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KLB-300 Amplifier Overhaul (2x 2sc2879's)

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Old 11-29-2005, 08:53 PM
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Default KLB-300 Amplifier Overhaul (2x 2sc2879's)


G'day Folks....
A few months ago i picked up a KLB-300 amp. The KLB amps were manufactured in Japan and were sold here in Australia back in the late 80's early 90's. Models include: KLB-110DX, KLB-240DX, KLB-300 and a CVS-450 UHF amp. These are models that i am aware of.
This particular amp i purchased was in fairly good condition for it's age. Besides the meter being pushed in, everything else was in good working order.
I fired the amp up into a 50 ohm dummyload and found that the input swr was high, and went up higher when i flicked the amp to Hi power setting.
Output power was; 3watt D/K from radio, amp 50w swinging to 100w AM and to around 160w SSB, on a Bird 43 meter with a 250H slug @14v.

Upon removing the cover i immediately found a few things that needed to be done to get this amp running to it's full potential.
Here is a list of things that are needed or need re-doing.
* The power lead; Lacking current capabilities and the cable itself was connected to the on/off switch. The on/off switch used in this amp is a standard miniture toggle switch rated at 2 amps. So thats approx 30amps of current going through a 2 amps switch...... :?
* No Negative Feedback.
* Hi/Lo switch affects input SWR....it's gotta go.
* Hi/Lo input drive switch, Again affects input SWR...gotta go
* No Regulator to control Bias Voltage.
* Bias Voltage too low, need to replace bias resistor.
* No Relay to switch Bias when TX & RX
* Thermal Tracking diode. In this amp the diode is under the pc board touching the heatsink, this is ok but could be better.
* All tunning caps, collector/emitter caps to be replaced with new Silver Mica Caps.
* Input and Output Transformers (cores) to be rewound with new Teflon wire.









This is a schematic of the bias circuit used in this KLB300, mods included (Reg, Relay, Resistors etc....)
Most of you could easily incorporate this bias circuit into their own 2 pill 2879 class C amp



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Old 12-12-2005, 03:40 AM
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Thanks Greg,
I am currently moving house so i will post all the rest of the info on this amp when i settled.
Just to let you all know though, i got this amp set up in the mobile at the moment and it's kicking ass!

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Old 12-12-2005, 05:36 PM
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nice job blue, where are the pictures?
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Old 12-14-2005, 10:15 AM
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Webshots doesn't seem to like it if you link to their site, so I put the images in the Forum photo album.

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Old 12-16-2005, 03:44 PM
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tnx blue, for helping to further educate some of us so that we may enjoy our hobby a little more. 73
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Old 11-14-2010, 02:47 AM
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Sorry to bring back an old thread but I have a klb-400 which has the same design as the klb-300 with 2x 2sc2879's. About 2 years ago I started modifying this amp with the diagrams and pics on this thread but family stuff came along and the project took the top shelf untill now. However I see that all the pics have gone from this thread and I looked on the home page for a photo album that Moleculo mentioned however I can not find it. Any help??

WR30 (VK2DXN)
vk2dxn@gmail.com

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Old 11-14-2010, 01:44 PM
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Quote:
Originally Posted by Rb30 View Post
Sorry to bring back an old thread but I have a klb-400 which has the same design as the klb-300 with 2x 2sc2879's. About 2 years ago I started modifying this amp with the diagrams and pics on this thread but family stuff came along and the project took the top shelf untill now. However I see that all the pics have gone from this thread and I looked on the home page for a photo album that Moleculo mentioned however I can not find it. Any help??

WR30 (VK2DXN)
vk2dxn@gmail.com
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Last Activity: 02-13-2007 02:19 AM

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Old 11-15-2010, 02:58 AM
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Quote:
Originally Posted by mackmobile43 View Post
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Last Activity: 02-13-2007 02:19 AM
Ok I have found the pics on another site so all is good, oh and btw Mack thanks for stating the obvious there captain

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