Will I pull the tranny out of my Astor parts chassis?

Prob not a bad idea Ian, it looks like sourcing the correct STC transformer is very unlikely.
Scott

Ian, that would be wonderful, its the only way for Scott to move forward.
Fred.

Thanks gents
I really appreciate the assistance from all of you. I’ll have to know how to modify the vertical output stage to accommodate the replacement tranny.
Cheers

When I pull the chassis out from the pile I'll also get the chassis number and send you a copy of the circuit.

It also has a good 23" 110 degree CRT btw. One of the naked variety, no bonded faceplate or mounting lugs.

Thanks Ian

That would be great.
I’ve spent considerable time on this TV and have to start focusing on other repairs
It will good to finally finish the STC off. The picture tube in it seems ok although brightness isn’t as good as I would have expected.
I imagine the CRT you have would be a different type so would not be compatible.

Cheers

Re the CRT, all you need to know is the diagonal size, mounting arrangements and deflection angle.

You STC is 23" with a separate safety glass? If so, the tube I have will fit.

Hi Ian
Yes it has a separate safety glass
Cheers
Scott

Oh one thing:

Some STCs of the period used a rare 114 degree 23" CRT (23WP4?) to reduce the cabinet front to back depth slightly. If, when it is fitted, the chassis is hard up against the tube bulb you might have one of those.

The Anodeon CRT I have is 110 degree.

I might get a chance to get into the garage today and retrieve the transformer from that chassis.

That’s Ian
I just checked and yes it’s the 23WP4.
Cheers
Scott

The 110 degree CRT will work, if it can afford to be 25mm "fatter", i.e. setback of the bulb measured from the screen face to the base of the neck.
..
I just checked the datasheets.

Thanks Ian
I’m away for a week and will check it when I get back. I think there is room for the tube to be deeper but not sure about the fatter aspect. Will the same yoke be used? Or the one that’s on your tube.
Cheers
Scott

Same yoke, I doubt you will be able to tell the difference.

If you are fussy you could change the value of the yoke coupler cap, Kriesler used to use both tubes and they had a link to connect the extra cap for 110 degree tubes. The slightly different deflection angle calls for a different amount of S correction to the horizontal scan.

Nobody else bothered (or indeed noticed), the effect is subtle and only seen by critically examining a test pattern.

Makes sense
Could try it first and see. If it looks ok, just leave it

OK, I pulled out the Astor chassis. It's a Series 2.

The transformer is actually a single tapped winding. It uses no feedback for linearity, just the old school adjustable cathode resistor. Very simple circuit which, as I recall, worked OK. It has some advantages in that interlace should be better than the STC because there is no path from the yoke crosstalk to the vertical oscillator.
.
Pentodes normally don't give as good linearity as triodes in this circuit but Astor seems to have been able to make it work. It must have been OK because they kept using the same circuit right up to the end of B&W.

There is a problem though.

Since your set uses video grid drive to the CRT, the vertical blanking is applied to the cathode. This means it's a positive pulse.

The Astor uses conventional CRT cathode drive so blanking goes to the grid. Hence it's a negative pulse.

We could try reversing the tap and the end of winding, applying B+ to the end instead of the tap. This has the disadvantage that it will result in a higher plate impedance reflected back to the 6BM8, which will affect the linearity. Probably within range of adjustment though. Pic will be upside-down, no problem, just reverse the yoke vertical connections.

So if I draw to a circuit, are you OK to implement it? It's pretty much just a matter of pulling out all the existing linearity circuitry and pots and replacing it with a 1k pot and series 390 ohm resistor in the cathode of the 6BM8 pentode. The height control works differently, it needs to be a 2 meg pot. Very simple, a 3.3 meg resistor from B+boost, then the pot, then the oscillator plate circuit.

How does that sound?

Oh I may possibly have to renege on the CRT offer. The wife has taken a liking to an Astor 3 in 1 that uses the same tube. It may well need a replacement...... Not definite yet though!