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 Re-wiring the Tone Control for Cambron radio.
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 Return to top of page · Post #: 1 · Written at 6:40:31 PM on 11 June 2016.
JamieLee's Gravatar
 Location: Clare, SA
 Member since 27 March 2016
 Member #: 1894
 Postcount: 501

As mentioned in my General Discussion post about my 1930's Cambron Console radio, the tone control pot has been disconnected from the circuit and simply sits uselessly, but the set really performs well now, however does need the tone back in the circuit to mellow up the sound, especially when there is a bit of white noise RF.
My bag of capacitors has finally arrived and I have zillions now of Electrolytic and polyester types.
It was mentioned that the pot must be connected to the "P- pin" of a particular valve.
Can anybody assist me in doing this? My main questions are
-Which valve? Line up= (LAK2, 6U7C, 6A6C, 6F6C, 5Y3GT)
-Which is the "-pin"? and how should I identify it? (I have a good multimeter)
-What value must I use? Electrolytic or Polyester"
-Do I connect the capacitor from the valve pin to the "sweeper" or Centre of the pot and ground one end of the resistor, or vice versa?
Any help is very much appreciated.
Thank you.


 
 Return to top of page · Post #: 2 · Written at 7:58:57 PM on 11 June 2016.
Robbbert's avatar
 Location: Sydney, NSW
 Member since 18 September 2015
 Member #: 1801
 Postcount: 1094

We know the line-up is actually EK2, 6U7G, 6B6G, 6F6G, 5Y3GT.

I don't recall the original suggestion, but you could try the following:

If you look at the back of the tone control, with the 3 connections upward, call the left one L (less) and the right one M (more).
Connect a 22nF 630V cap from the anode of the 6F6G (pin 3) to L. Connect the tone control centre terminal to ground. That's it.

Test it out. If you find the tone is too severe, decrease the cap to 10nF. If it isn't doing enough, increase the cap to 47nF.


 
 Return to top of page · Post #: 3 · Written at 10:18:47 PM on 11 June 2016.
JamieLee's Gravatar
 Location: Clare, SA
 Member since 27 March 2016
 Member #: 1894
 Postcount: 501

Cool ok will try that. Thank you!


 
 Return to top of page · Post #: 4 · Written at 8:16:16 PM on 12 June 2016.
JamieLee's Gravatar
 Location: Clare, SA
 Member since 27 March 2016
 Member #: 1894
 Postcount: 501

Oh no! my 22μF capacitors are all 450v! Are these no good, or could I use 2x 10μF instead?


 
 Return to top of page · Post #: 5 · Written at 8:37:58 PM on 12 June 2016.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 3791

Errrr! What?

22μF is not 22nF it is 0.022μF. If you want to get sound out of it don't go there with 22μF. That's a power supply filter and one of a voltage I will not put anywhere near a 5Y3 if the "B" Voltage is going to be 250VDC.

Marc


 
 Return to top of page · Post #: 6 · Written at 10:50:18 PM on 12 June 2016.
Robbbert's avatar
 Location: Sydney, NSW
 Member since 18 September 2015
 Member #: 1801
 Postcount: 1094

Yeah a nanofarad (nF) is 1000pF or 0.001μF. So you want a 22,000pF or 0.022μF .


 
 Return to top of page · Post #: 7 · Written at 11:09:02 PM on 12 June 2016.
JamieLee's Gravatar
 Location: Clare, SA
 Member since 27 March 2016
 Member #: 1894
 Postcount: 501

Oh silly me, I have 630v polyesters of that value!


 
 Return to top of page · Post #: 8 · Written at 2:36:56 PM on 13 June 2016.
JamieLee's Gravatar
 Location: Clare, SA
 Member since 27 March 2016
 Member #: 1894
 Postcount: 501

Great, the tone control works, but the pot is a bit dodgy, I'll keep my eye out for replacement.


 
 Return to top of page · Post #: 9 · Written at 6:31:52 PM on 13 June 2016.
Kakadumh's Gravatar
 Location: Darlington, WA
 Member since 30 March 2016
 Member #: 1897
 Postcount: 130

Try washing the pot track with some Isopropyl Alcohol & working it back & forth a few times to clean the crud off the carbon track.

Used that many times of late as my supply of the original Servisol in a can with a spout has been emptied & seemingly not much out there to replace it.

Cannot do any harm & I have seen no ill effects when I have used Isopropyl on pots.

Jaycar sell a product branded Servisol but I doubt that it is the same makeup as the old stuff but it is supposedly for cleaning switch contacts & the like. Sold as Servisol Electrical Clean Lube. cat no NA1012 for $11.50...looks rather similar to the stuff we used to use in Telecom when they stopped us using Freon based cleaners for cleaning relay contacts, but this is with a wee bit of lubricant added.

Lindsay


 
 Return to top of page · Post #: 10 · Written at 9:47:30 PM on 13 June 2016.
JamieLee's Gravatar
 Location: Clare, SA
 Member since 27 March 2016
 Member #: 1894
 Postcount: 501

Thanks Lindsay, worth a shot mate!


 
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