[Amps] Drake L-7 amplifier power supply requirements

[Jim Garland]

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. 
73,
Jim W8ZR
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From: A Lawrence Fibich
Sent: Monday, January 17, 2022 9:58 PM
To: Mickey Baker
Cc: amps at contesting.com
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 <n4mb at arrl.net> wrote:

Larry,
You’ll find a manual and a schematic here: https://bama.edebris.com/manuals/drake/l7/
Hope that helps.
73,
Mickey Baker N4MBPalm Beach Gardens, FL
On Sat, Jan 15, 2022 at 1:24 PM A Lawrence Fibich <lfibich at sbcglobal.net> 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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