GE Model 429 "Dial Beam" AM Radio

My dad had this radio in his living room in pieces.  Someone had tried to fix it and he picked it up at a garage sale for a few dollars.  The speaker was missing, the knobs were missing,  pilot light was burnt out, and it was covered in dust, dirt and grime.  Though, it's a nice looking radio and it caught my eye so I decided to fix it up.  Here it is the way I found it (with some knobs added for testing).





Nifty "Dial Beam" logo.


The radio is a typical "All American Five" tube radio with a 12AV6, 12BA6, 12BE6, 35W4, and 50C5.  This tube lineup was used in millions of radios.  If you are interested, there's a great Wikipedia article on the All American Five design. 

I hooked up my test speaker and powered up the radio. It had the typical 60hz hum that you get when the filter capacitors have failed so I replaced those first.  Here you can see the new ones soldered in.  I left the old red paper capacitor in place for comparison.  The new ones are the black ones to the left.



For those not familiar with this problem, it's pretty common.  Paper Electrolytic Capacitors tend to fail on old radios.  They are used in the power supply along with a rectifier tube (35W4 on this radio)  to convert your AC line current to DC.  When they fail, all you will hear on the old radio is a loud hum.  Changing the volume or station won't change the hum.  The only thing to do is to replace the old capacitors with new ones. It's a common problem so I keep several on hand.

I didn't have a speaker that fit properly so I ordered a few on line.  None seemed to fit just right.


However, turns out, my test speaker was exactly the right size, but had a lot of tears in the cone.  I awkwardly patched them with LocTite Go2 glue which is a really great all purpose glue.  It is strong, but somewhat flexible and glues most anything.  It didn't look pretty, but at least the speaker wan't full of holes any longer.



I still had weak and garbled audio at the speaker so I started to suspect the grid coupling capacitor that sits between the first audio stage (12AV6) and the control grid of the final audio stage (50C5).  It's what connects the audio signal between the tubes.  If it was off value, or leaking, it could be contributing to audio problems.  Unfortunately, this one was not going to be super simple to replace.  It was a multi-segment capacitor and no markings on the value.  The leads were mixed in with other wires and multiple components were soldered to each post.  Fun.



Since I didn't know the values of the K71J670 Multi Segment Capacitor, I was going to need to find a schematic of the same, or a similar radio.  I did some searching.  There was a schematic on RadioMuseum.org site, but I wasn't sure if it had the capacitor.

After a bit of searching, I struck gold on the Nostalgia Air Web site!  They had a schematic for a  GE 412,  that was very close.  The schematic showed the different sections of the capacitor and their values.

I used this as a guide to replace all the different sections of the old capacitor with brand new capacitors.  After replacing them all, the radio worked perfectly!!

However, I had to know...  Now that I had the capacitor out, I decided to test each of the sections to see what state they were actually in.   I  tested each section with my meter.  Here's the listed, and actual values as tested.

Section	Schematic	Listed Value	Actual Value
1	C11	.002 uf	.0022 uf
2	C10	400 pf	360 pf
3	C12	220 pf	210 pf
4	C12	.005 uf	.005 uf

Wow!  Actually tested pretty good!!  At least, the capacitance values are correct. (My tester does not test leakage).   Maybe the capacitor was fine.  (Hmmm... did I hook up both wires of the antenna properly when I tested it?)  Oh, well, it's got new capacitors now.

I gave the case a good polish, replaced the burnt-out dial lamp, replaced the missing case screws, and cleaned up the dial.  The plastic face had a lot of dirt behind the plastic and I cleaned it.  This removed the paint from the numbers so I had to repaint them with fresh paint.



I put it all back together with new knobs and brought it in to work where it sits now.