McAlister PP-150 Tube Amp - Hum

ken99

I have a McAlister PP-150 tube amp. It has a hum. When powered on, it has a slight hum. When the power finally goes thru the rectifier (30 sec. delay), the hum increases and the hum goes thru the speakers. Drives me crazy. Can't listen to it.

Had it back to McAlister in Barrie, ON, Canada 3 times. Still hums. Right side is louder than the left side. Tubes all check ok. Tried several sets of tubes. Same hum. It is not the preamp, because it still does it with nothing attached to the amp, except the speakers. The amp hums with no speakers attached. If I attach the speakers (tried several sets), the hum goes thru the speakers. Preamp (Wright WPL-20) works fine hooked to other amplifiers.

Anybody have any ideas as to what is causing it? Who can fix it? etc. I live in Eastern Canada.

Thanks
ken99

ken99

I finally got my McAlister PP-150 repaired by a local tech guy who once worked in tube radio in Toront for Collins for several years. He really knew his stuff.

He put shielded wire in the amp for the inputs (from back to front). This really reduced the hum. Also, he put in 2 pots to limit the input signals (it was previously wide open). Worked like a top. Hum is now nil. Can only be heard when I place my ear directly up to a speaker. This is normal (even his Eico amps which he did over himself do this). He knew every circuit in the amp and was impressed with the circuit design. He didn't need a schematic, as he understood the entire system inside out. I put the power supply on some foam and that really reduced the hum from it. As well, he tightened the bolts in it and removed a bolt that he found in it that was just lying on the bottom that was causing a vibration noise.

I am back in business and enjoying my McAlister PP-150!!!!! The sound is wicked. Unbelievable. The only thing left to do is to put some Dynamat on the bottom cover of the amplifier to reduce the vibration noise on the bottom cover. I am also going to sit it on some foam (not styrofoam). As well, I am going to have him drill new screw holes for the bottom cover, as the old ones are stretched from being opened so much - that should not be a problem now!

Peter McAlister replaced several transformers for me and gave me some extra capacity. He could not reduce or remove the hum for some reason, thus the trip to the tube radio repair guy. The work that Peter did do for me was excellent and did help to reduce the hum, especially from the power supply, which is separate.

I bought a Wright WPL-20 preamp to go with it. Very nice and hard to get. They gel quite nicely together.

later,
ken99

tonyb

Great pieces, glad you got it worked out and enjoying the flow of things.

ken99

Thanks tonyb! I am non stop listening! I have never owned anything that has come close to this sound (a Proton D1200 is the closest and it doesn't come near it).

later,
ken99

ken99

You are correct, even if you are joking around!

You can check out pictures, info etc. on the Wright WPL 20 here:

http://www.google.ca/imgres?imgurl=http://images.audioasylum.com/usr/y2010/02/32944/IMG_1333.jpg&imgrefurl=http://www.audioasylumtrader.com/ca/ca.html%3Fca%3D32944&usg=___szx74EB_oWLssiRAxvdvyXJM8E=&h=600&w=800&sz=184&hl=en&start=1&zoom=1&tbnid=oY4BhKFrwn3CHM:&tbnh=107&tbnw=143&ei=NLd6UOPiAajfyAH414CACA&prev=/search%3Fq%3Dwright%2Bwpl20%26hl%3Den%26gbv%3D2%26tbm%3Disch&itbs=1

McAlister PP-150 Reviews:
http://forum.audiogon.com/cgi-bin/frr.pl?ramps&1135444121&openfrom&6&4
http://www.stereomojo.com/McAlister%20review/McAlister_review.htm

Here are some pics of the McAlister PP-150 (it is the older model)

mcalister-power-supply.jpg

later,
ken99

ken99

Here is the main McAlister PP-150 amplifier. I attached it before, but it didn't like it on the upload. Hope this one works.

later,
ken99

ken99

A bigger and better picture of the McAlister PP-150. This one is not mine, but it is the mate of it.

mcalister1.jpg

later,
ken99