A KLH 21 FM Receiver (2009)

I dug back through the AudioKarma archives to get this gem. The radio is now with my parents. My niece loves turning the knobs to make the radio do ‘funny’ things. If all goes well we’ll be listening to ‘Alice’s Restaurant’ during Thanksgiving dinner this year.

This is a very incomplete write-up, from before I cared to write these things and just wanted to get on with it. If you have any questions, please ask.


I got this at the Westford MA Radio Fair this year. And I paid too much for it, as usual. After a couple hours of use, one of the knobs cracked off; a poor repair job by the former owner failed. So disappointed.

By summer, I got fed up with the polyurethane somebody slathered on. I wanted this radio to be just like the one I remember from my favorite old book store, with a resident cat patrolling the stacks and classical music from this Cambridge-made gem. So, I stripped it back to the veneer. I applied a Walnut Danish Oil to lightly stain back from the slight bleaching of the stripping process, then Tung Oil to finish, polishing with 0000 steel wool, then a couple applications of finishing wax. I’m happy.

klh21a
Nearly complete KLH 21 – waiting to push those fragile knobs on for later

The original and grungy plastic grill cloth had shrunken over the years. I could clean it but a noticeable gap would always be there. It looked ugly. I ripped the cloth off the Masonite front panel, and replaced with an open monks-cloth from JoAnne Fabrics. It was expensive, $10/yd.

klh21d
Application of monks-cloth on KLH 21 front panel board

Of course, you have to accept some things to use the stuff; It ain’t the original cloth; and cloth is a loose term for the original material. The threads in the original was a white PVC-like monofilament, woven in the same fashion of monks cloth, but with the occasional wide noodle-like white thread and yellow thin thread. Perhaps it went: white noodle – yellow – white – white – yellow – white noodle…

Anyway, I accepted the ramifications of this less acoustically transparent fabric material in exchange for the VERY nice look of it. I put down a single thin coating of spray-on contact adhesive (not Super 77, too thick and gummy) to attach. To protect it from being so easily stained and warped, I sprayed it with a clear uv/resistant varnish. I dabbed woodworking glue around the edges of the Masonite panel to reinforce the cut edges; a little glue in the hole edges made cutting them out worry-free.

The cloth I used gives slightly more resistance to airflow than the original PVC cloth, and while I’m not sure how much this will impact speaker frequency response, I cannot say it won’t. It is also all cotton, and if you leave it unprotected and touch it with dirty hands, you’ve now got an essentially permanent stain. (ed. – Three nieces and seven years later, no stains yet…) The overspray of varnish helps to stiffen and set the cloth and help protect the surface.

With all of that said, don’t it look pretty?

Because I’d like to use the radio 24/7 (music for the bird room), I recapped it completely and replaced the rectifier diodes.

In this original write-up, I left out MANY details. Here they are:

I completely left out how annoying working on this was is; KLH equipment always seemed to exchange serviceability for look and size. Look at the PCB, IF strip and tuner section. Each one needed to be removed to get proper access to it. The boxes were soldered shut, and PCBs mounted in the most inconvenient way. The main filter can replacement and the alignment was easy however. This is still nothing compared to how bad restoring the KLH 18 FM tuner is.

The knobs? They were all cracked and nearly falling off. I wonder if the combination of UV exposure, chemical composition of the plastic and the compression clip retention design makes the knob susceptable to this failure mode. Anyway, I went on eBay to buy a parts unit from a similar KLH FM/Turntable unit for the replacement knobs.

I also left out the process of refreshing the rubber on the rubber-coated fabric surround on the speaker with Permatex Black Rubber sealant. I also replaced the foam gasketing along the front and pack panels. Because the case acts like a traditional acoustic suspension enclosure for the single speaker, some degree of air sealing is needed for best effect from the speaker.

klh21b
KLH 21 Out of Case for Alignment
klh21c
Front View of KLH 21 without front cover, re-‘gummed’ speaker

Since those replacement knobs are still so fragile, I held off from pushing them on until I was completely  done working on the radio. Alignment was completed with no issues. I did such a nice job, my girlfriend thought it was way too nice to abandon in the bird room. So, it shall be a gift to my parents for the formal living room.

OLYMPUS DIGITAL CAMERA
All done – ready to play

Would you like see a master’s work on this radio? See Phil Nelson’s KLH 21 here. Enjoy!

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