Analog Meter Repair: Learn from my mistakle BK 375 VTVM - Page 1
Forum section: electronics / repair

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: March 04, 2016, 05:37:08 am
content: Hi,I am very ticked right now. I was trying to fix the movement in my BK 375 VTVM (which is an incredible analog meter that has a rotating display to only show you the current rangehttp://www.radiomuseum.org/r/dynascan_k_dynamatic_375.html). I was using a piece of tape to try to get the metal filings out of the movement. The tape caught on the movement coil and pulled the wire loose. There is no hope of reconnecting it. It would have to be re-woundSo I might suggest being extremely careful when using the tape method, and only insert the tape at an angle perpendicular to the meter face. I tried sliding if up around the center of the mechanism, and that is when it caught on the coil and could not be removed.So now I am looking for a donor unit with a working movement.

author: HAL-42b
author_rank: Frequent Contributor
timestamp: March 04, 2016, 05:46:53 am
content: Wow, what a loss. There is only one meter I'm aware of that does that scale thong and it is a much earlier and rudimentary Simpson (from the 30's I think).You might want to measure the diameter of the wire and the number of turns, just in case.

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: March 04, 2016, 06:35:43 am
content: This BK 375 was "supposed to be the Chosen One!" It was to be the VTVM that would stop me from buying more VTVMs...On a positive note I had one Eico 214 (with a HUGE 7"+ meter face) that had a bad movement. It came like that... Bad jewels I think. But I recently got another, and the movement is in great shape. Now I just need to finish restoring it (some caps, and a few bad resistors).

author: tautech
author_rank: Super Contributor
timestamp: March 04, 2016, 06:44:29 am
content: Wow, that is quite a novel movement. I feel your loss.It always amazed me the trouble AVO went to for cleanliness and it's outlined in their service documents.It'll be one of these from Kevin Chant's website.http://www.kevinchant.com/avo.html

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: March 04, 2016, 07:11:36 am
content: To be honest, the movement in the BK is of a poor design. Why? Because it is not sealed; it's not even enclosed in an attempt to be sealed. The movement is open down at the bottom of the meter. Never a good thing.But the FEEL of this meter is amazing. When you turn the knob to switch ranges it has this perfect "clunk" of both the wafer switch, and the rotating drum with the various range scales on it. The feeling is really amazing. When my dad came over (who would appreciate this type of thing) I had him feel this thing, and he said, "oooohhhh..." and then had to play with it a little.Given how cool the meter is (it has two light bulbs in it to illuminate the scale, AND a mirror for parallax) I will likely try to find another as a parts units (or vice versa).

author: trobbins
author_rank: Frequent Contributor
timestamp: November 02, 2019, 07:54:19 am
content: I'm just starting to restore what appears to be an Australianised version of the 375. The installed power transformer is an AWA 1L560543, which is the same power transformer as used in the Australian AWA Voltohmyst 1A56074. Apart from the power transformer, the internals are original OEM circa 1961-2 down to the B&K branded valves. Here's hoping parts haven't drifted, as the specs are still pretty nice except for the hassle of the chassis being grounded, which I will need to connect to AC mains protective earth in some manner unless I run everything off a 6V VRLA battery and use a dc/dc module for the 136Vdc supply.That AWA Voltohmyst has effectively the same ranges and specs, but a combo meter fascia without the nice drum scales, so it will be interesting to see what the subtle differences are in circuitry.

author: xavier60
author_rank: Super Contributor
timestamp: November 02, 2019, 09:04:52 am
content: I use a sharp steel needle to remove steel fragments from meter movements.

author: duak
author_rank: Super Contributor
timestamp: November 02, 2019, 06:20:49 pm
content: Bummer. I've often snatched total destruction from the jaws of defeat. It usually happens after I succeed at repairing something and think I have some skill. My hat is off to those who can build or repair this stuff.I ran across this link to a Triplett document on repairing movements:http://www.rfcafe.com/references/qst/rejuvenating-old-meters-feb-1943-qst.htm