L&N 4271 Linear Amplifier

[Vgkid]

After Looking at Conrad Hoffman's , “Mini Metrology Lab” article on a null meter , I decided on building one. Knowing that I wanted to use a Analog scaled panel meter , I started looking, with most units hovering around $30ish dollars(without shipping) . I decided to look for gear I could pull a meter from(heresy, I know. Just wait until I get a real job  ) looking at the current crop of microvolt meters , null meters , etc. I looked into my T&M PDF catalogs, and I went on a search.
Initial bidding on the unit resulted in a total cost , that was on par with the shippping cost of just a meter movement. Unfortunately a subsequent couple of bids almost tripled that cost. When the dust settled I received a unit, that pricewise was on par with the cost of the meter movement. So I figured that if the meter was good , I could salvage some parts out of it.
Well the meter looked to be a variant of this Linear Amplifier:

With this in mind, I went on and started searching , and came up with a L&N 4271 Linear amplifier. Subsequent searches revealed nothing at all. The 4270 was an older meter , and the 9829 bore many similarities , but one major difference. The range switch was rather cryptic , and laid out in reverse.
Well enough of the descriptors , onto the unit.

It shows many simialarities , but the range switch is cryptic. I know every has noticed the broken power switch. It does sort of work. I will need to find a way to remove it.
Turning the unit around we are greeted with the backside that matches the other unit.
The unit will output either a calibrated +/- 5mv or +/- 1v. The unit will accept a battery pack , but nothing is known on it.

For the input terminal, no low thermal magic is happening here
Next update , we will open it up(it is easy , as the unit is missing its outer case

[guenthert]

Uhm, moving coil meters don't have to be very expensive.  I like following: https://www.ebay.com/itm/253419987601?ViewItem=&item=253419987601
It's russion NOS (if you google for the type, you'll find a site in russia which has hundreds of those).  The seller is located in Bulgaria, but ships for a reasonable cost to USA.  I received one, but couldn't test it yet.  Looks good though.

[anymouse]

Well, that Linear Amplifier seems to be quite a good replacement for a null detector.

That range switch is indeed myserious. I'm expectong a colored switch elsewhere.

[Vgkid]

Since I haven't typed up part 2 of this yet , the voltage scale is not what one would  think. 

[Conrad Hoffman]

Well, that sure looks like a perfectly good null detector to me! I'd shine it up and use it.

[Vgkid]

Well, that Linear Amplifier seems to be quite a good replacement for a null detector.

That range switch is indeed myserious. I'm expectong a colored switch elsewhere.

Correct , that swith puzzled me at first. Good thing my edc mv106 has a 100/10mv scale.

Well, that sure looks like a perfectly good null detector to me! I'd shine it up and use it.

Correct . Unfortunately there is a stability problem that gets worse around null.