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Quick and Dirty Class "AB" mod for KL300p

2NC995

DAN
Feb 23, 2008
2,219
3,966
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Coastal NC
Yeah, I hope so. I can understand the written instructions, but the pictures would be nice. I have a 1x4 class C amplifier with Toshibas. Trying to decide if I should sell it, or remove the driver and try to properly bias it, so I can use it for...something. Lol.
 

binrat

WDX Club Coordinator
Staff member
Nov 5, 2008
2,534
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The Great White north
I did a board about the sametime as the OP posted this thread but can't find the notes I had. It work on a X-Force 2 pill I had very well.
Personally, drop the 1x portion of the amp.
 

Naysayer

Member
Mar 6, 2020
24
19
13
New York
Good to see some other working on adding Bias. I've been slowly collecting parts to redo the bias in a Palomar 900HD (4x2879). As such, the amp already had the Tip31c and 7805 Regulator circuit for bias. I began modding it to run at 28v with 4x MRF422's (I have HG's). My idea was replacing the 7805 and PCB trim-pot with a lower V regulator and using a panel-mounted 10T precision pot to adjust as needed. A calibrated 1v panel meter would fit nicely to aid in monitoring/setting bias v as needed. The variable bias idea I read long ago on R. Measures (Silent Key) SB220 website.

It was the ifw reference to G3SEK that got my attention. I built Ian's Tetrode boards where bias is 'steadied' by standing Screen current to help stabilize Screen voltage.
Anywho, we both got to the same place from opposite directions LOL.
 
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Naysayer

Member
Mar 6, 2020
24
19
13
New York
I'm having problem with regulator heat on paper when dropout V is factored in with 28v source.

Need to divide it down a bit...standing current. 4 MRF422's need 400mA for AB which is a lot of heat. Must include small fan. 1v meter from PRC is taking forever, Orange Connex is terribly slow.

 

Naysayer

Member
Mar 6, 2020
24
19
13
New York
The higher 28v will cause too much heat for a 7805 larger LT1085 will fit but I'm not sure it will go below 1v for .6. Ferrite beads on leads to panel mounted 10T pot and 1v meter.
Still working on it.
 

sp5it

Master of puppets
Jul 9, 2009
2,154
2,563
273
Poland
www.qrz.com
I'm having problem with regulator heat on paper when dropout V is factored in with 28v source.

Need to divide it down a bit...standing current. 4 MRF422's need 400mA for AB which is a lot of heat. Must include small fan. 1v meter from PRC is taking forever, Orange Connex is terribly slow.

Use buck converter, or high wattage resistor inline, before regulator. All the heat will be on resistor.
 

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