That's what I was thinking; that they may have run the heaters off DC to prevent hum and it would be easier to supply 150mA heaters than 300mA in the tube era. Now it would be simple to use a three terminal regulator IC to provide 6.3 volts.
Don Black.
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On 23-Jan-12 10:31 AM, David Wise wrote:
It's not hum - the mainframe supplies regulated +75 DC for
plugin heaters. It's Coarse Balance. The beautifully simple
circuit Tek used is only possible with 8393's.
Dave Wise
-----Original Message-----
From: TekScopes@...
[mailto:TekScopes@...] On Behalf Of Don Black
Sent: Saturday, January 21, 2012 7:55 PM
To: TekScopes@...
Subject: Re: [TekScopes] Re: Nuvistors.
Perhaps it was just easier to provide a DC heater supply of 12
volts at
half the current of a 6 volt tube in a tubes scope for hum reduction.
Don Black.
On 19-Jan-12 10:30 PM, phosphorphile wrote:
Yes, it may be a 13 volt filament is easier to run at
slightly lower voltage because perhaps the voltage being twice
and the current being half of a 6 volt filament would make for
a more constant current with line variations. Probably the way
tungsten filaments work?
The 8393 was used in early 453's and later 503's, I know.
Mebbe other models too.
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