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Old 19th May 2017, 7:37 am   #1
Dave Moll
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Join Date: Feb 2005
Location: West Cumbria (CA13), UK
Posts: 6,118
Default Valve-operated Fonadek telephone amplifier

In this long-closed thread from 2014 I commented:
Quote:
Thanks. I'll bear that [it uses a B114 battery] in mind if I manage to acquire the valve version - I currently only have a transistor one (which uses a PP9).
Well, I did acquire a valve version at a Telephone Heritage Group event last month. The HT+ battery lead was detached on acquisition, but with a combination of inspecting soldering for traces of possible broken-off wire-ends and help from @Keithinuk I managed to establish that it connects to g2 of a beam tetrode valve!

Having now stocked up with cheapo PP3 batteries from Poundworld, I connected seven in series to approximate the 67½V HT of the original B114 battery and a "C" cell for the 1½V LT. It now nicely amplifies the sound from the receiver of a 332 telephone's handset.
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