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Hi;
I'm sure that this has come up in the past but what is the wattage of the big wire wound 6500 ohm resistor running along the back of the chassis apron, mounted on a rod? It runs between B+ and the chassis, is labeled part #60, and is parallel with a 1 mf cap. Also does anyone know what the value might be of the RF choke in series with the antenna input? The one in mine has unraveled so is it necessary to replace or is it some sort of wave trap designed to block transmission from a long extinct source that can be bypassed?
Regards
Arran
(This post was last modified: 01-18-2014, 11:42 PM by
Arran.)
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Arran
Same thing I think is used in 18, which is also almost identical.
So, if your voltage there about 220VDC, well, the resistor will dissipate 7.5W, so if you make it 15W it will be OK I think.
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I just sort of remembered people talking about using a 25 Watt job in that spot which seems awfully high, not to mention that 25 Watt resistors are not cheap. I don't know if 6500 ohms is a standard size. If it was a 25 Watt I was thinking of using two 13Ks in parallel if necessary. I think that the 18 is very similar in terms of power supply design, but I think that the waveband coverage is different.
The original resistor was unraveling, and so I took it out, but I can't remember what I did with the thing or the threaded rod and washers that held it in. I'm positive that I did not throw it away.
Regards
Arran
(This post was last modified: 01-19-2014, 12:31 AM by
Arran.)
Posts: 18,427
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Posts: 5,652
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I had better see what I have in my collection of Welwyn power resistors before hitting the order button, though I am planning on ordering from Mouser soon.
Regards
Arran
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Arran, as far as that choke in series with the antenna input, you can just jump it out. It was part of a wave trap ( with a mica trimmer ) tuned to the 260 KHz IF freq.
Back when the radio was made there was a lot of communications activity on those low freqs and sometimes a strong enough signal would bleed into the IF causing interference. Today, that LF band is pretty dead so the trap is no longer needed.
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