C2A 270Ω 5Ws are glowing orange from heat!

[kurogle]

Hi - Please tell me it's not hopeless... I've built 2 Cracks w speedballs successfully and went into the crackatwoa maybe too confident. Pretty bummed out now.

I made two initial dumb mistakes:

1. I spray painted the wrong side of the chassis. Before the paint fully cured, I scraped it away down to bare metal around all of the holes and openings.
2. I initially connected the (2) 270Ω 5W wirewound resistors to 33L instead of 32L.

When I began my first voltage check after completing the board, the 270Ω 5Ws started smoking so I unplugged the C2A within 20 seconds of starting the test. After this is when I noticed they were connected to 33L instead of 32L.

I realized the two 270Ω 5Ws were cracked from the overheating so I purchased 2 new 270Ω 5W wirewound resistors online and the leads were a bit shorter than what bottlehead provided so I soldered them together to a small black cable to connect to 32L. The pictures attached are with the new resistors.

I had to pull out and reinstall all of my UF4007 rectifiers to accomplish this, so they look messy now but I triple checked they are all connected to the correct spots and in the correct direction.

After this, I went back through all C2A instructions to confirm there were no other wrong connections, and re-soldered any connections that looked poor.

For my voltage test attempt #2, all tubes glowed and all HLMP 6000 LEDs glowed (the LEDs on the two high current boards were much brighter than the very dim LEDs on the low current board). This is when I noticed the (2) new 270Ω 5Ws started to glow orange within 10 seconds. I quickly took the picture attached before immediately unplugging the C2A.

I never got to the point to be able to do the voltage test either time.

Let me know if you have any thoughts. Thank you.

 

[Jameson]

Did the amp pass resistance checks? Can you post more pictures from around the amp?

 

[Paul Birkeland]

I would suggest doing a parts purchase request for new terminal strips, 270 ohm resistors, and caps to go by the power transformer. The UF4007s have to be positioned relatively perfectly as they are in the manual so that none of the leads touch, and we still have 270 ohm 5W resistors with long leads available so you can get that patched up properly. The component leads need to be trimmed back quite a bit more than they are now, and the parts need to be attached (bend the leads up and around the terminals) before they are soldered. Those 220uF caps will be especially prone to breaking loose if you just have the leads poking straight through the terminal and are only relying on solder to keep them in place.

Without seeing the rest of the amp, it's tough to know what's causing the problem you're experiencing.

 

[kurogle]

Sounds good I will definitely do a parts exchange. Here are a bunch more photos of the amp. Let me know if you need to see anything closer and if this reveals anything else wrong. I will post again now with ago additional photos due to upload limit.

 

[kurogle]

Part 2 of additional photos. Thank you again.

 

[Paul Birkeland]

How were the resistance checks?

Getting a proper pair of side cutters will really help clean up all those leads sticking out. I typically recommend the CHP-170 from Hakko.