Jtm45 ceriatone kt66 bias

[Alshaheen]

Could someone help on how to bias the 2 kt66 in my amp?

[pdf64]

It looks like you’ve got 1ohm resistors in the output valves cathodes’ return to 0V common.
I suggest to adjust the black trimmer near the end of the circuit board to achieve a voltage at idle across those 1ohm cathode resistors to be in the range 30 - 35mVDV.
If you’re going to use those online bias calculator thingies, I suggest that you treat KT66 as having a 23W anode dissipation limit, eg a likely ‘design centre’ equivalent rating.

FYI to avoid foreshortening the operational life of the rectifier valve, don’t use the standby switch, ever, as it’s (probably) a hot switching type.

Where is the mains power inlet grounded to the chassis?

[Alshaheen]

Not sure put her back in her cage so do i test the 1ohm resistor with the amp on and at each side of the resistor if so does it matter which side +or-? Also could you id the 1 ohm res please

[pdf64]

Are you certain that you are able to keep yourself safe whilst tinkering around inside an operational amp chassis? Electrical sources greater than about 55V carry a fatal shock hazard, the voltages inside the amp chassis are far higher than that, and I don’t want to lead you into doing something that will get you killed.

For voltage to be generated across a circuit’s components, it must be powered up, its normal voltage will not appear if the circuit is not powered.

To measure the voltage across a component, connect one volt meter probe to one of its connecting leads, and the other probe to the other lead. Probe polarity is immaterial for our purposes in regard of this matter.

The 1ohm resistors are connected with one lead to terminals 1 and 8 of the output valve socket, and the other lead connected to 0V common / the chassis metalwork.

[Phil_S]

Edit: I read the pin numbers wrong, so I am deleting my post. Sorry.

[pdf64]

To me, terminal 6 of both output valve sockets looks to be used in the screen grid supply circuit?
Bit I’m guessing really, as I can’t see terminal numbering or the base’s locating key.

[Alshaheen]

Yes im safe guys

[Alshaheen]

No test points

[martin manning]

Measure DC mV at the red arrow, joined pins 8 and 1. That reading in mV will be equal to cathode mA, if the resistor going to ground is 1Ω.

[Alshaheen]

And at the other side of the blue resistor?

[martin manning]

And at the other side of the blue resistor?

Any convenient ground nearby will do.

[Alshaheen]

Many thanks

[Alshaheen]

Many thanks