Bias adjustment

DMM or Analog

A good DMM Digital MultiMeter will cost 30-75 dollars. Self calibrate, there is no analog issues as with stick meters. Analog meters are not accurate, they have to be calibrated with a DMM, so why waste your money, your time, or you breath? If your lucky, 2-3 years. In oil for vibration control, still 2-3 years, but normally can be calibrated, with a DMM. Analog looks good, but really don't trust them...

Digital SELF Calibrates. or battery change time, one of the features.

There is no arguing with the numbers then.  Normally when you burn out a valve, burn it up, use it up prematurally, it normally points to over bias. 
You, need to know, supply and demand go hand in hand, with any amp, valve amps, more so.  Maintain 120 vac.  Get good valves, well matched signal and power valves. Use a DMM and you'll be happy. You can tell the tec you DID bias the tubes correctly. But you'll find out they were probably correct...

Regards

BTW I got a pair of great DMM from PE, 49.00 each, will tell you the numbers through your phone. Just as good as my Field Flutes just not as rugged, or as visible (orange).

Regards

@ richfrank

I know what I read on the VOM and it was reading 80 mA as it should be,

Shouldn’t the bias be set at 75mA as the manual says?

Bias Adjustment
Set bias for both sides of the amplifier to 75mA

As oldhvymec mentioned in his post is the meter a DMM, digital multi meter? If the meter is a really cheap one its accuracy may not be all that good.
Can you provide a Web Link for the meter you have?

Just curious, how many hours are on the KT 88 tubes. General rule for power tubes life is around 1500 to 2000 hours.

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@richfrank Just to confirm what I think you said, the Cary tech insisted your bias reading was incorrect even though they didn’t have the amp in their possession to dispute your reading? Weird. Yes, the manual says 75mA but honestly 80mA shouldn’t be an issue. How old was your amp? Were they offering to perform warranty work and that’s why they said to ship it to them? If in fact "bias neglect" wasn’t the cause of your power tubes burning out why wouldn’t you want them to look at it and figure out what the REAL problem is? When I bought my SLI-80HS from them last fall it arrived with a buzz that seemed to be related to a wonky triode/UL toggle that I suspect was damaged during shipping. They paid for shipment both ways and fixed the issue 100% at no cost to me. The amp is a sweet little unit that I now run with KT-120s and some 60s NOS 6922 Mullards. I feel like they handled my situation just fine and would recommend them. Just another data point for what it’s worth.

jea483,321 posts04-16-2020 5:27pm@ richfrank

Just curious, how many hours are on the KT 88 tubes. General rule for power tubes life is around 1500 to 2000 hours.

I have KT-88 valves that are well over 5000 hours, with 40% left in the tank. 

VTLs El KT-90s AB amps 15 year old, 20 hours a week for 15 years, still sound very good and hold a bias.

The KEY is do they hold a BIAS. Good indicator of a healthy machine and valves.

Who makes the valve? MATCH the valves.
1 and 2, need to be close, 3 and 4 need to be close, not 1 and 3, 2 and 4 ok makes a difference, when matching. and then the bias will be closer per side...noise reduction and extend valve life..

If the valve is holding the bias, and you going through valves, it's usually to hot. Go down to 70ma for 2 valves, if it sounds good not muddy, leave it and listen...35ma per valve should be plenty, and extend valve live A LOT.. EL34 6L6, KT66, KT77, and 90 if you can. all at 70-75 per pair

Second if you bias to high it WILL distort quicker at higher volumes.
Not playing in the band, trying to listen to the band. AY??

Parts Express pt #390-501 under 8.00 usd get 30 dollars worth.. LOL
The ones I got there they may not have. LOOK 8-99.00 dollars. Several to choose from and great tec support..Even if you need to make up a pigtail for you meter, and amp, they'll help. Next day delivery if you want.

Regards