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VK6BE > TECH 21.04.11 05:05l 61 Lines 3002 Bytes #999 (0) @ WW
BID : B10167VK6BE
Read: GUEST
Subj: Re: Old Valve Radios
Path: IZ3LSV<IW0QNL<VE2PKT<CX2SA<VE3UIL<VK6ZRT
Sent: 110421/0330Z @:VK6ZRT.#BUN.#WA.AUS.OC #:1871 [Boyanup] $:B10167VK6BE
From: VK6BE@VK6ZRT.#BUN.#WA.AUS.OC
To : TECH@WW
Re the anode on the top cap of some valves in the past, I got caught with
one of the 1930s Phillips valves with a P type base. When a defunct radio
came into the shop where I helped out the standard procedure was to check
that the audio amps were working by touching the top cap (grid) of the
first audio valve and hoping to hear a healthy burp.These valves were
shielded not with the usual can but with the glass envelope sprayed with a
metallic substance, gilt in colour. The sprayed surface of the valve was
earthed and so if you touched it as the same time as the anode you got a
healthy 250 volts for your pains. A real trap for beginners! Later of
course I found that the 807 and other transmitting valves had the anode on
the top in order to isolate the output circuit from the input avoiding
feedback and consequent instability, and also to allow the output from the
anode to be connected directly to the output LC circuitry.BY then of
course we knew enough to keep our fingers off that top cap.RF burns take a
long time to heal.
BTW I had two very old BC radios but unfortunately at that time the
historical side of BC radio did not worry us here too much and I did not
keep them. One was a West Farmers Mulgaphone complete with 01As as the
valve complement and the original horn speaker, 1924 vintage. There was
also the original dry battery, long defunct but with the 1924 date on
it.The other set was a Gulbranson of a few years later.Valves in that were
the old type with a two figure name, forget the figures - 46's I
think.The old lady who lived next door owned and still used the Gulbranson
and one day complained that my 80 metre AM signal was spoiling her
listening. When I saw the set she was using I nearly had a fit. It was
wide open to any AM signal and my 80 metre antenna was close to her house.
Finally I decided to build an 80 metre trap and tune it to my frequency.
A ham friend of mine and I ran some checks and tuned the trap. No more
interference!! Later she upgraded and gave me the Gulbranson.
Cheers,
Bob VK6BE.
Bob VK6BE
>These 3 tetrodes have the ANODE as the top cap!
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