Hello All,

I have recapped and restored (NOS tubes, replacing frayed wiring etc.) a Hallicrafters S20R Ham receiver, which basically covers 550KC-40MC in four bands, and was produced 1939-45. I have tried aligning it as well, based on the original schematics.

My problem is that...the radio just isn't very sensitive as one progresses through the bands. BC is OK, but as one moves up through the bands to higher frequencies there is less effective reception or even 'hiss'. Band 4 (which tops out at 40MC) is virtually dead--no hiss, static etc. When I tested it using a CB walkie-talking @27MC there was click/thump through the S20R speaker when I pressed the transmit key, but at about 10 feet away there was no reception at all.

Is this insensitivity normal (I'm using an excellent antenna)? It's just that I've got an RCA 16T2 table model house radio from 1940 and it is much more sensitive on the higher frequencies 10-18MC, and the SR20 is supposed to be a specialist Amateur SW receiver?

Thanks.

I have a Hallicrafters S-20R myself. It's performance is great. The RF amp. in the front end helps make it that way. First thing I can think of, is the antenna connections. If you are using a long wire, jumper A2 and G together. Connect the long wire to A1. Also adjust the antenna trim for the best performance on each band. Clean the rotary band switch well. Swap the 6SK7 tubes around, see if any difference when doing so. Check all the B+ on each stage too. That's a start anyway. It should perform better than most radios.

What is the RF amp tube? Often, they will poop out at higher freqs. There may be a slightly different tube with better hi-freq response. Norm Leal might be able to help?
Doug

The RF amp tube is a 6SK7 in a S-20R Hallicrafters.
A 6SG7 might be better for more front end gain. won't hurt to try.

(As always on this forum), thanks for the advice. I've tried changing the 6SK7s around (including using a couple of NOS tubes) and the result is marginally better. I'll try the 6SG7.

Warren, as far as the 'antenna trimmers' are concerned, are you referring to the bank of 12 screws at the bottom of the chassis? In the alignment instructions I have, three screws for each of the 4 bands are adjusted in sequence; there are also 3 'pads', 1 screw for each band (there is no pad for Band 4, 15,2-44MC). I guess these are the ones you are talking about?

Cheers.

:The RF amp tube is a 6SK7 in a S-20R Hallicrafters.
:A 6SG7 might be better for more front end gain. won't hurt to try.
:

Hello again Leslie :

If you download the print from this site for the Hallicrafters S-20R you can see that CA, CJ,

Hi Warren,

Some of this message seems to be missing. Good old Cyberspace!

Leslie

: Hello again Leslie :
:
: If you download the print from this site for the Hallicrafters S-20R you can see that CA, CJ,
:

: Hello again Leslie :
:
: If you download the print from this site for the Hallicrafters S-20R you can see that CA, CJ, CG, CO, are all antenna trimmers. You can adjust those with the type and how long your antenna is for best performance.
You might also check the resistors in the RF gain circuits. Some may have gone up in value.

Thanks,

I can see that now on the schematic. More stuff to play with tonight in the workshop.

Checking the resistors (mostly dog bone type) is next.

Cheers.

: Hello again Leslie :
::
:: If you download the print from this site for the Hallicrafters S-20R you can see that CA, CJ, CG, CO, are all antenna trimmers. You can adjust those with the type and how long your antenna is for best performance.
:You might also check the resistors in the RF gain circuits. Some may have gone up in value.
:
:

I don't think gain, alone, is the problem. I would try a 6SK7Y or 6SG7Y. The "Y" suffix, as I understand it, is for a higher RF freq response specification.

My Hallicrafters S-40B uses an 6SG7 RF stage. At Norm's suggestion, I substituted a 6SG7Y to keep the higher bands from pooping out.
Doug

:The RF amp tube is a 6SK7 in a S-20R Hallicrafters.
:A 6SG7 might be better for more front end gain. won't hurt to try.
:

The Y at the end of the tube numbers as I know, has to do with the pin base material. The base of the tube has a yellowish color. Is made more not to drift at high frequency.