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.
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
This last one is a close-up of the cage &
More later, getting late here.
> Hi Gary,
> If you take a look at my 77D pictures here:
> 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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