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Old 4th Jul 2011, 1:56 pm   #1
frglee21
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Default Cossor Melody Maker 501 Tone Corrector Capacitor

Hi All,

I'm about to change the wax capacitors on my second valved radio - a Cossor Melody Maker 501.

For the life of me I can't find the tone corrector capacitor. Is it likely to be a wax capacitor as on the DAC90A and if it's been removed in the past would this have any effect on the performance of the set? - though I can't see any evidence of it being snipped out.

According to the circuit diagram it's C23 - a 0.005 microfarad capacitor connected to the anode? of V4

Assuming I'm looking at the underneath of the (rimlock) valve base correctly the anode of V4 is the second pin clockwise from the "pip"? There are two wires connected to that pin - one goes to the output transformer and one to V5 but no sign of a capacitor.

The only other 0.005 microfarad cap. I can find is the aerial coupling capacitor.

I'm still very much fumbling my way round here so any help would be much appreciated.

Regards, Lee.
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Old 4th Jul 2011, 2:14 pm   #2
westcliff
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Default Re: Cossor Melody Maker 501 Tone Corrector Capacitor

It's not on the output transformer, is it?

Gus.
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Old 4th Jul 2011, 2:35 pm   #3
oldticktock
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Default Re: Cossor Melody Maker 501 Tone Corrector Capacitor

Here it is see pic

Chris
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Old 4th Jul 2011, 3:42 pm   #4
frglee21
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Default Re: Cossor Melody Maker 501 Tone Corrector Capacitor

Hello Gus and Chris,

Thank You for your very quick replies.

C24 in Chris's diagram is the large 25 microfarad metal can capacitor shown in my picture; the bottom of the picture is the back of the chassis.

There is no capacitor of any type in the area shown in the diagram or the photograph so it looks like it might have been removed for some reason?

However, I'll have another look when I get home from work.

Best Wishes, Lee.
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Old 4th Jul 2011, 4:13 pm   #5
geofy
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Default Re: Cossor Melody Maker 501 Tone Corrector Capacitor

This seems a very crude method, a leaky capacitor could short the anode to the chassis.

In the AC/DC version the same capacitor is across the primary of the output transformer which doesn't have the tap used to use part as a ht choke. A capacitor across the secondary could be used if tone correction is really needed or just leave it out.

Last edited by geofy; 4th Jul 2011 at 4:21 pm.
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Old 4th Jul 2011, 8:04 pm   #6
Cobaltblue
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Default Re: Cossor Melody Maker 501 Tone Corrector Capacitor

The original Cossor service Data and the BRTR data sheet show the tone corrector across the primary of the LS transformer. I see the trader sheet shows it between the anode of the output valve and the grounded side of the speaker tranformer secondary. On a sample scrap 501 Chassis I had to hand which uses the loctal series of valves the tone corrector is mounted on the bottom of the 7Y4 (rectifier)between pins 4 (unused) and pin 7 the Cathode. A wire then connected pin 4 of the 7Y4 to pin 2 of the of the 7C5 (output valve). I found it was in the same location on a 494 I checked. I don't have a B8A version of the 501 on hand to check (they are all in Exeter) but they may have used a similar trick. Worth a look
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Last edited by Cobaltblue; 4th Jul 2011 at 8:06 pm. Reason: forgot to state function of the valves
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Old 5th Jul 2011, 10:33 am   #7
frglee21
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Default Re: Cossor Melody Maker 501 Tone Corrector Capacitor

Ah! the mists have cleared a little!

So, the location of the tone corrector depends on the type of valves used. I could then, have been looking at it without knowing. I have read that later models - mine's 1951 - used a 0.001 microfarad capacaitor instead of 0.005.

Mike: It's not mounted on the rectifier valve base or on the output transformer as Gus suggested but I'm now sure that it ain't gone missing!

I'm replacing all the waxies anyway - there's only five - and I'll see how it goes from there. I'll also get hold of the Trader sheet and Cossor's Service sheet to see if there is any mention of the B8A set-up ( Yes, I know they are up there at the top of the page )

Thank You to everyone for your help. I do try to find things out for myself before posting a request for help but sometimes i need a few pointers as to what I'm looking at and where to find it

Best Wishes, Lee.
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