Operating at zero bias would eliminate that problem if it actually exists.
Ive minimal experience in mobile operation but the Heath HA-14 didnt have
any filament issues that Im aware of.
Carl
KM1H
----- Original Message -----
From: "Alex Eban" <alexeban@gmail.com>
To: "'MIKE DURKIN'" <patriot121@msn.com>; "'amps fourm'"
<amps@contesting.com>
Sent: Sunday, September 06, 2009 3:03 AM
Subject: Re: [Amps] FW: 3-500z Silly question
> DC operation of a directly heated tube is problematic, to say the least.
> The DC component of the heater voltage combines with the bias voltage to
> produce a varying voltage along the filament, causing unequal emission
> from
> different parts. Not very healthy!
> In addition, the heater voltage source has to be left floating. A power
> rheostat of about 5 ohms or so is connected with the slider to the B-
> terminal and the ends to the heater pins. It's set at the middle point.
> Alternatively you can connect a pair of 2Ώ/ 5W resistors- one from each
> heater pin to the B- point. Don't forget to bypass the resistors for RF.
> Use
> RF power capacitors!! They carry both the input and the output currents.
> Alex 4Z5KS
>
>
> -----Original Message-----
> From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
> Behalf Of MIKE DURKIN
> Sent: Saturday, September 05, 2009 9:40 PM
> To: amps fourm
> Subject: [Amps] FW: 3-500z Silly question
>
>
>
>
> From: patriot121@msn.com
> To: w7ry@arrl.net
> Subject: RE: [Amps] 3-500z Silly question
> Date: Sat, 5 Sep 2009 10:25:16 -0700
>
>
>
>
>
>
>
>
> Center Tap ??
>
> Measurements have been made from the choke to each 3-500z filament ...
> then
> divided by 2 ...
> I have solved my issues with marginal voltage for my 24V relays. I was
> hoping that the 12V witch was running 17V would be enuff to energize them
> ..
> but alass no .... so a voltage doubler was added and now i have good
> voltage
> and action from/for the relays.
>
> New question .... im using a MFJ 259 analyzer to check the input C-L-C
> network's for each band ... and its not good.
> The question is - does not having plate voltage affect the input impedance
> and frequency that much ( alot !!!) - im thinking that the input caps have
> been overloaded and now cooked ( wich might mean that the tubes in this
> amp
> were over driven too )
>
> KC7NOA
>
>
>
>> Subject: Re: [Amps] 3-500z Silly question
>> Date: Sat, 5 Sep 2009 07:32:23 -0700
>>
>> How are you derive the center tap for the cathode connection with DC
>> supplied to the filament?
>>
>>
>
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