The AM Forum

Found a 7984 Compactron-style today in a box of 807's and 8008's. It looks expensively made and has a thick V-shaped low inductance strap to the grid supports. The plate is two U-channels with a heavy strap between them.

I don't find any information on it. Does anyone have the data? Rumor has it that GE Essential Characteristics may have it.

From what I can find, they are a beam pentode, GE used them in the Master Pro low band VHF radios. Here's the datasheet I found (hope this works): http://www.datasheetarchive.com/7984-datasheet.html

It's the first one listed under fulltext datasheet results.

Patrick,

This is what I found:

http://tubedata.milbert.com/sheets/123/7/7984.pdf

GL, Vic

Patrick,

  I have heard that Larry NE1S is using two 7984's in his  Central Electronics 20A and getting ~ 80 watts PEP. These are normally a 40W VHF Class C (FM) tube, but can be made to work at HF. Might also be good modulators.

Jim
WD5JKO

If it works at VHF, it will work at HF and even audio, they are basically a repackaged sweep tube and in GE mobiles they werent all that reliable due to almost no cooling except a slip-on aluminum heat sink. Typical non stop taxi cab use and haphazard VSWR tuning didnt help.

Ive worked on too many of those rigs for a local 2 way shop to even count.

When that gear was phased out I built around 20 6M AM rigs of 25W out to help get 6M AM a boost in the 90's. At that power and plenty of air circulation they stood up well.

Carl

June 1966 73 magazine has a very interesting article that uses a 7984 Compactron final - The title is "50 Watts on 50 MC for $50" It is an AM rig that also uses a 6AF11 in a single tube VFO-Xtal exciter combination.   

Well that's an interesting tube. It does have some nice qualities especially for 6M. I have only the one. It'll have to go on the tube shelves for now.

When it rains it pours. I was just given a 2M repeater with a 7984 in it. I was told it works but I won't be putting it on the air. Its the 7984 (now a pair) and power supply that are of interest. I almost turned down the repeater because I know I won't use it, there are bigger VHF amps here, and it is reaching the 'junk' stage of its life. I'm glad now I didn't reject it if only to find another 7984.

A pair of the tubes and parts from the power supply could make a nice 6M amp and it might not be too hard to get it going. It would be great for low powered 6M transceivers like the Shawnee, there is one of those here.

Here's the info on the item:

GE MASTR Progress Line
power supply 4EP38A10
transmitter "4ET57" 10-30 Watts, 132-150.8MC
This also has a fixed 132-174MC band-pass filter between the PA and antenna according to the manual. I wonder how much power the useful filter can take? Maybe they used the same one for all the models, in that case 80W was tops for this frequency band. I think it's a coil-in-cavity type.

The unusual power supply apparently can serve several models up to 100W output and has taps on the transformer for an interesting selection of potentials according to the book. It has two supplies which are put in series to obtain the final voltage.
This indicates that the Low B+ supply has to carry up to 375mA. It simultaneously carries up to 105mA for the driver stage plus as much as 270mA as the "lower half" of the plate supply. All this is with one power transformer and several pi-section C-L-C filters.

High B+ (plate)
+300VDC@200mA or 450VDC@160mA or 665-680VDC@280-220mA

Low B+ (screens, driver plate)
+300VDC@105mA

(bias)
-45VDC@10mA

(for solid state circuits)
-20VDC@100mA regulated

(for solid state circuits)
+10VDC@100mA regulated

(DC tube heater supply)
+13.4VDC@3A +\-5% 

Unfortunately the receiver manual does not seem to be with the papers. There is also CSI controller and some thick manual with it. Looks like computer programmable. The CSI is in a nice 1U rackmount cabinet that might be useful.

It all has to go in the corner for now but I thought it would be nice to share the info on the find. "somebody keeps dropping off all this junk" as they say.