VTL IT-85, Owner'S Manual

IT-85 Integrated amplifier  
Owner’s Manual 
VTL 

22

the VTL IT-85 Integrated amplifier.   

For checking the bias you should take the unit and this procedure to your authorized 
VTL dealer and ask them to check the bias for you

. 

Notes for the service/installing technician: 

Bias measurements are preferably taken with a digital multimeter equipped with the 
auto-ranging feature.  If you don’t have such a meter you can purchase one at a local 
electronics supply store such as Radio Shack.  The Radio Shack catalog numbers for 
usable multimeters are 22-166, 22-167, 22-163, 22-174 or even 22-179. 

Use the following procedures to measure and adjust the bias setting:

1. 

Make sure that the IT-85 is 

powered

off

.  Remove the protective metal 

cage of the IT-85, and make sure that there is sufficient room around the 
unit for you to access the bias measurement points at the back edge of the 
IT-85. Set the multimeter for resistance measurement (ohms).  (Consult 
the owner’s manual of the multimeter to make sure that you have used the 
correct settings.) 

2. 

Connect the negative (black, “-“) probe from the multimeter to the ground 
point on the IT-85or the negative (“-“) speaker binding post of the 
amplifier.   

3. 

Consult the following figure for the locations of the bias measurement 
points on the IT-85’s top deck. Insert the positive (red, “+”) probe of the 
multimeter into each bias measurement point.  The resistance reading on 
each point should be 10 ohms, within a 10% range.  If the resistance 
reading is outside the acceptable range, please consult the VTL factory 
customer service department immediately. Repeat the measurement 
procedure for all 4 bias measurement points. 

4. 

Remove the multimeter probes from the IT-85. Check to make sure that 
the IT-85 is connected to a loudspeaker or a load resistor. Power on the 
IT-85 and let it warm up for about 10-15 minutes so that the tubes 
become stabilized.   Either short the input or put the IT-85 in the mute 
state (or turn the volume down) to make sure that no signal is coming 
from the preIT-85 section.  

5. 

Change the meter setting to measure DC voltage.  Insert the negative 
probe (black) from the multimeter into the ground point on the IT-85 or 
the negative speaker binding post of the IT-85 fitting it into the post 
where the speaker cable is connected.  Insert the positive probe into the 
bias measurement point of each tube going from the #1 point to #4.  The