[Milsurplus] possible modifications for RBC receiver?

[George Babits]

Hi Ken,

Well, if I need to have a product detector, I just use my Collins S-Line 
gear.  Works great and saves a lot of ruination of older receivers.  Nothing 
wrong with the older receivers and I much prefer to use them the way they 
were designed to be operated.

73,
George
W7HDL


----- Original Message ----- 
From: "Kenneth G. Gordon" <kgordon2006 at frontier.com>
To: <Milsurplus at mailman.qth.net>
Sent: Sunday, September 18, 2016 6:53 PM
Subject: Re: [Milsurplus] possible modifications for RBC receiver?


> On 18 Sep 2016 at 18:34, George Babits wrote:
>
>> Dave,
>>
>> The RBB and RBS are grest receivers.  Why pervert them with a product
>> detector?   Just turn off the AVC, turn the BFO on,  and  you can copy 
>> SSB
>> just fine.  Over the years I have picked so many receivers that have been
>> ruined with crappy product detector conversions that I just can't imagine
>> why people do that.  Is it just so the S meter will read (maybe) on a SSB
>> signal?
>
> No. In order for THAT to work, one also has to pervert the AGC system. The 
> AGC voltage
> must be taken out of the IF chain before the detector so that the BFO 
> doesn't lock the AGC
> voltage high. All AGC systems of the day took the AGC voltage off the 
> detector.
>
> Actually, a GOOD product detector results in far more "recovered audio", 
> greater apparent
> receiver sensitivity, and reduced noise than the old diode detector ever 
> could.
>
> Furthermore, a GOOD single-triode product detector will operate as a very 
> good AM
> detector when the BFO is turned off. Although I haven't examined that 
> detector (used a lot
> by Collins and Heathkit) in any detail, I suspect that with the BFO 
> voltage turned off, the
> detector acts much like an infinite impedance detector for AM. But that is 
> only a WAG.
>
> That single-triode PD is simple and works very well. Most other PDs I am 
> familiar with are
> MUCH too complicated. One of the early PDs shown in handbooks of the 
> period, uses
> THREE triodes. Another uses a 6BE6 mixer tube. I don't like either one.
>
> After all, all a PD is is an audio-frequency mixer. In fact, the Pullen 
> Mixer makes an
> excellent PD.
>
> Anyway, I modified an almost new BC-779 many years ago with that 
> single-triode PD, and it
> made an immense improvement in the receiver. I was amazed at the 
> improvement. It
> became my favorite receiver.
>
> But as you say, George, most modifications were never thought out 
> thoroughly and just
> plain stink. And this includes many which were published in the ham 
> literature.
>
> The OT who designed the gear to begin with were no dummies. They knew what 
> they were
> doing.
>
> Ken W7EKB
>
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