Re: [TCML] 7.5V 52A Filament Transformer for 3CX3000 Needed

["Quarkster" <quarkster@xxxxxxx>]

Steve -

The biggest advantage of using a variac in conjunction with a filament 
transformer is the ability to "dial-in" the correct filament voltage. 
Depending on when they were made, you may find filament transformers with 
115, 117, 120, or 125 volt primaries.

With a variac, you can set the correct filament voltage regardless of 
transformer input voltage rating, variations in local line voltage, or line 
voltage "droop" in your equipment when everything is operating at full load. 
Obtaining maximum tube life is VERY dependent on maintaining correct 
filament voltage.

Regards,
Herr Zapp
----- Original Message ----- 
From: "S&JY" <youngs@xxxxxxxxx>
To: "'Tesla Coil Mailing List'" <tesla@xxxxxxxxxx>
Sent: Sunday, June 14, 2009 7:19 PM
Subject: RE: [TCML] 7.5V 52A Filament Transformer for 3CX3000 Needed


> Cameron,
>
> Regarding in-rush current control, hams have long controlled the inrush
> current on their larger transmitter plate power supplies, when first 
> turned
> on and charging their filter caps.  Typically, they use a relay activated 
> by
> a timer to add a big power resistor in series with the plate transformer
> primary.  This allows the filter caps to charge for a few seconds, then 
> the
> power resistor is switched out by the relay.
>
> You could provide a similar "soft start" circuit with your filament 
> supply.
> For example, let the filaments warm up at half-voltage for a minute or 
> two,
> then the timer-relay would activate to apply the full filament voltage. 
> The
> relay-timer circuit ought to be in the primary of your filament 
> transformer
> where the current being switched is much lower than in your filament
> circuit.  I believe such an arrangement would contribute to significantly
> longer tube life, as well as eliminating the need for a variac.
>
> Steve Y.
>
> -----Original Message-----
> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On Behalf
> Of Quarkster
> Sent: Sunday, June 14, 2009 1:20 PM
> To: Tesla Coil Mailing List
> Subject: Re: [TCML] 7.5V 52A Filament Transformer for 3CX3000 Needed
>
> Cameron -
>
> Another option (regardless of what transformer you use) is to use a variac
> on the primary side of a filament transformer. This allows you to have
> superior control over inrush current as well as being able to precisely
> adjust filament voltage at the tube socket.
>
> I appreciate your desire to use a commercially-made, appropriately-rated
> transformer as it just makes a "professional" appearing setup, better than
> any "home-brewed" transformer could.
>
> Regards,
> Herr Zapp
>
>
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