[ARC5] Deaf BC-454

[Scott Robinson]

Folks,

What I do in these cases is signal injection testing. You need a signal 
generator with a calibrated output to do this.

Turn the genny all the way up and feed the last IF plate...and do use a 
coupling cap to avoid wrecking the generator output attenuator! Note the 
RF level and audio output.

Now go back to the grid of that stage and see what RF level it takes to 
get the same audio output. Most IF stages have a gain of about x50. 
Proceed back until you find  low gain or, possibly, less than unity 
gain, and there's the problem.

Converters and RF amps generally have lower gain, maybe X5 for the RF 
and x2 fro the converter.

Good hunting!

/scott robinson

On 9/25/16 7:17 AM, J Mcvey via ARC5 wrote:
> 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 optusnet.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.
>
> *On* Sunday, September 25, 2016 3:23 AM, you suggested:
>
> Remove the RF coil pack and I F transformers.  Check the contact pins to
> see if any of the banana plugs is missing the "leaf" contacts, causing
> that contact tone open.  Seen that.  If so, let me kniw and will talk
> about how to fix it.
>
>
>
>
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