2. analog
  3. 162685-132884

TUBE BIAS, socket to me!

BIAS: (I'm starting from zero understanding) 

I have never measured/adjusted bias in the 3 tube amps, 3 tube receivers, and 2 tube preamps I have acquired over 47 years. I just switched my current Cayin from 6550's to KT88's. Adjust bias? Adjusters inside, scary electrocution warnings. I could pay someone else to do it, i.e. Steve at VAS 1 hr away in NJ, soooo, 

What really counts? (personally I don't care about either heat or life, but would like to understand)

Heat?
Life?
Output stays Matched when adjusted?
Acoustic Performance?
_________?

Over the years, fronts off, bottoms off, I hose em down with contact cleaner/lubricant, compressed air, all controls and switchers, any adjusters, swish full spin back and forth. Kill any spiders, look for, replace the rare burnt resistor. 
Then leave any adjusters (whatever they are) in the middle position, button it back up.

Two tube testers, my big hickock always agrees with small portable one, test strength, shorts, matched strength old and newly purchased. Large collection of NOS, used. Often used test essentially same strength as new ones.

When they go, it's usually a short.
elliottbnewcombjr
jjss49's avatar
Ag insider logo xs@2x
jjss49
6,612 posts
 
that sino made a88 amp has been out there for years, sold under various brands subbrands (line mag, cayin, grant fidelity yaqin etc etc) and with different front panels and biasing features (or lack thereof) as the chinese manufacturer matured and tried to move up market and sell effectively into different overseas markets

elliott if yours doesn’t have meters or accessible biasing pots you are best off getting it in the hands of a tech who knows tube gear...
oldhvymec
5,101 posts
 
OK yours is older.. Still no biggie.. I was taught by an OLD guy in the 70s.
I looked at a newer one..

You can looked up the pin out on the valve.  Find the ground, find the plate, you could see the wire going to the bias pot.

There are a lot of the older ones with internal bias pots..

If you don't feel confident, best to watch someone do it. Pretty easy though..

Regards
elliottbnewcombjr OP
5,529 posts
 
Everyone,

Thanks for the help as always,

I know how to do it, what the proper setting is.

These Cayins have high quality ceramic tube sockets, they are very tight. They are surprisingly beautifully made with high quality components, far beyond my old experiences of 'made in China'. I highly recommend them.

It sounds great, I don’t have any issue, except I changed from 6550’s to KT88’s, I thought, it’s time to learn. Electrocution warnings are the only thing holding me back.

........................

I don’t care about heat or tube life.

My questions were:

What are the benefits of proper settings (every 6 months) and what are the potential problems if simply ignored, (as I have done for 47 years)?

If the adjusters are simply set in the middle of their rotation, as I always do, and the thing sounds great, should I risk electrocution?
elliottbnewcombjr OP
5,529 posts
 

twoleftears

Thanks, that is the factory manual which I have, no mention of bias at all.

I found a discussion from audiogon member plangco, says ,4; he uses .35 for longer life and warmer sound.

It is his "the voltages can be lethal" that gives me late life cowardice.

That, and the very old but unforgettable memory of being kicked on my assss by a tv I had just unplugged. I replaced the cheap internal speaker with a better external one. That's when I realized, there has always been the potential of better sound out of TV signals.
elliottbnewcombjr OP
5,529 posts
 
millercarbon

thanks for providing that understanding, big help just knowing 'why' bias exists.

Is it fair to say, if it sounds great, don't mess with it, or why bother as some suggest?

As for 'right or wrong', 'better or worse' how do you know unless you have a problem, or a problem/change presents itself?

Up to now, those same 47 years, my friends and I: any and all of my tube stuff has always been preferable to SS (darn good SS) with 'middle of the adjuster' settings.
More to discover