MKIV Upgrade help

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MKIV Upgrade help

Postby justinsweber » Sat Sep 20, 2008 9:40 pm

I have a MKIV and it is in need of a new power tranny.
So its a dynaco MKIV, triode electronics driver board and a grafted MKIII cap board...

I want to buy the power tranny from triode for a MKIII.

1st question is, can I use a MKIII power tranny and a MKIV output tranny with EL34 tubes?

if not... then

2nd question: Can I run a MKIII power and output tranny with KT88 tubes with a MKIV driver board... the triode electronics board I think is a downsized MKIII upgrade board?

Sorry for the questions... Im just trying to put my amp back together.

Thanx

Justin
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Re: MKIV Upgrade help

Postby kheper » Sun Sep 21, 2008 1:54 am

justinsweber wrote:I have a MKIV and it is in need of a new power tranny.
So its a dynaco MKIV, triode electronics driver board and a grafted MKIII cap board...

I want to buy the power tranny from triode for a MKIII.


Why, when MKIV power transformers are available?

1st question is, can I use a MKIII power tranny and a MKIV output tranny with EL34 tubes?

if not... then

2nd question: Can I run a MKIII power and output tranny with KT88 tubes with a MKIV driver board... the triode electronics board I think is a downsized MKIII upgrade board?

Sorry for the questions... Im just trying to put my amp back together.

Thanx

Justin


You will be getting over 500V B+ with the MKIII transformer. My guess would be 525V. This is more than pushing the max screen grid rating on an EL-34.

You would also need to check the schematic on the driverboard. You may need to tweak some resistors for the correct voltage drop from the filter caps.

You need to check the voltage rating on the cap board as well.

KT88s will work with a MKIII power transformers and A470 output transformers.

Why redesign a well designed amp?
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Postby mesherm » Sun Sep 21, 2008 2:01 am

The MkIII PT is 430-0-430 while the MkIV is 370-0-370. So the MKIII PT will not subsitute.
Just buy a replacement MKIV PT.
http://www.dynakitparts.com/store/product.aspx?id=244
Mike's N-1 Rule: When looking for N number of components to finish a job, you have a 95% chance of only finding N-1 of them.
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Postby justinsweber » Sun Sep 21, 2008 2:07 am

very true Ill just replace it with the correct part...
I have a lead on a person who sells a MKIV cap baord that fits inplace of a bias caps and replaces the twist lock... I want to use him, but have not seen others make use of it... the idea of using a part that looks homebrew and not widely used worries me.


His baord uses : 60uf 700V, 135uf 500V, 47uf 500V x 2, 470uf 100V x 2 for bias section. Does this sound liek a workable selection? I really want to use a cap baord instead of the twist loc cap...

Thanx everyone for the advice.

Justin
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Postby TerrySmith » Sun Sep 21, 2008 5:56 am

If your referring to the Chong (Audio sound lab) cap boards sold on ebay, then buy it. I have two MK 4's, both with this cap board, sounds great and the boards fit perfectly.
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Postby justinsweber » Sun Sep 21, 2008 3:29 pm

I am.... Im so happy to hear some good news about is work... I had not seen much spoken of him.... THANK YOU.
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Postby kheper » Sun Sep 21, 2008 6:55 pm

mesherm wrote:The MkIII PT is 430-0-430 while the MkIV is 370-0-370. So the MKIII PT will not subsitute.
Just buy a replacement MKIV PT.
http://www.dynakitparts.com/store/product.aspx?id=244


The P782 S transformer, sold at triode is specified as 400-0-400.

http://store.triodestore.com/mq782.html
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Postby mesherm » Sun Sep 21, 2008 11:51 pm

The P782 S transformer, sold at triode is specified as 400-0-400.


I was taking my info from the Dynaco MKIII manual which listed the AC voltage at pin 4 and 6 of the GZ34 at 430 volts. I would hazard a guess that the newer replacements are probably made with lower voltage to reduce the possibility of original filter cap failures. A 400-0-400 with a higher voltage drop rectifier would be one possible modification.
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