If you have one of these TVs (the 17" or the 21") you'd have no doubt noticed the low video IF gain.
Even with a new set of valves it's quite marginal.
I have a 17 and a 21 and they are the only sets in my collection that I can't use on an 8 way modulator split.

But I discovered an easy fix!

Just replace the 1st IF (6CB6) with a 6EW6. They are pin compatible.

The 6CB6 has a transconductance of 8000 umhos, the 6EW6 has 14000 umhos.

With the change, the fine tuning no longer affects the contrast or the sound. And you actually get snow on no signal!

This has got to be the easiest upgrade you could do!

I have a restored AWA 202C used with the modulator you kindly sent to me a number of years ago.

While I get a good picture, the caption buzz is still very bad with most DVDs. Would this 6EW6 mod fix this problem?

I think I have some NOS 6EW6 valves in my collection

I do not seem to recall the 6EW6 valve.
Which sets were they in?

Wayne

They were pretty much used exclusively in AWA/Electrice/Westinghouse sets from the early sixties to the end of the valve era.

And the audio output in the P1!

"While I get a good picture, the caption buzz is still very bad with most DVDs. Would this 6EW6 mod fix this problem?"

That modulator design is fussy about its 12 volts. Try taking the series diode out and replace it with a short.

You can wire the diode in parallel with the 12V as reverse polarity protection, stripe to 12V, other end to 0V.

According to my pin-compatible cross-reference, the following could be swapped around to see what happens.

6AS6, 6AW6, 6BH6/6661, 6BJ6, 6BZ6, 6CB6/EF190, 6CB6A/6CF6, 6DC6, 6DE6, 6DK6, 6DT6, 6ES6/EF97, 6ET6/EF98, 6EW6, 6GM6, 6HQ6, 7693/E90F, 7694/E99F, 9001, 9003, M8196.

The 6EW6 has the greatest transconductance with 14000, followed by the 6GM6 with 13000.

The valve name sounded familiar, so I looked in the drawer and found 3x 6EW6. I remember they were in discarded TV sets.

€�You can wire the diode in parallel with the 12V as reverse polarity protection, stripe to 12V, other end to 0V.”

Thanks, I’ll give it a go.

I’ll also try the 6EW6 mod.

It won’t blow my telly up, will it? I’ve had it since 1992, three house moves ago.

No danger to the TV.

Re the modulator, are we talking about the one I designed, or before that? My memory fails me!

I think it was the one you designed and featured in Silicon Chip.

That's the one!
Yes the diode drop fix applies.
Unless you can adjust your plugpack to get 12.6 volts.
It's the Motorola modulator chip that's fussy about its 12 volts.