10-12-2019, 02:48 PM
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
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
Pliny the younger
“nihil novum nihil varium nihil quod non semel spectasse sufficiat”
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