Sencore PR-57 Powerite Variac Repair, Calibration, and Upgrade

[@keeper1855]

Nice to see you again Mark!

[@MikeM-Colorado]

I have one of these, and I use it every day. I depend on it. Mine works perfectly, but I have been concerned about what I'd do if something failed -- knock on wood. This video helps a lot! The isolation, current meter, and magnetic trip switch are great features for an amp tech -- they set this unit apart from your everyday Variac. I bought mine from a tech shop owner who retired. At one time he had 5 benches going full time, and each bench had one of these. They were doing 1000+ repairs a year! A little dab of silicone caulk will keep the buttons from falling off, and is less permanent than epoxy. Thanks for doing this video -- an obscure topic for sure, but it's just what I needed.

[@robharley9838]

Great video Mark. your clear, easy going, yet accurate and knowledgeable style is really enjoyable to watch. I always learn something! - jrh

[@pbaemedan]

Mark, outstanding video. The radar simulator test bench that I worked on in the Army used 6 of these Varacs in the high voltage section. The supplier told us not to worry about about the calibration because of the variation in the line voltage 110 - 120 VAC. Thanks for the great video. Dan KI6VBC

[@rankenfile]

Nicely done. Thanks for walking through your troubleshooting and fixes on the Sencore. The bench is looking good!

[@hamiltonstax334]

Have a BK Precision 1655 AC Power Supply that looks almost the same. Which came first? AC 0 -150 button replaces the line and output buttons, then 0-4 and 0-2 amps buttons, leakage com and hot, leakage sensor permanently wired in and a solder temp pot beside the meter with plug in at the back. The circuit breaker is also at the back, beside the fuse.

[@lloydspivey8296]

I have two of those units and it's always good to know about known issues and what to do if they happen to you. Welcome back. Have missed your presentations.

[@johna.hilljr.4990]

Want to sell one?

[@letsreasonthisout2898]

I have the PR-57 variac and isolation transformer. The weak link are the pushbutton switches. Excellent unit, and I don't worry about calibration...that's what my Fluke is for.

[@kb6dxn]

Glad to see you back..

[@carlespy7470]

Your bench makes me want to throw a flare into mine. I'm looking forward to more new content. Thanks for this one!

[@MrDoneboy]

I've been doing this as a hobby for 50 years Mark, and analog is approximate, but digital is exact...Well, most of the time Lol!

[@tracyenglish9998]

Welcome back, Mark 🎉

[@user-pq9ji7kt4l]

I got one of these too!!!! Works great! It is big and heavy, but a quality product.

[@richardbrobeck2384]

Nice I like that up-grade to the Sencore I too replaced a few items on mine and I also replaced my outlet but mine is still in the front.

[@user-mz6qu3hz6m]

I have several of these, and a couple of rhe 1.5A trimmers have gone open circuit. The resistive element comes de-laminated and tears. They are not good pots. I love these VARIACs.

[@myradiovideos]

Mark, on my PR-57 it was the 10uf capacitor that was causing a calibration issue. Thanks for sharing! My only concern is the 2 power strips being so close together it seems easy to accidently plug into the wrong strip, so when you think your isolated, you are not! Personally I would move the always on power strip to some other location, since 90% of the time everything is going into the isolated side... Robert San Diego

[@Blueglow]

I had both side by side on my old bench for many years with no issues. What's the worse that happens, I give something 120v out of the gate? Worse things have happened.

[@KG4JYS]

Nice bench!

[@robmoffatt4997]

very kewl!! I have a Sencore PR-570. Like the PR-57 but on steroids! I love it!! ^_^ Great content!!

[@jcwear89]

Really enjoyed it thanks for the video!😊

[@SinnerSince1962]

I mounted a meter on my variac as well. It sure makes it nice not to have to put a meter on it each time you make a reading.

[@alrtgy9642]

Great!

[@johnlimbach9267]

Great job Mark. Could use this meter on my PR-57 and outlet on the back. Close as I can read the ID Number on you digital meter is D85-2058. My eyes are not what they used to be. However, when I checked the part number, it brought back a meter that looks identical to yours but is listed with an AC voltage range of 200-450V. What am I missing? As others have noted, it's good to see you back here on KZbin.

[@Blueglow]

Here is where I got the one I used www.ebay.com/itm/134694231802

[@johnlimbach9267]

Thanks Mark. I bought one. I don't need all the info that one supplies, so I also bought this one from Amazon that only displays voltage and current. "KETOTEK Digital Ammeter Voltmeter AC 80V-300V 100A, 2in1 Multimeter Panel 110V/220V, Volt Amp Meter LED Display Voltage Amperage Detector Tester Gauge with Current Transformer CT" Haven't decided which I will use, but I'm leaning towards the V A only one. It has larger numbers which is helpful to me and the only other info I might need is the Watts. Luckily I can still multiply volts x amps. Let us know if you find one large enough to replace the entire meter. That would really get this thing into the 21st century. de John, K8NN@@Blueglow

[@andydelle4509]

Where did you get those boots for the 2x4's holding your upper shelf? BTW, love the 1970s wood paneling. I didn't know you could even buy that stuff anymore!

[@Blueglow]

kzbin.info/www/bejne/nafSmHeoetB4g9U

[@stacyharmon5865]

Hi mark, thanks for the videos. I really enjoy watching you trouble shoot and fix the old gear,especially like the restoration of the tube gear. Are you taking any customer pieces for restoration? I've got a marantz 8b that I'd love to have done.

[@Blueglow]

No, it will be a few years until I can. Day job keeps me on a jet almost every week.

[@PetervanVelzen-l1f]

Hi Mark, thank you for this video. Can I ask: I see the output from this Sencore unit delivers earth from the input earth, which, as far as I know, is connected to your neutral line. While the isolation-transformer part of the unit will float the output, the moment a DUT is connected to the output of the Sencore, where most DUT’s with three-prong connectors actually connect the earth to some point of the DUT’s power supply secondary side, this secondary side subsequently is not floating anymore relative to the mains AC. Question: what do you think of breaking the earth-connection to the output of the Sencore, or, at least, having this switchable? Thank you in advance for your time! From Amsterdam, NL, Peter.

[@harryshector]

The meter movement is a D.C. device. It is measuring A.C. currents. This means that the voltage generated by the current measured must be rectified. Diodes are not linear devices, and the non-linearity is more obvious at lower voltages. Digital instruments do a better job of measuring AC currents - especially small AC currents,than analog instruments do.

[@Blueglow]

For sure.

[@jonathanhendry9759]

What does the "Leakage" function do, and how do you use the probe socket?

[@Blueglow]

Basically, lets you use the probe to touch the metal chassis of the DUT to see if there is any voltage present, thus shock potential. This might indicate a bad grounding situation or leaky component in the device.

[@jamieostrowski4447]

Thanks for the great video. I have a question - since the meter is in parallel with the 10 uF capacitor, if the capacitor is leaking, how would it affect the meter? I could understand if it was in series, but it's in parallel with the cap so wouldn't it be unaffected by a leaky cap? The only thing I can think of is if the cap was leaking, the parallel circuit would be drawing more power than the rest of the circuit feeding the parallel circuit was designed to, and could impact the meter reading. I'm just learning electronics and really appreciate these videos. Just interested in checking my understanding.

[@user-mz6qu3hz6m]

The capacitor’s job is to protect the meter movement from voltage spikes and ensure the needle moves nice and smooth. When a capacitor is working properly, it appears like a short circuit when it has no charge, and appears like an open circuit when the capacitor is charged. When current begins to flow through the meter circuit, the capacitor is going to shunt 100% of the current, so none flows through the meter. When the capacitor is charged, it will block 100% of the current, and the current will flow entirely through the meter. If the capacitor is leaky, it is shunting current away from the meter, as if you had put a parallel resistor on the meter. These movements have a coil resistance of 1.9k ohms. If the capacitor is behaving like a 100k resistor, then it’s going to drag the needle down a few ticks.

[@jamieostrowski4447]

@@user-mz6qu3hz6m Thanks for the explanation! Now I see how we get that smooth action on some meter outputs.

[@tubeDude48]

You need some sound proofing to get rid of the echo.

[@Blueglow]

Working on it. I have 7 GIK 24x48" panels in the room already. Might need to treat the ceiling as well. Its an all wood paneling room...

[@dieselrauch1733]

Hi Mark you have not mentioned it, but I think this Digital Meter is not working below 40V? What I do not like on mine.

[@user-pq9ji7kt4l]

Can you share the link where you found the attached multimeter readout on the unit? Thanks

[@Blueglow]

www.amazon.com/gp/product/B09998YBHW

[@user-pq9ji7kt4l]

​@@BlueglowThank you sir!

[@BjornV78]

Nice video, but on some parts of the video there was only audio on one side. grtz

[@Blueglow]

Mind letting me know at what time stamp? I'd like to fix this.

[@truthreigns7]

What kind of stand are you using for your pliers/wirecutters, that is located on the far back on the left hand corner?

[@Blueglow]

If this link is dead, google Dental Plier Rack. www.prestigedentalproducts.com/Upright-Plier-Rack-PlasDent.html

[@truthreigns7]

@@Blueglow Thank you

[@polaraligned1]

What is that plier set you have on the left side of the bench?

[@Blueglow]

Rack is a dental plier rack, just google for it. Pliers & cutters are all Tronex, bought them individually over time as I can find them at a decent price.

[@polaraligned1]

@@Blueglow Thank you!

[@garygranato9164]

a couple of LED's behind the analog meter to illuminate it a little would be nice :) ps where did you get your 1n695's ??

[@Blueglow]

Had them for years.

[@myradiovideos]

I added 2 lights to my PR-57, they were actually Red LED's. Looked very cool. Held them in place with a Hot Melt glue gun.. Robert San Diego

[@kelboodha]

I've got the same unit. The magnetic on-off/trip switch is giving me trouble though (takes many times to get the "on" to stick). Anyone know if this switch is serviceable and if this is a common problem?

[@Blueglow]

I've not tried but I would imagine you could open it up and check it out.

[@Trex1268]

If you knew the output voltage why not just adjust the meter to match?

[@Blueglow]

I think that was the point of the video, the meter wouldn't adjust to match it. Unit was in need of some work to allow it to do so.

[@Trex1268]

@@Blueglow I didn't see you adjust the screw just below the meter center. Maybe i missed it.

[@Blueglow]

@@Trex1268 That meter is only for making sure the pointer is zeroed with no voltage applied. It didn't need adjusting.

[@thomass7877]

Greetings.. I have a noisy variac.. I need advice on how to silence it. Is it worth varnishing? Thanks in advance..

[@Blueglow]

Say more about how its noisy

[@thomass7877]

@@Blueglow Just a 50 Hz hum. It is heard without load, and becomes a little louder with load.

[@Blueglow]

@@thomass7877 likely an issue with the autotransformer. Unlike an EI transformer, not much you can do to service or help this.

[@thomass7877]

@@Blueglow Thank you.. Welp.. Time for new one i guess.. 😁. Its shame... Working good in all positions,im just iritated with that buzz... That is old Japanese Matsunaga SD 265...

[@ibrahimkocaalioglu]

Digitals are usually better :)

[@jdmccorful]

Nice repair! Thanks for the look. Enjoyed.

[@dlum1972]

Outstanding! If you decide to get rid of your switches send me an email b/c I’ve got PR57 with some broken switches.