wd hd3 problem

[Princo]

Just finished building HD3, and doing some tests, all checks out except voltage on pin 7 (bias), left channel, it is only 2v instead of 13v, right channel is fine, swapped valves and same problem.
Checked board soldering and looks ok, what else could cause this.

thanks

[Princo]

Here are my test voltages:

L chan
a 206v
b 205v
c 197v

d 0.9v
e 106v
f 212v
g 2.2v???

R Chan

d 0.9v
e 112v
f 197v
g 14v

[Princo]

I just checked all again and found the voltage on pin 9 (control grid) is -45v, that should be zero, yes? no DC should pass.

What would cause this? failed cap C6?

[John Caswell]

It sounds very much as though the grid is not returned to ground. Check with DMM on both channels that the grid has a resistance to ground and compare the two.
Once I have had a look at the blurb I will add further comments

John

[Richard]

Hi, yes Pin9 should be 0V.

Looking at the older HD83 circuit but it should be similar,

All with respect to signal ground,

Voltage checks,
Pin1 102V
Pin 2 0V
Pin 3 0.9V
Pin 6 192V
Pin 8 191V
Pin7 13V
Pin 9 0V

Resistance checks,
Pin 3 to ground 1K
Pin 7 to ground 750R
Pin9 to ground 1M as John says.

[Princo]

Thanks, i checked again all voltages and resistances and swapped caps C6/C9.

L Chan R Chan
1 107v 110v
2 -0.3v -0.1v
3 0.9v 0.85v
4 Htr
5 Htr
6 205v 196v
7 2v?? 14v
8 205v 197v
9 -47v?? 0v

Resistance

1 1k 1k
7 750r 750r
9 1M 1M

All resistances are fine.

Could there be a problem with the valve base?

What could give -47v at pin 9

Jim