KT77 Bias Question

[ctek]

Hi

I have been lurking here for a while and decided to try 2 KT77's in my Stiletto Ace.

In my enthusiasm I ordered them without specifying they were for a Mesa Boogie. Is this going to cause a bias problem?

So, have a made a cock-up and ordered the wrong tubes?

It is not a big deal as they were only £30 but I dont want to damage the amp

many thanks

Howard

 

[domct203]

Is it too late to call your dealer and change up the order?

Do you have any way to measure the tube's idle current draw? If the tubes are too cold for the amp it will just sound bad. If they are too hot, they could red-plate and possibly take out other components as well.

A bias probe is a great investment, especially when using non-Mesa tubes.

Dom

 

[ctek]

I have already received them and tried them. I dont have any way to do any sort of testing.

I have tried them in the amp and they sound good but I haven't run them very long or very loud.

I suppose I better take them out and ordered some with the correct bias.

H

 

[domct203]

Why not contact your dealer and inquire if the tubes you bought are ok for your amp first?

Checking idle current draw (bias) is real easy with the right equipment, and it is not expensive either. The Mesa's are not adjustable so there is no need to open up the amp and expose yourself to lethal voltages. Simply compare measurements between the Mesa tubes and your new ones. If the readings are within + or - 5mA you should be fine.

This is what I use:
Weber Bias Rite

I have the BR-AH Octal w/VI option, and use it with my own DMM. It's only $60 (US). Even the one without the VI option (even cheaper) is better than guessing.

Even if the tubes are correct for your amp, I strongly suggest the investment in a bias checking device.

Dom

 

[stokes]

If they sound okay and arent redplating,you can get away with using them safely.May not be the best for your tone,but they are safe if they arent redplating.Play the amp cranked and keep an eye on the tubes,if you see the large grey structures in the tube begin to glow red/orange,they are too hot and should not be used.A bias rite or similar bias checker is a good idea,you can then go one step further and learn to adjust your bias and use any tubes you want.

 

[ctek]

many thanks for the advice.

I have emailed the supplier and will wait to hear from them - that sounds like the safest plan.

I dont get chance to crank the amp except at rehearsals/gigs and the band is having a bit of a hiatus at the moment.

Cheers

Howard

 

[hfisher3380]

Hi

I have been lurking here for a while and decided to try 2 KT77's in my Stiletto Ace.

In my enthusiasm I ordered them without specifying they were for a Mesa Boogie. Is this going to cause a bias problem?

So, have a made a cock-up and ordered the wrong tubes?

It is not a big deal as they were only £30 but I dont want to damage the amp

many thanks

Howard

I'm under the impression that KT77 is a drop-in replacement for EL34, meaning there should be no problem in an Ace. Lots of people on here have stated their fondness for this particular tube in the Stiletto series. But as others have stated, best to check with your dealer if you're uneasy about it.

Howard (another one!)