bias with no CT ?

[Valvehead]

I dont own a scope . Ive always biased between the plates and the CT .

However , this amp , Soldano slo100 , shows the 2 wires going to the plates, but not labeled . But the "CT" wire is labeled "plates" . ?

Whats the deal here? and how can i check the idle current with my meter ?


Im getting about -64mv at the power tubes at pin 5 .

[Valvehead]

bump...

Im betting theres at least ONE guy on here thats adjusted the bias of a SLO ......

[Alex R]

Well I did but I forgot!

It just means 'supply to plates' (ie via the OT), as opposed to 'supply to screens', I should think.

The SLO has a conventional push-pull OT arrangement. In cases of doubt, identify the CT and plate wires where they come out of the OT and follow them home through the chassis, then it shouldn't be a problem to do the bypass thing.

[Amp Kat]

http://www.schematicheaven.com/newam...ano_slo100.pdf

I've built a few of these from the ground up and they rock. It is the same as any other amp as far as how the OT is wired. The plate supply is taken from the first filter caps as noted on the schemo plates. This is fed to the CT of the OT and is labeled plates because the plates derive this voltage from the primary windings of the transformer so essentually it is the plate voltage. Many amps use B+ or just label CT. It's Soldano's schematic drawers way but no different that any other amp.

[Valvehead]

ok--i see.


The reason i asked was, i was getting a super low reading , like 8ma . Believe it or not , the bias pot was turned down that low !

I adjusted it to about 34ma and the amp sounds WAYYYYY better .


i know that some amps will read weird/ low on one side of the trans (5150 , jcm900)