From: Garey Barrell 
Subject: Re: [drakelist] CM 12 Solution???



> On Thu, 29 Apr 2004 20:51:16 EDT, OTAKEBI{at}aol.com wrote:
> 
> 
>>Could Marty find out the resistance of the bulb he is looking for
and use the 
>>bulb base to wire in a resistor and then place the unit back in the rig?
>>Seems that this would solve the problem of a hard to find or obsolete bulb.
> 

Jim Shorney wrote:

 >
 > It would seem that there is more to it than just having a resistor
 > there.  The temperature characteristics of the lamp filament would
 > cause it to act as a sort of a surge limiter as well as a fuse.
 > Similar to the way Bose used a Chevy dome light lamp as a tweeter
 > protector in thier 301 bookshelf speakers.  Call it a 
primitive version
 > of the PTC "thermal fuses" used in modern electronics.  It 
should be a
 > simple matter to look at the specs on the lamp and find a more 
"modern"
 > equivalent.  What say the gurus?
 >

The #47  bulb is also 6.3V at 0.15A, so is probably close enough.

The object in the TR-4 is to protect the input winding of T9, a 
worthy goal which you can only appreciate after you've had to 
replace one!  The bulb won't do much for lightning induced 
transients or other HV spikes, but it should "fuse" before that 
coil fries.

So either solder a couple of pieces of wire to the bottom of a 
47, or even put in a "bare" bayonet type socket.

73, Garey - K4OAH
Atlanta


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