The AM Forum

I have acquired a mostly complete 4-400 GG amplifier.  The problem is that it was the project of a SK whose estate i was tasked with resolving.

The amplifier has a separate power supply that is complete and 99% of the amplifier wiring is finished....  but, there is one hole in the front panel not filled and above it is the stenciled word "level" and inside there is a single wire terminated but in the vicinity of the "empty" hole.

Maybe someone remembers the publication in which this amplifier may have been shown.

It is a a single 6JU6 driving a pair of 6LF6's in grounded grid configuration with those driving a pair of 4-400's also in grounded grid configuration.  

This amplifier could date back to the commonly available sweep tube era.

Anyone seen this configuration before?

Thanks and 73, tom

Front panel pix?

Labels will tell a lot.

Looks like perhaps that it is intended to be part of a larger rig?
A low level exciter/modulator driving the input??

Perhaps AM, perhaps SSB, or both??

Sure thing is that it wants maybe 1-5 watts max at the input.

                   _-_-

A pair of 4-400s in the common grounded grid configuration, with control and screen grids tied to ground will certainly require more than 1 to 5 watts to drive it.  One hundred watts would be more like it, depending on plate voltage.  Years ago, I built a 4-1000 in a grounded grid configuration with usual voltages on both control and screen grids.  The cathode was floated below ground by the amount of the screen voltage.  Even then, it required 80 watts or so to get it moving, although some of that was swamped in a semi-passive input circuit.  Originally it was built in typical GG setup and wanted well over 100 watts drive at 4 kv on the anode.
But the vast majority of ham 4-400 GG amps will use the generic GG circuit that varies hardly at all between tubes.   This can be found in the W6SAI series of "Radio Handbooks", and the ARRL handbooks of old have something similar as well.   What a "level" control on the front panel would be needed for escapes me at the moment.
73 de W1ITT

Where's the final tank circuit?  Or the driver tank circuits?  Is it possible this thing began life as a CB leenyar?

That was my thoughts as well. "non-leenyar"  ;)

Jim
Wd5JKO

"Level" sounds like an ALC control, but the little coil in the final looks like 11 meters.  Best use it for parts.

When I enlarged the picture, it looked to me that the final tubes perhaps are  3-400's, not 4-400's?  That is way better in value nowadays for money and gain. They could also be 3-500's but the age of the transmitter may suggest the latter?

I did find a lot of cb equipment in the stash....  The tank circuit looks almost non existent...

Darn.

Bump

Although they are not marked, when I put a known 4-400a next to them they seem identical ....

Tom

Someone wanted to be the channel master on CB. Double series amplifiers feeding 4-400's and a real small tank coil in the final are the clues. Typical CB rig could drive such a device.

That setup - one sweeper driving a pair driving a large tube, each stage grounded gris very likely. The small 3-6 turn coils and the cap sizes - low Q CB range tuning. I've seen this a lot, fortunately and unfortunately.  ;) Some of them only needed a couple of watts to make rated powe (which was much lower than "maximum overdrive").

There's enough room there to change out or otherwise deal with the socket/base cooling and add a blower on top to pressurize the chassis, and maybe fit the plate supply on as well. Got some great potential!