[RadioDR401]

I just finished restoring a model 89B code 123 that I got from a friend.  It was in pretty bad shape so I don't know how well or even if it played before the restoration.  I fired it up and did an alignment after which I am able to receive a few stations across the broadcast band.  Except for one station that is 3 only miles away, the others (about 30 miles away) are really weak, touchy to tune and hissy (white noise not interference).  The audio is not garbled and actually sounds pretty good except for the hiss.  I moved the antenna lead from the input clip to the grid cap on the 44 RF amp and the weak stations sound about the same.  Then I moved it to the 77 oscillator and again the weak stations sound about the same.  I'm wondering if there is a way to see if the RF stage is actually amplifying the signals since it seems like the set would work about the same without it.  I did rewind the tickler and changed the 36 to a 77 which seems to be working great.  All of the RF stage voltages are really close to spec and the coils all have continuity and resistances close to the values on the schematic.

[Radioroslyn]

If your RF amp wasn't working your symptoms would be poor reception at the ant post and grid cap of the rf amp, signal would be good at the mixer grid cap. I'm thinking that you've got a weak mixer, IF amp tube , or alignment issue if the plate, screen, and cathode voltage are correct. Oh also have a look at the bandswitch contacts are clean and making good connection.

GL

[RadioDR401]

Thanks for the tips!  I also hit upon another idea to test the stage gain.  I metered the AVC line with the antenna wire on the clip, then on the 44 grid and finally on the 77 grid.  The RF stage is definitely working since I got about -2.3 volts from a weak station with the antenna on the clip vs about -0.8 on the 77 grid.  The station sounds about the same but clearly the RF stage is working.  I'll try the IF stages next as you suggested.

[RadioDR401]

Well I wound up changing out my 75 detector/1st audio/AVC and it cleaned up the hiss nicely plus weak stations come in much better.  On the tube tester, the old 75 tested good but I noticed an significant imbalance in the diode plate readings with one much weaker than the other.  The new 75 has almost identical readings so I'm thinking is was somehow messing up the AVC line back to the RF and IF stages.  Best to have a few spares to swap around.

[Radioroslyn]

Hey Dave,
If you have some time to kill take your old 75 tube solder a couple 1N34 across the pins that connect to the internal diodes. Solder them up high near the bakelite so you can plug it in. Maybe you can save it. A month or so ago I needed a 12Q7 (12v newer version of the 75) and ended up making up an adapter using a 12av6 or 12at6. Worked fine.

[RadioDR401]

Just a follow-up that some might find helpful.  I located a PDF file of the 1937 Rider Philco Radio Receivers alignment manual and found a section that discusses dial alignment.  Since I had replaced my 89 dial strip with one from Radio Daze, it turns out that my initial dial alignment was off by about 1/8".  After adjusting the dial/tuning cap I followed the Rider alignment steps which are slightly different from the official Philco procedures.  It resulted in much better overall sensitivity and improved reception on the low end of the band.  Below is the link for anyone that might not already have it.

http://www.silverslingshot.com/PDFFILES/...s_1937.pdf