Steve
Society Members
vintageradio.co.nz
Posts: 727
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Post by Steve on Jun 11, 2021 0:02:19 GMT 12
But wait... here is my other Pacific 5V, with an earlier serial number and a 47 output valve. It looks very original apart from a couple of changes. T51 transformer, slightly toasty looking, and predominantly Aerovox componentry.  Ok, I'll stop looking now  |
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Post by Philconut on Jun 12, 2021 13:11:58 GMT 12
From my understanding the volume control achieves two results as you turn it down - wiper towards the aerial coil end. 1. It shunts the aerial coil primary thus reducing the signal applied to the mixer tube. 2. It increases the cathode voltage of the IF tube thus reducing its sensitivity.
I have found the discussion very stimulating and I will be revisiting the anode bend detector, a 27, which is only a medium slope characteristic, in my 1930 Clarion set. It has a 20k cathode resistor and a 30k plate resistor.
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Post by Philconut on Jun 12, 2021 13:25:20 GMT 12
I've just had a closer look at the 5B & 5C diagrams and suspect that there is an error in the 5B one. The 5C has the 25k/25k divider for the screen voltage and the completely separate 50k resistor for the IF cathode/volume control circuit which makes much more sense. As shown in the 5B circuit, the screen voltage will also change depending on the volume control position.
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Steve
Society Members
vintageradio.co.nz
Posts: 727
|
Post by Steve on Jun 12, 2021 16:37:35 GMT 12
Thanks for that info John, I also note that the volume control, when fully down, changes the screen grid voltage divider effectively from a 25k/25k to a 25k/75k arrangement, raising the screen voltages?
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Post by Philconut on Jun 12, 2021 19:12:44 GMT 12
Yes, it's that part that makes me think the circuit is in error - maybe even the set wiring?
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