'51 Magnavox vertical osc transformer

[DavGoodlin]

17" blonde mini console chassis "CT301" model MV-33J:

I found the original problem HA! right after recapping all papers and 'lytics 100%, since no amount of "waking up" or reforming of the original electrolytics was warranted. These originals were made by and branded Magnavox, not Mallory (code 240). At startup, I was happy to see at least a horizontal line and normal B+ voltages, so HV, horiz. sweep and sound were working.

The first voltage checked was vert. osc. 6C4's plate pin 5, which was -7 volts, thus immediately pointed to T2, the oscillators' transformer being open. Its rare that I zero in on an issue so efficiently. The part number is 320030 and one of 3 listed is a Stancor replacement per the Sams Photofact. Unfortunately, I dont have a TelAide for Magnavox and this is too old for ET digest, so no factory schematic.

After removal I tried my best to "surgically restore" continuity but this little thing has an internal open that is unreachable. The Sams does state a resistance of 950 ohms primary / 170 ohms secondary, so are these small "inter-stage" transformers fairly universal ?

[DavGoodlin]

T2 is the oblong hole in the middle of chassis, just below the 6C4 socket
Chassis CT301 bottom.jpg
MV33J BW TV.jpg

Edit: The Stancor A-8122 was found at Moyers Electronics, to be continued once I get up to Sunbury with my other parts-soldering tool needs.

[SueAnders]

Dave slightly off-topic, I think I gave you last visit a small Stancor new in a box from my late uncle's that looked like it could be some kind of interstage xfmr, any idea what it is?

[DavGoodlin]

Originally Posted by SueAnders

Dave slightly off-topic, I think I gave you last visit a small Stancor new in a box from my late uncle's that looked like it could be some kind of interstage xfmr, any idea what it is?

That was a power transformer that is very useful, along with most other goodies in that lot. Stancor made replacements for almost every one of them.

The vertical blocking (not necessarily interstage) transformer in this little set was the same in Muntz I'm working on, 1:4.2 turns ratio, and I got replacements from Merit for both at Moyers.

I should have this one working soon, just got parts yesterday after work trip up north.

[DavGoodlin]

The replacement part is a great deal different, I bought a different Merit replacement for the Muntz 21" but that looks like the original.
Mag CT301 vert blocking xfmr.jpg
Its ready to try a power up after a second round of dressing up connections, all caps now done.

The replacement electrolytic can cap is 500 volt rated, this set has high B+ compared to others Ive done, a good reason to go beyond a standard 450 volt rating if the originals were 475, almost 20% above applied operating voltage.

Some of my solder work needs cleaned up and some of the loose electrolytic capacitors get RTV'd together.

[DavGoodlin]

Update:
Replaced the vertical blocking oscillator transformer and got a dim but full raster. Sound transformer required a tweak and tuner cleaning brought in a nice picture on a very weak 17BP4. The RF-IF-Video and Sync were functioning perfectly using a DT converter box as RF source. Aggressive CRT rejuvenation still yielded near zero emission, evidenced by the poor cutoff (silvery infill of bright areas) as brightness is increased. Cranking up filament to 12 volts did very little to help, so cathode must have been stripped. I decided to part out a 1954 Motorola table model with a strong testing 17KP4.

Lowering the B+, which ran at 445v, 45v higher than the schematic stated. I had some NOS 500 volt 40 mf, so I used these on both the 380 and 400 volts supply. As I lowered line voltage with "Powerstat" variac from 122 to 117, it dropped to 405 volts with no effect to operation whatsoever. I tried the two 1N1007 in place of rectifier tube 5U4 and a series resistor to compensate for voltage drop of 5U4, (44 volts @ 225ma). A 200 ohm 10 watt resistor dropping 40 volts at 200ma got too hot and as line was increased from 115 to 120, B+ topped 430 volts, with 475 at the rectifier diodes junction. Not a solution where line voltage varies, even just 3-4 volts. There is only one solution left, make a buck or boost auto-transformer using a filament transformer. I this case, I found a 120v-5v@3A Stancor. This was a better solution than a pair of 2.7ohm 10 watt wirewounds in series with the 120 volt AC supply. The TV draws 1.7 amps, well within the secondary rating of the transformer. Power in at 120 volts, TV gets 115 volts to power transformer and B+ stays below 410v, only peaking at 480v before set warms up.

Current Issue: The replacement CRT looks good and bright but has electrostatic focus, so I removed the permanent magnet used for focusing the 17BP4. After connecting the CRT focus pin 6 to boost 520v, B+ 380v and ground, there is no difference. The center of the picture is out of focus but edges seem sharper? Adjusting the ION trap seems to make it clearer in center but not at the same position for max brightness, huh

Question: The CRT has an unused warranty tag listing it as "17H/KP4". 17H has pin 6 for electrostatic focus and 17K lists internally connected focus anode, yet pin 6 is there. Should I reinstall the focus magnet and leave pin 6 alone?