[Premium-Rx] R-220 VHF Rx

[Bruce Gentry]

I had an R-220,  I think all were built by Motorola,  but traded it and 
the manual away. I had an acquaintance who had several of the receivers 
and had restored many more. Aside from obvious problems like bad valves 
and power supply problems, the large 455 KC. IF filters on the bottom of 
the receiver are usually the problem when sensitivity is very poor. The 
culprit is silver mica condensers that are now over 60 years old and 
have developed dendrites and silver migration. The bad thing is they are 
in the sealed IF filters that are potted with resin to try to prevent 
anyone from repairing or altering the filters, under the guise of 
"exclusive sealed selectivety".  They called and trademarked these 
their  Permakay filter,  and used them extensively for decades in land 
mobile two way radios. In the early 1960s, the FCC required land mobile 
rigs to change from 25 KC channel spacing, and large numbers of older 
rigs and filters were easy to get at attractive prices. I do recall 
people soaking the filters in acetone, usually for a few weeks, to 
dissolve or at least drastically soften the potting compound so it could 
be carefully scooped out. The filters are interactive L/C, so to narrow 
the response the condensers that coupled  one stage to the next were 
replaced with smaller ones and the resonating condensers increased to 
stay on center frequency. In the case of the R-220,  the condensers are 
replaced with identical values. This process requires patience and care, 
but is worth the results. Once the filter is restored and working 
properly, it is wise to re-pot it with wax.  There are silver mica 
condensers elsewhere in the circuitry as well, replacing them is also 
wise. Once restored, these receivers perform comparably to an Eddystone 
770R in good condition, but  the Eddystone sounds far better for FM 
broadcast reception. The R-220 is  of the late 1940s or early 50s when 
American VHF practice was still  gaining experience, so don't expect the 
sensitivity of newer rigs. Also, the power transformers  are marginal 
and tend to fail. If you are operating it on 50 cycles, keep the power 
supply module cool, avoid giving it more than 220 volts, and try 
reducing it to about 210 once you get it restored and see if it performs 
satisfactorily at the reduced voltage.  Enjoy restoring this American 
early Cold War era rig!


       Bruce Gentry, KA2IVY


On 5/22/18 3:19 PM, agccyg wrote:
> Good Day to All,
>
> It is rally season....
> A Motorola produced R-220 VHF receiver fell into my hands over the 
> weekend.
> It's 40Kgs nearly killed me. But I survived...!
>
> I have been told it's deaf, but I have not powered up yet. A little 
> exploratory work must be done first.
> Can anyone help me out with a service manual.
>
> Best 73 to all - Andy G7JQL
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