new speedball upgrade blowing fuses

[Erekj3775]

Hello,

I am just installing a speedball upgrade. All resistance and voltage reading from stock crack were within tolerance. I installed and tested the small board and all voltages were on and LED's lit. When I went to install large board OA and OB resistances were over limit. Plugged in the unit and nothing.  Unplugged unit and checked fuse. It was blown. Reflowed solder at connections for large board and tried again. Fuse blew again. Here are the resistances I’m getting. Thanks for helping.

Small speedball board
OA - 317.6k
1A - increasing resistance
B/A-B - 0k
1B - increasing resistance
0B - 310.1k

Large speedball board
0B - over limit
G - 0k
B+ - increasing resistance
0B - over limit

Thanks again for helping me troubleshoot this issue.

Erek

[Erekj3775]

Here are some pictures of the build.

[oguinn]

It’s hard to tell from the photos, but are your PN2907As oriented correctly?

[Erekj3775]

Thank you.  Yes they are installed backwards.  Will correct and see if that fixes the issue.

[Paul Birkeland]

You also have not sufficiently soldered your PC boards.

[Erekj3775]

Hello
Finally got a chance to work on the issues with my amp. I fixed the PN2907A’s. I also looked into the soldering on the boards. Here are some pics of the boards now but I am still blowing fuses as soon as I power on.

Thanks for taking a look.

Erek

[Paul Birkeland]

If you take the Speedball boards and tubes out, then leave the loose wires poking up, does the fuse still blow? (I'd imagine it will)

If it does, then there's something wrong with the build excluding the Speedball, which is most likely.

[Erekj3775]

Hello,

I tried some different fuses and these new ones did not blow.  However my voltages are not correct and I have some LED's that did not light.  LED's above B+ on the large board did not light.  All other LED's did light however the small board LED's were very dim.  The transformer was also very warm when I unplugged the unit.  Here are the voltages I am getting on the small and large board.

Large Board
OA - 1.2
OB - 180
G - 0
B+ - 178

Small Board
OA - 178
IA - 180
G - 0
IB - 180
OB - 178

Thanks for helping out.

Erek

[Paul Birkeland]

During the Speedball build, there is a test to do initially to check operation of the small C4S board, did yours pass originally?

Are the tubes still glowing when you turn the amp on?

[Erekj3775]

Paul,

Yes, initially the small C4S board did pass checks.  I had the PN2907A's in backwards so I fixed that and worked on the solder.  The input tube is not glowing.  I do get glow from the power tube.

Thanks

Erek

[Paul Birkeland]

If the 12AU7 is not glowing, then the green twisted pair of wiring between the 8 and 9 pin sockets isn't soldered somewhere or is broken and needs to be fixed.

[Doc B.]

Also, it's best to check for tube glow with the room lights out. Some tubes glow pretty dimly.