TheRadioBoard

[Rob Lenski]

Does the type of resistor make a difference in the "noise" in a set? By types I mean metal film, metal oxide, carbon...


If so, is it likely to matter in the typical homebrew set?


Thanks!

"Rob"

[Curt Reed]

I think that carbon composition resistors are usually the noisiest, but they only appear to be that way in the input circuitry of really high gain amplifiers. For a radio set, you don't have to worry about them for being noisy, as the atmospheric noise will always be much greater.
Curt
_________________
Curt, N7AH
CW forever
Connoisseur of the cold 807

[Dan McGillis]

Rob, here's some things written in a 1965 Philbrick Research App Manual for Op Amps.

-- "Wire-wound resistors noise levels approach theoretical minima. But they have high shunt capacitance and series inductance, and are expensive.

-- film resistors offer flicker-free behavior and their white noise approaches theoretical, and they cost less than wire-wound resistors.

-- composition resistors are generally not employed as feedback or feed forward resistors in final op amp circuits, but are excellent for experiments."

So, FWIW, I assume from this that film resistors are less noisy than composition resistors.

Curt's comment makes a lot of sense.

73, Dan

[Rob Lenski]

I see. Just considering what type to use in my next set. I'd seen where some of the audio guys discussed this.

Thanks!

"Rob"

[peeblesoriginals]

Rob,

The capacitors that work the best in the RF sections of tube
sets should be: 1) Silver Mica, 2) Mica, or 3) NPO. The disk
ceramic types we have today, are quite stable and can be used
without much difficulty, also.

After-all we aren't listening in the Sahara, or South Pole, usually
As temperature is more the issue, than otherwise.

Resistors of today (Carbon Film) are very good, and highly
reliable. Carbon Comps are usually OK, and 5% the best (Gold Band).
I just don't see problems with resistors, and quite rare if any.

A great way to find out these things is to look at old tube projects in
magazine articles, that are older than the '60s. The parts lists and
diagrams will designate the critical types, usually.

Lead dress and parts positioning are really the highest considerations
with tube sets. Filament wiring in sets with AC current, should be
tightly twisted-pairs, and run very direct, and close to the chassis.
Ground one leg to the chassis ground of the string. Sometimes bypass
capacitors are used to chassis ground, if necessary. I've not needed the
latter, often.

Make certain that all RF components are positioned, so the leads and
wired components are as short and direct as possible.

Front panels should be metal and grounded, or use foil on the back-side
of non-metallic panels. Use non-metallic shaft extenders on controls
that aren't or shouldn't be grounded to the front panel. This is especially
true with any variable caps that are isolated from the front panel, such as
the antenna trimmer variable, etc.

As usual, the comments in the former posts are sound advice.

Hope this helps.

Mike
_________________
Radio experimenting is serious fun, so have fun and don't get too serious!
http://www.peeblesoriginals.com

[peeblesoriginals]

Members,

I just sent "Rob" an entire set of plans for what he is intending
to build. It's a real neat 3-tuber set, and if you PM either one
of us, I believe we can send a set of plans to you for this set.

This set has a schematic in the back of an old RCA tube manual.

I have the book that this set was featured in, in it's entirety.
The book is an old Popular Science publication, that my original
mentor gave to me, when I was about 10. . .54 years ago

Mike
_________________
Radio experimenting is serious fun, so have fun and don't get too serious!
http://www.peeblesoriginals.com

[exray]

[Rob Lenski]

[peeblesoriginals]

Rob,

I'd stick with the 1U4/1U4/3Q4 line-up.

1T4 or 1L4 will work for the 1U4's, but I'd still stick
with the 1U4's, if possible.

http://www.peeblesoriginals.com/catalog/84.php

In this case, I don't think that output tubes should be
used in place of the two RF tubes. That's kind of a 1 or
2-tube deal, where one is either untuned RF, or AF amp.

With one stage of tuned RF, and the detector stage, coupled
to a good audio amp, this set should "rock"

It may work OK, but that is a well-thought-out set, and
I don't see any place I would substitute anything.

Mike
_________________
Radio experimenting is serious fun, so have fun and don't get too serious!
http://www.peeblesoriginals.com