[Drakelist] L-7 fan failure due to heat

[K9sqg]

Fellow enthusiasts,


I'm wondering if any users of the Drake L-7 linear amplifier have experienced 
fan noise and lock-up due to excessive heat.  If so, I wonder how the problem 
was solved.  Other than the fan problem, amplifier operates properly, with 
correct output, on all bands.  The fan problem started about a year or more ago 
and I've worked on it on and off since then with no progress.  Prior to that, 
the amp worked fine.


How do I know the problem is heat?  Well, let me give you a brief description 
of some things done so far with no improvement.
Fan replaced four times with new models from different vendors.
Thermostat replaced twice.
Dropping resistor replaced several times.
Wiring in fan circuit replaced.
Fan wired directly to 110 vac with no change.
Known good tubes swapped with no change.


Here is how the problem can be induced.  With the amplifier on, standby, CW or 
SSB, tubes in or out, the fan will run continuously as it should, and with no 
problems.  If the amplifier is used on the air, regardless of CW or SSB mode, 
regardless of power level, the fan will start making noise and eventually stop. 
 If the amp is allowed to cool down, things start working normally.  In amp is 
put into transmit, with normal plate idling current, and NO input power (and 
thus no output power), the fan will start making noise and then stop after 
approximately 5-10 minutes.  Allowing the amp to cool down, the process can be 
replicated with consistency.  Note too, when the amp is operated normally and 
the fan uses the power source via the amp wiring, the fan will start making 
noise and eventually stop without it ever switching into high speed mode.


If you have experienced such a problem and have solved it, I would be 
interested in hearing what the solution is.  I have two other L7s that operate 
flawlessly so I'm still on the air but I like to keep my gear in proper 
operating condition if possible.


Enjoy those Drakes!  And don't forget the Drake HF nets.


73,


Evan, K9SQG
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[Drakelist] L-7 fan failure due to heat

[Woody]

*Evan, as you know that is exactly the way mine did, I think I about drove
you crazy trying to figure mine out. But since I went to the different fan
from All Electronics for I think about $7 and * * also I replaced the
resistor* *, I have had no problem. Now the Amp works great and I use it
quite a lot.*
*Woody
*

-- 
* ** **Of **all the things I've L**ost, I miss my Mind the Most~~~*
   * If you forward this e-mail, please delete the forwarding history*
*Thanks*
*Woody*
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