American Circuits

[Nowhere-Man]

Some interesting AVG systems in American receivers. One uses a basic diode detector tube on its own to detect the signal. There is the usual load resistor on the tuned circuit. The usual capacitor and resistors at the cathode feeds the AF to the amplifying stage. However, the AVG diode simply is a second detector tube also fed by the IF Transformer. The anode of this AVG valve is biased so it won't conduct unless the signal exceeds the bias. Once this happens it conducts along the AVG line to the Mixer and IF stages.

A lot of American circuits use separate tubes where they would all be enveloped as in the typical DDT. Many mixer tubes also are simply 2 tubes - one as Local Oscillator and one as IF amplifier.

I'd say there's a decent chance I'll be building one of these American receivers, just hope the tubes are affordable.

[pwdrive]

NM, There's some good stuff on AGC/AVC in RDH4, chapter 27, section 3:

http://www.paleoelectronics.com/RDH4/CHAPTR27.PDF

Lawrence.

[Terry]

I'd say there's a decent chance I'll be building one of these American receivers, just hope the tubes are affordable.

If you want to physically replicate one of receivers, then fine. But, if you simply want to copy the original circuitry, then more commonly available European multiple valves - triode-hexodes  and double diode-triodes - will work equally well in such circuits.

[Refugee]

I see what NM is doing as a good thing and that making a set with single valves can be done with common European parts such as EF80s triode wired if a triode is called for.
This will be a good learning set as each stage of the set can be built in isolation and tested in a common set by plugging or wiring to it. A set that has suffered bad worm so that only the chassis remains would be good for this.

[Murphyv310]

I see what NM is doing as a good thing and that making a set with single valves can be done with common European parts such as EF80s triode wired if a triode is called for.
This will be a good learning set as each stage of the set can be built in isolation and tested in a common set by plugging or wiring to it. A set that has suffered bad worm so that only the chassis remains would be good for this.

Yes I agree. I always keep old chassis for projects, one reason the loft is a mess!

[Refugee]

I saved a couple of old chassis assemblies that had both transformers in working order.

[Nowhere-Man]

I see what NM is doing as a good thing and that making a set with single valves can be done with common European parts such as EF80s triode wired if a triode is called for.
This will be a good learning set as each stage of the set can be built in isolation and tested in a common set by plugging or wiring to it. A set that has suffered bad worm so that only the chassis remains would be good for this.

I heard some people were using baker trays. Never tried it so can't comment.

According to the American theory I have, separate tubes are known to be less noisy than "all-in-one" Frequency Changer tubes. Not that it's a huge deal but I'm surprised by the variation of things tried out. For example, injecting the L.O. signal into the same grid as the aerial signal itself. Cathode injection did seem to be quite common also in American sets.

There were one or two good schematics of a simple diode detector tube, juxtaposed against an AVC diode tube. One thing that had me curious as the anode appears to be at RF ground. There was the usual load on the tuned circuit. If you wish I can give you the names of the tubes recommended and maybe you can let me know if they're likely to break the bank or not.

I'm lucky in a sense as I have huge amounts of data on American set design. Scores of circuits to make as many sets as you'd wish.


My "slot" is due to run out soon (it's 17.30 p.m.) 

[Nowhere-Man]

I saved a couple of old chassis assemblies that had both transformers in working order.

Yes, the transformers are a money consideration. I can see now why ACDC sets were made for economy reasons.

Interestingly, at the time my book went out in 1960, silicon rectifiers were all the rage. Lots of kit enthusiasts were turning to silicon for the rectifier.

Plenty of technical discussion of the transistor but back then people were feeling transistors were more "convenient" than any concept of being better than the tube. Some sets I think even combined transistors with tubes.

[Refugee]

I would start with an RF amplifier and detector and then after gaining a full understanding of that go on to make a mixer and IF stage later.
The audio stage will be easy and may be better built first.

[Crackle]

Some interesting AVG systems in American receivers.

What is AVG, what is it an acronym for?
thanks
Mike