[morzh]

I read it, Ron. I just stated my opinion on the concept of protecting BJTs from static.
I wanted to do so Friday but something held me.

[Ron Ramirez]

Well, you should have felt free to comment...

nevertheless, I don't think that adding or not adding the diodes caused the problem I now have. The Auto Magic still works...only now, it just works when it wants to, which is very seldom.

I've taken it back to the basement but have not done anything else with it.

[Ron Ramirez]

At the workbench.

This makes no sense!

Here in the basement, on headphones, Auto Magic works perfectly.

Is this thing allergic to my Bozak E-300s? That is the only difference that I can tell between conditions here in the basement and upstairs in my home office...and the speakers have nothing to do with the Auto Magic circuit.

Maybe I'll get out my little Minimus-7s (test speakers) and see how it does.

Edit: I did...and Auto Magic is still working fine.

[KCMike]

While I know this is turning into  a pain for you Ron. It's an interesting problem that I hope you resolve and we find out what the cause is for the erratic behavior.

[Ron Ramirez]

I can only think of one other difference:

The Terk amplified FM antenna in my home office.

Hmmm...???

[Ron Ramirez]

...nope...not the Terk...I brought it to the basement, hooked it up to the Realistic and...Auto Magic still works fine.

It is as if Auto Magic simply does not want to work in my home office.

Okay, so it shall be a basement receiver, then!

[sam]

ron
may be a dumb question
what kind of floor is in your basement and in your office
carpet , hard wood ,concrete ?   maybe its what your standing on ?
shot in the dark here

sam

[Ron Ramirez]

Sam

Nope, not a dumb question at all...a very good one, in fact.

The basement floor is concrete, although I have a rug on the floor in front of the workbench.

Upstairs, the floor is linoleum over wood.

Perhaps this is the issue. The Auto Magic in this receiver seems to favor the basement over the upstairs, and this makes as much sense as anything. As to why the Auto Magic does not want to work upstairs, I haven't a clue at this point.

[Eliot Ness]

Ron, I'm just curious how well the Auto Magic actually worked when these receivers were new.... do you have any direct experience or have you read how well this feature actually worked?   I'm just wondering if it was more of a gimmick that was more problematic than useful?  I did a quick search but didn't find much useful info on it.

[morzh]

What is Auto Magic?

[Eliot Ness]

What is Auto Magic?

.......Auto Magic now works as it should! When I touch the tuning shaft, the meter turns white and AFC goes off, allowing me to tune in a station. When I let go of the tuning shaft, the meter turns green again and Auto Magic locks the station into place.......

[Ron Ramirez]

Ron, I'm just curious how well the Auto Magic actually worked when these receivers were new.... do you have any direct experience or have you read how well this feature actually worked?

No direct experience other than with this receiver. I could only dream of owning something like this in 1975. I do not recall looking at any in Radio Shack stores back then...probably because I knew that I could never afford one when they were new and I was just a 15 year old kid.

I did see a YouTube video recently of one...and it worked as it should have. The tuning meter turns white, indicating that AFC (Auto Magic) turns off when the user touched the tuning knob to tune in a different FM station...turned green again when he let go of the tuning knob. That's how mine is working...in the basement at the workbench. But not upstairs.

I'm just wondering if it was more of a gimmick that was more problematic than useful?

That could very well be it, I think. Radio Shack only used Auto Magic in a few receivers in the mid-70s, then it disappeared. Maybe it wasn't as "Magic" under real life conditions as they had hoped?

[morzh]

If this is the case than it works on the same principle as all those "touch" brightness regulators or channel switching on old TVs or "On/Off" touch switches.

I have some around, like the lights in my bookcase or china cabinet. So Sam's question is valid. Though I never saw things that wouldn't work anywhere in the house. I guess it is a matter of the design.

So coming back to the sch, you could play with the value of R703 (might want to increase) and R702 (same thing). Especially R703 - this dictates the input impedance.
As a measure, try to find a "Super-Beta" transistor (those capable of working with microcurrents and having Beta around a 1,000) - this will increase the input impedance a lot and might make it work where it wouldn't before.

http://www.mouser.com/ProductDetail/Fair...8DGTVOs%3d

[Ron Ramirez]

Thanks a lot, Mike; very much appreciated. For twenty cents, that transistor is certainly worth a try. I have to make another Mouser order anyway...long story, different receiver...and I'll include at least one of these transistors in the order.

[morzh]

Ron

Just make sure the power voltage for that transistor section is not above say 40V or so, I cannot see it from the sch fragment. The Vceo for this one is 45V.

Else this one has 65V, same family.

512-BC546CTA

The "C" family has better Hfe - from 400.

http://www.mouser.com/ProductDetail/Fair...h74ZIqY%3d