eHam Forums => Amplifiers => Topic started by: KA1J on November 01, 2012, 02:00:17 PM

Title: Centrifugal blower fan blade removal, Alpha PA-77 variety
Post by: KA1J on November 01, 2012, 02:00:17 PM
I'd like to remove 30 years of crud on the blades in the centrifugal blower, if I can remove the fan, I can get to the blades that have the crud collected on them. I'm not sure how to properly remove it and don't want to get creative & be wrong.

Anything reasonably straightforward to do this? 

Title: RE: Centrifugal blower fan blade removal, Alpha PA-77 variety
Post by: K8AXW on November 02, 2012, 09:41:23 AM
Understand up front that I am totally ignorant about your specific problem/question.

It's been my experience down through the years whenever confronted with the same question, "What's the best way" including cleaning blower blades, is to evaluate what is going to prevent or impede removing the blower. Then the decision must be made, "is it worth it?" The second and probably most important question you need to answer is, "can I do this?"

If the answer is "yes" to both then disassemble what is necessary to get the blower out.  I've never seen a way to clean a blower except to remove it so the blower itself can be disassembled.

While this task will no doubt be daunting, if you feel that it's really necessary, do it.  Keep copious notes on the disassembly and keep all screws, nuts and bolts separate and label them if necessary to prevent confusion when you put it all back together.  The wrong length screw in the wrong place might mean tearing it all down again!

Title: RE: Centrifugal blower fan blade removal, Alpha PA-77 variety
Post by: KA1J on November 02, 2012, 10:24:24 AM
Thanks for the reply. I believe the answer is "yes" to both. I am a pretty decent monkey in that I can follow instructions well enough and I can "usually" get things back together if I've taken them apart. What I don't wish to do is more than is necessary because the more I disassemble than I need to, the more likely an old part will become un-necessarily damaged in the removal process. In the case of this blower, I can easily access the screws holding the center shroud to the main shroud but I still can't see deeply enough inside the cavity where the nut or fastener is that holds the squirrel cage to the armature, to visualize how the cage is held on. Because of that, I don't know how to get to that fastener and unscrew it. If I try to twist it off in the direction of rotation, I'll need to know how to hold the cage so it doesn't get warped as I apply pressure to keep it fixed while I undo the nut. Since the other end of the motor is sealed, I can't grip it there. I can remove the whole blower but again, that might be much more than I should do to do this properly. If I wedge say a screwdriver in there to hold the cage in place while I torque, I fear the cage will end up with a wobble.

If I can remove just the squirrel cage alone I can soak it in evapo-rust which will remove all the crud & rust without etching the metal like phosphoric acid will do, I can get the cage as new and that will certainly reduce the turbulence created by the roughness of the " rusty looking" crud/nicotine/attached dust that is asymmetrically lumped on the individual blades. Reducing the turbulence will have to reduce the noise of the blower. Hope springs eternal...

Title: RE: Centrifugal blower fan blade removal, Alpha PA-77 variety
Post by: K8AXW on November 02, 2012, 10:13:50 PM
The blower on my homebrew amplifier comes off the amp as a unit.  Then and only then can the blower be disassembled.  To do anything else would be like the joke of the gynecologist overhauling an auto engine through the exhaust pipe.

You shouldn't have to worry about hurting anything.  The only problem you might run into is to get into a situation where in order to get to some of the blower mounting fasteners you might be required to remove items that are simply too unreasonable to fool with.

This is where you simply back out and go to Plan B which is to call the manufacturer and get their opinion and then there's Plan C which is to simply forget it.

I'm sorry I can't give you specific instructions on how to disassemble this blower.

Title: RE: Centrifugal blower fan blade removal, Alpha PA-77 variety
Post by: KA1J on November 03, 2012, 08:07:27 PM

My initial feeling was the fan in this amp was much too loud. Being an Alpha meant they used quality components and it should be quiet. After noticing the crap on the impellers blades I had to believe this was causing a turbulence along the lines of a bruit.

I was informed the impeller (I couldn't recall that name) is removed by loosening an Allen screw and to first pull off the beveled intake. Indeed that was the solution and the impeller came out. The fan/impeller was coated in nicotine crud in ways that would make a non-smoker out of a smoker. Looking on the inside of the shroud I could see a collection of the same where the centrifugal force of the accelerated air rammed the nicotine & dust into the inner surface of the shroud.

After removing the impeller I tried washing it off with soap & water and using an old toothbrush. After 10 minutes of scrubbing I gave up and soaked it in denatured alcohol & wearing gloves, scrubbed it in the alcohol with the toothbrush. That dissolved the crap pretty quickly.  I folded paper towels and soaked them in the alcohol & wiped the inner side of the shroud till it felt smooth & the gunk was removed. While the top was open I replaced the vacuum T/R relay (read about that in a separate post). It's amazing but the lower chamber where the pressurized air goes was almost totally devoid of that nicotine gunk, it's as if the majority of it truly was snagged in the impeller blades, and plastered out onto the inner part of the shroud. Being sticky it trapped dust and just accumulated over the years.

Starting up the amp was like starting a new amplifier, the noise coming from the amp is at least 1/2 the volume that it was this morning. The impeller is balanced like a car tire, there was a tiny weight tagged to one of the blades and just like having dried mud on your wheel will throw off your balance & make the tire wobble, this accumulated gunk made the impeller unbalanced and not only was it loud but the amp had little constant rattles & I thought it was because of the new side & top panels fitting poorly. All of that is gone now, no vibrations, nothing.

Turns out this was a wise choice for me to experiment with. If you have an old noisy amp with a squirrel cage, especially if it came from a smokers QTH, check it out & maybe you'll have the same success I did.

Title: RE: Centrifugal blower fan blade removal, Alpha PA-77 variety
Post by: K8AXW on November 03, 2012, 10:06:24 PM
1J:  Very good!  Congratulations!  And.... thank you for coming back to the forum with your results.  Many don't.

Apparently the Alpha has a first class blower that doesn't have to be removed to get to the impeller.  You cut a break there.  Along with the reduction in noise you will also reap the benefit of a better air flow.  It doesn't take much crud on an impeller to cut the flow.

Now I'm wondering about the tube(s).  Have you checked for crud buildup in this area.

I used to work on CB radios for awhile for pocket money and some of those things were so crudded up with tobacco tar it made me half sick.  I used to take them to work and wash them down with Chlorothene and blow them dry.  So I know where you've been.

Title: RE: Centrifugal blower fan blade removal, Alpha PA-77 variety
Post by: KA1J on November 03, 2012, 11:39:56 PM
The tubes had been fairly recently replaced before I got it & they were mostly clean, I ran them through the dishwasher & they look fine. I later replaced those with a pair of 3CPX1500A7 that were pulls & were made in 2009 I bought a couple of months ago. When I went to buy the amp I saw the PO smoking so I knew what to expect. When I got back, the first thing I did was put 4-5 hours into opening it up and cleaning everything off with alcohol that didn't have lacquer on it like the chokes might have.  It was a PITA but worth it.

Title: RE: Centrifugal blower fan blade removal, Alpha PA-77 variety
Post by: K8AXW on November 04, 2012, 06:50:35 AM
It's a shame for a beautiful piece of gear to be ruined or put into that kind of shape by a smoker.  I have a ham buddy who smokes and he uses a homebrew auto air filter and computer fan to suck his cigarette smoke away from his gear.  It does great job.

While it was a PITA to go through what you did, you now have a great piece of gear!

Title: RE: Centrifugal blower fan blade removal, Alpha PA-77 variety
Post by: KA1J on November 04, 2012, 07:35:13 AM
yours ago I made an electrostatic filter to deal with the dusty environment and it worked really well. Kudos to your friend for being proactive with his equipment.

This amplifier really is an incredible piece of gear and it works so well that it's hard to believe it's 30 years old. I had to replace the vacuum relay because it
was sticking and i replaced it with a silicone covered version and it's so quiet now can barely hear the relay when I transmit. The normal vacuum relay makes the slightest tick but this one is nearly silent, its much like PIN diode quiet.

Title: RE: Centrifugal blower fan blade removal, Alpha PA-77 variety
Post by: K8AXW on November 05, 2012, 08:37:18 AM
Interesting.... never heard of a "silicone covered vacuum relay."  I build a homebrew amp about 30 years ago.... still using the same 3-500Z tubes.  I swapped out the two changeover relays about a year ago with two new vacuum relays that I found on eBay for a song.  They are indeed quiet. 

But since I'm now almost deaf as a fence post I could have a couple 400A contactor relays in there and it would be fine!   :D

On a serious note, there isn't anything nicer than to have a fine piece of equipment to use.  Especially something that you've either salvaged, saved or simply cleaned up as you did.  Good job!

Title: RE: Centrifugal blower fan blade removal, Alpha PA-77 variety
Post by: KA1J on November 05, 2012, 09:46:19 AM
The relay is a Jennings RJ1A styled vacuum relay and is a # RJ1A-26N969 The usual source to find these (Max-Gain) has found it difficult to obtain these surplus as of late, I bought the last one he had and he doesn't expect to be getting any in for a while. Sometimes they show up on ebay and you'll see them at Dayton. Do a google to find a photo of one. Here's a link to W6MQI web page where he used two of them in his Alpha 76A (

I've thought about this and it would be easy to make the equivalent:

Drill a hole in a piece of thin scrap aluminum, plastic or phenolic and mount an existing RJ1A or HC1A relay on it & finger tighten the nut to keep it in place.
Solder 3/4"" maybe 14 gauge wire into the relay terminals, the largest wire that fits inside the relay terminals.
Cut a PVC or other hard tube that the ID is 1/4" or so wider than the metal ring on the relay and tall enough that only 1/4" of the soldered wires show above.
Put this tube over the relay & center it on the aluminum.
Draw a line around the base so as to keep the position correct.
Mark on the aluminum, outside the ring, where the COM, NC & NO are located (The com is at 6 o O'clock, the NC is at 2:30 & the NO is at 9:30 )
Apply silicone grease to the inside of the tube and on the top of the aluminum sheet & a bit past the ring you drew.

Now fill the tube & envelop the relay with silicone caulk till the caulk is flush with the top.
Let it cure for at least a day for the thick silicone to solidify throughout.
Now pull off the tube which never adhered because of the silicone grease you put on earlier & then remove the relay which will also be unattached to the aluminum for the same reason.
Wipe it off & you'll be good to go.

When I say this relay is almost completely silent, it's about as loud as dropping a fresh pea 1/2" onto a counter top. Amazing how much difference that silicone makes. I will definitely do the same with a homebrew external QSK box which uses a pair of RJ1A vacuum relays which I used with my AL-1500. I'll keep that ext. relay when I sell the amp and will use it with an old Canadian Vector amp that uses two 3-500Z but has a loud relay. As I almost only use CW, a silent QSK relay is a real pleasure on full break in.