Dumble 102 ODS testing

[martin manning]

For a start, dial it down to the most negative voltage on pin 5's, and you will need a way to measure the current flowing through the output tubes.

[desertmouth90]

-17V is much too high (not negative enough). You will need around -50V there.

Edit: above you had -50V available for biasing. Have you just not set the bias yet?

Bloody trim pot, I manhandled it abit and now I got -52v

Weird

[desertmouth90]

For a start, dial it down to the most negative voltage on pin 5's, and you will need a way to measure the current flowing through the output tubes.

I was thinking of buying a bias meter, but I have a multimeter. Each Half winding has a resistance of 18ohm

[martin manning]

ok, you can use that. Did you have a look at the document here: https://ampgarage.com/forum/viewtopic.p ... 60#p474160 ? You will be measuring current as shown at C in the diagram.

[desertmouth90]

ok, you can use that. Did you have a look at the document here: https://ampgarage.com/forum/viewtopic.p ... 60#p474160 ? You will be measuring current as shown at C in the diagram.

Got an A in maths at school, that was the last time I used it. Will go through this with my sister (she’s an electrical engineer)

[martin manning]

Well alright, great resource there! She should be able make sense of it, but I’m betting she hasn’t worked with valves before ;^)

[desertmouth90]

Well alright, great resource there! She should be able make sense of it, but I’m betting she hasn’t worked with valves before ;^)

No she has not, big gas turbines yes!

I will be able to work it out eventually.

It appears somewhere in the circuit the signal is getting pushed to ground.

Also appears that SPK2 Output is the main output for some reason… who only knows!?

[timrobertson100]

It appears somewhere in the circuit the signal is getting pushed to ground.

Also appears that SPK2 Output is the main output for some reason… who only knows!?

Can you please post new pics, including a closeup of your output socket wiring?