[ARC5] 10 meter BC-454 - testing

[Kenneth G. Gordon]

I am starting the testing of this receiver.

First of all, I had to get my URM-25D back in operation. That took a new 6X4W.

In addition, I have installed a 12SG7 in the receiver's RF stage instead of the 12SK7.

I'll install the 12SK7 and retest just to see how much of a difference the 12SG7 makes.

I have not done an accurate S+N/N ratio either.

If we accept that the URM-25D is fairly closely calibrated, I can easily copy a 1 microvolt 
signal at 30 MHz when in CW, and can still hear it with the BFO off in AM when modulated 
50% with a 400Hz audio tone.

Of course, it is very much weaker in AM, and I doubt if I could copy a voice signal at that 
level, but I can hear the tone.

I would have no trouble copying a 1 microvolt CW signal. In fact, I can still hear the carrier at 
0.5 microvolts input.

I am using the MX-1487 50 ohm adapter, but there is no difference with or without it.

If the signal generator is properly calibrated (I'll check that next week), I am impressed...and 
very surprised.

At this point, the reciever drifts pretty far from turn on to 30 minutes later but it does finally 
settle down. I'll check that later too.

I just tested the audio power output with a resistor in place of the speaker. I found a 10 watt 
521 ohm wirewound resistor in my junque which I have used to accurately measure audio 
power output.

With an input of 200 microvolts at 28 MHz, modulated 50% with 400 Hz, measured pk-to-pk 
audio voltage into that 521 ohm resistor, is 40 V before distortion occurs as measured by 
both my 'scope and my VTVM. Both read the same.

If I have calculated that correcty, that is not quite 384 mW, which is within spec. That sounds 
more reasonable too. 

As I said, it hurts my ears with the volume all the way up. There is more than enough audio 
output, even with a speaker. From this, I still cannot figure out why the early hackers decided 
they needed an additional audio stage.

BTW, although I am not sure what is causing this, the BFO signal is modulated with 
something that sounds like AC. I suspect that there may be a cathode to filament leak 
somewhere, perhaps in the 12SR7 DET/BFO tube. 

Ken W7EKB