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Old 4th September 2012, 09:45 PM   #1
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Default kt88 PP rectifier.

I am in progress of rebuilding a kt88 pp stereo amp power supply.
currently using 170~AC in a voltage doubler rectifier to 420/430 volt DC.
the current for the +B transformer is running very hot (can barely be touched for some seconds before getting too hot) on idle,
so i thought about building (rewind) a new one.

But my question is mainly about the rectifier, since i want to drop the voltage doubler with a proper bridge rectifier,
i have some high voltage rectifiers laying around, mainly a GPJ15M and a KBL407 bridge rectifiers laying around,
can any of these be used for the +B?
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Old 5th September 2012, 01:01 AM   #2
VA2GXB is offline VA2GXB  Canada
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Of course. Heatsink them if drawing anything over 2A. Some say silicon rectifiers impart switching noise at the rectified mains frequency...
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Old 5th September 2012, 01:43 AM   #3
Loren42 is offline Loren42  United States
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Originally Posted by VA2GXB View Post
Of course. Heatsink them if drawing anything over 2A. Some say silicon rectifiers impart switching noise at the rectified mains frequency...
I use DSEI12-12A FRED diodes. That will minimize the noise.

Look up the specification data sheet and that will tell you what the maximum ratings are and when to use heat sinks. I always run my components well below maximum ratings.

Last edited by Loren42; 5th September 2012 at 01:46 AM.
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Old 5th September 2012, 02:41 AM   #4
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My initial thought is whether the design of the PP stage, or the selection of the transformer, is your main concern, and hence to first focus on them.

What idle current are you drawing from the B+ supply ?

What rms current are you drawing from the PT HT secondary, and do you know the transformer's rated secondary rms current rating? (This measurement requires an rms handheld meter and something like a sense resistor in series with the secondary winding - and so is a 'hazardous' test).

Also, is the PT ok - if you disconnect the B+ rectifier circuit from the secondary winding, and turn the amp on for an hour, then does the transformer reach a concerning termperature. (Unfortunately, touch temperature is often a misleading indicator of whether a PT is under stress, as the internal operating temperature limits of insulation can be quite high. It is difficult to generalise, but if a temp probe was reading say above 80-90C at the core/winding intersection then you may have a transformer fault.)
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Old 5th September 2012, 02:53 AM   #5
AJT is offline AJT  Philippines
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i have used 16 amps brigde rectifier in one of my 16kt88 amp build...these rectifiers are dirt cheap....use if high amp rated rectifiers means it will not be stressed in normal use....
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Old 5th September 2012, 07:54 AM   #6
multi is offline multi  Australia
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Where do you get high voltage16 amps bridge rectifiers Dirt cheap?
They always are very expensive when i search.
Phil
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Old 5th September 2012, 08:00 AM   #7
AJT is offline AJT  Philippines
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from hawkers at the sidewalks of Raon in Manila, imported discarded equipment harvested of parts by local metal recyclers......

something like this:
Click the image to open in full size.
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Old 5th September 2012, 09:07 AM   #8
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Originally Posted by multi View Post
Where do you get high voltage16 amps bridge rectifiers Dirt cheap?
They always are very expensive when i search.
Phil
You can get HV rectifiers from PC powersupplies and other SMP powersupplies. they offen have some good HV capacitors in them aswell.
i just pulled out 4 270uF 450volt 105c caps from some server PSUs.
works perfectly for my amp since it runs at 420-430 volts.
Rectifiers in PSUs seem to be rated for around 700volt RMS at 1.1 voltage drop.
and have a peak current of around 250 amps. and 25amps rms (heatsink)
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