cossor 805 current plate

xico

New Member
Sep 16, 2019
5
0
1
54
can somebody help me ? bought cossor 805 tube to substitute Original ones, now ...original ones are biased at 120ma, the cossor following the given data sheet that comes in the box are biased at 65ma ! ...can this be ??????!!!!!!! huge difference in bias hence the question. thank you.
 

cjfrbw

Well-Known Member
Apr 20, 2010
3,325
1,316
1,730
Pleasanton, CA
Maybe 120 is a single adjustment which divides in two for the two tubes if there are a pair in the amp i.e. each tube gets 60 ma.

Because it is a transmitter tube, the data sheets don't show much for audio use, but it does look like grid current should not exceed 70 ma for 805 (assuming you are talking about grid current, you don't specify the nature of the bias).
 

xico

New Member
Sep 16, 2019
5
0
1
54
thank you for the answer,
well, I have a line magnetic 805ia integrated amp, this amp has two meters , each meter should be at 120ma with the Original 805 tubes (following the manual) .
i can't find more information online about the cossor 805 tubes so that i know how to bias them .
on the data sheets(carts) that come with the cossor 805 tubes i see only the following :
-filament current at Uw=10v / measured:3.25/ value: A
-plate current at Uw=10v
Ua=1500v
Ug1= -10v / measured value: 65ma

once more thank you for the help, i am a bit loss .
 

xico

New Member
Sep 16, 2019
5
0
1
54
-on the operation manual : -select the tube you want to adjust (from V01 and V02) ,then position the bias current and adjust the tube bias with a small screwdriver .make sure all the bias level of V01 and V02 are the same.
-inspect the ampere meter on the front panel and make sure the needle is in the same area ia=120mA.
 

cjfrbw

Well-Known Member
Apr 20, 2010
3,325
1,316
1,730
Pleasanton, CA
The two main 'currents' are plate current and grid current. The grid current is lower, and might be what the new tube refers to. The amp must be measuring the plate current, which can be higher depending on the B voltage.

Most of the time bias describes the grid current. The question is do your meters actually measure plate current, in which case 120ma would be appropriate. It obviously is too high for grid current. Why your amp does it that way I don't know.
Screen Shot 2019-09-17 at 2.03.59 AM.png
 

xico

New Member
Sep 16, 2019
5
0
1
54
i am now even more confused ,
i do think the meters from my amp measure plate current, hence the 120ma per tube for the Original ones, (it can not be grid , is to high for that),
what confuses me is that (as i posted above ) the data sheet says :plate current : 65ma,
but indeed it perplexes me that the plate current for the cossor tubes can be so low,....it looks more like grid.
 

About us

  • What’s Best Forum is THE forum for high end audio, product reviews, advice and sharing experiences on the best of everything else. This is THE place where audiophiles and audio companies discuss vintage, contemporary and new audio products, music servers, music streamers, computer audio, digital-to-analog converters, turntables, phono stages, cartridges, reel-to-reel tape machines, speakers, headphones and tube and solid-state amplification. Founded in 2010 What’s Best Forum invites intelligent and courteous people of all interests and backgrounds to describe and discuss the best of everything. From beginners to life-long hobbyists to industry professionals, we enjoy learning about new things and meeting new people, and participating in spirited debates.

Quick Navigation

User Menu

Steve Williams
Site Founder | Site Owner | Administrator
Ron Resnick
Site Co-Owner | Administrator
Julian (The Fixer)
Website Build | Marketing Managersing