I had not looked at it that way.

The Suppressor grid is positioned closest to the plate and most likely has a course pitch so it would not "track" the screen if tied at the same voltage.
 In pentode the voltage could be optimised but I would have to question the distortion %. 
  Looks like it's going to take some experimentation.

 I can power up the tube on a metered and regulated multi DC supplied test chassis which I used to check these types at a KV plate and about 400 or so screen and grounded grid.
 That should show me some of the suppressor grid voltage characteristics.
Just have to dig it out and wire it all back up to the supplies. That's the hard part.

Bill,
KB3DKS

[WD5JKO]

I recall that Astabula Bill, W8VYZ used a transmitter with a pair of 803's (RF) modulated by 805's. Was that right?

Jim
WD5JKO

[w1vtp]

Why not just use a 572B, get a neut.. cap. Drive with a MBL 150 tank for the 180 out of phase connection from grid circuit to plate ( http://amfone.net/Amforum/index.php?topic=24415.0 ).  Plate diss.. on the 803 is the same as the 813 but RCA doesn't give it much of a performance in plate modulated service (see http://tubedata.tubes.se/sheets/049/8/803.pdf ).  It's a looonnng tube - bet the maximum usable freq isn't very high.

Although I couldn't find data for plate modulation for the 572B ( http://tubedata.tubes.se/sheets/084/5/572B.pdf ), the plate diss... is higher, the required grid bias is much more reasonable - as opposed the -500v for the 803 and the 572B is being mfg'd today.    

A

[kb3ouk]

and something i didn't know till recently, 813s are still being made. I think i might use a pair of 572Bs modulating 813s or just use another pair of 572s in the final of the rig i want to build.
shelby

[KE6DF]

805s are also still being made and are good modulators.

The Chinese also make a 805A tube which is an 805 with plate connection on the base and no plate cap.

Basically the same as an 838.

805s probably are good RF tubes, but no one seems to use them that way.

[KB3DKS]

OK
Lots of good suggestions and info but the thread is diverging from my reason for posting
 I have a TBW HF section. It uses the 803 in screen mod service.
I also have the two power decks from a Meissner 150B which uses a pair of 811s
 to mod an 813 in the RF deck which I DO NOT have.
These supplies would be perfect for the TBW with basically only the wiring and control interface to build.
Just do not know how to properly deal with the suppressor supply. I could use an 813 but would like to see what I can get out of the original tube type.
 It is getting very difficult for me to handle heavy Iron so the less drilling and blasting the better. Can't build from scratch anymore.
 Already have plenty of 803s, 813s, and 814s and enough 811s for now.
 Just thought I would ask.
Bill
KB3DKS

[W7TFO]

I have TO-9/TBW schematics if you need a copy, PM me.  They will answer some of your questions.

The RCA TT books have schematics showing plate-mod for 803's.

73DG

[Opcom]

Suppressor is like any other grid, and low power in most cases. The voltage is usually low, can be + or - depending.. A supply for it should be simple. Suppressor current (static) is usually low like control grid current. Decently regulated supply and maybe able to sink as well as source a little current if you intend to modulate. Oddly the TT-3 does not mention suppressor current.

[KE6DF]

Here is a plate modulated circuit from an RCA manual.

[WA1GFZ]

These big old tubes look cool but their long internal leads are a pita at RF above 40m.

[The Slab Bacon]

They are kool looking tubes, kinda like an 813's big brother. But since it is a pentode and not a beam tetrode, it probably has a little less emission than it's big brother.

The class C circuit looks pretty standard to me. Pretty much anything that can run class-C can be plate, screen, or cathode modulated to pretty much "normal" ratings.

Suppressor modulation is another animal. Because of the intent and puropse of a supressor grid, it has a lot less control of the total electron beam. It's real puropse is to repel any stray electrons that bounce back off of the plate (secondary emission) back towards the plate. (and normally runs a somewhat negative biass) If you bust a pentode open and look at the supressor grid, you'll see that it has very corse spacing. Therefore it doesn't have much control over the total electron beam. Therefor you have to run them at anemic power levels for this to be effective.

The dramatically reduced power levels that they have to be run at make it somewhat (if not very) unattractive to designers and builders. The only real advantage that I can see with supressor modulation is the somewhat minute amounts of audio needed to do it. But you pay for that in only being able to get 20w out of a tube that can normally make 200w in other forms of modulated service.

But a pair in shove-yank audio service would probably kick butt and take names.
AND.......... No one really wants them so they are still pretty cheap and easy to find.

[w1vtp]

OK Bill

So, "run what you brung."    Guess the answer is, "yes - it'll work."  Now you have a schematic for the toob too.  I didn't know you already had the 803's.  One comment I might add -- I'm getting a bit cautious about these "New Old Stock" stuff.  Got burned one a 304TL this way and so stopped collecting them..  Again, good that you already have the 803's  -- go for it. 

So this has been a fun and informative thread.  I never thought to look in the RCA transmitting manual - I have that book. HMMM!

Good luck and keep us posted on your progress

Al

[KM1H]

Take a look at the 837 and PL-175A as well as the 5-500A for pentode applications. The PL-175A is a direct swap for the 4-400A and has higher gain. All can be run with a slight suppressor voltabe of 30-50V for a bit more gain.voltage.

Ive run the 803 as a GG CW/SSB linear at 3000V and 1000W input without damage, that anode is huge compared to the 813 and barely shows color.

The only caveat with Class C AM is to be sure it can handle the peak voltage, Id suggest a hi pot before nailing it with 2KV DC plus audio.

BTW, I worked on those T series rigs in the Navy, extremely reliable. AM used mainly to talk to harbor tugs in the US and foreign ports. CW used for back up to the various TBn family and emergency readiness exercises on MF and LF.

Surprisingly I havent run into any 813/814 gas problems....yet. Use them both.

Carl

[W7TFO]

803=classy family patriarch.

813=neighborhood bully.

One humble opinion

73DG

[KA3EKH]

I used a TBW for several years on 40 meters for AM and have a YouTube video of it in operations if you search under TBW transmitter. The 803 is an amazing tube being that it’s almost indestructible, the stock TBW transmitter runs full screen voltage and no plate to the 803 while in the tune mode and it has no effect on the tube, try that with a modern power tube. From what I recall I ran around eighteen hundred volts on the plate and 450 volts for the B+ for the rest of the TBW and that gave me about fifty watts of suppressor modulated AM and over a hundred watts of CW that I never used. After I got the transmitter and while I was building the power supplies I obtained a couple spare 803 tubes because I though they would be a problem but all three tubes I had were solid on 40 and 80 including one tube I bought for $2 off a table. The 803 was also used in the WW2 navy TDE and TCM transmitters along with several other common transmitters and once I asked over on Millist if anyone had experience with a failure of one and no one had. So if you got a TBW may find that the 803 is the least of your problems. I had more issues with the 837 tubes failing in the LO and IA and to do it right you will need a 10 volt center tap filament transformer, also if you never heard the T/R relay operate your in for a surprise.
 

[kb3ouk]

that relay does sound unusual.

http://www.youtube.com/watch?v=sd4gPNGNYRU

[Steve - K4HX]

Yes.

I recall that Astabula Bill, W8VYZ used a transmitter with a pair of 803's (RF) modulated by 805's. Was that right?

Jim
WD5JKO