On 10/5/2010 1:22 PM, Jim Brown wrote:
On 10/2/2010 7:28 PM, CSM(r) Gary Huber wrote:
It seems to me there are several different lamp supply voltages depending
upon the build date and the version of the 425 in question.
I have 28 VDC replacements for my early Titan (S/N 425-00516) which was
export model and I believe the lamps in my Titan 425E are in parallel.
That's right -- it depends on the vintage of the Titan 425. All use two
bulbs, but some versions use two 12V-14V bulbs in series and others use
28V bulbs in parallel. You'll need to open the amp up and look to see
which version you have.
So there must also be a difference in the series resistor shown as R5 on
the display board. 20 ohms 1/2 watt should be toasted by two 1820 in
parallel drawing 200 milliamps dissipating 0.8 watt. Though I'm
suspicious that resistor value is inaccurate because that's not a 10 or
20% standard value and a lamp resistor doesn't need to be a 1 or 5%
resistor. Then the lamp selection for 12 volts 100 ma is small and to
give the same light as the 1820 based on power in the two in series
would need to draw that 200 ma too. I'm suspicious the schematic
draftsman missed a digit on his lettering instrument and put down two
instead of 1. I know that happened with schematics of the Collins
wattmeter where the schematics show 290 microamp meter when its really
200 microamps.
You can be sure that if one lamp stays lit with one out, that they are
in parallel, but if both go out at the same time they most likely are in
series.
BTW -- there are 425 schematics (about 95% complete) on my website as
pdf files. I've not drawn the details of the various resonant circuits
(which also vary with vintage).
Nor the lamp circuit with current limiting resistor.
Can any with a 425 solve my resistor analysis by looking at the resistor
called R5 on the display board. Is it 10 or is 20 ohms, or is it more
than 1/2 watt dissipation rating, or is it charred?
http://audiosystemsgroup.com/publish.htm
73, Jim Brown K9YC
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73, Jerry, K0CQ
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