1946/1947 Transvision Kit

[benman94]

My plan for the moment with the tuner is to replace the missing caps, align the tuner for the one channel I have a grid coil for (channel 2 or 5 I believe) and simply leave the set on that channel. Then, if that works, try to repair the remnants of the one coil form that is still present, giving two channels. If I can get that to work, then I'll try to make a wild ass guess as to final, completely missing, coil and tack in a replacement of a reasonable looking inductance.

If I can get the tuner to work on one channel at least I can restore the set. If all three coils were missing I would be up a creek.

[Electronic M]

Originally Posted by benman94

If all three coils were missing I would be up a creek.

Not if it uses a standard IF frequency. If it uses a standard IF frequency you can just grab a tuner off a junker chassis and hook it into the 1st IF until you can figure out the original...Ain't pretty but it is an option.

[benman94]

Originally Posted by Electronic M

Not if it uses a standard IF frequency. If it uses a standard IF frequency you can just grab a tuner off a junker chassis and hook it into the 1st IF until you can figure out the original...Ain't pretty but it is an option.

I had thought about that. The frequency is low, 21.9 MHz I believe. I'd prefer to keep the set as original as possible, but if the original three channel tuner can't be salvaged I can try an early Inductuner (if my memory is correct they use the same IF frequencies).

[benman94]

I may have found a CRT for this set. I really don't like the look of the getter flash, but I'm desperate for a 7EP4 to at least display the set with. Hopefully the owner will accept my offer for the jug (I think $150 is pretty fair) and I can stop the CRT hunt and focus on other missing parts.

[dtvmcdonald]

Unless you demand original look coils, with only three channels its easy.

Get some forms, new or used, even with wire on them, that
mechanically fit and are for VHF. Install them and play with new windings
and a grid dip meter until they are right.
Stray inductances are so big that calculations are useless.

I wish I had had a dip meter when I was working on my hacked TRK-12 RF
area that had been hacked apparently TWICE by the RCA engineers themselves
during the pre and post-WWII channel moves. I did use the dip meter
on my Pilot prewar FM when I redirected it to (part of) the modern band.

[benman94]

Originally Posted by dtvmcdonald

Unless you demand original look coils, with only three channels its easy.

Get some forms, new or used, even with wire on them, that
mechanically fit and are for VHF. Install them and play with new windings
and a grid dip meter until they are right.
Stray inductances are so big that calculations are useless.

I wish I had had a dip meter when I was working on my hacked TRK-12 RF
area that had been hacked apparently TWICE by the RCA engineers themselves
during the pre and post-WWII channel moves. I did use the dip meter
on my Pilot prewar FM when I redirected it to (part of) the modern band.

Third person today to recommend using the dip meter. I'll probably go that route.

I'm going to assume that since the set was found near NYC that the tuner was built and aligned for channels 2, 4, and 5.

[benman94]

Originally Posted by benman94

I may have found a CRT for this set. I really don't like the look of the getter flash, but I'm desperate for a 7EP4 to at least display the set with. Hopefully the owner will accept my offer for the jug (I think $150 is pretty fair) and I can stop the CRT hunt and focus on other missing parts.

Well the CRT is mine. I'm fairly certain it is a goner, but I would still like to find someone in South-East Michigan with a working pre-war 5 inch chassis to test the tube on. Can anyone help me there?

[EdKozk2]

Originally Posted by benman94

Well the CRT is mine. I'm fairly certain it is a goner, but I would still like to find someone in South-East Michigan with a working pre-war 5 inch chassis to test the tube on. Can anyone help me there?

If you have an older oscilloscope , like a Sylvania 400 you could swap crts. Another idea would be to wire up a jumper harness with with the necessary plug and socket connections to a newer oscilloscope, like a Heathkit that uses a 5UP1. You would just have to be sure the 7EP4 anode voltage is not exceeded.
The picture I included is one I made up for repairing Philco split chassis sets.
Ed

[benman94]

Originally Posted by EdKozk2

If you have an older oscilloscope , like a Sylvania 400 you could swap crts. Another idea would be to wire up a jumper harness with with the necessary plug and socket connections to a newer oscilloscope, like a Heathkit that uses a 5UP1. You would just have to be sure the 7EP4 anode voltage is not exceeded.
The picture I included is one I made up for repairing Philco split chassis sets.
Ed

That's a nice idea actually. I may buy a cheap 5BP1 based scope just for testing 7EP4s and 5BP4s. My current scope is a modern PC based digital scope. I also have a late model Tektronix for backup. Nothing old enough to sub the 7EP4 into. In any case, a collector in the Detroit area has graciously offered to help me test the CRT in a working chassis when it arrives from Pennsylvania.

[benman94]

I've come up with a solution to the "use" vs "display" question I've been wrestling with. 7EP4s do not grow on trees, and if I should happen to find a good one, I won't want to use it too much. There is a pin for pin compatible tube that would work in the set with no modifications: the 5BP4. The only real differences between them are screen size, 5 vs 7 inch diameter, and max ultor voltage (which I'll ignore; running a 5BP4 at 2500 isn't going to bring about the end of days).

If the set works well enough to warrant daily driver status, I'll cut and finish two new front boards, one with an opening sized for a 5BP4, the second for the 7EP4. On special occasions I'll swap in the 7 inch board and CRT, the rest of the time I'll just use the 5 inch board with a 5BP4. I can have my cake and eat it too...