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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