[ARC5] Deaf BC-454

[J Mcvey]

If I understand this correctly, you have audio "blips" at the det output INSTEAD of a tone? 
Did you disable the osc/mixer ( pull mixer tube) when you did that? Thid will kill the RF an mixer stages and leave the IF and audio operative. If not,Maybe there was destructive interference from the previous stage?
'blips' would  indicate some kind of oscillation to me. Oscillation is often caused by bad bypass caps. ( in the pots)
According to my manual pin 4 is not used on the 2nd if , so the IF is just picking up a very attenuated signal to begin with.


    On Monday, September 26, 2016 8:35 AM, Brian <brianclarke01 at optusnet.com.au> wrote:
 

 Hello all you helpful folk, I have checked all the resistors, including the screen Voltage divider chain – all OK. I checked all the fixed capacitors and replaced all the faulty ones. One at a time, I replaced all the tubes – none had been cold, and none was excessively warm. I’ve loosened off all grounding screws a couple of turns and retightened, and with the potted capacitors, loaded the screws with Almanox before reaffixing the caps – so, I know all grounding points are OK.I have set the HT at 170 V and the screens get 73 V. Current drain is about 35 mA. Operating the RF gain control gets all the cathode Voltages rising in step.For a signal generator, I use an HP 8640 B and for an audio level meter, a Marconi terminating output Wattmeter.I measured along the chain from antenna input right to output of the 3rd IFT. All the results show this set as being attenuated between 40x and 5000x. For instance, when I apply 1 V of 1415 kHz 30% modulated by 400 Hz to pin 4 of the 2nd IF amplifier, I get 4.6 mW AF output; the op and maintenance manual says that 110 mV should give 10 mW AF out. So, attenuation is 10 log 10 / 4.6 + 20 log 1000 / 110 = 3.37 + 19.17 = 22.5 dB down.The audio output waveform from the detector to the output side of the AF output xfr is 400 Hz blips spaced 20 ms.In all my repairing of Command Rxs, I haven't met such a deaf one before. Usually when I've aligned the IF strip, the rest is pretty close. But not this time. Pain. 73 de Brian, VK2GCE. From: J Mcvey Sent: Monday, September 26, 2016 12:17 AMTo: Brian ; arc5 at ix.netcom.com ; ARC-5 Subject: Re: [ARC5] Deaf BC-454 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? 

   
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