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Post by cadillaccharlie on Aug 5, 2021 8:12:12 GMT -5
Hi all !
I'm ready to wrap up restoring my Browning Eagle R 27/S 23. Recapped receiver & transmitter and it receives & transmits with a nice sounding ping on a dummy load. I have this final issue standing in my way before I can call it a wrap. When I give it a short key up it pings nicely each time & goes back in to receive audio. If I key it more than 5 seconds or say a long audio to check modulation, it will transmit & modulate but when I release the key the carrier cuts off but it will not give me back receive audio on the receiver. Sometimes it comes back after short consecutive keys but it is hit or miss ! The only way I can get the audio to come back on the receiver is to power down for a minute or so then power it back up. I have cleaned the transmit / receive relay contacts carefully with a dollar bill but it does not help. I'm pretty sure now that the relay is not the problem and I am leaning towards a tube issue such as the voltage regulator 0B2. I can leave the receiver on for hours with no receive issues at all. The issue always happens after a few keys of the mic especially the long keys . Sometimes I can get it back in receive audio after keying and speaking loudly into the mic then releasing. I ordered a new 0B2 tube to start with as that was a tube that tested marginal at best. The remaining tubes appear fine as they tested good and I get excellent audio on receive. Its only on a key up release switch back to receive that this issue happens. Any help is always greatly appreciated !
Dave
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Post by 2600 on Aug 5, 2021 23:18:59 GMT -5
Clearly the problem is not a contaminated relay contact. You cleaned it. Makes it sound like a worn-out relay contact. Do you have a DC meter? If you can find the PING capacitor, measure the DC voltage on the positive lead of this capacitor, especially when the receiver is being silent.
If the relay is causing this, you'll have a low reading.
73
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Post by cadillaccharlie on Aug 6, 2021 8:12:41 GMT -5
Thanks for your advice ! Being that these are two separate units & the B+ comes from the receiver through the transmitter then back to the receiver threw me off in my troubleshooting logic. My 0B2 tube tested bad and needed to be replaced anyway but now I see your point very clearly now. I do see some arching on the relay when it goes back to the normally closed position so I am looking at the total picture now. I will measure the voltage at the + side of the ping cap when I lose the audio. My first instinct was the relay causing the problem but I violated my own troubleshooting rules by not starting at the source and working backwards. The two units being separate threw me off my logic track a bit Thanks so much again !! You are a great help !
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Post by cadillaccharlie on Aug 6, 2021 16:06:09 GMT -5
Okay I measured 250vdc volts at the plus side of the ping cap. When I key the mic the voltage drops off to zero as the cap discharges. When I release the key, the voltage goes immediately back to the 250 vdc. After a long key then release I lose the white noise audio on the receiver but if I talk very loudly in to the mic while still holding the PTT on the mic and then releasing it. I can usually get the audio white noise back then. Sometimes I can key the mic but get no ping and the audio white noise will come back. The book says that the second oscillator(1/2 12AT7 tube) is voltage regulated by the 0B2 tube so now I am going to look at that area. The fact that sometimes I get no ping on transmit but the radio goes back to receiving audio white noise has got me scratching my head a bit. If I wiggle the 12AT7 tube sometimes, I can get the ping to come back very strong for a few times then it goes back to the same problem with no return receive audio white noise on key release. To make a long story short, I can short key the transmitter with a good ping and get back return receive audio white noise. I f hold down the key for 5 or 6 seconds or so then release, the receiver will lose receiving white noise but still have B+ on the audio circuit which could be the issue in the second oscillator where the 31.4 MHZ is attached to pin 2 of the 12AT7 second oscillator section who's voltage is controlled by the 0B2 VR tube. Hopefully I explained this well enough to make some sense Dave
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