1949 9PC41 projection set

[Electronic M]

Originally Posted by Radiotronman

I'm going to order mica caps for the horizontal hold circuit, should I order ones at 1,2 or 5% tolerance?

What is the tolerance of the originals? As a general rule of thumb order the same or lower tolerance (i.e. if the original is a 10% order a 10% or a 5%, but never* a %20).

*Unless you have high accuracy measuring equipment and you can buy a bunch of sloppy tolerance parts to cull a good one from cheaper than the correct tolerance part.

[wa2ise]

Do they even make 20% tolerance parts anymore?

[Smoky Pond]

Hey Radiotronman! Are you still making progress with that 9PC41 I just came across your post tonight or I would have chimed in earlier.

I can't really say that I restored my 648PV recently. It's been almost 16 years now and it's still working fine. I watch it between 50 and 100 hours per year, so it has a fair number of hours on it. My late wife Janet and I used to enjoy watching old movies and TV shows on it.

I saw that you got the FM radio working. Mine gave me fits, all related to the oscillator coil for FM. Eventually figured things out.

I admit that the focus blooms with the brightness turned way up, but my sets focus is fairly stable at regular viewing levels. I have not made any HV mods to it.

To help keep your interest piqued, here is a short video clip of my set in operation:

https://youtu.be/r-SDEA5KP98

[Radiotronman]

Hey Matt!

Yes I'm still working on it. Contrast and brightness controls have no effect and the horizontal is still touchy. I'm checking all resistors now in the video section.

[earlyfilm]

Originally Posted by Radiotronman

Yes I'm still working on it. Contrast and brightness controls have no effect and the horizontal is still touchy. I'm checking all resistors now in the video section.

Check your local/remote switch (the switch on the far right below the screen) for being in the wrong position and/or having dirty contacts and/or one of the leads not being plugged in.

Do any of the two pair of Contrast and Brightness controls do anything?

EDIT:
Get your contrast working before working on the horizontal sync. The contrast control shifts AGC voltage on the entire video IF strip, so that alone could be causing your sync issues.

If you have the remote switch unplugged, you must have a shorting plug in the empty main chassis connector. See the schematic for wiring the shorting plug.

Jas.

[Kevin Kuehn]

Originally Posted by Smoky Pond

To help keep your interest piqued, here is a short video clip of my set in operation:

https://youtu.be/r-SDEA5KP98

That's a very impressive picture that your set is producing. I don't own a projection set, but it would seem that they produce very good picture contrast in a reasonably well lit room, way more so than a direct view CRT.

[Radiotronman]

So far, this crummy picture with lots of noise in it is all I can get.

[Smoky Pond]

Originally Posted by Radiotronman

So far, this crummy picture with lots of noise in it is all I can get.

How are you feeding the signal into the set, and what is the source? Also, did you determine why the brightness and contrast controls don't function?

[Radiotronman]

Still haven't figured out the Brightness and contrast yet. I am using an Digital converter box with a 300ohm coax converter adaptor through the tv antenna terminals.

[Smoky Pond]

You're not really that far away from having things working well. While the picture looks a little dull (are you running the original 5TP4?), it looks like the RF is weak as well.

I ran into trouble with the RF AGC going to the tuner.

Take a look at the junction of R192, R167 and C175 coming off the plate of V106, the 6AT6 AGC amp. There is a wire going to the tuner from that point. If the value of the 2 resistors and C175 check good, try this: disconnect the wire from this point to the tuner, connect it to ground and see if that improves things. I don't know why, possibly due to a problem with the tuner, but I've worked on 2 of these, including mine that respond well to this change.

It's worth givin' a try and it ain't gonna hurt nothin'!

[Smoky Pond]

I forgot to mention that depending on which schematic diagram you're working from, the junction of R3 and R13 in the tuner is connected through R12, a 1K resistor to:

1.) The junction of R192, R167 and C175 off the plate of V106, the 6AT6 AGC amp, if you're referencing the RCA diagram.

-or-

2.) Connected to ground if you're referencing the Sam's diagram from Set 90 Folder 9 dated 3-50.

What's interesting to note here is that in either case the wire from the tuner goes all the way to the area around V106. If it was designed to be connected to ground, why not just ground it at the tuner?

[earlyfilm]

Originally Posted by Smoky Pond

. . . . . it looks like the RF is weak as well.

I'll repeat:
On this set the Contrast Control is the AGC control.

Find where the trouble is and fix it, first.

The contrast control should vary the AGC voltage. Find out why it does not.

As Smoky Pond said, it does look like a tuner issue, too, but you cannot tell for sure until you fix the video IF section.


After you get the contrast and brightness controls working, and have confirmed that your HV is up to specs, you can trouble shoot the focus issue:

First, you will need to find an RCA schematic diagram, as the light barrel is not the same one that is in the Sams, which was the 1947 to 1948 version. The focus and alignment methods are different. The 9PC41 only carried the 1949 light barrel. (I've seen a few late production 1948 sets that carried the "1949" barrel.)

You first will get the electrical focus as sharp is possible. You will need to be able to get it to go out of focus on both sides of the best focus. Then do the mechanical focus, and go back and repeat the electrical. This process is continued until no improvement is seen.

Warnings:

Make sure the yoke is level before you start, as yoke adjustment can shift the electrical focus.

An very easy assembly mistake to make is to put the donut lens back upside down after cleaning in the 1949* model. The flat side goes up. If this lens is inverted, you will never get good mechanical focus.

Clean this Lucite donut lens very carefully, as it scratches easily.

* I've never worked on the older model barrel

James

[Smoky Pond]

I should have also stated that James is absolutely correct. It's imperative that you get that contrast control working.