Noisy Fan on SB-221

Would like to hear feedback on how one could quiet the fan in a SB-221. I don't do AM, FM, nor CW so just use it for SSB.

Does anybody know of any sources of quieter fans for this model heathkit? The amp has a new fan in it, just more noisy than I like when sitting in the room ragchewing.

 

If its just the air noise you dont like then get used to it or use headphones; any 1200W output tube amp is going to be noisy.

If its the high speed Harbach its a lot noiser than the original which can easily be taken completely apart, cleaned and lubed.

Carl
KM1H

 

Where did you get this replacement fan?
IF from Harbach, did you BALANCE the fan blades as advised by Jeff?
Any obstructions?

You need sufficent air flow for 3-500Z glass RF tubes.

w9gb

 

Recently I did a rebuild of an original SB-221 and refurbished mine in this manner I disassembled the motor, and cleaned the phospher-bronze bushing with a q-tip dipped in isopropanol. Use your favorive gun oil (I used GunSlick's Ultra-Lube) and add drops of oil around the outer felt around the bushing until is stops soaking it in. None should run out when inverted. I also replaced my 250~270cfm @ 3000 rpm original blade with one from Grainger which was 400cfm @ 3000 rpm, and slightly larger in diameter. I then shrouded the fan with 1/16" thick, 1.5" wide aluminum from the local hardware store, which did wonders for airflow, not to mention the reduction of noise. A shrouded fan of that size with 30mm or so of shroud can increase it's airflow as much as 15%~20% over a blade with it's tip in free air, which does in fact create noise.

 

Can you post some pictures?

 

The replacement blade was Grainger, part #5C175, 400cfm @ 3000 rpm, 3/16" shaft. After removing the fan, I used existing screws and holes which are in the RF deck. There are actually 2 pieces, an upper section which resembles the symbol used to denote "ohms" and a lower section. The SB-220/221 was well engineered to begin with, but the fan area was something I felt needed improvement. Most of the directional air, using a small hand held anemometer, was showing much of the air was being directed nearly strait out (upwards) from the blade tips, and afterwards were much more directed over the 3-500Z's anodes and directly across the cathode pins underneath. It was a worthwhile modification. We know from other areas like the automotive industry and HVAC arenas, that fan shrouds are a worthwhile, and sometimes required, addition for cooling. I think I paid less than $3.00 for the blade and under $5.00 for the 4' section of 1/16" aluminum from the local hardware store.

I included a graph from testing shrouds over free air blades, and as you can see in the push configuration, a significant improvement in airflow, as well as noise reduction can be realized by using something as simple as a shroud.