[Amps] Cheap auxiliary amp cooling

[Jim Barber]

To quote Microsoft,
"This [poor] behavior is by design." ;-)

WRT the 3KA, if I ever found time I'd like to:
. Put in a single 8877 socket
. Lift B- off of ground enough to meter
. Ground the grid directly and meter through the cathode
. Deal with the other implications of the above, including a new heater 
xformer.

Considering I won't ever have time, I'll probably put in a variable bias 
regulator and raise the key-down bias voltage to just short of where the 
IMD gets ugly.

73,
Jim N7CXI


On 3/30/2012 12:54 PM, Carl wrote:
> That sounds like a shorted zener and running at zero bias or just poor
> engineering but you cant blame the tubes. Mine run at 120ma at 3000V in
> the LK-500ZC and IMD 3 is in the low -40's.
>
> Carl
> KM1H
>
>
> ----- Original Message ----- From: "Jim Barber" <audioguy at q.com>
> Cc: <Amps at contesting.com>
> Sent: Friday, March 30, 2012 1:21 PM
> Subject: Re: [Amps] Cheap auxiliary amp cooling
>
>
>>
>> Yep, but really no different than my Henry 3KA running 200ma ZSAC @ 4KV
>> with a pair of 3-500Z's. That one isn't good either. The tubes will glow
>> orange after a minute or so just keyed with no drive.
>>
>> 73
>> Jim N7CXI
>>
>> On 3/30/2012 8:41 AM, Carl wrote:
>>> Isnt that exciting having to run almost 1100W idle with 2 tubes only
>>> rated at 1200W dissipation total? No wonder they dont last long and
>>> availability is drying up.
>>>
>>> Carl
>>> KM1H
>>>
>>>
>>> ----- Original Message ----- From: "Jim Barber" <audioguy at q.com>
>>> To: <Amps at contesting.com>
>>> Sent: Friday, March 30, 2012 3:29 AM
>>> Subject: [Amps] Cheap auxiliary amp cooling
>>>
>>>
>>>> While playing with my new toy, (QRO HF2500DX) I found that I was
>>>> able to
>>>> confirm that it does indeed need auxiliary cooling for high duty cycle
>>>> modes. Even at relatively low or no power output - just the ZSAC is
>>>> 450ma @ 2400V, or over 1000 watts of just plain old heat.
>>>>
>>>> I decided to check my computer parts supplier to see if there was
>>>> anything that looked like it might work for a "booster" exhaust fan,
>>>> and
>>>> it turned out that a 250mm (10"!) 12V PC case fan has a brushless
>>>> (no RF
>>>> noise) DC motor, turns slow and makes little audible noise, but manages
>>>> to move 105 CFM of air. (at zero back pressure, of course) They cost
>>>> $26.99 USD in single units.
>>>>
>>>> I haven't built a sealed mount yet, but just sitting the fan on top of
>>>> the case above the tubes dropped the exhaust temp 40-50F during
>>>> 375/1500-watt AM transmissions. The noise of the "booster" fan is so
>>>> low
>>>> compared to the internal 50CFM blower that I can't really hear it.
>>>> Legal-limit SSB conversations (with modest compression) get the
>>>> airstream only lukewarm now, instead of 130F+ .
>>>>
>>>> I also bought a 243 CFM 8" 12VDC Conair-Rotron hurricane generator that
>>>> I want to build a temperature-ramped PWM controller for when I get A
>>>> Round Tuit. (probably 25khz, 30-100% duty cycle to copy the newer PC
>>>> controllers, which work well) In the meantime, the cheap PC case fan
>>>> seems to be getting the job done.
>>>>
>>>> 73,
>>>> Jim N7CXI
>>>> _______________________________________________
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>>>> Amps at contesting.com
>>>> http://lists.contesting.com/mailman/listinfo/amps
>>>>
>>>>
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>>>
>>>
>>
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