[Amps] Shaded-pole Tube Blower

[Karl-Arne Markström]

I have the same experience with 4CX250B's.

Sometimes the phase-sequence sensor for the 3-phase blowers in the
Standard Radio CT1000's 1 kW autotune PA's failed to sense backwards rotation 
and the consequent very low cooling airflow. The net result of half an hour or so of "soak test"
usually were 4 very black tubes, that promptly were exchanged for new,
and the old ones run through a dishwasher and used for amateur radio projects...

These tubes had the same output as their "non blackened" brethren as far I can remember.

73/

Karl-Arne
SM0AOM

----- Original Message ----- 
From: "Ian White, G3SEK" <G3SEK at ifwtech.co.uk>
To: <amps at contesting.com>
Sent: Monday, November 22, 2004 12:55 AM
Subject: Re: [Amps] Shaded-pole Tube Blower


> Joe Isabella wrote:
> >Seems reasonable to have some kind of interlock for this -- a couple 
> >dollars worth of parts could easily save several hundred in new tubes. 
> >A friend of mine switched to a pair of 3CPX800s because the squirrel 
> >cage fan came loose from the motor shaft in his Alpha.  Tubes pretty 
> >much melted.
> 
> Another experience, for what it's worth...
> 
> I once wired the blower capacitor on the 2x4CX400A 2m amp so that the 
> motor ran at about half speed, and backwards. (The motor was going 
> round, lots of rushing-air noises, right?)
> 
> By the time I eventually noticed there was practically no air coming out 
> the exhaust, and maybe the tuning was drifting just a  little at the 1kW 
> output level, the poor 4CX400As were practically black from overheating. 
> But when the motor was wired correctly, they came back like new.
> 
> 
> -- 
> 73 from Ian G3SEK         'In Practice' columnist for RadCom (RSGB)
> http://www.ifwtech.co.uk/g3sek
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