1971 Magnavox 1T5034 19" B/W Hybrid

[fsjonsey]

I found another set down at College, Buried under a bunch of junk up in the attic of the Auditorium. It's a 1971 Magnavox 19" B/W Hybrid.

It's a hot chassis set with a solid state IF strip, Tuner, and video sections.

I powered up the set last night, and the filaments lit, and nothing more. I checked most of the voltage test points on the PCB and couldn't find b+ on any of them. I'm guessing that either the main electrolytic can or the rectifier diodes are shot. I ordered replacement electrolytics just to be safe. The wirewound resistors in the power supply tested good. I'm having trouble actually finding the rectifier diodes on this chassis. I'm guessing it's a voltage doubler circuit just based on it being a hot chassis set. It's a pretty crowded PCB. Is anyone here familiar with magnavox sets of this period?

[radiotvnut]

Nice set! I've had a couple of all tube Magnavox 19" B&W's from a few years earlier and they were decent performers.

On your set, don't overlook a possible defective circuit breaker. Many of these sets have the CB in the B+ line. If they become defective, you won't get any B+. If bad, you can replace it with a fuse for testing purposes.

[fsjonsey]

Originally Posted by radiotvnut

Nice set! I've had a couple of all tube Magnavox 19" B&W's from a few years earlier and they were decent performers.

On your set, don't overlook a possible defective circuit breaker. Many of these sets have the CB in the B+ line. If they become defective, you won't get any B+. If bad, you can replace it with a fuse for testing purposes.

I checked the circuit breaker. When I held the reset button down, the tube filaments extinguished. When I let go, they came back on. The breaker is placed in series with the main power switch.

[radiotvnut]

I can't find that model number in the Sam's index. Is there a chassis number? It will probably be on a small paper sticker somewhere on the chassis and it usually begins with a "T".

[Findm-Keepm]

Looks like a T94X chassis - perhaps a T946? Tube complement of 17BF11, 21LR8, 8FQ7, 22JU6 and a 17CT3, with a 1K3 HV rect.

If so, there's a 4.7 ohm fusible feeding D6, the B+ rectifier. Some of the models with quick-on have a DPST on-off switch, and you may have the B+ side open up (filaments, but no B+). B+ is 140 volts or so. Easy way to check for B+ is right at the red lead to the audio output transformer - should be ~120 to 130VDC at the red lead.

Hope this helps! Fixed many of those old Maggies!

Cheers,

[fsjonsey]

Originally Posted by Findm-Keepm

Looks like a T94X chassis - perhaps a T946? Tube complement of 17BF11, 21LR8, 8FQ7, 22JU6 and a 17CT3, with a 1K3 HV rect.

If so, there's a 4.7 ohm fusible feeding D6, the B+ rectifier. Some of the models with quick-on have a DPST on-off switch, and you may have the B+ side open up (filaments, but no B+). B+ is 140 volts or so. Easy way to check for B+ is right at the red lead to the audio output transformer - should be ~120 to 130VDC at the red lead.

Hope this helps! Fixed many of those old Maggies!

Cheers,

The Tube Compliment is an exact match. I'll take a look at that fusible resistor and the power switch tonight.
Thanks for the great advice!

[fsjonsey]

It was the resistor!

I clipped out the old resistor in line with D6, temporarily tacked a new 4.7 ohm 5W wirewound under the board, and the set came right up!

There seems to be one issue from the get-go. The CRT seems to be a bit out of focus around the edges. Is there a way to adjust this, or is it just a weak tube?

[zenithfan1]

Sometimes a weak or slow tube will take a while to "look right". At times they can look washed out or out of focus after a long period of sitting. I have a few slow ones that test great but look like a bad tube after sitting a few months. 15 min of run time makes 'em snap back to normal. Does it focus better if you turn the brightness down? If so, it's one of these causes. I also have some weak ones that do the same thing. I think it's just how a B/W tube shows it's age.

Neat set by the way, I rarely if ever see those anymore. I'd say it's been a good ten years since one has crossed my path. I'm glad you got it working.

[zenith2134]

Glad it was a relatively painless repair. I also like the style of this Magnavox.