[MRCA] Navy MAK day two!

[J Mcvey]

 The old mica capacitor color codes are tricky. Each manufacturer seemed to have their own "style". You have to know the mfr then look up what the postions of the dots mean!  It's a real PIA. As brock says, measuring is the best way to go.Even with that, the value may be be skewed by high ESR , but will generally be in the ballpark. The caps have probably changed with age and that's why the adjustment is out of range. If they are leaky, this will also affect the Q of the circuit as well.

    On Monday, July 22, 2019, 10:04:50 PM EDT, B. Smith <smithab11 at comcast.net> wrote:  
 
 Be sure and check the grid dip meter on a near by receiver for the exact 
frequency while you are dipping. Why not just disconnect one of the caps 
and measure its value? Have you tried some crystals on a lower frequency 
below such as in the 3.5 , 3.6 range? That would confirm you theory.
Z

On 7/19/2019 9:00 AM, Ray Fantini wrote:
>
> Spent a little time playing with the MAK last night and developed a 
> new theory. Although the radio has a published specification of being 
> capable of operating from anywhere in the 2 to 4 MHz band the four 
> channels that were in the radio when I got it were all within 2.1 to 
> 3.0 MHz The output tank has six taps that can be selected in advance 
> for each channel depending on the frequency of that channel and that’s 
> how they match the PA for the band that the radio is using but the 
> oscillator only has a signal LC circuit for each of the four channels. 
> Using old school techniques learned from Mr. Smith brought out the 
> AN/PRM-10 grid dip meter and found that I can check the resonance of 
> the four oscillator tank coils and found that with the coil backed out 
> to the end of its range it only peaks at around 3.7 MHz, and that’s 
> with the slug backed all the way out of the coil. There are four 
> capacitors located just under the coils, one for each coil and I am 
> going to now speculate that maybe the reason the capacitors are so 
> easy to get at is because they were intended to be swapped out 
> depending on what section of the band the radio was on? And perhaps by 
> changing out to a lower value I will be able to get the oscillator to 
> osculate. Know for a certainty that until the LC tank for the 
> oscillator tunes to 3.885 the oscillator won’t work, just need to 
> figure out what capacitor I need. If I were smart I would know two 
> things. First, what’s the value of the existing capacitors? Take a 
> look at the picture. And second, what would the value of the new 
> capacitor be? Recall something about determining resonate frequency of 
> a tuned circuit and knowing the value of C can determine the value of 
> L and with that knowledge be able to determine what C would be at 3.9 
> MHz but just not that smart. If someone can tell me the value of the 
> capacitors, all four are the same then I will know where to smart with 
> smaller value capacitors and try to determine where the tuned circuit 
> is at that time.
>
> Think that they are 50 pf being green is 5 and red for a multiplier is 
> two zeros? Or would that be 500 pf?
>
> Ray F/KA3EKH
>
>
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