Bias for cayin a88t

[ck_ian69]

Hi probably many bros here still use this classic amp back from the halcyon days of precision audio. Does anyone know how to bias it? It doesn’t have external bias pots and from internet, seems like one needs to remove the bottom cover. Anyone done it or knows someone who can do it?

[Eric Teh]

Yes, me.

 

The bias pots are internal and the procedure is a bit dangerous because of the lack of dedicated test points.

[ck_ian69]

Well I think I am too inexperienced with electronics to do this. Do you know anyone else who can assist (for a fee)

 

Thank you

[Eric Teh]

If you are willing to bring your amp down, there are quite a number of professionals that would be able to help you. Let's see whether anyone here can help you with this. Otherwise if you can find a friend with a digital multi-meter and is comfortable working around high voltages, PM me and I'll share with you the biasing instructions.

 

BTW, there is no need to bias your amp unless you haven't done so for a long time, or you have changed power tubes. If you have changed power tubes, I would advise you not to use the amp until it has been biased properly as your previous bias settings could be wrong for the new tubes and running them too hard.

 

Cayin learnt their lesson from this, subsequent models have easy bias methods that can be done without opening the amp.

[spiff1624706012]

The mk1 is a dangerous to bias on your own, lethal voltage if u accidentally touch wrong area of amp.

Cayin mk2 is safer as there is built in bias meter all ready for easy biasing.

Better still, the Prima Luna has adaptive biasing, just plug in tubes and it will get the optimal bias for you everytime, you need not do any biaising, plug and play. 

[Zeng_tubesamp]

Bias power tubes without signal each power tube tuning to 0.4volt At the PIN number 8 and check very one hrs after heated up