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Vintage Test Gear and Workshop Equipment For discussions about vintage test gear and workshop equipment such as coil winders. |
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Thread Tools |
20th Aug 2019, 10:57 pm | #21 |
Pentode
Join Date: May 2018
Location: Cologne, Germany
Posts: 104
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Re: No AC measurement on HP 410B VTVM
I have the military version named ME-26D/U, basically the same schematics but different looks(and meter). I might even have a nos complete probe but without the valve. If you need any measurements I could take it out and check. Below is mine:
https://www.radiomuseum.org/r/milita..._voltmete.html |
21st Aug 2019, 2:50 pm | #22 | |
Tetrode
Join Date: Apr 2017
Location: Minocqua, Wisconsin, USA.
Posts: 86
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Re: No AC measurement on HP 410B VTVM
Quote:
Sven, I appreciate your offer and will certainly take you up on it if I need to. |
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21st Aug 2019, 6:41 pm | #23 |
Tetrode
Join Date: Apr 2017
Location: Minocqua, Wisconsin, USA.
Posts: 86
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Re: No AC measurement on HP 410B VTVM
Excellent suggestion, David. Thank you. I injected 1.5 VDC from a flashlight battery into the center conductor of the triaxial cable and indeed it registered correctly on the meter. I now am very suspicious of my 2-01C rectifier tube or its intimate appurtenances.
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21st Aug 2019, 10:02 pm | #24 |
Tetrode
Join Date: Apr 2017
Location: Minocqua, Wisconsin, USA.
Posts: 86
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Re: No AC measurement on HP 410B VTVM
I've been very reluctant to do much with the spare EIMAC 2-01C tube I bought several years ago. But armed with the verification that the triaxial cable can in fact pass DC to the VTVM gave me some confidence. It seemed to me that the 2-01C in my HP-410B was not rectifying. There were only a limited things I thought I could check on that tube due to its small size and geometry. One of those things is continuity of the heater/filament. Although the EIMAC fact sheet on the 2-01C does not specify filament resistance I thought just checking basic continuity might reveal something. I checked and my 2-01C showed NO continuity on from heater to heater-cathode whereas the 2-01C I bought as a spare some years ago did show resistance, so I thought I'd give it a try. The new 2-01C does reciify AC and I see voltage on the VTVM meter. The only anomaly that remains is that the AC ZERO control is approximately 95% fully clockwise in rotation whereas the DC ZERO control is at its mid-point of rotation. Perhaps this will straighhten itself out after I calibrate the meter (which I have not done yet). But if anyone has any suggestions as to what might make the AC ZERO control need to be almost fully clockwise I am grateful for any help. By the way, to illustrate what is going on now with my new 2-01C...when I insert the probe in a 120 VAC wall socket I read about 85
VAC on the 300 VAC scale. Again, this might all be only due to my need to grind through the whole calibration process. But that pesky AC ZERO control being nearly fully clockwise has me still scratching my head. |
21st Aug 2019, 10:28 pm | #25 |
Octode
Join Date: Jul 2009
Location: Cheshire, UK.
Posts: 1,733
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Re: No AC measurement on HP 410B VTVM
It does say to check AC calibration after replacing V1, but also to check DC calibration first as well as the diode heater voltage. There is a mention of some diodes causing a greater than 2% change in reading.
David |
21st Aug 2019, 10:33 pm | #26 |
Moderator
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,871
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Re: No AC measurement on HP 410B VTVM
OK, well that's got you a big step forwards.
Next thing is to try the calibration process and see how it goes. Maybe the diode has gone slowly to air. Eimac's glass/metal seals have proven iffy on a number of power valves. David
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done |
21st Aug 2019, 10:36 pm | #27 | |
Octode
Join Date: Jul 2009
Location: Cheshire, UK.
Posts: 1,733
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Re: No AC measurement on HP 410B VTVM
Quote:
David |
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22nd Aug 2019, 2:32 pm | #28 |
Tetrode
Join Date: Apr 2017
Location: Minocqua, Wisconsin, USA.
Posts: 86
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Re: No AC measurement on HP 410B VTVM
I didn't have time to check that last night, David but I plan to today and will report it back here. I am anxious to do a DC calibration and see how everything downstream responds.
Radio Wrangler David: Boy I hope the replacement 2-01C hasn't gone to air; they're pretty expensive! I didn't realize that EIMACs were prone to seal leakage. Is this just their speciality tubes like the 2-01C or is it all EIMACs? Is the EA53 superior or is it also an EIMAC tube? I mustr admit, since reading your posting I have been mulling over saving up my pennies to buy an EA53 even though I know I'd have to add its conversion kit. |
22nd Aug 2019, 6:26 pm | #29 |
Octode
Join Date: Jan 2003
Location: Guildford, Surrey, UK.
Posts: 1,959
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Re: No AC measurement on HP 410B VTVM
My EA53 was made by Amperex, which I believe is an American Philips company. It was supplied in a Mullard industrial valve box.
Ron |