Speedball Part 1 Voltage Problems

[dkeen]

Hello all,

This is my first "real" electronics project. I finished up the base Crack kit recently, and it went off without a hitch (and sounded awesome).

I decided to dive into the Speedball addition, which is going a bit less smoothly.

This may or may not be relevant, but I was having trouble stripping the teflon coated wires with my Ideal strippers (which go down to 22 ga, but weren't doing the trick). I have been using a pair of strippers on the 24 ga setting, and while it knicks the wires a tiny bit, I didn't see anything that seemed like it would compromise things (but worth mentioning in case my problems stem from there).

Anyway, I completed installation of the first half of the Speedball kit, and my voltages are not right. Additionally, the two right LEDs are not illuminating (but the 9 pin ones are, with the one closer to the front of the amp much less bright). Both tubes are glowing.

Voltages are as follows:

OA: 154 (starts out higher and quickly drops to this number)
IA: 157
B-A/B: 0
IB: 156
OB: 63 (starts out higher and quickly drops to this number)

When I measure the resistances at R1, I just get an overlimit reading.

Thanks for any and all help!

 

[dkeen]

I reflowed the solder for a second time, and seem to have resolved the issue. All voltages are within spec now. R1 resistance is still reading overlimit, but I don't see anything about resistance checks outside of the troubleshooting guide, so I will assume this is okay (or a user error on my end with the MM, although I got that reading in both Ohms, M and K).

Thanks!

 

[Paul Birkeland]

63V at OB is a bit on the low side, so be sure the PN2907 transistor isn't in backwards on that side.

 

[dkeen]

The voltages after reflowing were as follows:

OA: 62
IA: 179
B-A/B: 0
IB: 179
OB: 63

Those transistors appear to be correctly installed (matching the outline on the board - both in the same direction).

The amp is performing very nicely by my ears. Is it a problem that the OA and OB are still reading on the low side (but within spec?)

Thanks!

 

[Paul Birkeland]

That may just indicate a very strong 12AU7.