EEVblog Electronics Community Forum
Products => Test Equipment => Topic started by: Anson on November 06, 2013, 01:34:57 am
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I need to build a set of probes for a Hickok 209A VTVM. The tricky one is the AC probe which houses a 6AL5 Vacuum Tube in it and uses it as a double diode to rectify the AC. I'll include the circuit for the probe. Things I know so far. The connector to the unit is an Amphenol 91 MC4M mic connector at least thats what I have read. It uses a 4 conductor shielded wire 48" long. The heater voltage for the 6AL5 is 6.3v and 0.3 amps. The probe is meant to handle 300 volts. The tube has a diameter of 3/4 inch but the socket of course will be slightly larger. I haven't found a suitable socket. It is a 7 pin miniature socket needs to be round obviously so that it can fit in a tube. I'll include a picture of an original probe.
I also need to make a dc probe and the other two test leads. I just need to find probe bodies and tips. Anyone have a source for these?
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Here is the socket
http://www.oldradiosnstuff.com/4-cinch-ts102p01-shielded-7-pin-tube-socket-6au6-6c4-6ab4-6x4-6al5-etc (http://www.oldradiosnstuff.com/4-cinch-ts102p01-shielded-7-pin-tube-socket-6au6-6c4-6ab4-6x4-6al5-etc)
tubes can be found on ebay. To bad there arent much any specs on the tube, as you could make a diode replacement for it.
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Thanks for the link. I had thought about using diodes instead of a tube. Not sure if there would be any issues with that or not. Would cut down on the bulk of the probe and eliminate the need for a couple wires.
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Hello Steve,
There is a guy on ebay selling what seems to be a military version of the Hickok probe with a tube aboard. I'm not sure whether links are permitted here, but you can just search ebay for Hickok probe, or email me for the link.
Cheers,
BrianBurns
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You could just replace the diodes with BAT41 diodes. Similar voltage rating and similar capacitance, and probably will work well enough as a drop in replacement. Leaving the heater wiring open on pin 3 should do no harm. Will enable you to do 100V peak, and more if you place 5 or so in series, but probably I would not probe more than 200V with it.
Don't know how they get a 1200V rating for AC with that probe, as the valve is only rated for 300v max. It might be 1200V DC across the coupling capacitor, with 100 VAC peak only.