[Amps] Current draw fan Alpha 77

Wed Oct 25 06:31:27 EDT 2017

Hi Gary,

Definitely a later model, you have a pcb for the RF meter circuit 
whereas mine is just open wired around the socket and that sure is some 
gunk on the blower.

If it were me I would first slide that wiper on the blower resistor to 
almost the other end, to set up a default low speed for the blower 
during rx periods then I think you could do like Jim said and wire a 
relay, coil from 12v to the PTT line and with some suitably rated 
contacts just short out the resistor or parallel in a much smaller 
value. That would cause the blower speed to go up and down with keying.

A dry contact thermostat could be used in the same way but would just 
vary the blower speed based on temperature. I don't think you would need 
a supply voltage for that.

On 25/10/2017 09:01, Gary Smith wrote:
> Hi Martin,
>
> Thanks for the link & the info. There are
> some differences, our Plenum's are
> different and this one doesn't have the
> temperature switch in it. I will open it
> tomorrow and see what I can do, taking
> current photos. I need to find a 12V DC
> source inside the amp for the thermostat
> or I'll have to come up with something
> else, I have some ideas that will do.
>
> Here are photos from when I brought the
> amp home; the first photo shows the
> Wirewound Resistor as it sat and still
> does. Very high RPMs & noise.
>
> http://doctorgary.net/673.JPG
>
> This one is dark but it shows a view of
> the plenum and it also provides a view of
> the dirty squirrel cage I was saying
> needed cleaning and when cleaned, the
> noise went remarkably down. All that junk
> caused turbulence you could hear at higher
> RPMs
>
> http://doctorgary.net/671.JPG
>
> This last one is a close-up of the cage &
> junk.
>
> http://doctorgary.net/672.JPG
>
> More later, getting late here.
>
> Thank you!
>
> 73,
>
> Gary
>
>> 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
>>>>> _______________________________________________
>>>>> Amps mailing list
>>>>> Amps at contesting.com
>>>>> http://lists.contesting.com/mailman/listinfo/amps
>>>> _______________________________________________
>>>> Amps mailing list
>>>> Amps at contesting.com
>>>> http://lists.contesting.com/mailman/listinfo/amps
>>>>
>>>
>>> _______________________________________________
>>> Amps mailing list
>>> Amps at contesting.com
>>> http://lists.contesting.com/mailman/listinfo/amps
>> _______________________________________________
>> Amps mailing list
>> Amps at contesting.com
>> http://lists.contesting.com/mailman/listinfo/amps
>>
>
>
> _______________________________________________
> Amps mailing list
> Amps at contesting.com
> http://lists.contesting.com/mailman/listinfo/amps