Dyna Clone A470S OP tranny

a DIY, modified Mullard 5-20 monoblock design

Dyna Clone A470S OP tranny

Postby Marshman » Mon Dec 06, 2010 2:19 pm

I just got done modding my sons diytube ST35 to fixed bias. I just cannot believe the difference in sound. I am lead to believe that the fixed bias in conjunction with the 565 trannys is what I am hearing.

Thinking of upgrading my Ikes with the A470S transformers. Can I just swap the Hammond 1650's out for the 470's?? Looks to my inexperienced eye that the specs are close.

mm
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Postby EWBrown » Mon Dec 06, 2010 3:34 pm

The A470s can be used, and most likely with better results than with the Hammonds.

If the mounting hole dimensions are the same, it will be a simple "drop-in" swap-out. Otherwise you may have to do some more chassis drilling

IIRC, the Hammonds may have a "reverse" primary to secondary phase relationship, if the amp sounds like a fog horn after the tranny change-out (Positive feedback, instead of negative FB), it is easy enough to swap the connections - the easiest way to do this, involving only two connections, is to swap the wiring from the two driver board outputs to the power tubes' control grids.

BTW, I just unboxed a 2003 vintage rev C ST-35, and will be giving it the EFB modifications, I just have to get myself an LM373, if I can't excavate one from the cellar goodies...

/ed B
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Postby Marshman » Tue Dec 07, 2010 6:28 am

Thanks Ed!

I think I will give it a try. Chassis drilling is definitely not a show stopper!! Now to find an extra couple of hundred bucks at Christmas time... sigh.

I think you will be pleased with the EFB mod. It sure opened my ears!!


mm
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Postby Geek » Tue Dec 07, 2010 7:22 am

Marshman wrote:Now to find an extra couple of hundred bucks at Christmas time... sigh.


Convince the wife it's what your REALLY want for Christmas ;)

Cheers!
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Postby TerrySmith » Tue Dec 07, 2010 9:14 am

If you have room you could use the A-431 (Mark-3) output transformers, same electrical specs just more iron!
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Postby Marshman » Tue Dec 07, 2010 2:15 pm

@geek - no wife, no girlyfriend, no problem!! ;-p

@terrysmith - wow!! those things are 12lbs each!! seriously more iron! Not sure they would fit, but I will take a more serious look at them. $130 a piece too... whew...

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