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Re: [Amps] Drake L-7 amplifier power supply requirements

To: A Lawrence Fibich <>, Mickey Baker <>, "" <>
Subject: Re: [Amps] Drake L-7 amplifier power supply requirements
From: Jim Garland <>
Date: Tue, 18 Jan 2022 11:11:15 -0700
List-post: <>
Larry, do you have a complete circuit diagram of your homebrew HV power supply? 
 If so, you should check and see if the power supply has a B- current return, 
as opposed to a simple chassis ground connection. In my experience, many old 
timers didn’t understand the reason for routing the return current through B-, 
which should be kept separate from chassis ground. Drake amplifiers require an 
independent B- return. Without it, the amplifier bias and metering circuits 
won’t work properly. There is no easy fix for this, other than rebuilding the 
power supply and changing its circuitry. It’s not a hard conversion, but it 
requires an understanding of the nuances of the power supply and L4B metering 
and bias circuitry. 
Jim W8ZR
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From: A Lawrence Fibich
Sent: Monday, January 17, 2022 9:58 PM
To: Mickey Baker
Subject: Re: [Amps] Drake L-7 amplifier power supply requirements

Thanks Mickey but I have them. The difficulty is trying to connect this home 
brew power supply to what the amp needs. HV no problem; as well as 120vac via 
the in/ off switch but the rest of the pins into the amp are the puzzles. I 
charted all the output from this ps but it is unlike the original Drake ps But 
thanks for your help73Larry FW6EF(916) 966-0266

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On Monday, January 17, 2022, 8:30 PM, Mickey Baker <> wrote:

You’ll find a manual and a schematic here:
Hope that helps.
Mickey Baker N4MBPalm Beach Gardens, FL
On Sat, Jan 15, 2022 at 1:24 PM A Lawrence Fibich <> wrote:

I could use assistance from anyone who knows this Drake Amplifier and it's 
power supply. 1st I have advertized widely for an original one to buy - 
nothing.2ndly I did get a 'home built' power supply but at a road block as how 
to connect parts of it.  The HV section OK, and a secondary transformer 
provides a 120VAC to run through the on/off switch of the Amp to work the 
finals heaters circuit.  But I come to 'stop' in trying to know/figure out what 
more it needs into the circuits to the right of the finals on the schematic - 
like the interlock, ALC, meter, etc.  This homebuilt power supply does put out 
5 VAC on the secondary but I don't know how to connect that to the Amp.Any 
assistance really appreciated.
73Larry FW6EFFair Oaks, CA (Sub of Sacramento, CA)
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