Marmax Electronics Alamogordo, NM

[kb3ouk]

Anyone know anything about this company? I recently got a neat little mobile transmitter that they apparently made, looks like it uses plug in coils and has a 6AG7 oscillator. The final is a mystery since that is unmarked, i thought a 2E26 at first but where some of the connections on the socket go don't match up with a 2E26.

[kb3ouk]

The wiring looks a little sloppy, not sure if this might've been a kit or someone did some mods.

[kb3ouk]

I found a manual for a Marmax KW52 modulator on BAMA that mentions a mobile transmitter using a 6BQ6, which would match up with the way the socket is wired. So as far as i know this transmitter uses a 6AG7 oscillator and a 6BQ6 final.

[KK4YY]

Looks like you have a Marmax MT52 there. I found this on the web.


MARMAX ELECTRONICS.
710 New York Ave.
Alamogordo, NM.

MARMAX MT52. Introduced: 1952.

Description: Transmitter. AM. 75 -10 meters.
Plug-in coils. Controlled carrier modulation.
Crystal controlled. Under-dash mounting.
Power-Input: 50 watts. Power-Supply: Requires
400-500 VDC @ 100-150 Ma. Price: $79.50


Don

[KK4YY]

Also here:
http://www.rigpix.com/mischam/marmax_mt52.htm

[KK4YY]

The 6BQ6 tube was first registered by RETMA in 1949 so that's a possibility.

mods.dk appears to have the manual. You'll need to register at that site.
https://www.mods.dk/downloadmanual.php?RefFil=Marmax_Electronics_VFO-52_KW-53_MO-52_PS-52_MT-52_Manual.zip

Nice find on that transmitter!

Don

[kb3ouk]

Thanks. Apparently i made an account for that site at one point and was able to download the manual. The final is a 6BQ6 like i thought. Looking at the schematic, mine doesn't actually look to be hacked up as much as i thought. Looks like there is a plug in modulator that hangs off the back of it to provide controlled carrier modulation using something called the Rothman method of modulation, that appears to have been invented by someone at Marmax. There's no info about the plug in coils but that shouldn't be too hard to reverse engineer. The modulator isn't too hard either, just a 12AU7 and 6J6, so i might actually make a replica of the modulator since it looks like it is designed to work correctly with that setup if i want to use it for AM.

[KK4YY]

Sounds like a fun little project. Good luck with it. And if you figure out what a "hotshot battery" is, let me know.

Don

[kb3ouk]

The "hotshot battery" had me baffled too when i looked at the rig but seeing the schematic it makes perfect sense. The antenna relay is a 6 volt dc unit. For normal mobile operation the 6 volt battery in the vehicle (this is the early 50s) powers the tube filaments and the relay power is taken from the filament line. For base station use, the filaments would be running ac, you would hook a 6 volt battery to a 1/4 inch plug and insert it into the hotshot jack, which breaks the connection to the filament line and the battery now powers the relay. The Marmax power supply that they offered used a selenium rectifier to make 6 vdc to power the relay, and brought that out on a plug that plugs into the hotshot jack.

[AJ1G]

Hotshot another name for the rectangular 6V lantern battery?  Kind of remember them being marketed by someone under that name.

[KK4YY]

After a bit of searching, it looks like a hot-shot battery was used on the Model T Ford to aid starting. This, for cars without a normal starter, battery, or generator. So doing a "hot shot start" used this small battery instead of relying solely on the magneto while manually cranking the engine. Apparently, the term "hot shot" lived-on long after the "T" was out of production. Those were the days, eh?

Don

[KK4YY]

Here we go!

[KA0HCP]

I did spot checks of Advertiser Index of QST and CQ for Jan, Jun, Dec from 1951 to 1954 and did not find Marmax listed.  Dunno how they advertised.

[Opcom]

Here we go!

Granddad had an old lantern with that battery.

[nq5t]

If you google Rothman Modulation, there are quite a few discussions about it.  Plus what may be the patent for something similar (under a different name than Rothman).   And an article in a 1952 issue of QST (forget the month, but it will come up in one of the discussion threads in the search results).

[KK4YY]

I did spot checks of Advertiser Index of QST and CQ for Jan, Jun, Dec from 1951 to 1954 and did not find Marmax listed.  Dunno how they advertised.

Try CQ magazine July 1952 page 51

[AJ1G]

A little more digging into the Hotshot battery indicates it’s name may have come from them being used to power electric cattle prods...commonly referred to as Hotshots.

https://en.wikipedia.org/wiki/Cattle_prod