Junque of the Day

[Opcom]

The last couple of weekends nave been used to clean out the 10x20 storage building and bring all the stuff home to the new building in the back yard. Some interesting stuff has shown up. As I go through it, maybe some posts about the weirder stuff will be interesting.

There is an aircraft radio. These are always good because that are AM and you can hear the local tower and other announcements on them. Some scanners don't do AM. It says "Cessna Crafted 300" but it is actually an RT-528A made by ARC. It looks "collector modulated" via a transformer. I would like to find the operating manual and pinouts for it so I can set it up to listen in on the local small airport. It also has a NAV receiver built in. Not sure what would be on that except a racket. If anyone has the info, I would appreciate that very much! Alternately it has crystals usable for 20M and 6M inside, but I don't want to break it for parts if it can pick up the tower. It may remotely be possible to change a crystal and get it on 2M. It looks totally solid state. 9-3-1971 vintage according to the 'FAA frequency check' card signed by an ARC technician.


A Bogen E75 two channel PA amplifier was found. I thought it might be interesting as a low power speech amp chassis. Unfortunately what I have does not match the Sams Photofact. Mine has a bunch of Loktal tubes in the front end and a different feedback system, and the schematic has Octals in a different architecture, not the same. It will probably be stripped of the old R &C parts and wiring, as all the wiring is brittle and unsafe, and every resistor measured is off by more than 20%. It's as well to redo it completely. Why, I always ask, MUST people put 4A and 8A fuses in where 2A are specified? The amp is interesting because it uses a Triode connected 6F6 to drive a pair of 6L6Gs via an interstage transformer. It runs the 6L6Gs at the 47-Watt AB2 voltages, but uses a 5000 Ohm CT transformer, for 35W per channel. There is one set of mono inputs for mikes, etc. This feeds two power amps each having a separate volume control, for running two sets of speakers I guess.


Found mixed in with the un-ending stack of scope CRTs, a 5948 Thyratron. It's 16" tall, 5" diameter. no doubt its box was confused with a CRT carton. It probably isn't very useful. It needs at least 5KV on the anode to work, and although it is "zero bias", it takes a minimum of an 800V pulse into the grid's 80 Ohm impedance to trigger it. On the other hand it can take up to 25KV on the anode and and up to a 1KA current pulse. A chart says 1500pps, 15KV, 500A peak, 1.3us pulse (70%). So anyone working with radar can understand that. Oh well just another pretty and monstrous tube for the collection. I'm not going to test it. A drop-in metal-ceramic replacement is made by Excelitas, so aside from a museum radar set, no one would likely want it. There is a nice paper on the evolution of the hydrogen thyratron:
http://aobauer.home.xs4all.nl/Evolution%20of%20Hydrogen%20Thyratron.pdf
Crowbar for someone's QRO set maybe.

[KA3EKH]

Use to have a couple Thyratrons in a dual IOT analog television transmitter, they were part of the “Crow Bar” circuit that protected the IOT by shorting out the 33 kV beam supply to ground in the event of anything going wrong before damaging the IOT. There was a little button on the front of the Comark that allowed you to test fire the thyratron and short the power supply but never pushed it myself. The power supplies ran 33 kV @ 1.6 Amps in normal operation so imagine those tubes had to be fairly tough to survive shorting that. Although from what I recall they did not look like a tube. Also recall years ago seeing a theater lighting dimmer system that used huge tube thyratrons for each dimmer channel before the modern systems that used SCR technology.
And last but not least my General Radio 1931 AM modulation monitor has a thyratron that is used as a switch to fire the modulation peak light.

[W2VW]

Use to have a couple Thyratrons in a dual IOT analog television transmitter, they were part of the “Crow Bar” circuit that protected the IOT by shorting out the 33 kV beam supply to ground in the event of anything going wrong before damaging the IOT. There was a little button on the front of the Comark that allowed you to test fire the thyratron and short the power supply but never pushed it myself.

Heh. I tried not to test those either 

The Comark IOT thyratrons looks like a little like 4CX5000 with no cooler.

The isloation transformers from those IOT cabs are FB surplus. 

[Opcom]

No IOTs here! That is big stuff!

There is a 12KV 42uF pulse rated capacitor here, seems like it might match the tube. It was used for electrohydroforming, an air gap was closed by a bar, causing an underwater arc in a 55 gallon drum. The plate to be formed into artwork was on the bottom, and whatever die or artistic arrangement of die-like objects, under that.
The gentleman said much of the water was blown out of the drum. I think the practice was to bury the drum in the sand so only the top opening was exposed. Anyway the current might be more than 1000A. I am actually too scared of it to do this without a lot of advice or someone to show me the first few times. Coin shrinking might be another fun thing for it however the voltage and energy are so dangerous.

[Opcom]

From the bottom of a musty, deteriorating box of nasty old microphones has sprung forth an equally musty issue of the Old Old Timers Club Blue Book, from 1962.

It was owned by the famous Dallas ham, Leroy W. May Jr. W5HN (/WA5JG/AF5AJG). Leroy May was an early pioneer of UHF and SHF communications, active with UHF EME, and achieved a QSO with a ham in Italy on 1296MHz, and also was a member of the NTMS North Texas Microwave Society, which does a lot of experimentation in the GHz range. Leroy was also the chief engineer of KRLD, a 50KW local news AM station.

OOTC
http://www.ootc.us/

Who here is a member?
Perhaps we should join if not members.
The requirements are participation in a two way radio communication >40 years ago.
CB, Military, Commercial, Amateur. Apparently, any 'recognized service' communication counts.

Those old mikes need to be looked at more closely. A few may have that coveted Buzzard Breath quality. Maybe clean up nice. I think one is a ribbon.

The rest of the evening was spent rebuilding two of the burners on the stove. Many of the little slots and hoes were closed with the hardened grease of the decades. remove, uncrimp, disassemble, bathe in vile chemicals in the 811-powered ultrasonic cleaning tank, hand-cleanup, reassemble, re-crimp.. At $50 each it was worth it.

I'm not getting much time for QSOs these days, looking for work takes more than a days work, and chores do for the rest.