Kolster K-22

[Bill R]

Today a 1928 Kolster K-22 radio followed me home. As if I don't have enough projects already. Found it at a local antique mall for the clearance price of $39. There was a couple looking at it to use as a display piece (potential repurposing project). When I looked at it and explained what it was and dated it for them they thought it would be better if I took it and restored it . Anyway, a couple of things, I have never worked on a TRF set and I am sure the theory is simple but I would appreciate any help and insight folks may have. I also do not have experience with electrodynamic speakers. The cabinet has the usual bad finish and peeling veneer on the outside, but open the doors and the inside looks perfect. Even the grill cloth looks great. It uses 4-26 tubes, an 27, 71A, and an 80 rectifier tube. I will post some pictures when I get it out of the van. It is much heavier than it looks. The antique mall was the wife's suggestion, so it is her fault. Love her!

[Electronic M]

Have you ever worked on a superhet with an RF amp tube before the converter (or mixer/osc.) tube. If so a TRF is basically 2-5 of those RF amps cascaded feeding the detector. Each amp has a tuned LC filter that tunes the AM band, and an amp tube the L part of the LC should be a transformer to couple the cascaded stages. If the tubes are good the L not open, the C's not shorted, the PS detector and audio good then it should pass signal. TRFs tend to be less selective and sensitive so unless there is a reasonably powerful station close by you will need a long wire antenna (50'-150') to get proper reception.

TRF radios with single knob tuning also can benefit from an alignment of sorts...If the tuned elements (L or C) are not ganged disconnect the mechanical linkage from one at a time adjust for strongest reception of a station, reconnect linkage and proceed to the next tuned element until all have been adjusted...If the tuned elements are ganged there likely will be individual trimmers to adjust to achieve the same thing.

[old_coot88]

Schematic here..
http://www.nostalgiaair.org/pagesbym...4/M0040094.pdf
Interesting vol. control setup.

[Bill R]

I have been looking at that as well. I have not pulled the chassis out yet, but there are 3 controls on the front. I know one is tuning, one has to be volume, but what is the other one. I see R4 on the schematic, looks like it would change the sensitivity or the final RF amp stage. I could see that controlling volume. HA1 and HA2 on the schematic look like maybe they are used for hum balance. One for the 26 filaments, and one for the 27 filament and pilot lamp. Maybe those are ganged and are the third knob on the front. That would seem odd, but I don't see any other controls on the schematic. Other than the switches of course, one for power and one for sensitivity of the antenna coil. I am not familiar with the speaker either. This looks like a large magnet with an armature that connects to the cone instead of a voice coil. I will get some pictures up as soon as I get it unloaded from the van and in the house.

[Bill R]

Finally got it out of the van. Here are a few photos.

[DavGoodlin]

Looks like everything is there and very restorable. Does that chassis slide out with a board under it?

I got a Kolster K-28 cheap at Habitat ReStore. It looks like the same set and schematic.
The speaker, knobs and the escutcheons were gone.
It looked traded it to another collector for a TV who wanted a "basket case".

[Bill R]

I don't know if it comes out on a board. I know the 20 21 22 and k27 are all basically the same. It is complete. Even the grill cloth looks nice. I don't even have a tester for the 4 and 5 pin tubes yet. This will be an interesting project.

[Sr.Radtastic]

Wow! 1928! That's as old as Mickey Mouse! Best of luck restoring your radio to its former glory.