Garey Barrell <[EMAIL PROTECTED]> made an utterance to the drakelist gang
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Hi Gary -
Well the filament wiring in the TR-4/C is important because it's a
combination series/parallel arrangement. The three final tube filaments
are in parallel, and that is then in series with eight other tubes and
the SSB pilot lamps. The Dial and S-Meter lamps are in series across
the 12.6V filament supply. Ohm's opinion still works on series/parallel
resistance combinations! :-)
Don's (N9OO) very nice LED replacements are not offered for the TR-4/C
for that reason. It would be possible to make a series/parallel/LED
arrangement to allow the proper LED current while maintaining the
appropriate current for the filament string, but would require two
resistors, one of which would have to dissipate most of a watt. Not
easy to build into a #47 bulb base.
I have been using #755 bulbs for years. They are the same voltage and
current as the #47 but with a design life of 20,000 hours rather than
the 2,000 hours of the #47. Roughly 2-1/2 years instead of 1/4 year of
continuous use. The filament is also more rugged and is less prone to
vibration or turn-on surge failure. I probably have 50 of them in
various Drake gear, and have yet to replace one since about 1965!
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 4-B & C-Line Service Supplement CDs
<www.k4oah.com>
Gary Poland wrote:
"Gary Poland" <[EMAIL PROTECTED]> made an utterance to the
drakelist gang
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Garey,
I have heard that filament current balance is important and using
incorrect pilot lamps can upset the balance of current distribution.
Does this prevent the use of the LED replacements? I am just curious,
I still use the #47 lamps.
73, Gary W8PU
http://home.cinci.rr.com/w8pu
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