[Boatanchors] Re: Collins R-388 vs 51J4

[jeremy-ca]

Ive found that a good portion of the hum blamed elsewhere is due to the AC 
line bypass caps. Replace with an AC my 30 years of ownership was one of the 
caps. Leakage as well as normal coupling to the chassis from .05 or .1 caps 
will cause hum as well as generate a shock hazard.

Carl
KM1H



----- Original Message ----- 
From: "Al Klase" <al at ar88.net>
To: "Bill Cotter" <n4alg at qx.net>; "Boatanchors List" 
<boatanchors at mailman.qth.net>
Sent: Wednesday, October 03, 2007 7:29 PM
Subject: Re: [Boatanchors] Re: Collins R-388 vs 51J4


> Hi Bill,
>
> Actually, that was my original comment, and I stand by it.  The R-388 and 
> 51J4 are similar in this respect.  You have to get back at least to the 
> 51J2 to see the difference.  I looked around the web, but couldn't find 
> the appropriate schematic.  I had one of these sets 20-some years ago, and 
> someone at the plant was kind enough to send a schematic, which I still 
> have.  The antenna input is a three terminal (A A G) affair connected to 
> floating primary windings on the RF coils (actually, the middle terminal 
> has 100K to ground to bleed off static)  Good engineering practice for 
> 1948 or so.  I'd wager the input impedance is 400 ohms or so, a good 
> compromise when you don't know what antenna will actually be connected.
>
> As someone pointed out, the military wanted good performance on a whip, 
> and the design got changed.  There was a article somewhere describing the 
> procedure for putting the primaries back in.
>
> For those who believe Collins could do no wrong, pull the rectifier tube 
> out of a 388/51Jx.  You'll find there still low level hum in the audio 
> output.  The output and power transformers couple magnetically.
>
> Al
>
> Bill Cotter wrote:
>> Robert,
>>
>> Examining the 51J4 schematic on the CCA site, the 51J4 uses the identical 
>> Hi-Z input design as the R-388 and 51J3 use.
>>
>> http://www.collinsradio.org/51J-4-_4th-ed-09-58_-Sec7.pdf
>>
>> I don't see the difference you are referring to regarding Lo-Z and 
>> well-healed civilians.
>>
>> 73 bill n4lg
>>
>>
>>
>>
>
> -- 
> Al Klase - N3FRQ
> Flemington, NJ
> http://www.skywaves.ar88.net/
>
>
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