Damage From New Interconnect

[Quiet_Storm]

I just made and installed a new DIY silver interconnect (http://www.venhaus1.com/diysilverinterconnects.html) on my left channel 2A3 Paramount v1.1. (I didn't install my right channel yet because I wanted to do some A/B comparisons.) After 30 minutes or so my left speaker went out. My 2A3 tube is no longer warm, but the 5670 is. I powered it down and tried the tube on my right channel Paramount, and it's still working.

Next I powered my left channel back up and took a couple readings. My B6 is around 300 V like usual but my A2 was >500 V. I went ahead and powered back down out of fear that I could cause more damage.

Any thoughts on what might have caused this? I'm surprised an interconnect could cause have fried something after working momentarily. I double checked and the signal and ground are connected correctly. I did wiggle the connectors some when I realized they weren't seating all the way. (I'm not used to such tight connections.)

 

[Quiet_Storm]

Actually I just looked more closely and one of the ground wire solder joints came loose. I'm not sure if it was the ground wire on the RCA plug on the Paramount side or the Foreplay side.

 

[Grainger49]

I think that the new interconnects and the problem with your Paramount just happened at the same time, not causation.

If the interconnect opens, then you get a hum or buzz, if it shorts together you have a shorting plug.  Neither of those are likely to harm your Paramount.  But I'm not going to say I wouldn't jump to the same conclusion first, I probably would.

Since you say the 2A3 was no longer warm check out everything in the heater circuit.  You can check/chase voltages with the 2A3 out.  See if something came loose with the wiggling.

 

[Quiet_Storm]

Thanks Grainger I'll feel a little better if I didn't fry it with a bad interconnect solder joint.

So I'm thinking it's my PSU board. I'm getting too high of a B+ voltage (540 V) and no voltage out to FC-1 which would explain why my heaters out. The AC heater to the 5670 looks fine.

So maybe I fried a diode or a solder joint went bad? Unfortunately that board is a huge pain to desolder since its attached to the transformer. Any other checks I can do to figure out which part is acting up?

 

[Doc B]

The B+ is too high simply because the 2A3 isn't working without filament voltage. You need to trace voltages of the filament supply circuit from the filament supply secondary on the transformer through the Schottky diodes and the filament choke. Somewhere there is a bad connection or possibly blown diodes.

 

[Quiet_Storm]

I did some more checks. The filament supply secondary appears to be working and the voltages going into the Schottky diodes looks right. The major difference I'm seeing is that the anode side of the 1N5818 diodes is higher on the broken amp. 3.23 v 2.15 vac. Also the voltage on the cathode side of the 1N5820 diodes on the working amp is 208 vdc vs 0 on the broken amp.

My guess is that one of the 1N5818s isn't working. Does this sound right?

 

[Quiet_Storm]

I just did some resistance checks. The resistance across the 1N5820s is about 1 ohm on the good amp and 1kohm on the broken amp. Maybe they failed open? I'm thinking I should just get some new diodes. Could there be another explanation before I run off and do that?

Also I just realized I left out a potentially important piece of information. My left (broken) channel would have static for a few seconds during startup. Is there potentially something else I need to fix to prevent breaking it again?

Thanks for all the help. As a mechanical engineer I know enough to get myself into trouble but not enough to get myself out.

 

[Doc B]

Do you have 2A3s in both amps when taking the measurements?

 

[Quiet_Storm]

Yes both 2A3s are in.

 

[Doc B]

Since you have AC voltage at the secondary terminals and nothing at the fc-1 I'm guessing you have the right culprit.

 

[Quiet_Storm]

Thanks Doc! I'll give it a shot and report back.

 

[Quiet_Storm]

It turns out it wasn't the diodes but replacing them led to the cause. It turns out some of the traces on the transformer board had partially delaminated. I did some creative rewiring such as soldering the ac mains straight to the transformer. I also had to wire a jumper to one of the CSD01060s. I used some of the buss wire I received with the kit. I believe it's the ground for the B+.

Any reason to be concerned about the buss wire? My only other option is to get a new pcb.

Thanks for the help everyone. I feel better now that I found the issue.