[Milsurplus] BC-342/BC-344 Question

Sat Nov 9 07:29:45 EST 2019

Robert -

"I intend to produce a run of new collars for these caps, as repair 
efforts I've tried on the collars to date just haven't been very 
successful."

I have a few BC348 sets that use the same trimmers - How will you 
procure/produce these replacement collars ?

I my have to do the same for my sets.

Thanks

On 11/6/2019 10:09 AM, Robert Kilian wrote:
> Another capacitor-related area to be careful with is re-alignment.  
> The trimmer caps on the back of the RF/IF cans are held together by a 
> press-fit collar on the shaft.  These collars are often cracked, and 
> the slightest movement of the shaft will allow the spring tension 
> (intended to hold the rotor & stator apart) to overcome the tension of 
> broken collar, causing the rotor and stator to mesh, and shorting B+ 
> to ground.
>
> I intend to produce a run of new collars for these caps, as repair 
> efforts I've tried on the collars to date just haven't been very 
> successful.
>
> On 11/6/19 8:00 AM, Robert Kilian wrote:
>> Joe --
>>
>> Yes.  And those are the wax/paper units (black, rectangular, angled 
>> corners) so must be replaced for good measure (once you've gone to 
>> the trouble to removing those cans, you might as well, if not just to 
>> avoid having to repeat the process later). There are other Micamold 
>> branded capacitors in the set that are a mica-based (not wax/paper), 
>> those are usually red & square and problem-free for the most part.
>>
>> The manual for -342 (312, 314, 344) lists all of the capacitors, 
>> their composition, values, and locations which is very handy when 
>> overhauling one of these radios.
>>
>> Rob Kilian
>> K6RBK
>>
>> On 11/6/19 7:56 AM, Joe Connor via Milsurplus wrote:
>>> Thanks, Miles. One question: isn't there one Micamold carrying B+ in 
>>> each of the under-the-chassis RF boxes? Those concern me.
>>>
>>> Joe Connor
>>>
>>> On Wednesday, November 6, 2019, 11:40:34 AM GMT-4, 
>>> k2cby at optonline.net <k2cby at optonline.net> wrote:
>>>
>>>
>>> A number of years ago I did a complete overhaul of a BC-348R 
>>> (similar to the BC-342) and wrote up the results.
>>> I had no problems with either the “bathtub” capacitors or the actual 
>>> mica capacitors.
>>>
>>> Here are my observations regarding the “Micamold” (actually foil and 
>>> paper, having no relation whatever to mica) bypass capacitors:
>>>
>>> Eighteen .01 μF 500 Volt “postage stamp” paper capacitors are 
>>> scattered throughout the set and used primarily in plate, screen and 
>>> cathode bypass applications.
>>>
>>> Experience has shown that these have a nasty habit of deteriorating, 
>>> generally taking out any associated voltage dropping resistor. With 
>>> this in mind, a random sample of five was pulled out for testing.
>>>
>>> Subjected to an ohmmeter check with a Simpson 260, one showed a 
>>> resistance of 650k. The remaining four all tested above 3 Meg and 
>>> one went to infinity. While hardly spectacular, these results
>>>
>>> might be marginally acceptable in a non-critical application.
>>>
>>> An electronic capacitance meter showed values ranging from 21 nF to 
>>> 75 nF (.02 to .075 μF), bearing little relation to the specified 
>>> value of 10 nF.
>>>
>>> An EICO Model 950B R-C bridge, on the other hand, showed a far 
>>> different result. None of the five tested would produce a null of 
>>> the bridge circuit. Four of the five showed unacceptable leakage
>>>
>>> above 50 volts, and the remaining one bowed out at 80 volts.
>>>
>>> The final test was to apply 250 Volts dc and measure the resulting 
>>> current. The result was nothing short of alarming. Two capacitors 
>>> showed a bit over 200 μA and a third 420 μA. The other two,
>>>
>>> however, produced current that steadily rose, reaching a peak of 40 
>>> milliamperes, when the test was terminated. (The entire BC-348 is 
>>> supposed to draw only 40 to 50 mA when operating.)
>>>
>>> /The only reasonable conclusion is to replace each and every one of 
>>> them./
>>>
>>> The good news, if there be any, is that none of the offending 
>>> capacitors is located inside the Antenna, RF Amplifier, Converter or 
>>> HF Oscillator compartments, so these do not have to be removed.
>>>
>>> For the most part, they are on the back sides of circuit boards 271 
>>> through 274 and the two small circuit boards either side of the dial 
>>> lamp rheostat. It is easiest to clip the lead as it passes over the 
>>> top edge
>>>
>>> of the board and then physically yank the capacitor off its other 
>>> lead with a pair of pliers, being sure the remaining pigtail doesn’t 
>>> short to anything else. The capacitor can be replaced with a much 
>>> smaller
>>> .01 μF 500-Volt ceramic capacitor wired to the front terminals.
>>>
>>> Miles, K2CBY
>>>
>>> Miles B. Anderson, K2CBY
>>> 16 Round Pond Lane
>>> Sag Harbor, New York 11963-3821
>>> Phone: (631) 725-4400
>>> FAX: (631) 725-2223
>>>
>>> e-mail: k2cby at optimum.net
>>>
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>>
>
>
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