Advance VM77 Valve Millivoltmeters

[ppppenguin]

I think it's closer to the 4th power with the Stefan-Boltzman law being involved somehw.

[signalman4]

Hi Alan,
I've been reading the whole of this thread with some interest as I have just become the owner of a VM77A.

I haven't seen any mention of this A model in your posts and wonder if its new to you.

From a quick look through the circuits you have posted, they all look the same although I read somewhere there are some slight differences so apart from the obvious difference where one is landscape and one is portrait style, I would be interested to know how the VM77, VM77A and VM77B differ.

My A model has only one cal pot that I can see and it looks like the pot is 50 ohms whereas all the circuits I've seen state 100 ohms.

I downloaded the 77B instruction manual and as you say, there are no pictures or drawing showing the location of the various components.

Is there another manual that gives full servicing info? They appear to be impossible to dismantle to get at the innards so any clues here would be welcome!

Best,
SM4

[NigelP]

I have had a VM77C for many years without use, which after some surreptitious IPA spraying, appears to be functional but needs a calibration.

I've managed to pick up some schematic info via this forum and basic VM77 manual from another but I don't have any complete "C" version. There seems to be quite a common set of schematic crossovers but I'm not entirely sure how exact or different it is.

Does anyone have an actual VM77C manual and know what the real differences are?

[NigelP]

I have now acquired (purchased) an original paper copy of the VM77C manual and I have scanned it to pdf. Is there a repository on this site for such files that can be shared with members?

It's in quite good condition although it does annoyingly contain a number of (no-doubt well-meaning) annotations regarding calibration and component references which were mostly done in biro and hence are non-removable   ; some I Tippexed out.

[ppppenguin]

Buying, scanning and sharing a manual is definitely giving service to the community. Very welcome.

The Archive is the place for such PDFs: http://golbornevintageradio.co.uk/forum/...php?fid=65

As a new member you may not have access yet. Message a moderator if necessary.

[AlanBeckett]

Sorry SM4, I've only just seen your Post.
I didn't know that there was a VM77A. I have a VM77, VM77B, VM77C and VM77D.
As far as I can tell, although I haven't checket the circuits 'Line-by-line', they're all pretty similar, apart from the 'D' which for its sins has a PCB.
So, there's a 'Missing Link' in my collection :-)

Alan

[Lew]

Hi all,

I just found a couple of VM77Ds in my basement, and consideration of what to do with those led me to this great forum.

I bought them at an amateur radio meeting a few years ago, and thought they might be good for measuring Noise Quieting of FM receivers, but then I bought a solid-state SINADDER 3, so it never happened.

Meanwhile, when I switched them on last weekend, I was pleasantly surprised to find that that both still work.  From some stickers,  I know that that they came from a Technical College (probably in Sydney, Australia, where I live), and that leads me to think that they might have been very well maintained over the years.  However,  I can smell and hear some things happening in one of them, so I need to open them up and have a look.

After fixing obvious visible issues, I thought it might make sense to measure all the voltages marked on the circuit diagram.

Looking at the circuit of the VM77D (which does not show component values), and comparing it with those for the original VM77,  VM77B and VM77C, I don't see any likely differences, except perhaps in the 150V power supply, where the neon tube (V7) seems to have been replaced by a diode as the voltage reference, which looks a bit dodgy to me!

Any helpful suggestions will be gratefully received.

Best wishes,

Lew.

Cheers,

Lew.

[Lew]

Hi VM77 community,

As I mentioned in my previous post, I have a couple of VM77D meters.  I haven't done anything with them since that post.

I have decided that I would like to pass them on to someone who would care for them.   I don't care about money.  I just want to find a good home for them.  

I am in Sydney Australia, so I would want you to pay for postage, but I don't think that would be too prohibitive.

Please send me a message if you are interested.

Best wishes,

Lew.
VK2ZIP

[Diabolical Artificer]

Joe aka Joe Bog lives in Oz & might be interested, shipping to the UK is too expensive really to be a viable option.

[joebog1]

I am interested in at least one Lew.  I am in North QLD  postcode 4880.
Can you weigh one and we will see what postage will be. 
After all Auspost needs to make 4 trillion profit this month.

I just bought two resistors from Sydney. Postage ??  $6.95.
Standard 1 watt resistors. 4 times what the R's cost.

Joe