Tech-Master NIB TV Kit #5516

[Crist Rigott]

I got a new 21FP4C rebuilt CRT. A big thank you to El Predicta who donated the CRT for this project. He also donated a spool of solid 20awg white wire. Thank you very much for your generosity!

Here are a few pictures of the CRT.




I tested the CRT on my B&K 467. It checked out at 1.7.


And the Life Test showed a drop from 1.7 to 1.65.


Here is a picture of the straight gun. Yeah, I have to glue the base back on.


Again a big shout out to El Predicta! Thank you.

[Crist Rigott]

The new CRT fits very well to the chassis.

[Crist Rigott]

I started working on re-stuffing the E-Caps. The first one is the multi sectioned C43. It has a 20uf 150V, 10uf 150V, and a 100uf 25V.



After removing the cardboard cover, this is what I found:



I was a bit taken back but decided that what I should use is what the schematic and parts list calls for.

What do you think?

[Crist Rigott]

I'm in the middle of re-stuffing the E-Caps. I used my heat gun to heat up the cardboard cover and pulled it off the can. I then cleaned off all the black tar/wax from the capacitor. I then made some marks 3/8 inch up from the base of the cap. This is where I'll make the cut using my band saw. I cut each cap on the marks then dug out the caps innards. Cleaned up the bases and on the 2 single 200uf 150V caps I drilled 1/16 hole in the center and the other one near one of the mounting lugs. I'll run the wires through the holes and solder them to the correct lug.

I then took some 1" thin walled PVC tube and cut 1 inch lengths and trued up one end which was then marked.

After the bases were cleaned up and de-burred and the PVC tube de-burred and cleaned up, the marked end were epoxied into their bases. the excess epoxy was then wiped off and the assembly was cleaned using rubbing alcohol and then the new caps will be wired in.

[WISCOJIM]

Originally Posted by Crist Rigott

I was a bit taken back but decided that what I should use is what the schematic and parts list calls for.

What do you think?

I'd measure the cap and see what it truly was, and match that.

.

[Crist Rigott]

Originally Posted by WISCOJIM

I'd measure the cap and see what it truly was, and match that.

.

That would be kinda hard, seeing it's been cut in half. anyways I don't have any way to measure it.

[dieseljeep]

I restuff my cans in much the same way. The only thing different is, instead of the PVC pipe, I use the thin aluminum salvaged from a beverage can.
I cut the can apart with kitchen shears and roll the metal up as a sleave, then I use silicone sealant to hold it all together.

[dieseljeep]

Originally Posted by WISCOJIM

I'd measure the cap and see what it truly was, and match that.

.

I looks like they used more of those scrappy grab-bag parts.
The label made on a spirit duplicator shows some real class. Reminds me of school days, where some weekly tests were ran off on them.
The cap has a Sentinel part number from 1953.
I would use 22mfd for the 10, 47 for the 20 @250 volts and 100 @160 volts for the 100 section.
BTW, Is there any truth to the theory that operating too high of a voltage rated 'lytic on lower voltage, IE a 450 volt cap at 150 volts, that they never seem to form properly, or just another urban tale.

[Kevin Kuehn]

Originally Posted by dieseljeep

BTW, Is there any truth to the theory that operating too high of a voltage rated 'lytic on lower voltage, IE a 450 volt cap at 150 volts, that they never seem to form properly, or just another urban tale.

I tend to think they form up good enough for whatever voltage they're operated at. Admittedly it's one of my armchair theories, but to the best of my knowledge I've never had a cap fail because it's been operated at too low of voltage.

[kvflyer]

Originally Posted by Crist Rigott

After removing the cardboard cover, this is what I found:...
I was a bit taken back but decided that what I should use is what the schematic and parts list calls for.

What do you think?

That is quite normal. Capacitor manufacturers would often use a can that was already stamped and stuff whatever they needed into it when they knew they were going to put a cardboard sleeve around it. I have seen it several times.

[Crist Rigott]

Originally Posted by kvflyer

That is quite normal. Capacitor manufacturers would often use a can that was already stamped and stuff whatever they needed into it when they knew they were going to put a cardboard sleeve around it. I have seen it several times.

I was thinking along the same lines. Remember this cap has never been installed, it is a part of the kit.

[N2IXK]

Originally Posted by kvflyer

That is quite normal. Capacitor manufacturers would often use a can that was already stamped and stuff whatever they needed into it when they knew they were going to put a cardboard sleeve around it. I have seen it several times.

I'll second this. And it wasn't just budget manufacturers or short runs like training kits that they ended up in, either. Have seen them as OEM parts in RCA and DuMont sets, at least. Real obvious stuff like a 4 section cap that is stamped for a single section cap on the can itself.

Just the cap manufacturer "reclaiming" perfectly usable scrap from a previous production run, and using it where it presumably wouldn't be noticed.

[Crist Rigott]

Originally Posted by N2IXK

I'll second this. And it wasn't just budget manufacturers or short runs like training kits that they ended up in, either. Have seen them as OEM parts in RCA and DuMont sets, at least. Real obvious stuff like a 4 section cap that is stamped for a single section cap on the can itself.

Just the cap manufacturer "reclaiming" perfectly usable scrap from a previous production run, and using it where it presumably wouldn't be noticed.

Yes, I agree.

[Crist Rigott]

Here is how I re-stuffed the E-Caps. Once the epoxy is dried, I attached some wires to each E-Caps, then used some hot glue to glue them together. I routed the wires together and secured them with some string tie. Then they were inserted through the hole and hot glued into place. Then the wires are soldered to each terminal.

I then slid on the can and fixed it into place with some clear tape. Then I wanted to increase the diameter of the can because the cardboard tube is a larger diameter that matches the base. This was done so when the E-Cap is inserted into the clamp, the cardboard tube is not crushed. I used some masking tape and manilla folder stock.

Then the tube is slid over the whole assembly. No glue is required here because of the clamp method of mounting.

The E-Caps were then inserted into their proper clamps. I did re-position TB20 by turning it 90 degrees to give me more room between TB20 and C43.

[Kevin Kuehn]

Keep in mind that maximum contrast on these old sets is a bit of an illusion that relies heavily on the ambient lighting in the viewing room. Of course the screen can never get darker than it is when it's off for a given ambient light level. So considering the relatively bright room lighting in your below picture, I'd say your set is putting out about the best contrast it's capable of. The modern set next to it likely has a darker screen filter, yet to me it looks more washed out than your Tech Master. Also remember that the contrast of the old program material was not all that consistent. Your set has a darn good picture with your DVD test pattern on it, so just be careful that you don't go chasing rainbows in an attempt to correct for a lousy picture that your OTA converter box may be responsible for.