>Subject: [AMPS] L4-B mod
>Sent: 3/30/1997 5:20 AM
>Received: 3/30/1997 5:28 AM
>From: QROKING@aol.com
>To: amps@contesting.com
>
>Ok fellas, lets let Heath, Ameritron and kenwood off the hook for a moment
>and lets look at the Drake L4-B. My guess is that this unit can easily
>handle 4000 volts on the plate instead of there mere 2600 that is stock.
I talked to several people who were in the process of doing it. The RF
components will withstand the higher v. The RF output increases about
2db--i.e., one third of one S-unit, and the tubes need fewer watts to
drive to 800mA, however, installing better VHF suppressors is not an
option due to the increased gain IMO, this is a lot of money and trouble
for a third of an S-unit. If you need more suds, you need a tetrode with
handles--especially with your moniker. However, an L4 that has a kaput
HV transformer would be worth putting a (tapped secondary) Peter W. Dahl
Hipersil core transformer in. There are two other windings that would be
a good idea. High speed switching would be a good idea in any case. See
Figure 7B on my Web site.
> I am thinking of doing this, but I think their method of bias is not
>appropriate for the high voltage, they do not use a zener diode, looks like
>put 125 volts from the bleeder string. I think the better way to go would be
>the zener as the newer amps do. Question is here, Is 8.2 volt zener the
>right one to use or does it need to be higher like 12volts?
The bias v depends on how much anode v you go with. I would use a series
string of forward conducting diodes mounted on perfboard. Diodes can be
shorted as needed to adjust the ZSAC to the needed 75mA per anode. The
trouble with Zeners is they are neither adjustable or cheap.
> ...Seems a though
>the rest of the components could handle the job.
You will need a different filter C string for the HV supply.
cheers
R. L. Measures,ag6k,805-386-3734
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