Here you go.
HEV90 Tube Bias Procedure
Use variable resistors P2 & P3to adjust ECL86 tubes to a anode voltage amounting to 390-391V.The power tubes(ECL86) should be biased with no input present.
( another version of the HEV90 uses 300v;there where three versions in all).
I know early versions had a red power switch no key.
From the ECC83 package you can see the voltage drop across ECC83 to be adjusted with variable resister P1(unbalanced).
(I never saw a voltage reading on any ECC83 tube packages)
Another way to bias the ECC83 tubes (12AX7) input tubes a constant input
present is needed.We used a 1000HZ signal from a test CD,put on repeat.
With the signal going into the amp,you measure the voltage at the outputs
of the amp (Headphone Jack) there is no single correct output voltage.
The Idea is to match the voltages,so that R+,R-,L+,& L- all have the same voltage.
All sttings are to be checked after a operating time of about 5 hours & corrected if need be.
Once That is done the tubes are biased properly.
I have pics of the testpoints on my hard drive ,but I have to fiqure out how to resize them so I could put them in a post.
