Problem with ARC REF150

[Ed944t]

Recently bought a Ref 150. When I check the bias 3 pairs of KT120 are OK. On the fourth pair one tube measures 65mV but the slave tube more than 24V!
There is no audible distortion or R/L unbalance in the volume. The concerning tube doesn't glow extensively and isn't extremely hot. Any advice???

 

[Nemal1]

Initially you could try swapping the good and bad tubes over and checking the bias again which will indicate the tube quality prior to investigating other possibilities
good luck

 

[microstrip]

A reading of 24V is probably due to a faulty cathode resistor - if you are using a multimeter, disconnect the power cable , put the multimeter in the 200 ohm range and measure the resistance between the test points - a good resistor should show between 1 and 2 ohm - the 1ohm cathode resistor added to the multimeter cables resistance.

Remember that the .065V reading is carried reading the voltage across the 1 ohm cathode resistors. No way a faulty tube can cause 24 amps going through a 1 ohm cathode resistor - it will usually blow the fuse or unfortunately sometimes the resistor .

In such case the tube is simply not operating - you should have less maximum power and somewhat lower sound quality due to an unbalanced push pull.

 

[Ed944t]

I was thinking about faulty measering points - is in fact the resistor- because the tube was glowing normal and wasn't running super hot.
But in case the tube is not working, should it then not glooiing at all??

 

[microstrip]

I was thinking about faulty measering points - is in fact the resistor- because the tube was glowing normal and wasn't running super hot.
But in case the tube is not working, should it then not glooiing at all??

The glow you see is due to the filament - if a tube plate goes red it means it is getting too hot due to excessive plate current!

 

[Addicted to hifi]

I gave up on tubes because of there reliability.

 

[Pacha]

What was your final solution to this issue?
Hopefully it was not too expensive.

 

[Phantom-Audio]

few of my clients have complained about ARC gear reliability issues especially stuff they are releasing in the last 10 years. Hope you get it sorted soon.