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Power Transformer rating of Yaqin MC-100B, MS-12B

J

jsnh62

New Member
Hi,

Does any one know the ratings of the power transformer of Yaqin MC-100B/MS-12B/MS-300C? Mainly the current capacity for the tube heaters.

When rolling tubes, the current required by the tubes is always a concern.

I have asked Yaqin factory about using KT-120. They said, it is OK to use KT-120 on MC-100B and bias setting is still 0.5v.

Then, how about 12BH7 to replace 12AU7 in MS-12B?

I have also searched online, but found nothing.

I have sent Yaqin another mail for requesting the rating of the power transformer just now.

Maybe some experts here know about this?

Thanks!!
 
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You can calculate yourself. Measure idle voltage, then DC resistance. It should give you a base data to calculate loss in secondary. Transformer itself can handle more power, I run tubes at 85 mA idle current and power transformer temperature is within acceptable limits in that mode. I do not think you get much improvement from KT120. The max I would do is KT90 with 100 mA idle. In that mode you would get it running almost all power range in class A. Higher idle current gives you more sound improvement than simple tube swap. It reduces THD significantly (I have evidence of it both from simulation and actual measurements). Higher rated tubes lets you use higher idle current without exceeding its limits. I wouldn't recommend more than 100 mA at idle, as output transformers get quite hot.
 
Thanks for_p1.

I asked Yaqin about KT120 was to know if the amp can handle that by original design. And since this information was replied from the manufacturer, I would like to share with guys here.

In Chinese, we have an old saying:

A country folk, sitting under the sun in a winter day, enjoying the warmth and comfort from the sun light, he said to himself: I want to tell our king about this and let him enjoy the sun, too.

kind of silly, but true-hearted.

Currently, I am quite happy with the KT88.

My question is about the power transformer (not output transformer). The 6.3V for filament. Say, if use 12BH7 to substitute 12AU7 in MS-12B

12AU7, 6.3V, parallel, 0.3A
12BH7, 6.3V, parallel, 0.6A

Is the power transformer capable of supporting this 0.3 * 2 = 0.6A (two tubes) extra current requirement?

That is why I asked the ratings of the transformer for these 3 models.
 
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