#1
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1946/1947 Transvision Kit
I purchased a 7 inch Transvision kit set (the type with the plywood board front panel, not in the factory cabinet).
Anyway, it is missing the HV transformer. I'm going to have to call Arlynn at Heyboer transformer and see if he can wind a suitable replacement. I know the primary should be 117 or 118 volts, with two secondaries, one wound for 2.5 volts at 2 amps for the 2X2 rectifier. It's the HV winding that I'm not sure what to spec. The originals I believe were wound for 2500 or 2700 volts (depending on which version of the service info you trust). But at what amperage? 1000 to 2000 microamps sounds reasonable to me, but I know that if I spec it too high, and the regulation of the transformer sucks, that the rectified HV could shoot up. I believe the 7EP4 has a max anode voltage rating of 3000 volts (design center) as opposed to the 5BP4 from which it was derived (which has a max anode voltage of only 2000 volts). Any ideas? I suppose if I have it wound and the HV is too high, I can tack in a string of Zeners to regulate the HV at whatever voltage I want but I'd like to avoid going that route if possible. |
#2
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Another question for the Transvision gurus... what woods were available for the front panels of the kits? I've seen a blonde kit at the ETF, two mahogany sets in the flesh, two walnut, and I have a photo of one with what appears to be burled American Chesnut. I'm trying to determine which were original and which were modifications from the builders.
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#3
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I'm a moron. I managed to find the specs for the transformer in a VK post... from myself. I posted about another Tranvision kit I had, and sold, to Don because frankly, it was uglier than sin and very poorly constructed. After doing a search based on the specs I had posted in the other thread, I was able to find the source of my info: an advertisement from mid-1947 from Transvision. If you need a Transvision HV tranny, call up your winder and spec the following: 117 rms VAC (or whatever line voltage) to 1700 rms VAC at 4 mA, with another secondary of 2.5 rms VAC at 2 amps.
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#4
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I know what I did wrong... I was assuming that the "2500 volt" rating given in the parts list was a rating of the transformer. It would have been more accurate to call it a "transformer for the production of 2500 volts". The peak DC voltage after the 2X2 rectifier does come out to 2700 volts in a simulation, and the average DC value after the rectifier and filter cap is 2500 volts.
My mistake when trying to work backward from the schematic to determine the voltage rating of the secondary was neglecting to use the peak value of the line voltage, which would be 117 volts times the square root of 2, or 165.463 volts, instead I was using 117 volts as the peak. Been a long day... |
#5
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That set used a brute force HV supply. The transformers were notorious for failing. I converted 2 Transvisions to RF high voltage, using HV unit from junked 7 inch Motorolas. Many of the later Transvision sets used the 7JP4 CRT, which was an improvement over the 7EP4
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Audiokarma |
#6
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Quote:
I can certainly understand why you would replace the HV supply with a Motorola RF coil. My set will be getting a replacement from Heyboer so I can see how the kit may have worked for the original constructor. |
#7
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The set arrived from Vaughn today. It is EXTREMELY rough, but as advertised. Thanks Vaughn! The front plywood (particleboard?) panel is a total loss. I'll keep it around, but I'll just use it as a template to cut a new board...
I intend to use a burled walnut or chesnut veneer over a sheet of plywood or fiberboard for a replacement. The set is missing the electrolytics, one HV cap, one power supply choke, and the HV tranny. Nothing that can't be replaced. Otherwise it is quite rusty up top, but surprisingly clean and complete underneath. 5 channel tuner (was hoping for the rare 3 channel job), but from what I've traced of the set as wired, it uses the early 6N7-6SN7 sweep circuits, not the late 6SN7-6SN7 circuit. AM sound circuit with the 6SQ7. Not sure what combinations of tuner, sweep circuits, and sound circuits other collectors have. Photos to follow. |
#8
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I borrowed Steves blonde one from the museum and had cabinet shop close to me make one . Its perfect and he also made the wooden blocks for the crt. He has the template to make more. You pick the veneer of your choice.
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#9
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Good news and bad new: The good news is that the tuner is actually a 3 channel tuner, so the set is likely late 46 or very, very early 47. Yay!
The bad news? The tuner is missing two of the three grid coils, all three antenna trimmers, and the bandpass trim capacitor. The capacitors I should be able to find replacements for, the coils will be impossible... |
#10
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Photos as promised... it's a basket case, but any of these Transvision sets are worth saving in my opinion. At $200, the price was right too! They're just plain hard to find. I'll do my damnedest to find the missing parts or have suitable replacements built. This set deserves to live again.
Last edited by benman94; 12-17-2017 at 06:11 PM. |
Audiokarma |
#11
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Wow!!!
__________________
"Restoring a tube TV is like going to war. A color one is like a land war in Asia." |
#12
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Real piece of shit, ain't she? Worthy challenge for my abilities... while Nick is working on the Westinghouse I'll fight with the Transvision.
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#13
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I mean... is there no way to know the value of the coils? If they're not known... couldn't they be guessed?
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#14
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Tunable coils with a slug. It is possible to find a reasonable replacement, but I would need some measurements from actual coils in a surviving 3 channel tuner. I doubt I'll find another owner willing to measure for me
Last edited by benman94; 12-18-2017 at 12:44 PM. |
#15
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rip
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Audiokarma |
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