what model cayin, elliott?
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.
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.
Showing 6 responses by jjss49
https://forums.stevehoffman.tv/threads/tube-integrated-with-autobias-equivalent-to-cayin-a88t.784890... if you haven't seen this elliott - some interesting background and discussions |
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... |
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)? i would say that if the bias is well set at the start (when new quad of kt88’s are installed) then over time as the tubes age the bias will run a bit low for ideal sound but if you can’t hear a difference, then leave it be... the tubes will become under biased as they age and they will run cooler/easier and actually last marginally longer in use - once again, if you cannot sense a sonic penalty then leave well enough alone, just enjoy the music middle of rotation on bias pots don’t mean much, as there are different sensitivities in the pots and more importantly different bias needs of the tubes set being driven... so best to have a tech read the correct bias voltage for your tubes set and set properly once, then go from there... as an audio research tube amp user for years i have become kinda OCD on bias settings as there is much lore about failing power tubes and how bias resistors can be damaged in the amps when a power tube fails - so i am conditioned to check bias conditions fairly frequently (once a quarter, say) - but to be honest i have never let the bias run way off under or over the recommended setting, and so i cannot speak to whether the sonic penalty is noticeable... if anything i set the bias 5-10% below the recommended level to get a little more tube life, and i feel there is no sonic penalty i could hear with various arc amps running 6550/kt88's -- vt50, vt60, vt100, ref 75, ref 110 etc etc... |
@elliottbnewcombjr yes a wooden or plastic stick with a screwdriver blade at the end of it would insulate you from any spurious shocks for sure... that is why audio research supplies the skinny long plastic screw driver for bias adjustment -- here is one you can just buy quick from amazon https://www.amazon.com/Potentiometer-Tools-Hardware-ADJUST-TOOL/dp/B06Y6FTGNT/ref=pd_bxgy_img_2/139-... you probably know this but a proper bias setting is specific to a particular set of power tubes (it is not to the amp, irrespective of tubes)... change power tubes in the same amp, you need to re-bias... i have had different tube sets (even of the same make/type of tube - say a sovtek 6550c quad) need quite different bias settings to achieve the correct biasing level question -- you use a wooden or plastic handled screwdriver as per above, cool - but how are you going to measure the correct bias level for each kt88 pair? i did not see instructions for your a88 amp how/where to measure it... @oregonpapa dunno if your ref75 is your first arc tube amp -- they made power tube biasing much easier on that amp (long overdue)... on earlier models you needed to open top cover, use multimeter with hook prongs clip onto both sides of a bias resistor and read 65 ma at proper bias level... reaching into the running amp with hot tubes with the clips or with the biasing screwdriver took some nerve and fine motor skills lol here is the process for the vt100 -- point is, you need a way of reading the correct bias setting!! https://www.youtube.com/watch?v=GnBuI0sLhcg |