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Hi all,
Does anyone have the instructions for the orig. sds st-70 capboard?
I installed one years ago, then more recently installed the new driver board.

The amp sounds o.k., but checking the voltages as shown in the driver board instructions show that most are way off. Before I dig in any further I could use some advice. If someone could walk me through these measurements and offer some guidance I would be eternally gratefull

thanks much,
scott

If you can reply to this message and fill in the voltages you
are getting, I'll try to figure out what's going on.

Don't worry about the filament (6.3 VAC) pins.
Make sure your negative lead is clipped to the chassis, and keep one hand behind your back, and be careful.

V1 12AX7
PIN#
1 190V
2 0V
3 1.2V
4 6.3VAC |
5 6.3VAC |
6 190V |
7 0V |
8 1.2V |
9 6.3VAC |


V2,V3 12AU7
PIN#
1 245V
2 0V
3 13V
4 6.3VAC |
5 6.3VAC |
6 245V |
7 0V |
8 13V |
9 6.3VAC |

Tom,
thanks so much for the reply.

V1
1 166
2 0
3 1.24
4 6.36ac
5 6.36ac
6 163
7 0
8 1.25
9 4.6-77.3 cycles back and forth

V2 V3
1 243 231
2 0 0
3 12.27 13.7
4 6.37 3.3
5 6.37 3.3
6 232 243
7 0 0
8 12.1 13.0
9 4.45-75 3.14

pin 9 cycles same as on V1, taken with all tubes in, shorted inputs, 8ohm load, 117vac line

bad cap? voltage reg.?

thanks again,
scott

Are you setting your meter to AC when reading the filaments?
You need to measure across, not to ground.

As far as the rest of your voltages, they are almost perfect,
a few percent either way isn't a problem.

I'd leave it alone.

I did set my meter to ac but measured to ground, will recheck tomorrow.
thanks again,
scott

Tom,
where is northfield? I grew up in summit and spent my first 43 yrs in the garden state.

scott