I got VTL power amp with 6l6 tubes. They were perfectly match. Unfortunatelly when I was recently moving, took out tubes and forgot to mark tubes against sockets. Now I’ve connected back whole my set up, most luckily tubes in wrong sockets, it doesn’t play as it was. I don’t have tools to check bias and it really difficult to find any place dealing with tube amps in my city. Any ideas to solve this issue, which makes me crazy :(((
Contact VTL tell them the model no. of your amp. Ask how to check and adjust the output tubes' bias (milliamps). You will only need a multimeter and a screwdriver to do this. Be sure to have a load (speakers) connected when doing this! Otherwise damage to the amp will happen!
Worth every penny. You can plug a DVM in to verify the analog meters accuracy. Analog meters can be calibrated, mine were dead on from the factory though. You don't have to use test points or speaker terminals. Makes it much safer to bias.
You could measure the operating temperature of the tubes. Just install tubes with the closest temperatures in pairs. I know this sounds crazy, but I got matches that sounded better this way from a lot of 24 NOS tubes. Hand held thermometers with digital readout are inexpensive & read instantly.
I had a VTL Stereo 50 and it has external bias points. The voltmeter's positive probe goes in the test point and the negative probe goes in the negative speaker binding post of the channel you are biasing.