Hallicrafters S-20R Project
 

I finally cracked open the S-20R I latched onto a few months ago.

When I first powered it up I could tell the audio amp section was working but no RF. It seemed like a stage was missing. I figured it was the usual wax capacitor that had seen better days or something similar.

What I found was interesting. The components were new (but not modern). By that I mean the caps and resistors all appeared new and shiny but of a '70s or '80s vintage.

A whole section of the converter/oscillator stage was missing! Just wires, resistors and caps hanging, not connected.

A shield had been added between the rf sections and the audio/power supply sections. While well made I don't think it's original since components jam right up to it and electrical tape used as insulation.

There are some interesting component substitutions like large wattage wire-wound resistors where a watt or less would suffice.

Anyway I think I have chased down loose ends and there are only a couple of components missing ... so far. A few wrong value components so I'll have to check the entire circuit.

Anyone out there with an s-20r? If so some pictures of the underneath would be helpful if they were handy.

It's alive! It's alive!

Wrapped up the repair and fired her up. Lo and behold it works. Very good reception an US AM/Broadcast band and 2 of the lower shortwave. Not much on band 4 (15.5mc to 44 mc ) but under less than optimal operating conditions.

More to follow.

15 mc. and up will be dead at night but you should hear something during hours of sunlight between you and the transmitter.

Around 26-28 MC you should hear CBs...

I know. I'm fairly close to an interstate so there should be some activity there. I'll have to dig into it. To complicate matters my RF generator appears to be dead on the highest band as well. I do get signal between 15 mc and 20mc (the highest working band on the rf generator) so that band is partially working.

Some tubes may not want to oscillate at higher frequencies. Trying another tube might work.

Good idea. The tubes are JAN types but there is no telling how old they are. I've heard that the S20R is weak in the upper frequencies but I should get something. Overall the performance on the lower bands is quite good so I am optimistic it can be tweaked up.

Don't expect great performance on the higher frequencies with your S-20R...it's a rig that's a little weak in that regard. Sounds like you've got her dialed in elsewhere, though!

Yeah, from what I've been kinda been able to "Read between the lines", lots of these older receivers technically WOULD "Receive" way above 30 Mc, but since precious little or nothing was actually transmitted up there, it was sort of a moot point...The old FM band was at 40-48 Mc, but almost none of 'em could demodulate an FM signal...I think it was a case of "advertising ploy' as much as anything...

Yeah that's what I have heard (and posted earlier).

I have not dialed in anything yet. So far I have restored a section around the the converter/oscillator (components and wires hanging unconnected) and remove some 'mods' and incorrect values.

It's a curious mix. Looks like someone tried to do a ground up restoration and quit.

However before I do too much more I'll have to figure out why my RF generator isn't working at it's high band. Sheesh.

Is the CB band around 27mhz still active? I honestly have not heard alot about CB since the cell phone era.

Oh, yeah...there's PLENTY of CB activity. Google "CB Superbowl" or something like that. IIRC it refers to Channel 6...which is where the high-power (1-10kW & more) CB "outlaws" hang out. Almost like a car stereo battle goin' on between some of these guys.

My mom's old house backed up to the interstate in Houston. Sometimes the signals would bleed over to the stereo. Even when set to phono!

BTW I am getting reception on the high band. It's uniformly low but its there. Including the CBers still up to their old antics.

What I see (or hear) is that around 15mhz where band 3 and 4 overlap, I get good signal on the high end of band 3 but weaker signal at the low end of band 4.

I think this tells me 1 of two things. Either there is a problem in the band 4 circuit or band 4 is just anemic which is a possibility.

Of course at this point I'm still in the basement and using just a piece of wire as an antenna. So I expect overall performance will improve.

I did pick up a couple of hams in Nashville yesterday afternoon (I'm in Atlanta).

BFO works for CW but not SSB.

Finished chasing down wiring mistakes and final changes. Also re soldered a bunch of chassis ground connections. Put it all back together and did the alignment. The IF was way off as electronjohn suggested. Big difference now. Excellent reception on all bands including the highest.

Latest aggravation: once I got everything back together the dial string on the bandspread started slipping. DOH!