Troubleshooting chirping sound from 6112HS

2nd harmonics for the masses

Troubleshooting chirping sound from 6112HS

Postby ashok » Mon Dec 28, 2009 8:38 pm

Hi all,

I just completed my GetSetGo referenced in the other thread. I will update the pictures soon.

In the meantime, I powered it up, and am getting a constant chirping sound from one of the James 6112 OPTs.

I am using the 3.5K tap. B+ at both OPTs is around 294V DC. The manual gives 319V as the number here, so my reading is lower by about 25V and outside the +/- 5% range.

At the 3.5K tap, I measure 285V on the transformer that is NOT chirping.

On the OPT that is chirping, I measure 255V DC at the 3.5K tap.

Inputs are shorted to ground. At the speaker terminals, I have 8 ohm /20W resistors connected.

I can make the chirping sound almost disappear by simultaneously touching the 0 ohm of the speaker terminal and an exposed part of the chassis plate.

Chassis plate is not connected to PCB ground. Incoming AC power earth is not connected to chassis plate. Even with incoming earth connected to chassis plate does not make any difference to the chirping.

PCB ground is isolated from chassis plate.

I have swapped the 6B4Gs, but the chirp stays with the OPT.

I have not swapped the OPTs yet, but could do it if it would help.

Any advice and troubleshooting suggestions gratefully accepted.

Thanks!!

Ashok
ashok
 
Posts: 83
Joined: Sat Feb 21, 2004 12:39 am
Location: Lexington, MA

Postby ashok » Mon Dec 28, 2009 9:32 pm

Well, I was reading an old thread on the ST-35 forum, and realized I was missing a connection between the PCB ground and the chassis. Once I added this jumper, the chirping has disappeared. The safety earth is not connected to chassis at the moment.

B+ at the OPT has now risen to around 305V. At the 3.5K tap, it is 294V on both OPTs.

Should have realized this from my ST-35 building experience. Plus the answer was staring me right in the face in my previous post - touching the 0 ohm terminal to an exposed part of the chassis plate make the chirp almost disappear. Duh!
ashok
 
Posts: 83
Joined: Sat Feb 21, 2004 12:39 am
Location: Lexington, MA


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