Tube Biasing

[ryan.kroemer@bigpond.com]

I'm building a jcm 800 2203 style amp from a kit as i want to get into amp repairs and building. i was wondering if someone could tell in a simple way how to check amp once finished, bias tubes, tell plate voltage ect. as i am building the amp from scratch i have to test all the tube socket's voltages before inserting valves. i'm confident in building the amp just need advice testing it and biasing tubes
thanks in advance

 

[DragonSarc]

check out eurotubes.com it shows how to do it

 

[ryan.kroemer@bigpond.com]

I should mention that it will be point to point handwired

 

[Brett Blackmore]

Hi,

I have a kit amp too - but I do not want to fiddle with it as the capacitors inside hold hundreds of volts for DAYS after it being switched off - be very, very careful.

Cheers Brett

 

[Adwex]

Hi,

I have a kit amp too - but I do not want to fiddle with it as the capacitors inside hold hundreds of volts for DAYS after it being switched off - be very, very careful.

Cheers Brett

Brett,

Test the caps with a voltmeter before you mess around. Just because they sat for days doesn't mean they're discharged. They're not going to discharge by themselves, they need to be grounded to drain the charge.

 

[Adwex]

check out eurotubes.com it shows how to do it

Here's the video you need:
euro-m

 

[ryan.kroemer@bigpond.com]

Thanks, how do i work out plate voltage of my new amp if i can work that out i know the formula to then work out what Ma to set the poweramp tubes at.
Do i have to bias pre-amp tubes on a newly built amp or are the self biasing.
the video on that website is not loading and yet i have broadband, is it availible on youtube
thanks

 

[Adwex]

Thanks, how do i work out plate voltage of my new amp if i can work that out i know the formula to then work out what Ma to set the poweramp tubes at.
Do i have to bias pre-amp tubes on a newly built amp or are the self biasing.
the video on that website is not loading and yet i have broadband, is it availible on youtube
thanks

The plate voltage has to be measured with a voltmeter. I believe it's on pin #3 of the power tube socket, but double check that. Be careful, its gonna be somewhere between 300-600 volts!

Preamp tubes do not need to be biased.

Here's a short youtube video on biasing...it's just one in a series of "how-to" videos.
YouTube - How to Change Tubes on Vacuum Tube Amplifiers : Pulling Pre-Amp to Change Tubes on an Amplifier

 

[ryan.kroemer@bigpond.com]

Checked out joepopp jcm 800 2204 build he checked pin 3 for amp plate voltage would this be the same for the 2203.
thanks guys very helpful

 

[ryan.kroemer@bigpond.com]

got it all sorted now thanks!