Checking bias with MULTI-METER? JerryP ?? Somebody??

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SyxStringSlayer

SyxStringSlayer

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OK again. Im doing the bias mod on my 5150. Found 2 pdf documents on it... Pretty sure one was the old one that was on Jerrys site. Its all easy.. But I want to install the test terminals as well, Which I will find at radio shack, And IM making
the pot accessable from the outside. I mean this is basic engineering and IM not going to screw anything up. Its mostly finished... Except I dont have a bias probe or access to one.

I have a nice multimeter though. The layout is going to look about like the XXX with the terminals.
I was able to get a ballpark reading somehow using volts, i think i had it set to like 42.5 or something on
the XXX. These powers are sovtek wxt 6l6 tubes with about 40% life left.

How do I use the meter to adjust it in volts or whatever... All the little thingies the meter has on it.
What number should I make it. Im using a 6.8 resistor and a 10k pot.

So when I stick the probes in the terminals... What numbers am I looking for here?
Thank you very much :thumbsup:
 
Bump. Hate to be bumpin like that but... Im about to start installing everything. At which point I will need to know what to do on my multi meter. And btw Im using a 5.7K instead of 6.8k resistor....

Multi Meter ... Hook it up please :yes:
 
To measure the bias you need to have a 1ohm resistor in series with pin 8. So basically you have to break the pin 8 connection on the power tube and put a 1 ohm resistor there. bridging those 2 connections. That is what most bias probes do.

Then you measure the voltage (milivolts) across the resistor. V=I or in other words voltage = current since R is 1 ohm.

You probably need a 2-3Watt resistor, not really sure the current that can go through this resistor.

I hope that helps a little....
 
Well Ive already done it all.


Got everything hooked up.
Just need to know what voltage I should put it on.

IThe damn XXX was like 42.5 or something for el34 tubes.

Whats the best for these wxt 6l6 tubes?
 
SyxStringSlayer":5dfec said:
Well Ive already done it all.


Got everything hooked up.
Just need to know what voltage I should put it on.

IThe damn XXX was like 42.5 or something for el34 tubes.

Whats the best for these wxt 6l6 tubes?

Depends on your plate voltage man, you need to know the plate voltage so you can work out what to set the plate current at. There's a bias calculator webpage somewhere, think its by Weber.
 
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