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 Post subject: 3 Tube SW Battery Radio Question (from Peebles Original)
PostPosted: Oct Sun 22, 2017 11:57 pm 
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Joined: Sep Sun 29, 2013 4:56 am
Posts: 60
Location: Joppa, Maryland 21085
I am very interested in building the "3 Tube SW Battery Radio" posted on Peebles Original website.
From what I can tell, the schematic calls for a midget dual 50pF variable capacitor (C8) & (C11) and 2- 2-30pF ceramic trimmers (C6) & (C10).
In my parts box, I have a dual 365pF variable capacitor with trimmers already built into it. I don't know the capacitance of the trimmers are yet,
but I was wanting to know if I could use this variable capacitor in this radio?
I'm sure it will effect the number of turns in each coil. Also, I want to add a BCB coil to receive broadcast stations as well.

I am including a link to the schematic and coil winding sections:

http://www.peeblesoriginals.com/radioar ... w3tub2.jpg


http://www.peeblesoriginals.com/radioar ... w3tub4.jpg


thanks


Kirk


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 Post subject: Re: 3 Tube SW Battery Radio Question (from Peebles Original)
PostPosted: Oct Mon 23, 2017 4:23 am 
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Joined: Dec Sun 14, 2008 3:33 pm
Posts: 865
Location: Tokyo
In theory, yes, you can use your dual 365pF VC instead of the dual 50pF. The tuning range will be much greater. But...

One likely problem example: as your 365pF VC is tuned beyond its 50pF point, towards maximum capacitance, the regenerative detective may no longer oscillate. To correct this, you'll have to make circuit changes, eg, increase the number of turns on the tickler coil L8. But this change will likely adversely affect regeneration and oscillation control at the high end of the tuning range. You'll also probably have to change the values of R4 (the regeneration control, 50K) and R5, the 30K voltage dropping resistor.

This is not to say it can't be done. But you have to expect to do some experimenting and adjusting. Just takes a bit of time and patience.

I'd build a prototype version, using the parts you have on hand, winding the coils as specified. When you run into problems, ask for help here. When you get all the kinks worked out, then you can build a proper finished version.

Rob


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 Post subject: Re: 3 Tube SW Battery Radio Question (from Peebles Original)
PostPosted: Oct Mon 23, 2017 10:12 pm 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Perrysburg, OH, U.S.A.