Marshall 2203KK questions

[nbarts]

Well, their customer support is sure great. Their technical department just got back to me that they are not qualified to answer my questions. So here it goes, if anyone can help me out here:


I understand it has 2 bias trimmers inside. I was wondering which trimmer is for which pair? Does it go as inner/outer pair or left, right?

What power tubes can I use without making any modifications to the amp other than KT88s?

Since it has a bias trimmer per each pair, I assume I'm safe mixing 2 different types(pairs) of power tubes?

 

[FortinAmps]

Here is a link to the 2203KK schematics
http://docs.google.com/fileview?id=...DUtYzYzYS00YjBlLTkxOGItZmE3ZWQ2ZTk1MTc0&hl=en
http://docs.google.com/fileview?id=...GUtODdkMC00ODFjLWJjN2QtNmY4MzI3NDdlZDM0&hl=en

Bias_1 adjusts V101 and V102
Bias_2 adjusts V103 and V104

Best way to confirm is to pull the outputs and measure the bias feed to the output tube sockets while adjusting the bias pots but it seems that the orientation is the 2 left tubes are on one bias adjustment and the 2 right ones get the other.
Cheers,
Mike

 

[Digital Jams]

Hey Mike

I like the 800KK and like the KT88s in there, cool amp.

 

[nbarts]

Thank you very much!

I saw the schematics & those were my thoughts too, but I like the idea of checking it.

Mike, am I safe mixing 2 types of tubes in this thing?

Here is a link to the 2203KK schematics
http://docs.google.com/fileview?id=...DUtYzYzYS00YjBlLTkxOGItZmE3ZWQ2ZTk1MTc0&hl=en
http://docs.google.com/fileview?id=...GUtODdkMC00ODFjLWJjN2QtNmY4MzI3NDdlZDM0&hl=en

Bias_1 adjusts V101 and V102
Bias_2 adjusts V103 and V104

Best way to confirm is to pull the outputs and measure the bias feed to the output tube sockets while adjusting the bias pots but it seems that the orientation is the 2 left tubes are on one bias adjustment and the 2 right ones get the other.
Cheers,
Mike

 

[Marvel]

What power tubes can I use without making any modifications to the amp other than KT88s?

6550

Since it has a bias trimmer per each pair, I assume I'm safe mixing 2 different types(pairs) of power tubes?

No. Each pair is one "leg" of the power amp. You know how it works/ looks when you mix two different pairs of shoes.

Marcin

 

[FortinAmps]

Thank you very much!

I saw the schematics & those were my thoughts too, but I like the idea of checking it.

Mike, am I safe mixing 2 types of tubes in this thing?

No problem for the schemo.
No on the mixing of different tube types as it is. First you'd have to modify the circuit so that R109 and R107 gets one bias and then R112 and R104 gets another bias. Then you'd have to modify the bias circuit to supply 2 independent bias voltages to the 2 above nodes. Depending of what tube types you want to mix, the next issue is if that OT will handle the mismatch on the primary side
Cheers,
Mike

 

[nbarts]

Very helpful! You guys rock!

Thanks!