[Amps] Current draw fan Alpha 77

[Martin Sole]

Hi Gary,

If you take a look at my 77D pictures here:

http://www.hs0zed.com/gallery/

In the 77D gallery about the 6th picture. You can see the thermostat 
switch mounted to the side of the exhaust plenum. The two orange wires 
exit the RF compartment through 1,000pF feed through capacitors and are 
then wired to short out the blower rheostat. You can see the rheostat 
mounted on the rear panel just below the top cover interlock switch. As 
you can see it is set almost at one end so the blower is running only 
slightly faster than its slowest speed. Even on 50Hz this seems enough 
for the single 8877. With the blower at full chat I can imagine its 
deafening, quite the howling banshee I'm sure.

I will be home again shortly and plan to pull the blower and do the 
bearings, assuming they are standard and readily available. I also want 
to arrange a way to monitor filament voltage and I will probe the 
exhaust temperature to see what values I have. Perhaps someone here 
could suggest reasonable exhaust temperatures. Your 150F (66C) at 
maximum seems quite low.

73, Martin, HS0ZED



On 24/10/2017 20:45, Gary Smith wrote:
> Hi Martin,
>
> They made several of the 77 line and I
> should have been more specific, this is a
> two tube variety. I'm not sure if it came
> originally with two or a 2nd was added
> along the way. It's an amp with a lot of
> overhead available to me as I leave it in
> the CW/Low Volt mode and it loafs along at
> legal limits regardless of what contest
> I'm in.
>
> The blower is just plain loud and it is
> set at full speed by the setting on the
> adjustable wire wound resistor, it came
> that way and I haven't lowered the speed.
> It's running right now and moving curtains
> 10 feet away & that doesn't make sense if
> I don't need the CFM. I don't see a
> thermostat or probe located anywhere
> (except for the Sunbeam oven thermometer
> probe I have in the back to keep track of
> the exhaust temp), it ranges from 91F at
> idle to between 130-150F, tops.
>
> I just bought a thermostat & probe with a
> 10 amp relay which I'm going to utilize.
> I'll have to figure out which way will
> allow me to have the fan run at a slow
> speed & run a connection to the other end
> of the adjustable enamel wire-wound
> resistor, to the relay. When it reaches
> the target temp (I'm guessing 110F should
> be a good point to engage full speed),
> it'll run the fan at maximum till it cools
> down and defaults back to slow.
>
> Noisy bearings are a bugger and I don't
> hear that kind of sound, it's just a loud
> blower running at maximum. I rarely
> transmit any more, I listen more so a
> slower speed & less noise just makes
> sense. I did just recently post my
> cleaning the squirrel cage when I first
> bought it, and how that made a marked
> difference in the turbulence & sound. That
> was 6-7 years ago and I'm going to do it
> again while I have the top off, just to be
> sure.
>
> I remember the cage had a very small
> amount of surface rust which I removed,
> that roughness added to the turbulence. If
> I see any has returned maybe it would help
> if I made it spray painted the cage with
> enamel to increase the laminar flow & make
> it a snap to clean again, easy to do and
> wouldn't hurt anything.
>
> I'll let you know how the thermostat works
> out.
>
> Thanks for the reply & 73,
>
> Gary
> KA1J
>
>
>> Hello Gary,
>>
>> My 77D(x) has a rheostat in the blower supply. I'm not sure if that
>> was the same for all. Since mine is an early model it also has a
>> thermostat switch mounted on the exhaust plenum that shorts out this
>> resistor. I believe that was later deleted. I have the blower set
>> quiet slow with the rheostat but the air out the back never seems to
>> get too hot and the thermostat has never switched to high speed but
>> then I don't tend to use it for high duty cycle modes.
>>
>> My blower is quite noisy, definitely worn bearings and I plan to
>> replace them in the next few weeks. If that proves successful maybe I
>> can run the blower a bit harder without needing ear defenders.
>>
>> Whilst some might argue the original 77 transformer was a bit weedy
>> and the tank circuit somewhat undersized in some situations (2 tubes
>> on 160m) the blower by comparison seems almost excessive in the 77,
>> almost able to achieve that desired state of being able to lift the
>> tube from its socket :) This on a 50Hz supply where a lot of blowers
>> are distinctly under sized.
>>
>> 73, Martin, HS0ZED
>>
>>
>>
>>
>> On 23/10/2017 18:35, Gary Smith wrote:
>>> Not sure why my message didn't send
>>> properly but I'd sent:
>>>
>>> Got it. Thanks for the direct replies.
>>>
>>>
>>> I am finally getting around to adding a
>>> thermostat to the amp to allow slower fan
>>> rotation at idle and full rotation when
>>> transmitting. The blower on this thing is
>>> a beast.
>>>
>>>
>>> 73,
>>>
>>>
>>> Gary
>>> KA1J
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