|
Vintage Test Gear and Workshop Equipment For discussions about vintage test gear and workshop equipment such as coil winders. |
|
Thread Tools |
30th Nov 2020, 10:27 pm | #1 |
Pentode
Join Date: Jul 2006
Location: Bedfordshire, UK.
Posts: 211
|
AVO VCM MK4 meter movement transplant
I have recently completed the restoration of my AVO VCM MK4 valve tester. Although the original meter movement is still working it has some problems with the needle sticking mostly at around 80% of the scale. I would like to get the original meter refurbished if possible, but sadly Herts Meter Company can no longer undertake the work and I haven’t yet found anyone else with the necessary skills.
As such I decided to follow in the footsteps of others on this forum and replace it with a new Simpson 29T taut band rectangular meter with a 25µA movement. It is driven by a meter protection amplifier to a design posted elsewhere on the forum and constructed on a piece of Veroboard. The greatest challenge for me was in producing the artwork for an AVO VCM meter scale to accurately align with the Simpson meter with its 100-degree deflection. As others have done before I spent quite a while learning how to use the excellent Galva scale drawing software package to produce the necessary scale artwork which I printed onto some decent quality inkjet paper and laminated. I am attaching the following photos with this first post 1 & 2 = Rear mounting of Simpson Meter; 3 = Meter Protection Amplifier; 4 = Simpson Meter with VCM scale fitted Richard |
30th Nov 2020, 10:30 pm | #2 |
Pentode
Join Date: Jul 2006
Location: Bedfordshire, UK.
Posts: 211
|
Re: AVO VCM MK4 meter movement transplant
I have also made a test plug fitted with some resistors between different valve pins to allow me to easily check the resistance scale of the VCM at several known points.
I am attaching the following photos with this second post 1 = Test plug with resistors fitted; 2 = VCM in Set Position; 3 = VCM with 1Mohm leakage; 4 = VCM with 25Mohm leakage Richard |
30th Nov 2020, 11:03 pm | #3 |
Octode
Join Date: Nov 2010
Location: Ross-on-Wye, Herefordshire, UK.
Posts: 1,648
|
Re: AVO VCM MK4 meter movement transplant
Well, I can only say I am very impressed with the quality of your workmanship. I will be interested to hear what results you get with the unit.
Richard |
1st Dec 2020, 12:32 am | #4 |
Octode
Join Date: May 2009
Location: Linkoping, Sweden
Posts: 1,463
|
Re: AVO VCM MK4 meter movement transplant
Really nice!
__________________
Martin, Sweden |
1st Dec 2020, 9:10 am | #5 |
Octode
Join Date: Jan 2007
Location: Dorridge, West Midlands, UK.
Posts: 1,475
|
Re: AVO VCM MK4 meter movement transplant
Nice job and the Simpson movement looks just the right style for a period look to match the MK4.
__________________
Chris Wood BVWS Member |
1st Dec 2020, 11:08 am | #6 |
Octode
Join Date: May 2016
Location: Oxfordshire/Bucks borders, UK.
Posts: 1,604
|
Re: AVO VCM MK4 meter movement transplant
Where did you find the Simpson movement?
__________________
Avometer, vintage Fluke and Marconi collector. Also interested in vintage Yaesu and KW. |
1st Dec 2020, 9:10 pm | #7 |
Pentode
Join Date: Jul 2006
Location: Bedfordshire, UK.
Posts: 211
|
Re: AVO VCM MK4 meter movement transplant
Thanks for all of the positive comments.
The meter I used is Simpson Part No. 03951. It is a 4-1/2” Model 29T DC Taut-Band 0-25µA Microammeter. I purchased it from Mouser Electronics in the UK and their Part No is 529-03951. It was shipped from the USA and arrived within a couple of days – admittedly I bought it back in early February, pre-lockdown, so it might take a bit longer these days. Richard |
4th Dec 2020, 6:32 pm | #8 |
Octode
Join Date: May 2016
Location: Oxfordshire/Bucks borders, UK.
Posts: 1,604
|
Re: AVO VCM MK4 meter movement transplant
I just looked it up, quite pricey!
__________________
Avometer, vintage Fluke and Marconi collector. Also interested in vintage Yaesu and KW. |
5th Dec 2020, 11:58 am | #9 |
Octode
Join Date: Dec 2008
Location: Wincanton, Somerset, UK.
Posts: 1,757
|
Re: AVO VCM MK4 meter movement transplant
Amazing job: well done.
Presumably you now have a master Galve file which others could use? John |
6th Dec 2020, 3:47 pm | #10 |
Pentode
Join Date: Jul 2006
Location: Bedfordshire, UK.
Posts: 211
|
Re: AVO VCM MK4 meter movement transplant
John,
The AVO VCM MK4 scale for the Simpson meter was drawn with F5BU's (Jean-Paul Gendner's) Galva software. The latest version of the program can be downloaded from his website f5bu.fr. I used version 3.00. I used one of his example scales as a starting point together with scans of the Simpson meter scale. Here is a PDF printout of the scale. AVOvcmMK4.pdf If you want a copy of the Galva code I can send it to you, but please be aware that I haven’t fully commented it or translated all of the original comments from French into English. Richard |