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Bring out ya' dead! Restoring a scavenged Ludlum 3

Posted: Thu Nov 05, 2020 3:40 am
by Richard Hull
The title here is reminiscent of Monty Python.... and the "I'm not dead yet" plea of a Ludlum model 3.

I have just restored a seriously worn out, beat up, scavenged and left for parts Ludlum 3 GM counter.
I remember I got this for free in a buy some many years ago as part of "here take this" along with other things I bought.
It had a note on it ….. “ Richard, You might want this for parts”.
It lay about for years and in cleaning out some junk, I took pity on it.....

It had alkaline battery destruction all over the battery compartment. I had to re-machine a couple of the terminals in brass. ( I hate alkalines! They are the worst battery made by man related to corrosion)
The corrosive vapors had spread over much of the circuit board damaging IC pins and traces, etc. (this is common when alkaline batteries are left in a device over time.)
Both battery compartment springs were completely eaten into three pieces. Luckily, I have a huge selection of smaller compression springs and easily found two suitable replacements.
Once I got the batteries in, following the compartment repairs, the circuit board would not generate High Voltage.
Found two bad IC’s and got the HV working.
The two toggle switches were corroded, cleaned those. The main knob was missing. (scavenged) I put on an old bar-pointer knob, circa WWII.
I plugged in a pancake probe after adjusting the HV to 875 volts. No clicks on the audio. (little annunciator was OK)
Found and replaced defective audio amp IC that had alkaline corrosion all over the pins. Also two of the 1/8 watt resistors had their leads corroded completely through. (replaced)
The speaker now worked great….IT WAS COUNTING!!!

The counter's meter had been scavenged (missing).
The meter presented a problem as it was small and the original was square faced with special scale and of unknown movement sensitivity.
I knew that the battery position, with good batts, moved ~7/8 of the way to full sale on all my other Ludlum counters.
I hooked up a multi-switched 1ma to 50 ua meter I had for years. Turned on the model 3 to BATT, and as I worked down range on the meter, it turned out to be a 50ua meter movement in the original Ludlum 3 GM counter.
Now, what did I have in the way of 50ua meters that might be made to work? I had (23) 50ua meters in my inventory and it turned out a Radio Crack “Archer-Micronta" 50ua meter would cover the hole and only needed me to drill two new holes in the Ludlum's front panel.
I put it all together and re-calibrated for 5000 cpm full scale on X1 and so on for all the other ranges using my NIM pulser.

The handle was also missing (scavenged) but it will be a snap to make…No problem…

Now full of new life, via the resurrection that I afforded this badly wounded warrior, it will join my menagerie of Ludlum meters and detectors. It was a 4 day part time project while working on fusor V activation efforts.

I attach two images.

Richard Hull

Re: Bring out ya' dead! Restoring a scavenged Ludlum 3

Posted: Thu Nov 05, 2020 12:48 pm
by Dennis P Brown
Richard, you are a true crasftman! Great restore!

Re: Bring out ya' dead! Restoring a scavenged Ludlum 3

Posted: Fri Nov 06, 2020 12:39 pm
by Richard Hull
Thanks, it was a fun restoration that needed stuff I had in my lab stores here, (read vast collection of junk boxes). I finished making up a nice handle for the counter today...'er last night just before dawn.

Workin' in the lab every day and night, doing lots of reading from my large scientific library. The old gal and I are watching our myriad of DVD and VHS PBS masterpiece theater series and PBS who dunit series. Not much on TV worth watching these days. Still have 12 working VCRs and 4 DVD players, Gotta' have backups. Well, it's 7:30 am and I've been up all night in the lab. I'll take a shower and hit th' hay. Just another normal day... 'er night.

I have three more old relic GM counters from the 50's to restore (vacuum tube portables). I have little boards already done to create the 120 volts needed for the tube plates in these babies. They and the 6 volt batt needed to power the boards fit easily into the old dual 67.5 volts battery bays. More as I finish them.

Kickin' back and havin' a blast

Richard Hull