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If this has already been covered on the forum, my apologies.  My searches didn't turn up anything relevant to servicing these prewar "MULTIVOLT" transformers.

Ok, before you say it, yes I know many of you may be thinking "Why would you want to mess with this death trap, use a modern transformer?" or "Just put it on the self to look at." To answer these first, let me say, I like bringing old things back to life and I have a healthy respect for, training, and experience with electrical device repair.   This unit seems to be in relatively good condition and I'd love for it to be actually working and not just a static display piece.  I also plan to have it's output running through a 5 Amp Airpax Instant Breaker.  If I can replace the cord and get this to where I feel its relatively safe for adult use, I may use it for accessories.  When finished, I plan to connect it to a Variac and gradually raise the input voltage to ensure that there are no internal shorts or voltage leakage.

Before I open up the case to replace the power cord and any other recommended service, I'd like to ask for some advice from any of you who've done this, about what to be careful with inside to avoid unnecessary work or damage to the internal wiring.

To remove the top panel, after straightening the four tabs on top where the red arrows are pointing in this image>

Multivolt Type T Front panel 2-mu

My questions are:

  1. Do the 9 binding post retaining nuts need to be removed to get at the internal power cord connections?
  2. Does the knurled knob at the lever base also need to be removed?
  3. Any thing else need to come apart?
  4. On another forum, there was mention of the inside being filled with tar (or something resembling it).  Any suggestions on dealing with this?
  5. Is there anything else that needs to be done to access the power cord connections inside the case.
  6. Any other helpful hints?

Thank you, SteveH

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  • Multivolt Type T Front panel 2-mu
Last edited by SteveH
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One like this belonged to my dad, and I have it, although it lacks the sweep arm to change voltage. At one point I had the lettered posts connected to a rotary switch and used it as a yard cab, but it didn't really have enough juice for that. I've never taken it apart, but look forward to hearing about your progress with it.

I have worked on a number of the prewar multi volt transformers.  I do not recall if any were specifically the T, but I think they are similar.  The top does not come off, it just folds back. It is tight working in side. As I recall the cord is spliced to the magnetic wire that the primary coil is wound with.  The splice is taped.  There may be a lot of asbestos sleeving in side.   The problems I have had are there is little room to work and nothing is marked. All of the copper is corroded black.  Cleaning it prior to soldering can be difficult.

Prior to changing the cord, even prior to dissassembly, check for resistance between the prongs on the plug. There should be little or no resistance. Then check the resistance between the prongs on the plug and all of the terminal posts and the case. One Megohm or greater would be nice.   If the transformer does not pass these tests, there is probably no reason to go any farther, unless you can verify the problem is limited to the cord that is going to be changed.

Last edited by David Johnston
@SteveH posted:

...Ok, before you say it, yes I know many of you may be thinking "Why would you want to mess with this death trap, use a modern transformer?" or "Just put it on the self to look at." To answer these first, let me say, I like bringing old things back to life and I have a healthy respect for, training, and experience with electrical device repair.   This unit seems to be in relatively good condition and I'd love for it to be actually working and not just a static display piece.  I also plan to have it's output running through a 5 Amp Airpax Instant Breaker.  If I can replace the cord and get this to where I feel its relatively safe for adult use, I may use it for accessories.  When finished, I plan to connect it to a Variac and gradually raise the input voltage to ensure that there are no internal shorts or voltage leakage....

Thank you for a) wanting to do this, b) clearly stating your background and qualifications, and c) being cautious. IMO, too many folks (probably including me at one time) open up old transformers without understanding the risks and pitfalls.  Having seen many of your previous posts on electrical topics, I'm confident that you'll have a good outcome.

@David Johnston and @Chuck Sartor Thank you for the tips and suggestions.

Resistance between the 2 power cord prongs is near zero, as it should be.  No measurable resistance (2MΩ setting) between the power cord prongs and any of the terminals or wiper arm.  So far so good...

@Ken Wing and @Mallard4468 Thank you for the encouragement.

After the resistance checks, I opened it up.  I was pleasantly surprised to find that this one has no tar like substance inside.  The windings are actually coated with shellac.  Maybe this one was made towards the end of the pre-war era?

Everything actually looks pretty good inside for being at least 85 years old.

Here are some pictures of the insides (click to enlarge):

IMG_2063IMG_2064IMG_2065IMG_2066IMG_2067IMG_2068IMG_2069IMG_2070

After tightening the loose retaining nuts on the binding posts, I looked online and ordered these items to replace the line cord:

Cloth covered 18/2 cord

and

Retro look non-polarized plug

Once these parts arrive, the rest should be fairly straightforward.  Thanks again for the assistance.

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@harmonyards posted:

Steve, ….one thing I know about these, and David touched upon this, they do have  asbestos inside them, …..I believe the sleeves are 100% asbestos, …..when you get to them, try not to make them into dust,…..do use the proper PPE buddy!….we’d like you to stick around here for a while!!……😉

Pat

Thanks Pat.  It's ok, I didn't inhale.

Seriously though, PPE is a good idea.

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