Electronic Instruments Ltd VVM Model 26 - UK Vintage Radio Repair and Restoration Discussion Forum

Ed_Dinning · 16th Nov 2020, 10:30 pm

Hi Folks, I was recently given one of these rather nice valve voltmeters with a 7" scale and I will be restoring it.
Has anyone the schematics or other details about it?

It comes complete with active probe and reads up to 250v AC & DC

Thanks, Ed

WME_bill · 17th Nov 2020, 11:18 am

EIL 26A valve voltmeter.
EIL aimed to produce test instruments a bit different and higher performance than the general run of the mill stuff.
This valve voltmeter was a huge improvement upon the earlier EIL22 or CT54 with it's unstable zero. The design seems to be very similar to the Scroggie design of Wireless World Jan 1952, and his Radio Laboratory Handbook 6th edn 1954.
A similar circuit is used in the Marconi TF1041.
Scroggie says in the article that his design was for a commercial firm, but I have never confirmed which firm that was.
I attach the circuit and specification of the EIL instrument, taken one lunch hour hurriedly about 30 years ago.
Incidentally, I have the EIL 35A valve Megohm-meter not working, and would like the manual or circuit please if anyone else has this.
wme_bill

Ed_Dinning · 17th Nov 2020, 9:51 pm

Hi Bill, many thanks for the data, sorry I can't help on the other equipment.

Hopefully soon have this one up and running again

Ed

winston_1 · 17th Nov 2020, 11:40 pm

Gosh this thread takes me back. Spent 9 years of my life after leaving school with EIL. Was an apprentice there and ended up in the electronics lab until I left in 1970.
No longer have any contacts from there (I guess many are now in the electronics lab in the sky). Neither do I have any circuits etc of their equipment only memories so I cannot help in that respect. Their vibron vibrating capacitor are what made that company.

WME_bill · 18th Nov 2020, 10:29 am

Winston1, EIL. What is the vibrating capacitor, and what did it do. I am curious. wme_Bill

winston_1 · 19th Nov 2020, 7:36 pm

Quote:

Originally Posted by WME_bill

Winston1, EIL. What is the vibrating capacitor, and what did it do. I am curious. wme_Bill

It was a small capacitor in which one plate was on the armature of a solenoid which was powered at 6.3v AC. The whole thing was in a metal case with an octal base that fitted into a valveholder. When operational the capacitance varied at 50Hz. A DC voltage applied to it became AC which could then be amplified easily. The input impedance was something like 10^16Ω, pretty high.

WME_bill · 20th Nov 2020, 12:13 pm

EIL vibrating capacitor.
Winston1.
I have come upon vibrator switches to chop the DC input for industrial process control chart recorders and potentiometers, such as made by Honeywell or Kent. And also chopper DC amplifier voltmeters, such as early versions of Marconi TF2603 using a chopper relay as switch.
So how was the variable capacitor used please.
Did it shift the frequency of a tuned filter, or modulate some oscillator. I have seen one used as a FM modulator in a wobbulator generator, as Airmec-Racal Televet.
Or was it acting as one arm of a capacative attenuator.
wme_bill. m0wpn

16th Nov 2020, 10:30 pm	#1
Ed_Dinning Dekatron Join Date: Jan 2004 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 8,194	Electronic Instruments Ltd VVM Model 26 Hi Folks, I was recently given one of these rather nice valve voltmeters with a 7" scale and I will be restoring it. Has anyone the schematics or other details about it? It comes complete with active probe and reads up to 250v AC & DC Thanks, Ed

17th Nov 2020, 9:51 pm	#3
Ed_Dinning Dekatron Join Date: Jan 2004 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 8,194	Re: Electronic Instruments Ltd VVM Model 26 Hi Bill, many thanks for the data, sorry I can't help on the other equipment. Hopefully soon have this one up and running again Ed

17th Nov 2020, 11:40 pm	#4
winston_1 Hexode Join Date: Oct 2012 Location: London, UK. Posts: 498	Re: Electronic Instruments Ltd VVM Model 26 Gosh this thread takes me back. Spent 9 years of my life after leaving school with EIL. Was an apprentice there and ended up in the electronics lab until I left in 1970. No longer have any contacts from there (I guess many are now in the electronics lab in the sky). Neither do I have any circuits etc of their equipment only memories so I cannot help in that respect. Their vibron vibrating capacitor are what made that company.

18th Nov 2020, 10:29 am	#5
WME_bill Octode Join Date: Oct 2007 Location: Exeter, Devon, UK. Posts: 1,554	Re: Electronic Instruments Ltd VVM Model 26 Winston1, EIL. What is the vibrating capacitor, and what did it do. I am curious. wme_Bill

20th Nov 2020, 12:13 pm	#7
WME_bill Octode Join Date: Oct 2007 Location: Exeter, Devon, UK. Posts: 1,554	Re: Electronic Instruments Ltd VVM Model 26 EIL vibrating capacitor. Winston1. I have come upon vibrator switches to chop the DC input for industrial process control chart recorders and potentiometers, such as made by Honeywell or Kent. And also chopper DC amplifier voltmeters, such as early versions of Marconi TF2603 using a chopper relay as switch. So how was the variable capacitor used please. Did it shift the frequency of a tuned filter, or modulate some oscillator. I have seen one used as a FM modulator in a wobbulator generator, as Airmec-Racal Televet. Or was it acting as one arm of a capacative attenuator. wme_bill. m0wpn