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JLH Enhanced 15W Kit: Lost instructions....
JLH Enhanced 15W Kit: Lost instructions....
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Old 15th May 2019, 12:50 PM   #1
mikmm is offline mikmm
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Default JLH Enhanced 15W Kit: Lost instructions....

hi,
Many years ago, I built this Hart Kit.for my son.
When he married, he left it with me and it has been unused for ages.
As a project I have decided to bring it back into use and do some upgrading.
I have misslayed the build notes and cannot remember how to do the set-up...
There are so many pages of jlh threads that I am finding it confusing to decide what to do.
Can anyone supply me with a copy of the original Hart notes for the kit, please?
Amp is 15W with 22,0,22 supply and 4.7v zenner and 15v regulator in cct.
Many thanks,
MICK
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Old 15th May 2019, 02:41 PM   #2
gannaji is offline gannaji  India
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If there is a PCB, please post the photos, both sides, list out the BJTs and how many each. This will help others to identify.
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Old 15th May 2019, 08:39 PM   #3
mikmm is offline mikmm
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Thankyou for the prompt reply.
The amplifier is working but I need to check the mid point voltage and the quiescent
current and I cannot remember the correct point for metering...
RV1 and RV2 are thr relevent pots.
Here is an exact copy of the cct as built.
The pcb's are in the chassis and I do not want to remove them at this stage.

MICK
Ooops. Sorry, I do not know how to insert the picture...
Google: http://www.kaschei.com/classa/jlh1996.pdf
Page 7 shows it....
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Old 15th May 2019, 10:09 PM   #4
rayma is online now rayma  United States
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Quote:
Originally Posted by mikmm View Post
I need to check the mid point voltage and the quiescent
current and I cannot remember the correct point for metering.
For midpoint (offset) voltage, connect an 8R dummy load, and measure the DCV across it.
Adjust for 0VDC.

For idle current, connect a DVM across the 0.33R and set to the desired current, I = Vmeas / 0.33R.
If you want 2A idle current, adjust for a voltage of 2A x 0.33R = 0.66VDC.

Last edited by rayma; 15th May 2019 at 10:13 PM.
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Old 16th May 2019, 08:02 PM   #5
mikmm is offline mikmm
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Hi, rayma,
Thanks for that info. That is exactly what I needed...
there is clearly a difference in temperature between right and left amp. The left one is quite a bit warmer than the right...
I'll get on to that in the morning.

MICK.
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