RCA WV77E Repair and Restoration
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- เผยแพร่เมื่อ 21 มิ.ย. 2023
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In this video we take a look at a RCA VTVM meter that is destined to head down to the maker space in Greeneville TN. On these meters the calibration is quite quick only 3 adjustments but with most of these they were not stored properly and have damage from the Ohms battery took out more parts then I was expecting so a bit of troubleshooting to go along with this one. As well some alignment and tube testing.
** Repair exposes the Tech to mains electric and should only be done by trained personnel. Errors can be fatal. ** - วิทยาศาสตร์และเทคโนโลยี
I got mine in Thursday , it has the original tubes and a RCA VSO35A battery which is soldered in like yours ..... I don't have that selenium rectifier in this one , it is a RCA 1N3756 can style part ... Like the old germanium transistors ...... I am going to leave that one in there ..... What is the yellow cap you put in your unit ? Mallory ? The one in mine is 400 volt .047 uF ..... My unit is in MINT condition , no idea how many hours on it , the lady said her dad bought it new and used to use it for repairing in the shop, But I will check caps for esr and values also ...
I put in a voltage regulator for the ohms function. Didn't know about the kits so I built it myself on breadboard. I see somebody at the Antique Radios forum went berserk about replacing one component with several, but it's rarely used; passes next to no current even when it is used; and the regulator saves you from ever having use Ohms-adjust again, more or less.
Mine is completely unfused, which I will fix. An AWA build in Australia, but much the same thing. I was told that all the different RCA models seem to have come out of different divisions of RCA.
Those precision resistors are ageless even after all these decades. I measured them all in mine and every one was spot on.
Yours looks to have had some of the valve support circuitry renovated. Those carbon film resistors aren't original.
The meter movements are rugged, as they can be when driven via amplification like this.
I am fairly sure in a past life these units came from a university. So I am sure the range selectors were abused during the course of education. I was under a time crunch but I am thinking about making a regulation circuit to replace the battery permanently. At the moment The maker space is still in the process of setting up the lab space so I have quite a bit of time that I can whip something up.
I think I ran in to that thread on Antique Radios when I looking around at what to do. Oddly enough in both meters the 20Meg resister was out of spec and need to be replaced. But that will have to be a future project and a future video.
For calibration for DC being off, for most of these vtvm's there was a one Meg ohm resistor in the probe for isolation.
I actually like the 3 regular jacks with no Uniprobe mumbo jumbo lol. I have the original leads and the 1M ohm resistor is installed in the probe tip with no buttons or switches. I have at least 100 meters of all sorts and this 3 probe setup is by far my fav.
I'm having the same issue on mine where the R4 is over 21M ohms and I can't calibrate the AC ranges. I will purchase a new resistor as you did and pull C2 and check it as well.
Does this require a special probe to read 4kva? Also the 4kva is in red so I assume that means it's AC? You are now my new favorite channel on the Tube. Thanks.
I was 2 for 2 on that resister being out. I will dig in to some documentation and see most meters need a voltage divider probe for the extreme high ranges. But when needed to measure 4Kv things like meter lead insulation start to matter a great deal. This is going to sound weird to say but "normal" meter probes "only" go up to 1kv is isolation on the lead rating. This is normally due to insulation withstanding. Also dirt and things is the enemy here contaminants like oil, dirt, and dust can create conditions for arc over. Also with AC specifically as the frequency goes UP the withstanding voltage goes DOWN. High frequency high voltage AC is much harder to contain than low frequency high voltage AC. So the correct engineering answer is usually "it depends". But always take care.
@@ZenwizardStudios I’m asking because I need to measure 3kva DC in a scope. I think I’ll play it safe and just buy a modern high voltage probe like Fluke makes. This way I’m not relying on 40 or 50 year old insulation…..plus I really don’t want to blow my wig off lol.
Yes modem HV probe is VERY recommended both for tech safety and for equipment safety. I have a video out as a HV primer Link is here. th-cam.com/video/ev7qc9bfwYQ/w-d-xo.html
Flukes 80K-6 sees a fair bit of use here in the lab
@@ZenwizardStudios yes that one or the 40kva model are the ones I was looking at. I can’t imagine I would need a 40kva though. I’ll check out the video. Thank you for reaching out.
Wait, so what;s the deal with the fuse skyscraper? Did I miss the answer?
Indeed! Never seen this one before. SWAG: somebody's idea of a low-resistance shunt?
That is my though. It is either something lower resistance than a single fuse or some one blue the fuse and was lazy in changing it. Oddly enough there is a unit 2 that I also did a video on and it has 2 fuses stacked but not 3 so I can not say with certainty if it is factory or a bodge, I am stuck in the middle.
White vinegar is good for dealing with battery puke.
Hello to everyone.. I recently bought "Teletest RV-12" vtvm without HF probe. I found the schematic online, but there are no component values listed. For reference, the vacuum tubes in vtvm are ECC82 (12au7) and EAA91 (6al5). Please help.. Thanks in advance...😀
You forgot to tell us it is German. However the HF probe ( TA-2) you are missing could be made. If you search
for Heathkit probe 337-B or C you will find it. It is essentially them same. The connection to the probe can
be made into a BNC type connector on the body of the unit and the probe body can be made with a one inch diameter tube. Each end can be plastic of your choice unless you can find a Heathkit style probe and convert it.
Which can be found on a popular selling page. The schematic for a Heathkit probe is sufficient for your VTVM.
@@hestheMaster Thank you very much for your answer and help..
Why are they called a voltohmyst and not a VTVM? anyone know?
Thank you
I think voltohmyst was a trade name. Similar to how some meter were called VOMmeter. All they can measure is Volts and Ohms. Though some VTVM's do measure current as well. Usually DC not AC. But there are exceptions to this as well.