The AM Forum

Hi guys.I am new here but have been reading for quite some time.I am presently rebuilding an old Heathkit DX-60B,HG-10 VFO,and HR-10 receiver as my AM station.I want to build an amp for it and have several 833C tubes that I pulled from broadcast use.The C version has a heavier plate.I was wondering what kind of performance they have toward the higher end of the HF spectrum.The amp would be used mostly on AM on 160m and 80m but I would like to use it with the rice box if I needed the extra power a pair of them would deliver.Just considering 833's because I have them on hand.Maybe a quad of 572B's would be better?

Some guys have built 833A linears. I know of a few. But, unless
they are grid driven and neutralized, they are pretty dead in
GG service.... needs lots of drive.

The problemn is that the 833A was not designed for linear service
and not really a clean tube for good 3rd order intermodulation
distortion figures. You'd be lucky to get -20-25db, which wud
cause splatter problems in congested areas.  It is an excellent tube
in audio service where you can run negative feedback around it or,
of course, in class C RF..

Your thought of using 572B's is much better for an AB2 linear amplifier,
as it is a zero biased triode designed for linear service. IMD figures
of -30 to 35db are more realistic.  

If you had access to them, 3-500Z's are even better on all accounts,
but more $, unfortunately.

Good luck,
T

The low and medium Mu tubes like 833 will probably oscillate if tried in a typical cathode driven configuration. That leaves you with grid driven neutralized or just plain swamped. Problem is that the cathode driven configuration gives a cleaner output due to degenerative feedback. The grid driven amp will not without lifting and NOT R.F. bypassing the cathode. Not really a good choice.
Maybe someone will swap you for a 4-1000.

Thanks for the replys.I am just toying with the idea of what to use for toobs.I do have some 833's and was originally thinking about a quad of 811A's but wanting to run them on AM I figured I should have something a little more robust in the plate dissipation department.I can muster about 2200 volts unloaded with about 48 microfarads of filtering and 1 amp of current available.Money is a bit tight to go for the bigger tubes like new 3-500's or 4-1000.I have the rest of the stuff to build the amp,mostly old broadcast parts.Nice and heavy 10KV Jennings vacuum variables,big plate blocker,huge tank coil,and a 42 inch high rack to put it all in.It will probably be the heaviest amp around in it's power class. :D

The deal of the century is the Russian GS-35B triode. About
$75 new. Zero bias power grid triode like an 8877.  1500 W
tube in GG.

Do a Google on the tube. APE built a nice amp using one.

Highly recommended for a linear. Make your own socket.

T

My problem is that I like the glow of the filaments. :) The plan is to put this thing in a nice rack cabinet and have a window in the front to see the tubes lit up.May sound corny but that is what I want.I want to build a "new old" amp.Like they say,glass has class.I thought of 813's as well but now I am leaning towards the quad of 572B's.

Probably one of the nicest looking glass toobs for linyer service imo is the 4-1000 if your looking for glow in the dark. I have a mono bander for 160 that works ok. The toob is triode connected, tuned cathode driven and will do about 325 carrier out. Im only running about 3000 volts HV on the plate. Problem with that toob is the price.

Don't screw around.
Put the 833's to work in class C.
http://www.criticalradio.com/833%20Rig%20Project/Web%20Pages/Default%20WA1HZK%20Page.htm

ha, I love the afterburner for the dx-100 - I have 5 of
em running (catching up to irbs 11 ;;)  great glowing
beast. I ran lights out with my 304tl x 2 833's xmtr.
ur right, warms the room and lights your shack

I have good luck with clean audio out of 833's, but
I idle em up. a GS-35b eh? 1500 poob for 75$, that
is a bargin. does a real filament and real grid?

Hi Deenie. Try this link.

http://gs35b.com/gs35b/

hey tx Dave, 26watts of grid dissipation. snot bad at all, graphs
shows it likes the volts. how much do you have on it? what
a buy at 75 bucks!

This has some numbers that you can work with.

Same site has parts and a lot more info.

http://amp.w4zt.com/w2ape/index.html

Amazing deal. Yeah, I just rechecked out those specs and didn't
realize the Russians used a copper plate structure!  And they are
saying it's good for 2500W with the right amount of air.  8877=1500W.

Also, it goes up to 1000mhz vs: 250mhz for the 8877.

The 500 hours for military service is probably several thousand
hours as the guys says.

Dino, I understand you can get them for $75 on eBay and other
sources, as of a coupla months ago. It wud make a great tube for
6M or HF for that matter.

I wonder how long the price will stay that low. The only concern I
have is the 3rd order IMD figures. Never saw anything on it, but
I understand the guys run them w/o complaints.

T