[ARC5] Deaf BC-454

[WA5CAB at cs.com]

With a consistant -20dB sensitivity across the entire tuning range, my 
guess would be either seriously low supply voltage (like screen voltage) to all 
or most stages or one stage is dead.  

In a message dated 09/25/2016 09:27:54 AM Central Daylight Time, 
arc5 at mailman.qth.net writes: 
> The AGC is effectively shorted out at max volume on the BC-454. 
> 
> I once encountered strange issues with an ARC-5 radio, which was traced to 
> a mis-wired front panel plug-in.
> The gain control ground ran through the audio output winding!  This caused 
> poor gain, distortion and oscillation.
> 
> Did you restore the "capacitor pots" ?
>  don't remember ever finding a bad half watt resistor in one of those 
> radios, just bad "paper caps" in the "pots"
> I cut them open with a pipe cutter and replace them with ceramics, then 
> solder the pot back together. Looks "legit".
> 
> The 7K /10W wire wounds are often bad, which provides screen voltages 
> could cause gain issues too.
> 
> If you have a scope and RF generator , you can check divide the problem in 
> half by checking the IF chain.
> 
> 
> Maybe it's just a bad RF or MIxer tube? 
> 
> On Sunday, September 25, 2016 4:27 AM, Brian <brianclarke01 at optusn
> et.com.au> wrote:
> 
> Hello Dave,
>  Thanks for the thought. That’s exactly what was wrong with a Navy R-1051G 
> I have - but not this BC-454-B. I checked the banana plugs for the RF coil 
> set and all the IFTs – they were all OK. 
> When I wrote yesterday, I had only aligned the IFTs and gotten uneven 
> response across the spectrum. So, today I did a really thorough alignment of 
> the front end, with the result that 100 uV at the antenna post gives 1 mW 
> audio output across the whole spectrum of 3 to 6 MHz. So, the set is about 20 
> dB deafer than all the other Command receivers I have aligned. This set is 
> still approximately linear up to 300 uV antenna input, but after that the 
> audio output doesn’t increase. 
> What next? Over-active AGC?
>  Cheers, Brian, VK2GCE.
> 

Robert & Susan Downs - Houston
wa5cab dot com (Web Store)
MVPA 9480
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