[Boatanchors] Advice Request on Heathkit HP-20 Power Supply

[Bry Carling]

Plenty of radios and most audio amplifiers do not connect the heater supply to the chassis.  It is fairly common to see pairs of twisted green wires bringing the LV supply all over the place to the little glowing orange guys.

Anyone need some boxes of good used 6SN7 and 12SN7s? 
Bry

Glen Zook <gzook at yahoo.com> wrote:

>Are there bypass capacitors from each side of the filament windings to
>ground?  If so, there is a very good chance that what you are seeing is
>just like the old bypass capacitors from each side of the AC line to
>ground when the chassis is not grounded.
>
>In most radios, one side of the heater ("filament") voltage is
>connected to the chassis and that should eliminate this voltage
>problem.  You can remove the bypass capacitors and that shouldn't hurt
>anything.
>
>Also, installing a 3-wire cord should definitely be done for safety
>reasons.  Connect the green wire to the chassis, connect the black wire
>so that it goes through the fuse and then to the power switch.  The
>white wire goes directly to the "other" side of the primary winding.
> 
>Glen, K9STH
>
>
>Website:  http://k9sth.com
>
>
>________________________________
> From: D C _Mac_ Macdonald <k2gkk at hotmail.com>
>To: "boatanchors at mailman.qth.net" <boatanchors at mailman.qth.net> 
>Sent: Tuesday, January 22, 2013 6:46 PM
>Subject: [Boatanchors] Advice Request on Heathkit HP-20 Power Supply
> 
>
>I just bought a Heath HP-20 power supply on the bay. 
>It arrived today and is in beautiful physical condition. 
>
>I opened up the bottom and found a lot of stuff that 
>was NOT in the Heathkit manual. 
>
>While I didn't try to draw a schematic for it, what 
>was in the manual was mostly correct for the high and 
>low B+ and C- supplies. 
>
>The filament supply was something else!   It appears 
>that a prior owner tried to rectify the filament supply 
>to provide DC to "something." 
>
>I removed all of that stuff and rewired the HP-20 to 
>original wiring status. 
>
>Next came a test of the outputs (no load).  Both B+
>and the C- bias supplies had reasonable voltages. 
>
>The rewiring of the filament section gave me a bit over 
>14 VAC, no load. Again, reasonable without load. 
>
>Then I decided to check the filament windings against 
>ground.  OH, OH ! !  About 48 VAC from one side and 
>about 36 VAC from the other side to ground! There is 
>NO wiring from either side to ground. 
>
>I'm guessing (never ran into this in 59 years as a ham) 
>that the power transformer is leaky.  The HP-20 has 
>had a two-wire cord installed; the known dangerous 
>in-line fuse plug is gone. 
>
>What are the dangers?  Could installing a three-wire cord 
>help out here?  I sure don't want to risk electrocution! 
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regards,
Bry Carling

-- 
Sent from mobile phone.