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Plug in IF transformer

 
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Location: Lancashire

Plug in IF transformer

Post by Sparks » Wed Apr 15, 2015 12:25 pm

I am just coming back to radio after an absence of a few months. My latest development is the plug-in IF transformer. This is for a proposed 4 valve battery superhet using TP25, VP23, HL23DD and PEN25, Mazda octal valves. I require plug in IFs so that I can experiment with making my own IF transformers once the set is working. Also planning on plug in coils.
The IFs are mounted on old octal valve bases. I have removed the internal 65pf capacitors, and these will be replaced by trimmers on the chassis. I need to clean the pins up a bit, but this was just the prototype. The Ifs came from an old suitcase battery set.
Bob
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Plug in IF

 
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Location: Worksop

Re: Plug in IF transformer

Post by Refugee » Wed Apr 15, 2015 11:16 pm

That is a good idea for a testbed for sure.
It would be over the top for a general daily use radio though.

 
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Joined: Wed May 02, 2012 3:35 pm
Location: Worksop

Re: Plug in IF transformer

Post by Refugee » Wed Apr 15, 2015 11:59 pm

I got the Megger out to play today.
C20 phase splitter control grid was awful at 400K. I found a Mustard that looks like the replacements that had already been fitted to the oscillator section and tested it before fitting. C21 on the anode side of the phase splitter was 5 Meg and C22 cathode side was 25 Meg. The other two blue capacitors read 500K and 1 Meg so they were bad too.

I use the bung drill method for the metal canned types and this worked well. I de-solder the old wires where they go through the rivets in the bung and pull them out to leave the clear hole on one end and do the same at the other end The drill does not suffer badly with snatching due to it landing on the internal roll of foil that then rotates. The foil then needs to be dug out.
I then feed the new capacitor in with the lead through the original rivet and solder it and at the drilled end fit a grommet to fill most of the space and top off with epoxy.
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