Valve amp bias

[anthonyTD]

For future refrence;
You need to adjust the bias with no signal, if your amp has a volume control, then turn it all the way off, and make sure what ever is plugged into the input ie; CD, Streamer, etc is switched off.
And just be careful where your sticking your meter probes!
Hope this helps.
A...

well ive just done it,i set it with the amp on hooked up to a reciever and speakers connected,should i have done it without anything connected then?
1 thing i did notice is the 1 valve (no 3 from left to right) was out compared to the others,this was the same valve that was out when john adjusted it,does this point to a worn valve?

[Cyrus]

For future refrence;
You need to adjust the bias with no signal, if your amp has a volume control, then turn it all the way off, and make sure what ever is plugged into the input ie; CD, Streamer, etc is switched off.
And just be careful where your sticking your meter probes!
Hope this helps.
A...

Good shout; the amp needs to be in a quiescent state. I'm not sure what the result of pumping a signal in while biasing - should the OP revisit and reset the bias do you reckon? I probably would.

[karma67]

For future refrence;
You need to adjust the bias with no signal, if your amp has a volume control, then turn it all the way off, and make sure what ever is plugged into the input ie; CD, Streamer, etc is switched off.
And just be careful where your sticking your meter probes!
Hope this helps.
A...

Thanks mate, yep I’m using crocodile clips and only using 1 hand etc.

[Cyrus]

Thanks mate, yep I’m using crocodile clips and only using 1 hand etc.

Mine was on its side, not particularly well lit and I was laying on my side! Also, I was having fun adjusting a pot while monitoring the bias current of a totally different valve!

As long as you don't get a bolt it continues to be fun.

[karma67]

You right it is fun, I also noticed when you set 1 valve it changes the bias of anther one slightly so you end up going back and forth.

[Cyrus]

You right it is fun, I also noticed when you set 1 valve it changes the bias of anther one slightly so you end up going back and forth.

Tweak, tweak, return to V1, tweak - V1 & V2 happy. Tweak V3, twek V4, return to V3, happy. Quick measurement - V1 is out, and it starts again!

[karma67]

Lol spot on!

[anthonyTD]

If the amp is being modulated with signal, then the steady idle current will not be correctly set, hence The reason for biasing with no signal present!
Again, hope this helps.
A...

Good shout; the amp needs to be in a quiescent state. I'm not sure what the result of pumping a signal in while biasing - should the OP revisit and reset the bias do you reckon? I probably would.

[anthonyTD]

No worries, just stay safe, there is very high DC voltage in there, especialy around pin three and four of the output valves, in excess of 400v !!!
The bias of each valve in the channel you are adjusting will change slightly, as said, its a balancing act, dont beat yourself up though for a fraction of a ma, its not that critical!

Thanks mate, yep I’m using crocodile clips and only using 1 hand etc.

[Audio Al]

I will have a go at doing my amp as its a loooooong way from London to Nottingham and back