Jim,
We just went through this with a friend's 87A. Best resources were amps on
contesting.com and alpha 87a on yahoo.com which had lots of info but seems
inactive now. Here are my notes:
1. An Alpha tech had suggested installing the fan without an on/off switch
(that was their later offering).
2. He also had said (paraphrased) "70 cfm will be enough; more will get you
more air with more noise". I personally think a lot of this is due to
additional velocity, and don't blame all the change on the second fan (if
you're relatively careful on fan selection).
3. No data on pressure drop at 70 cfm was available. I didn't look for a
performance curve for the existing fan, or attempt to quantify the flow and
pressure drop with one fan.
4. We went with the fan listed below, which is plumbed for 230 VAC;
"low-noise"; 60,000 hr expected life. Less than $17 delivered, via
Arrow.com.
5. The fan is easily secured with 4 ea #6 x 2" machine screws, into PEM
nuts in the back. We just moved the fan guard to the outside of the fan.
6. The fan comes with tabs and not wires. There is a handy grommet. We
wired and heat-shrunk at the tabs and routed wires to the terminal strip at
the primary side of the transformer. We used the inner 2 of the screws that
were already in use. Crimped spade connectors on, turned them upside down,
and put them under the existing ones (they fit better that way).
7. There is a threaded hole in the fan (for a #8 machine screw). We had the
fan oriented so that the threaded hole was up, but not on the grommet side.
Put a small jumper in between it and the adjacent #6 x 2" screw.
The unit is somewhat louder but not annoyingly so. If we were to do any
more planning on this, it would be to find one with an external fan, take
it off, light it up, and measure airspeed and therefore airflow at about 0"
WC and pick a fan from that. But we are happy with this one, and notice
(subjectively) that it's running cooler. We are not monitoring doing any
temperature monitoring.
There was another offering of the same brand with higher airflow and higher
fan speed (and higher noise). I think the one we chose was fine for the
87A, as well as for minimizing additional noise.
Good luck! 73,
Dave N3AC
On Wed, Feb 27, 2019 at 4:24 PM Jim Brown <jim@audiosystemsgroup.com> wrote:
> I have two 87As, both bought used. One has the second fan, the other
> does not. I'd like to add it to the one that doesn't. Can someone
> provide model numbers for one or more suitable fans?
>
> Thanks and 73, Jim K9YC
>
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>
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