How to bench test an unknown vintage tube high voltage power transformer

[@AIJenkins]

After all these years of ignorance, I’ve been transformed. Thanks for the video, well done! 😊

[@curtisprice9806]

My Dad has a few dozen transformers of all sizes....big and small, tube, etc. in his electric shop. He was head engineer of power systems at Union Carbide. I will inherit a ton of electrical "everything". He is 86 years old, and sadly Alzheimer's has reared it's ugly head. It started a couple years back, and now that I have time to be with him...basically communication is over. Love your family because time flies! Great KZbin channel! ❤

[@Marwatt]

great video... please make one for the output transformer too

[@julesl6910]

Extremely helpful guide, thanks D-lab!

[@danrussell9357]

Iron is often the most expensive part of an amp. Thanks for a video that can help keep costs down and give new life to these old parts.

[@tomsherwood4650]

If you need tubes that are popular and in demand, those can be about as expensive!

[@danrussell9357]

@@tomsherwood4650 Yes, I miss the days when you could pick up a cheap pair of 6V6 tubes. Fortunately you can still pick up the 6AQ5 which is 90% the performance of a 6V6 but only 10% the cost.

[@edwardhannigan6324]

Great video Terry, very informative..Now I just need to find one of those transformers in my basement..! Ed..uk.😀

[@elinbenson]

I use a door bell transformer to give me a 16V AC low current source. Once you find the output voltage with 16V input, you can calculate the turn ratio of the transformer, and calculate what voltage it will have at line voltage

[@PaulSmith-oy8xp]

For any that are doing pre-step-down voltage reduction (def good for safety's sake); it's to be expected that there will be "interaction": Between the supplying transformer and the device-under-test, there is often _sag_ so the actual output, following reversing the ratio back to mains, might be a bit higher than that suggested by xformer-xformer measurement.

[@ryanearnhardt8598]

Thank you! I have a old 20 lbs x former from an organ and didn’t know how to test it.

[@zulumax1]

This is great information that benefits everyone in the electronics community. Please liberally share the old school tribal knowledge of the old radio folks! Even if one knows such things it is good to hear it repeated. Great job Terry! Please share more of these bits of treasured knowledge, thanks.....

[@bobblum5973]

Thanks, Terry! Years back I knew someone who made up a board with a set of screw-terminal barrier strips, physically spaced far enough apart for electrical isolation. They then did the same basic tests Terry demonstrated, with the wires from each group of windings securely held in place. They worked with a fair number of transformers, so making a test jig like that made sense.

[@electrolytics]

Great demo. Very interesting. Thanks alot.

[@ronkwiatkowski340]

Thanks Terry, that was an excellent demonstration.

[@joeteejoetee]

Love this video because: safety first! What a treat to find a transformer with a 5 V winding too!

[@tomsherwood4650]

Those are pretty common in vintage tube gear because tube rectifiers were used alot like 5Y3, 5U4, etc. Thru at least the 50s. Maybe longer.

[@joeteejoetee]

@@tomsherwood4650 Yes, I know,: I''m 61. Been there and done that - we used to have a separate switch just to turn on the filaments 1st, especially for Mercury Rectifiers!

[@sincerelyyours7538]

Good info Terry, thanks. It was a transformer like yours that almost ended my 50-year tech career before it began. I was a freshman EET toot and in my dorm room I wanted to review the day's lecture on transformers by testing the voltages of an unknown one that I had acquired from salvage. Not knowing about the color code, nor the need to test resistances first, I dove right in and hooked what I thought was the primary right into the nearest wall socket... Didn't know I could jump that far... Landed backwards on a couch all the way across the room... Learned a new respect for high voltage that day but almost killed myself doing it. Now when I test transformers I wear gloves.

[@veritasconc.75]

Nice shirt! Thank you for your always easy-to-understand lectures!

[@RA-Arg]

This kind of bench is the reason I am suscribed to this channel!! Incredible lesson! cheers

[@keithschreiter3885]

Terry, Before I put 120 VAC into the Transformer I put A Signal Gerearter at 60 Hz at about 5 to 10 VAC into thr primary and measure the output leads and then take 10 volts and divide that into 120 volts. Then you have the ratio. then multiply the other output windings and come up with the output voltage on those wires it Lower the potenional high voltage before I put 120 volts into it and continue testing then you know what you are dealing with. .

[@2tallB]

This is how it’s done 👍🏼

[@ruhnet]

Great video. Thanks especially for the reminder about making sure your meter can handle the unknown voltage coming out. 👍

[@ross302ci]

A very good reminder! I fried my first meter with high AC voltage last year. That's what buying cheap gets you... but on the bright side at least it was cheap.

[@douglasstewart1380]

Excellent presentation - As an old Tech. School teacher you are the best. Thanks

[@ShawnWrona]

You’re the man, Terry! Thank you!

[@tokashila]

Thank you D-lab for the concise tutorial. I now feel confident to SAFELY test transformers to prevent damaging high value gear!

[@vintagetubeamplifiers]

Another excellent lesson, thank you Terry. Now I feel confident measuring the replacement transformer from a Mercury 1000 for my Mercury 2000 tube tester that has 22 taps.

[@ross3818]

May I impress the advantages of putting all the secondary leads into mains style terminals. An enormous one is the inability of completing the circuit of an HT winding with your hands or fingers. Accidents can happen to the best of us.

[@ernestschultz5065]

This is the best video about this subject I have seen. Clear and easy to understand.

[@CH_Pechiar]

Terry, I would also have checked cont. between the different windings to verify there is no short between one winding and another. 73!

[@mikegLXIVMM]

Great info.! Thanks for making this video.

[@Easton21]

This was the 4th video I watched on transformers and the ONLY one that actually explained the real-world application. All the others focused on the technical aspects of stepping up and down. WELL DONE!

[@unclefrogy743]

just in time I have been doing an inventory and testing of that box of transformers and there are a few of unknown tube high voltage in there which I have not gotten to yet. never stopped to think about the possible voltage across the CT high voltage. thanks for the tip!

[@andygozzo72]

if not using a variac i'd advise a filament mains bulb in series with the mains input, such as 25w, that'll limit current in case of incorrect wiring or shorted turns , i've used this method for years when first testing transformers or complete equipment

[@patprop74]

Thanks Terry, Cheers!

[@martynone8937]

Good vid thanks Terry.

[@johnbravo7542]

Thank's Terry,very well explained.

[@tomsherwood4650]

Also I have one of those suicide cords but I use it with an isolation transformer that has fuse protection and an on-off switch so I am ready to measure before I throw the switch and can shut it off fast if need be.

[@MaBaKar]

Very helpful. Thanks!

[@timbianco5325]

Great info sir!

[@ross302ci]

Thanks so much for this clear step-by-step guide, Terry. Really helpful. Fingers crossed I can find a usable transformer in the garage.

[@ericheder777]

Some valuable information/advice. Thanks Terry, love the videos!

[@therealjammit]

I also put a 100 watt lightbulb in series with the AC mains the first time I test.

[@ewetoobie]

good tech tips, and good safety tips too!!

[@amberyooper]

I usually use an isolation transformer to plug the AC into when I test transformers, but I realize that not that many people have one of those either.

[@andygozzo72]

a filament bulb current limiter was also be a good idea

[@blackimp4987]

very useful advise about testing half the highest tension from the transformer when we are unsure.

[@flintdavis2]

Thank you D-Lab! Can wait to find a transformer to test. Hope you keep these basic lessons coming. I want to build an amp from scratch.

[@kirkh.2522]

Awsome video. Found a transformer the other day.

[@pumpdumpster]

Thanks for the video. Clever words. 👏👏👏

[@shafqatmustafa9166]

Old is GOLD my bro.

[@GScott50]

When I'm checking out transformers I like to secure each wire end into a separate way on a 'chocolate block' connector strip - that way there is no risk of shorting out or shocking myself!

[@ianbutler1983]

Good advice. I just twist a small wirenut onto them, same thing.

[@Tom-W7TMD]

Great info! Thanks Terry!

[@gregmetzler6828]

Transformational. Thanks for sharing!!!

[@dhpbear2]

One more rigorous test would be to verify that no windings are shorted to each other. :)

[@d-labelectronics]

Yes Sir

[@RobynTapps]

You'll find that out real quickly when you plug it in to let the magic smoke out 😆

[@reubensylvester8818]

This is a lovely video, thanks Terry. Could you also show us how to test an output transformer?

[@andrefiset3569]

I do this test quite often but i use a 12 volts AC transformer to be safe and to prevent fireworks. After reading I move the dot one digit. I use the same method to find the ratio of an output transformer before using the formula.

[@patprop74]

I think that is how Uncle Doug showed how to test them as well.

[@Realroyrogers]

Great info

[@bbmade]

Excellent video, crystal clear and very helpful. Thank you.

[@waynegram8907]

D LABS, Testing various Unknown power transformer how would you know if the power transformer winding and current rating are meant for a GZ34 rectifier or 5U4 rectifier? what types of tests can you do to confirm this

[@TheGuitarShow]

thanks!

[@PhuketMyMac]

Awesome! Thank you D-Lab!

[@josephmagedanz4070]

Helpful info, thanks.

[@f.k.burnham8491]

I remember seeing an article in the 1950's or 1960's in either QST or CQ magazine on building an electronic load to test the current capabilities of the transformer, and over a period of time you monitored the rise in temp of the unit to determine if it would provided the current you needed for a project. It used either 4 or 6 6BG6 tubes. Sorry I cant remember more. That was about 50 years ago I read the article.

[@RyansCustomShopandGearOutlet]

Awesome! This is a big help. I want to convert an old Peavey ValveKing 212 to a handwired amp, and I can't find the specs on the transformers anywhere.

[@RyansCustomShopandGearOutlet]

As a follow up, the power transformer for my Peavey ValveKing 212 (labeled 602G-30538789-1 CMP 976104 Chuang Meei 0637) measured the following: purple: 76.7 VAC (labeled -BIAS on PCB), orange: 26.6 VAC (labeled +LV on PCB) red leads: 334 VAC (labeled +HV on PCB) The mains leads are black (labeled HOT XFMR on PCB) and blue (NEUTRAL XFMR). I measured 115.9 VAC in from the wall outlet.

[@l6srob990]

great info thankyou

[@rickshear495]

Is there any way to determine the current rating of the outputs?

[@tomvarley4344]

one problem with testing a valve power transformer with a digital multimeter is that the back emf created when you disconnect the meter clips is so large that it can lock up the electronics of the meter. I had discovered this whilst testing a Leak stereo 60 - it froze the electronics in my Fluke 87 for quite a few seconds and it looked like the primary was O/C. I now only use my AVO MK V for testing inductive circuits.

[@a2phil]

Hi, it's the guy with the Tempo one, you must've KNOWN this was going to be my next stupid question!!! Thanks!!! DE KE8NFK

[@Mr.Obvious-]

Great video big help it was. thanks.

[@pauldow1648]

Love it. Thanks.

[@TechTed1]

thanks for the video it helped me so much 😊

[@michaelanderson5560]

Thank you

[@raymondmenard5444]

Thank you so very much Terry, this will be more than useful as i'm about to pull a tranny out of an RCA-Victor 86-T table radio to transplant it in an 87-K console. This couldn't have come at a better time, thank's for sharing. Be well, God bless.

[@rustyrobinson8027]

Thanks again

[@ItchyBrother]

Thank you so much for this video! Yes, I'm one of those people that has acquired a box full of transformers, and want to do something with them. But I was too worried that I would blow something up, so I bought new iron for my projects. Its time to start using all the cool Triad transformers I've found. Thank you!!

[@jamesgauthier6550]

Also good idea to put a dropping resistor in if the transformer is out of a TV or something that had a lot of 6.3 volt tubes otherwise they will run a little bit on the high side as far as filament voltage 😮

[@chadith]

This is great info. My next concern would be what level wattage amplifier that transformer can be installed into. Because even 5F1 and a 5E3 are two different power animals. So, what further details would we need to measure in order to realize the build?

[@IanMorpeth]

Being a very nervous type, I put the leads in choc block first.

[@matthewbloom1474]

But how do you figure out the VA rating of the XFRM or the ampacity of the filament windings?

[@mikefinn2101]

Great video miss the Johnson repairs thanks for taking the to share. no wine this time Terry?

[@hestheMaster]

There is no magic here because the RMA codes are followed by all manufacturers in the USA. After checking resistance measurements you can see by applying voltage to the primary and check to see if all the secondary wires are putting out the expected voltage. Thanks for reminding your viewers about checking the high voltage wires correctly Terry. If one is going about restoring an old tube radio or amplifier please get yourself an isolation transformer and a variac! So maybe Terry should delve into how about trying to find those items and their proper use in a future video?

[@c_b5060]

And before using the isolation transformer, we must check it for proper operation too.

[@jeanlawson9133]

Thanks 😎

[@zulumax1]

Might not be a bad idea to put a low wattage dim bulb in series with the primary. Since there is no load a small wattage light bulb will not glow at all, unless you accidentally touch those secondary windings together, then it would limit current to the transformer windings, and alert you to the short before the magic smoke gets let out. It does not make it any safer for the human doing the testing however, unless you use 12 volts AC on the primary and x10 the output voltages. 66 volts = 660 volts.

[@tomsherwood4650]

Yea if you had a variac, it might have the safety feature of a fuse or circuit breaker as might an isolation transformer. Also now you know the unloaded output voltages but there must be some way to guesstimate the current ratings. Like a percentage of drop with a known load or???? And you can use a variac to check HV output by say, setting the variac to say 30V to the primary and then you can maybe test the HV winding and multiply by 4 to get the 120 V input HV output without stressing your meter. Like if 30V in gives you 100V out, you could probably say it is around 400 with normal line voltage.

[@vonklock6807]

Awesome videos, very informative. I‘ve just started my first restoration. A 42 Philco model PT-7 five tube. It was suppose to “ hum” but no signal. Upon receiving it, it’s completely dead. Nothing lights up. I do have ac power going in. Any tips for a novice on what to check next? Many thanks!

[@PapasDino]

Dumb question Terry...are any HV windings with three leads ever not center tapped but have a different winding ratio other than half? Maybe a special application transformer?

[@d-labelectronics]

I have not run across that situation. Most of these tube and & radio transformers are pretty standard

[@PapasDino]

@@d-labelectronics Great to know, TNX! 73 - Dino KLØS

[@amberyooper]

You might find a power transformer with 2 taps on the high voltage winding, 4 wires in total. 1 would be a center tap and the other would be a lower voltage tap to use for the negative bias voltage for the power tubes.

[@PapasDino]

@@amberyooper TNX, that's kinda what I was thinking about. IIRC a lot of the Novice style homebrew rigs used transformers with multiple taps in the HV line to do just that...and many of them were from old TV sets.

[@darrellkelly7614]

That was cool

[@ross3818]

Is a chapter on output transformers soon in the offing?

[@dazzlenconfused]

what amp would be a great fit for this transformer and what would the HV voltage drop be?

[@ronfrey5327]

I have some completed amps built side by side but neither pass sound. I would like them to both pass sound and just be fixed the bias set correctly and for them to be quiet but also sound great full and warm... What would you charge to get one working if not both they appear mostly finished out but not passing sound. Id like to get them both working and. Play them through 15s or 10s but if you might look at them give me an idea of triple checking fixing to make sound.. i think if one was fixed and the same things done to this one here then tested it should work also what ever fixes any issue and produces the great tone, if those parts are it and they make sound and those are best together then sold as is if made to do other things show those also,,,,Wondering what you might charge to get these making sound. im in Texas might send one or both depending on $$ would like you looking at it.. see what grabs ya,,

[@Scooter110]

When doing the live tests I would probably terminate the open leads in an insulated screwed terminal strip (such as gey terminal strip) mounted on a block of wood for safety reasons.

[@nathkrupa3463]

Thanks thanks sir

[@zedcarr6128]

I would check the insulation of a transformer with an insulation meter that can put out at least 500VDC. Testing high voltage transformers with a multimeter will ONLY tell you if it has failed catastrophically, but it WON'T ''Test'' the transformer insulation resistance.

[@pinballpsycho]

Great channel! Two questions if I may. I was just measuring a transformer that I am not sure about. When I measure across the coils as you have just done, I get the measurements one would expect to see (and slightly higher as you've demonstrated). But if I take a measurement from chassis to either side, the voltage is quite high. For instance, across the coil I might read 7.3 instead of 6.5, but measuring either side to chassis (case) I get in the area of 335 volts (slightly higher or lower for other coils). Is that because it's not a valid reference with all the leads disconnected, and is it something I should be concerned about? There is no continuity from any secondary to primary or to chassis, BTW. The second issue is that I measured the windings against one another, most were isolated but one pair of windings indicated a very weak reading of about 8 or 9 megaohms between them. I suspect this is a failed insulation test? BTW, your advice about not measuring fully across the high voltage coils is spot on, I smoked my meter today doing just that.

[@stirlingschmidt6325]

Good stuff! Going a step further, how would you go about estimating the current capacity of a single winding, and in a related matter, the VA capacity of the transformer as a whole?

[@dougc314]

do you have any rule of thumb for estimating how much current the windings are good for? May be based on weight of the transformer or resistance of the windings?

[@lesstime1678]

By Area of trans core and wire size , BINGO , my job was design and re-design trans, motors and gen -sets for the company i work for, to design a trans,motor,and gen here is more ten 12 formulas , GAUSS law , maxuel law , henry's law,ohms law,SEN ,CO-SEN, TANG, CO -TANG etc,etc,etc i was good at that

[@matthewridgeway9250]

I am going to follow your process, but I will screw each wire into a terminal block screwes to a board.

[@brentnearhood8874]

Thanks! D-Lab💀

[@moorec1053]

There are 140 comments, so i did not read them all. Sorry if it has been asked already....... How do you know how much current the secondary windings can supply.? Thank You 🙂

[@starcarrier1874]

Thanks, I used this system to identify nine leads on my old transformer. However, there is a tenth lead that eludes me. Ohm readings show mega ohms when tested with all the other leads. Any speculation? Rather not plug it in to test voltage until I have an idea what it could be.

[@starcarrier1874]

@@GeeBee135 Thanks for the info, that may lead to an answer. Hoping to build a little guitar amp with it.

[@scottbc31h22]

Great video, but the next question I have: How does one determine the current capabilities of said transformer?

[@d-labelectronics]

Yes, seems to be a common question. I am working on a solution

[@tomsherwood4650]

@@d-labelectronics I saw something about this in an old ham magazine. I forget if they looked at secondary current after a certain percentage of voltage loading, or what. I remember the article had some graphs with curves on it. But it may have still been a WAG.

[@terrymatvichuk1421]

From what I remember an autotransformer maybe internally grounded does that sound right?

[@tomsherwood4650]

Does it have a 3 conductor power cord?

[@umajunkcollector]

How do you determine watts capacity? If it fits, same size?

[@tomsherwood4650]

Not necessarily a reliable way but obviously if a new transformer is half or two thirds as big, it might not cut it. I suppose as last resort you could see if the new transformer heats up too much!

[@Moonlightshadow-lq4fr]

What can you do if the wires are all the same colour?

[@jurmalare]

And the good question - how to determine if the current is sufficient for your application?