[Jake Blake]

I'm not really ready to dive into this tombstone just yet, (  I still have the 39-6CI begging for attention downstairs ), . . . but Kirk's amusing anecdote about plumes of smoke in the thread "What did you fix today?"  got me anxious to test the power transformer for voltages.

First stone wall : I 've removed the knobs and the 2 screws from the bottom ( with those sleeves and rubber washers),  but the chassis  isn't wanting to come out. It's moving slightly, but I better ask if there is something else that someone knows about, that I need to remove , before applying too much force to get it to slide out.

[klondike98]

The front of the chassis has some posts that fit into rubber washers on the front panel.  here are a couple photos.  I suspect the rubber has hardened and is holding the chassis in.

[Image: https://www.dropbox.com/s/jxfobgi9ofzkjq....jpg?raw=1]

[Image: https://www.dropbox.com/s/71sp0wtamzerah....jpg?raw=1]

[Jake Blake]

"The front of the chassis has some posts that fit into rubber washers on the front panel."


WHOA!!!   ONE picture, . . . a thousand words!   Thank you!

[Simon Wa3uay]

Interesting that Phlico indexed the cabinet to locate the chassis, or was there some other reason?

[Radioroslyn]

It was to dampen vibration to the chassis. At the back of some of the chassis's they have square gum rubber mounts at the corners. Sorted floating it on rubber. If the front ones are bad the shafts and dial won't set in there proper positions.

[Jake Blake]

Got it!

[klondike98]

[Jake Blake]

I've done some power transformer voltage measurements : 
One side of the high voltage secondary measures 400 volts,
the other side seems to have the 4 in the wrong decimal place ,
and the rectifier filament voltage is just 332 volts.

I measured  continuity of the rectifier filament and there is none, verifying the worse...a shorted power transformer.  At least now, I don't have to 2nd-guess whether I damaged it after I got it, (re-insulating the leads, like what happened with the 39-6CI.)

So, for now, back in the cabinet the chassis goes,  until I start shopping for another (2nd) power transformer (unless I decide to take on re-winding both of them).  But , at least I satisfied my Kirk-inspired curiosity.

[Radioroslyn]

Hi Jake
You kinda lost me. Are you saying that without the rectifier tube in place measuring the AC voltage from the 80's socket skinny pins you got 400vac? If you measure the AC voltage across the two fat pins what do you get?

Or another way is to measure the resistance from the wire that goes to #70 to the transformer against each of the skinny pins of the 80 socket. Should show several hundred ohms and be fair close in resistance like 100 ohms or so.

GL

[Jake Blake]

"You kinda lost me.. . ."

Yes Terry, . . . I had ALL the tubes removed...I looked up on the tube manual just as you said  ( about the 2 skinny pins being the HV connections), but my meter doesn't go high enough to measure the full HV amount...I thought it safer to  just measure the two halves ; from one skinny pin to the center tap, then from the other skinny pin to the center tap.  On one I get 400, on the other I get 4.  The kicker was measuring the voltage across the two fatter pins : 332 volts!  What is it supposed to be?...like 5?

[Chas]

Jake,

Do this test to determine if the transformer is toast...

Be sure that all the pilot lamp assemblies are not shorted. Leave all the tubes in place except the rectifier.

A series lamp can be used but the outcome is the same if the transformer is bad.

Turn on the power. If the transformer is bad sometimes almost immediately the line fuse blows or there is smoke or internal crackling sound as the windings heat up. Sorta like a Weller transformer soldering gun. Just like the Weller, shorted turns become a heater.

If that does not happen keep waiting. Give it a half hour, if the transformer iron is cool or slightly warm and the tubes still lit, the transformer is O.K.

So there is no 5 volts for the filament of the rectifier...

Very likely an open connection in the filament winding.

To fix, use a heat gun to soften any brittle wire insulation transformer leads and the windings too. When they are hot the insulation is flexible.

Remove the transformer and open using using the heat gun method, open the top case again using the heat gun. Once open find the filament leads as they go into the transformer bobbin. Very possible the 5 volts is the top winding. Make an assessment, where is the break? Again using the heat gun unwind counting turns if the break is inside at the start of the winding. Check wire size with a micrometer. Replace the start lead wire and rewind with new magnet wire. Properly insulate using transformer materials available online. Dipping the transformer is impractical but a fast drying varnish will work, pop in oven at 200F will hard cure the varnish and lock the windings in place. I would be tempted to use gummed paper tape, but Kapton tape is the new transformer insulation...

If the secondary windings are roasted there really is no hope as that winding and the primary are critical in the wind and layer insulation. Very good skills or a winding machine starting from fresh, an empty bobbin...

If the primary and HV secondary did not get damaged then put it together for a simple test. Find the primary , insulate the secondary and all other leads except the 5 volts leave them well spread apart. Power the transformer and measure the 5 volts, do expect a some what high volts. If you want, clip-lead the filament of the rectifier tube, use good clip leads. If should light fine...

Reassemble, should be good to go... Do keep up heating the brittle wires or change them all out when the transformer is apart. Do try to keep to the wire color code. Use a felt pen to make a stripe if need be on the wires...

There is a transformer high voltage liquid "paint-on" insulation, FWIR Glyptal should work...

Heyboar can rewind the beast if need be...

You might have to pull the laminations, ugh, they are usually stuck so tapping with a hammer may loosen them.

Do not attempt to energize the transformer without a core..

YMMV

Chas

[Jake Blake]

"So there is no 5 volts for the filament of the rectifier..."

I know this sounds like I may have just gotten my connections mixed up, Chas, . . . but I measured 332 volts for the filament voltage.  I'd like to think the 4 volts I measured was the filament , and the 332 was the other half of the high voltage winding, . . . . but I don't think I mixed it up.  ;-(    And I did measure no continuity across the filament pins of the rectifier tube, .....surely  that 332 volts cooked it.  

But I'm beginning to  feel I should start all over again.

[Steve Davis]

I can’t think of a transformer failure mode that  would give over 300 volts across a 5 volt winding. 

Steve

[Simon Wa3uay]

Well, Chas, that sure was Power Transformer Test 101, probably 2nd nature to you, but music to the ears of the ignorant!
Thanks,
Simon

[Jake Blake]

"I can’t think of a transformer failure mode that  would give over 300 volts across a 5 volt winding.'

Yea,  it seems odd.
I guess I better do all my measurements over.   But the tube filament continuity measurement was pretty simple.  It's open , whether that 332 volts is correct for the filament voltage or not.