HV transformer ground

2nd harmonics for the masses

HV transformer ground

Postby jwhitmor » Fri Feb 20, 2015 3:25 pm

I searched the Get.Set.Go build photos, and noticed that some builds connect the C.T. of the power transformer high voltage winding to the supply ground (earth ground) and others leave it floating. The B.O.M. specifies a two wire cord, so my "guess" is, that no C.T. grounding is intended. My experience has been mixed, and I would say gounding causes as many problems as it solves. I don't plan on grounding the C.T., but if there is a good reason to, could someone set me straight?
Thank you,
J.W.
If it is not making X-rays, your B+ is too low.
User avatar
jwhitmor
 
Posts: 58
Joined: Tue Jan 20, 2015 5:42 pm

Re: HV transformer ground

Postby Shannon Parks » Sun Feb 22, 2015 2:09 pm

1) The HV center tap always has to connect to the PCB ground for the amp to operate.
2) When using a safety ground cord, connect green safety ground wire to chassis (not PCB).
3) Then connect a separate wire from the PCB ground to the chassis.

Hope this helps.

Shannon
User avatar
Shannon Parks
Site Admin
 
Posts: 3762
Joined: Tue Mar 18, 2003 5:40 pm
Location: Poulsbo, Washington

Re: HV transformer ground

Postby jwhitmor » Sun Feb 22, 2015 3:57 pm

Thanks Shannon,
I did exactly what you recommended. I already had the (green) earth gound connected to the metal chassis, and I conntected the transformer C.T. to the PCB "J6" terminal as the schematic indicated. I was not sure about also tying the transformer C.T. to the earth ground. I tested first with the C.T. only connected to the PCB, and there was a little residual hum. Then I checked to see if there was any significant voltage difference between the C.T. connection on "J6" and the chassis. I also checked to see if any current was going to flow between them if I connected them.* Both checks indicated no ground loop, so I ran a wire from the chassis earth ground connection to the C.T. common connection on PCB "J6" and the hum went away. I also had a nasty "crunch" sound when I switched the amplifier AC off, so I put an X2 rated safety cap (.047uF-250VAC) across the switch and it fixed the shutdown noise.

* (Someone may wonder how this is done. I bought a few 0.01 amp glass cartridge fuses years ago, and I put one in series with my milliamp meter test lead and then check for a current loop.)
If it is not making X-rays, your B+ is too low.
User avatar
jwhitmor
 
Posts: 58
Joined: Tue Jan 20, 2015 5:42 pm

Re: HV transformer ground

Postby Shannon Parks » Sat Feb 28, 2015 11:30 am

Great work, Jim! Thanks for documenting your troubleshooting, too. Very good tips.

Shannon
User avatar
Shannon Parks
Site Admin
 
Posts: 3762
Joined: Tue Mar 18, 2003 5:40 pm
Location: Poulsbo, Washington


Return to get*set*go

Who is online

Users browsing this forum: No registered users and 1 guest