[Heath] HV modification of Chippewa KL1

Mon Sep 10 19:33:44 EDT 2018

  John, 

  I own a Chippewa as well.  Glen is correct, you could place the meter in the ground lead of the filament.  It would read screen and grid current as well.  Since the Chippewa has positions for screen and grid currents, you could always subtract the readings.  Again, it probably isn't a big deal since we are more interested in output rather than input power.  It will easily do 1500W out on CW and 1200-1300W cleanly on SSB.  It will do 1500W on SSB, but friends and ham neighbors may not be too happy.  I have some PL-175a's to try in the unit but haven't yet.  It does not provide a very nice 50 input load. A transmitter with a pi-net out is not an issue, but trying to drive it with a  solid state transmitter will require a tuner of some sort. 

   Because the filament transformer doesn't have  a center tap, you will see a 60 cycle hum induced on the output carrier.  My solution was to float both filaments above ground and I added an 18V 1.5 amp ct transformer secondary across the filaments. I then grounded the CT.  Hum problem solved.  Again, if you are going to run, the unit as an SSB linear, probably no one would notice. On CW it is noticeable without the modification.  

  I made up a circuit for mine with a Honeywell hall effect current sensor in the high voltage lead that is isolated. With a  couple of op amps and a fet, I was driving the original meter; now isolated with 3vdc.  I started this project in May of this year, and I have not completed it yet. Still working on linearizing it.   It's summer and a lot of other activities take place here. Ham radio is more of a wintertime activity.  I'll keep you posted. 

  I can tell you I have received an email from K8IHY stating that the shock hazard is real. He was bitten through the meter face in the late 60's, and was lucky to survive with just some serious burns to his hand.  The manual states the meter is a special meter specifically design to withstand the HV. I can tell you it is just a standard Weston 1721 meter. You can find nos meters around still to grab a newer face without stress cracks.  I have originally specs on the 1721's and then do not have a maximum voltage rating stated. 

  Mine has the original power supply and on today's line voltage, HV is 3300-3400.  If you haven't seen the problem yet, mine was a tremendous TGTP oscillator. You could swing the grid tuning control through its range and the unit would suddenly pin the plate current meter and blow the line fuses. It would also take out every power meter that I had in line with the output. I worked diligently to try to get rid of this. The problem seems to be one of poor grounding through the aluminum top plates where the tuning capacitor is located. These are now screwed to the steel chassis, and these step down to another aluminum plate that the tubes are mounted to. The AL to steel combined with 50 years of moisture led to some interesting grounds. I elevated the aluminum plates and polished all the aluminum and steel. I then made sure all the star washers were actually installed, and cleaned all the other grounding points. The amp has been stable ever since.  I thought of a copper strap from the ground of the tuning condenser over to the grounding points of the 4-400's, and some finger stock, and I may still do that, but so far it is un-necessary.  This problem had been around for a while as mine had extra parasitic suppressors installed I supposed in an attempt to eliminate this. 

  I will be using mine with my Apache/Mohawk/SB-10 combo. All have been highly, but tastefully modified.  The apache and SB-10 both work on 160M; not sure if I will modify the Chippewa for 160 or not.  My rules are normally "no extra holes", so that if someone wants to put it back to "stock" they can. 

  Good Luck on the rare beast! 73's

  DE  KB1VWC 
Steve Harris

Message: 1
Date: Sun, 9 Sep 2018 17:30:49 +0000 (UTC)
From: John King <k5pgw at yahoo.com>
To: Heathkit List <heath at puck.nether.net>
Subject: [Heath] HV modification of Chippewa KL1
Message-ID: <1988474337.2476419.1536514249601 at mail.yahoo.com>
Content-Type: text/plain; charset="utf-8"

Has anyone modified the High Voltage metering circuit of the Heath Chippewa KL1 amplifier to take the HV from direct connection to the HV meter. I am looking for a modification to make the amplifier that I just acquired safer by getting the 3,000 vdc plus off the HV panel meter. Thanks and 73, John, K5PGW
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Message: 2
Date: Sun, 9 Sep 2018 19:50:04 +0000 (UTC)
From: Glen Zook <gzook at yahoo.com>
To: John King <k5pgw at yahoo.com>, Heathkit List <heath at puck.nether.net>
Subject: Re: [Heath] HV modification of Chippewa KL1
Message-ID: <504036265.2139272.1536522604302 at mail.yahoo.com>
Content-Type: text/plain; charset="utf-8"

Looking at the schematic (I don't have a KL-1 nor have I worked on one), from Pin-1 of the 4-400A, which is one side of the filament (which is the cathode in the 4-400A), there is a direct connection to ground.? It might be possible to move the meter from the B+ to where this jumper is located.? That is, the ground connection would go through the meter.

You would have to bypass Pin-1 to ground using a capacitor.? Also, a capacitor on the + side of the meter to ground.

In the moved condition, the meter would read cathode current (this is done in most transmitters) which also includes the screen current.? When the KL-1 was made, the regulations were for plate input power and by having the meter directly in the plate line, the reading was more accurate and higher power could be run since the screen current did not have to be estimated.? Today, the regulations are for power output so absolute accuracy of input power is no longer required.

?Glen, K9STH?
Website: http://k9sth.net

      From: John King via Heath <heath at puck.nether.net>
 To: Heathkit List <heath at puck.nether.net> 
 Sent: Sunday, September 9, 2018 12:32 PM
 Subject: [Heath] HV modification of Chippewa KL1

Has anyone modified the High Voltage metering circuit of the Heath Chippewa KL1 amplifier to take the HV from direct connection to the HV meter. I am looking for a modification to make the amplifier that I just acquired safer by getting the 3,000 vdc plus off the HV panel meter. Thanks and 73, John, K5PGW
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