Tube amplifier - tube bias and time to warm up
Power Amplifier
I have a Cary Rocket 88R tube power amp, it is not an integrated, power amp only, but my questions are pretty basic.
The specs for biasing my amp are 195-220 Milliamps.
Currently it has:
Status
All tubes light up.
No tubes are glowing hot.
All fuses (2) are working.
When I power up my amp to do the tube biasing, I'm not getting any milliamp reading on my Multi Meter. Am reluctant to leave amp on after 30 seconds with no milliamps showing. Worried I'll blow something.
I get a rise up to about 40 Milliamps when I turn the amp off. But nothing within 30 seconds when it is on. The Bias LED's are lit, which indicates that there should be bias current available.
When I remove the Bias headphone jack, I do not get any sound out of the amp.
All tubes light up - but no sound. But again, I'm shutting the amp off after 30 seconds for worry that I don't have the Bias set properly and I could damage it.
I've had the amp in the shop months ago and I don't recall how long it takes to warm up to get a bias read, and long enough to put out sound.
Questions:
Thanks for any thoughts.
Graham
Ralph, I see. I think, Brent from Audio Tubes does this kind of matching for extra charge. I was somewhat surprised that VAC Avatar's manual says nothing about tube matching, even output tubes matching. mulveling, this continuous auto biasing, is it done only for sound quality or also for tube longevity ? |
@inna VAC does recommend sourcing replacement tubes from themselves - which would include the necessary matching and low noise screening for your amp.
VAC's stance is a 3-way benefit: sound quality, tube life, and reliability / fail safes. I can only say that as a user of iQ amps for 4 years, they've been 100% reliable, with no incidents, and never any worry nor need to recheck bias. If a tube looks like it needs replacement soon, a front panel LED corresponding to that tube is supposed to light up. If it starts to go REALLY bad, a different LED color lights up and the amp shuts off. I haven't had any LEDs light up on me yet. I've compared the 200iQ directly to its predecessor Phi 200 (without auto bias) and yeah, the iQ absolutely sounds better. Since this year, I've been running Master 300iQ. |
It is tempting to experiment with this, to buy a few brands of totally unmatched tubes, mix them randomly and see what happens, see if I can hear the difference with perfectly matched same brand quad. Judging by what you all say, I should be able to hear the difference. In my conversation with Kevin about tubes he said absolutely nothing that could be interpreted that he recommended getting replacement output tubes from him. He kind of suggested getting 12AX7 tubes from him but not 12AU7 or EL34. It was an excellent conversation, by the way, I liked Kevin. |
STATUS: 11-10-23 APPRECIATION Thank you all so much for your detailed responses. The response was far more than I ever expected. Content and detail is exceptional. |
Maybe somebody with real technical chops can correct me, but I don't even bother to check bias when I first turn my main system amps on-- Lamm ML2s. I run them for 45 minutes to warm them up and may check bias at that point, using a Fluke meter, but often, let them play in for a while longer--usually three LP sides after the 45 minute warm up. One amp is always rock solid; the other varies by a few increments. It used to bug me out, but as long as it isn't red plating, I'm good. One thing I found- I also have 12ax7s on the front of the amps- and the "pulls" typically varied. Getting actual never used old stock made the amps far more stable. Go figure. |
