[Amps] 3CX800 and blower

[Bill Coleman]

Randall, Randy wrote:
> That was a stupid design.  Did the blower use two windings or two caps to change the speed or just a resistor?  In the resistor type just shorting out the resistor would provide the same functionality AND provide a fail safe mode.  If the switch failed at least the fan would be providing air to the system.  K.I.S.S. is the way to go here.
>
> Randy AB9GO
>
> -----Original Message-----
> From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com] On Behalf Of Bill Coleman
> Sent: Tuesday, September 08, 2009 10:30 AM
> To: Carl
> Cc: David J Windisch; amps at contesting.com
> Subject: Re: [Amps] 3CX800 and blower
>
> Carl wrote:
>   
>> Yes, according to the Eimac spec sheet.
>>
>> It also sounds like a good reason to install a 2 speed switch as is in a few
>> commercial amps with that tube.
>>
>> It can be as elaborate as a thermal switch that runs the blower full speed
>> when necessary, to a simple toggle switch and a resistor.
>>
>> Carl
>> KM1H
>>
>> ----- Original Message -----
>> From: "David J Windisch" <davidjw at cinci.rr.com>
>> To: <amps at contesting.com>
>> Sent: Monday, September 07, 2009 10:26 AM
>> Subject: [Amps] 3CX800 and blower
>>
>>
>>
>>     
>>> Does a 3CX800A7 require airflow any time the filament is lit, like, say,
>>> 3-500Z glass tubes with tender seals and 70-watt filaments?
>>>
>>> I'm thinking of leaving the (unobtanium) blower turned off, to lower wear
>>> and tear, until I need the power.
>>>
>>> Yep, I'm aware of the potential hazard of a senior moment: I have in mind
>>> a no-blower-no-operate interlock scheme.
>>>
>>> Tia & brgds,
>>> Dave, W8FGX
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>>>
>>>       
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>>
>>
>>     
> A quick story regarding a 2-speed switch...   I had a 1st generation
> TenTec Titan (pair of 3CX800s), its 2-speed fan switch is located on the
> power supply.  I regularly operate wearing headphones & one day was
> running RTTY.  I set the switch to high speed with my toe as the power
> supply was on the floor under the op table.  A while later after many
> contacts I went to change bands, grabbed the bandswitch on the Titan to
> find it extremely hot, the case of the RF deck was too hot to touch.
> Yep, mid-way on the HI/LO fan switch was NO fan.
>
> This never happened again as I wired around the switch to force high
> speed all the time.   I was very lucky, the amp is still around and the
> tubes still going after 20+ years.
>
> I still wear headphones all the time because my present amps make lots
> of noise but both are protected by air flow switches.   The switch in
> one is a simple microswitch with a long actuating arm & a brass vane. No
> big deal to fabricate.
>
> I'm not a 'fan' of two-speed fan switches!
>
> 73, Bill   N2BC
>
>
>
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>
>   
Cheesy rocker style switch that would easily sit mid-throw....  OFF!