canadia-ma: Marconi 206/7 components list error?

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Forum » Apparate: Physik - Radios - bis TV » MODELLE IM RADIOMUSEUM » canadia-ma: Marconi 206/7 components list error?
Alistair Thomson
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25.Nov.18 00:14

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This is my first renovation, and my first post, so I'm a bit reticent in case I have my finding wrong. But I don't think so!

This is the Marocni 207, electrically identical, I believe, to the 206, and I'm looking at R18 / R19 in parallel, which feed voltage to the screen grids of the first & second stages of the RF path. The components list shows these as 2K6, 2W each, to give a combined value of 1K3 at 4W.

In my restoration of serial no. 4511, the parallel pair shows 40K instead of the advertised 1K3. That's a clue! But the resistors themselves have colour coding for 26K, not 2K6. Looking at the specs for these two valves (sorry, I can't get used to calling them "tubes," even though I now live in Canada), it's clear that a value of 1K3 for the resistor pair just doesn't work. 13K is better.

So I'm postulagting that the components list has the values wrong. Does that make sense? If I get agreement, I'll re-post this as information.

I'm finding that antique radio restoration is a combination of detective work, logic, and hard-earned knowledge. I love it!

Rolf Beckers
Rolf Beckers
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26.Nov.18 16:12

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Dear Alistair,

It was my gut feeling too that a resistor of 25 to 50 kOhm would be right. But when I looked at a bunch of my circuit diagrams I realized almost every value from 1 kOhm to 50 kOhm. I must admit that I've not the expertise to explane this. May be one of our experts at RM can explaiin this.