[AMPS] L4B

[km1h@juno.com]

On Tue, 13 Oct 1998 22:37:53 +0100 "=?ISO-8859-1?Q?Tomas_Tanb=E4ck?="
<sm6vvt@kungalv.mail.telia.com> writes:
>
>Dear QRO lovers,
>I am a happy owner of a Drake L4B . I have replaced the tubes to
>new ones, RFP 3-500ZG. I have change all
>components except the transformer in the power supply. The amp works 
>great.
>
>The maximum HV is abt 2500 volt from the standard Drake power supply. 
>I have order a new transformer according to my own specifications,
>primary 2 x 400 volt 2-phase,(not ordinary 220 volt 1-phase), 
>and secondary 700, 900, 1100, 1200, 1300 volt, 1200VA 100% duty. I 
>will get
>
>from 1900 to 3600 volt DC.
>The data sheet for 3-500Z says maximum dc plate voltage 4000 volt, ( I 
>will
>use max 3500v) 
>Now to my question:
>1."Typical operation" says:"Zener diode positive bias at plate 
>potentials of 3 Kv or more"
>How do I make +10 - +15 volt positive bias?

The stock L-4B uses a voltage divider to select operating and stand by
bias. You can either use a similar circuit and select a value for R-7 in
the PS.
Or you can series a reverse connected string of 1N5408 type diodes and
select the correct number of diodes for 200-220ma of idle current. Use a
circuit that has been published in various handbooks, etc and be careful
you do not disturb the metering circuits.


>2. Can the Drake L4B circuits handle an output power of 1,5 Kw?

Yes

>3. A positive voltage of 120 volt from a resistor divider is applied 
>to
>the cathode during standbye. Do I need to increase this voltage when I
>increase the plate voltage?

No, that places the tube in full cut off.

GL   Carl   KM1H



>
>73  Tomas  /  SM6VVT
>
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