No AC measurement on HP 410B VTVM - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

sven_swe · 20th Aug 2019, 10:57 pm

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

IsquaredR · 21st Aug 2019, 2:50 pm

Quote:

Originally Posted by Radio Wrangler

OK, time to ignore the diode head. Just inject some DC from a small battery into the cable that the diode would have driven.

Thank you David. That is an excellent idea. I'm headed down to my bench right now to do that.

Sven, I appreciate your offer and will certainly take you up on it if I need to.

IsquaredR · 21st Aug 2019, 6:41 pm

Quote:

Originally Posted by Radio Wrangler

OK, time to ignore the diode head. Just inject some DC from a small battery into the cable that the diode would have driven.

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.

IsquaredR · 21st Aug 2019, 10:02 pm

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.

factory · 21st Aug 2019, 10:28 pm

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

Radio Wrangler · 21st Aug 2019, 10:33 pm

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

factory · 21st Aug 2019, 10:36 pm

Quote:

Originally Posted by IsquaredR

The only voltage I can find that is off (compared to the schematic) is the plate voltage on V2A and V2B which is 17 instead of 22 volts. Conversely the plate voltage on V3A and V3B is high, 195 VDC instead of 165 VDC.

Are these voltages any closer to what the diagram says now that the probe is working? Or is this not a problem?

David

IsquaredR · 22nd Aug 2019, 2:32 pm

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.

ronbryan · 22nd Aug 2019, 6:26 pm

My EA53 was made by Amperex, which I believe is an American Philips company. It was supplied in a Mullard industrial valve box.

Ron

20th Aug 2019, 10:57 pm	#21
sven_swe Pentode Join Date: May 2018 Location: Cologne, Germany Posts: 104	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, 10:02 pm	#24
IsquaredR Tetrode Join Date: Apr 2017 Location: Minocqua, Wisconsin, USA. Posts: 86	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
factory Octode Join Date: Jul 2009 Location: Cheshire, UK. Posts: 1,732	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
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,858	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

22nd Aug 2019, 2:32 pm	#28
IsquaredR Tetrode Join Date: Apr 2017 Location: Minocqua, Wisconsin, USA. Posts: 86	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
ronbryan Octode Join Date: Jan 2003 Location: Guildford, Surrey, UK. Posts: 1,959	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