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Re: [Amps] wanted suitable blower for 8877 tube

Subject: Re: [Amps] wanted suitable blower for 8877 tube
From: "David G4FTC" <>
Date: Sun, 19 Aug 2007 06:08:28 +0000
List-post: <>

>From: "Tom Rauch" <>
>Reply-To: Tom Rauch <>
>To: "Mike, K6BR" <>,"'Fern Rivard'" 
><>, <>
>Subject: Re: [Amps] wanted  suitable blower for 8877 tube
>Date: Sat, 18 Aug 2007 22:20:47 -0400
> > How about using the Fan from the Ameritron AL-1500, I
> > think you can buy it
> > online from Ameritron, It works well and is pretty quiet
> > if you drop a
> > resister in line and slow it down a bit.  I think the part
> > is
> > Number is 410-3737.
>That blower is already at the minimum possible size with
>full line voltage for ICAS duty at 1500w output CW or SSB.
>If you add a resistor to "slow it down", you will not make
>safe airflow under almost any duty cycle.
>For heavy duty cycle applications Ameritron recommends the
>larger capacitor run blower, but no one ever likes it. The
>extra 20dB noise stops people from using it.
>When initially released the larger blower was used but about
>2/3 of the amps were returned  because of noise, so the
>slower G2E085 was substituted.

Following on from my earlier posting, I've just realised the OP is in 
Canada, and for 60Hz operation the correct EBM blowers should be prefixed 
with an R,  i.e. R2E 085-AA 01-05, R2E 120-AR 77-05 etc., instead of the G 
which is for 50Hz operation.

Also according to the EBM datasheet the G/R2E085 would seem a little 
undersized for high duty cycle (CCS) operation - the EBM datasheet gives 
25CFM at about 0.32" WG whereas the Eimac datsheet states a required airflow 
of 38CFM at 0.6" WG (at sea level). The R2E 108-AA 01-05 datasheet quotes 
about 40CFM at 0.6" WG which nicely fits the Eimac recommended figures.

Having said that the G2E085 or rather the R2E085 blower would probably be OK 
for most typical ICAS amateur use and would no doubt be selected by a 
commercial manufactuer for reasons of lower noise and also cost. However if 
I were homebrewing an amp, personally I would go for the larger unit.

BTW I thought there was a trend by the commercial manufacturers to use 
variable speed blowers with thermal sensors on the exhaust to reduce airflow 
and hence noise when the amp is in standby or in low duty modes and then 
speed up to give the required airflow when things warm up.


David G4FTC

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