[R-390] Carrier Level Meter Issues

[Renee K6FSB]

Hi All-
I replace C551 on sight....on 16 (IIRC) IF decks I have never found one 
that does not have leakage current ( maybe just my bad luck, tested on 
Sencor LC102)...oil/paper....i went with mylar anywhere between 1.5uf or 
1.8 uf ( I liked these best) to 2.2uf.
I machined small rectangular aluminum cans (with teflon feed thru for 
the leads) for them to fit in the original space. and as Jordan suggests 
the 1.5uf will fit in the original can......I drill a small hole before 
heating to disassemble the can. I do not like hot oil everywhere......
some of the postage stamp Micas are starting to have shorting issues due 
to impurities, moisture intrusion and what is called silver 
migration...so do not rule them out because they are mica.
Renée, K6FSB


On 3/6/22 4:25 AM, Jordan Arndt wrote:
> Hi again group...
>
> Any leakage of C551 will dramatically alter the AGC characteristics, 
> with the results of leakage being seen as a longer to much longer AGC 
> recovery time and a lower and "softer" AGC voltage.
>
> I rebuilt C551 in my three 390As using non-polarized 1.5uF @ 450Vdc 
> film caps which just fit inside the original square can. The result is 
> a "stiffer" AGC voltage, and a noticeably quicker return to receive 
> than with a 2uF cap.
>
> I use a restored Sprague TO-6 to detect leakage, and these film caps 
> show no measurable leakage at all, where all of the original C551 caps 
> clearly showed varying degrees of leakage. I'd expect that most, if 
> not all, of the original C551 caps are leaky by now and should be 
> replaced/rebuilt...
>
> 73...Jordan VE6ZT
>
> ----- Original Message ----- From: <gary.biasini at shaw.ca>
> To: "'Larry H'" <larry41gm at gmail.com>
> Cc: "'R-390 Forum'" <R-390 at mailman.qth.net>
> Sent: Saturday, March 05, 2022 10:13 PM
> Subject: Re: [R-390] Carrier Level Meter Issues
>
>
>> Larry,
>>
>>
>>
>> Thanks. In fact, I started on one tonight which will be the subject 
>> of a separate post once I do a bit more work.
>>
>>
>>
>> I checked the manual for the IT-11 and in fact, when properly 
>> calibrated, on the setting for “Paper, Mica, etc.” capacitors – i.e. 
>> anything other than Electrolytic or Mini-Electrolytic capacitors, the 
>> eye will not open if the leakage is more than 2 ua so, the C551 that 
>> I tested leaks less than 2ua.
>>
>>
>>
>> By the way, the threshold for Mini-‘lytics is 15ua and the threshold 
>> for Electrolytics is the 2ma.
>>
>>
>>
>> Thanks again for your response. 
>
> ______________________________________________________________
> R-390 mailing list
> Home: http://mailman.qth.net/mailman/listinfo/r-390
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:R-390 at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html