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Kenwood KA-801 Control Board

ajfink

ajfink

Member
Hi all,

The commonly available service manuals for the KA-801 are incomplete in their parts lists, especially with regards to the phono and front control boards. Some elements can be pieced together from what is there, but I recently had three resistors in the control board go up in smoke while replacing the meter lamps (not sure what shorted, yet, but that's another topic). These are burnt to the point where telling the colored bands off of one or two of them isn't possible, and I believe they're each different values. Push comes to shove, I make some guestimates, but I'd really rather not.

Does anyone know of a fully complete:
  1. Schematic of the control board, or
  2. Parts list of the control board
with parts values?

For reference, these are R61, R63, and R69, I believe - and I'm also going to replace D3.

Cheers in advance.
 
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gort69 said:
Schematic here, but not very good quality. If you squint you might be able to make out the values
Click to expand...

Brilliant, I think I can make out the values on that schematic.

Thanks!

An aside - anyone else have one of these? I saw another rebuild/refresh thread from the last year or two, but it seems pretty slim for what is otherwise a great-sounding and well-build tank of an amplifier.
 
For future reference, R61/63 will be same value as R62/64 (470 1/4W) and R69/70 will also be the same value (75 1/4W). HINT: study the right and left side of the circuit board. Does anything jump out at you?

D3 is a 28V 1/2 W zener. Good Luck
 
ovaeasy said:
For future reference, R61/63 will be same value as R62/64 (470 1/4W) and R69/70 will also be the same value (75 1/4W). HINT: study the right and left side of the circuit board. Does anything jump out at you?

D3 is a 28V 1/2 W zener. Good Luck
Click to expand...

This is what I'm gathering from the schematic, thanks!

I haven't had a chance to take a look at the actual board again, only the schematic. Next step is pulling the board out so I can work on it freely - time allowing o_O
 
Here is my Schematic with some erata. The KA 801 has some more "Bugs" but this is another story. Hope it will help you.

Kenwood KA-801 schematic detail both power amps voltage amplification st....png

Richard
 
Hallo ajfink,
the last Kenwood KA 801 that i made i modified some things:
  • Current sorce for the fist Stage of the Amplifier, Replace the R53/R54 with a LM 334 with a set- Resistor with 33Ohm. for 2,1 mA current
  • Current source für the second stage, Replace R65/R66 with an LM 334 and a Set resistor 14,3 Ohm for 5,0 mA current. This values are taken from the board, not from the original SM
  • Current source for the third Stage. Befor you do that you have to redim the second and the third stage. Change R61-R64 to 910 Ohm so the Voltage over R69 will be a little bit higher. And the third Stage will work much better now. The äquivalent Value for R69/R70 is now 100Ohm. Because the Voltage at the R75 is stil note very high an LM 334 or even an LM 317 wont work. You have to solder a current source with two Transistors
IMG-20180501-WA0004.jpg

The current for the third Stage should be 15mA, for that reason R1 = 0,65/0,015A = 43 Ohm, R2 = 56 kOhm

When you so this you have to redim the Lead and Lag compensation:
  • C53: chnage the 820 pF to the new value 330pF
  • Change the Miller cap Q9/Q10 to 390pF
This mods are a little bit more you than i do normaly. But it works fine and the sound is much better. So now its your part what you will do

Richard
 
ajfink said:
Brilliant, I think I can make out the values on that schematic.

Thanks!

An aside - anyone else have one of these? I saw another rebuild/refresh thread from the last year or two, but it seems pretty slim for what is otherwise a great-sounding and well-build tank of an amplifier.
Click to expand...
Just don't blow it up with less than 4 ohms like one I sold to a (not so bright) guy did. The original output transistors are non existant, the equivalent replacements are becoming scarce too. Had to rebuild both sides of power amp. Recapped the whole thing & sold it back to him with a warning plus more money. Also have the 8011 still, the European version with grey faceplate, I'm not using it but it looks nice on the shelf with all the knobs polished. I have a nice 11 x17 schematic also. Forget which site I got it off of it was on my old computer before it crashed. There was everything Kenwood for free.
 
THD said:
Just don't blow it up with less than 4 ohms like one I sold to a (not so bright) guy did. The original output transistors are non existant, the equivalent replacements are becoming scarce too. Had to rebuild both sides of power amp. Recapped the whole thing & sold it back to him with a warning plus more money. Also have the 8011 still, the European version with grey faceplate, I'm not using it but it looks nice on the shelf with all the knobs polished.
Click to expand...

No worries, there. It's survived quad Advents already. I also have a set of output transistors one step up in the power rating from the same series, just in case. :biggrin:
 
THD said:
Just don't blow it up with less than 4 ohms like one I sold to a (not so bright) guy did. The original output transistors are non existant, the equivalent replacements are becoming scarce too. Had to rebuild both sides of power amp. Recapped the whole thing & sold it back to him with a warning plus more money. Also have the 8011 still, the European version with grey faceplate, I'm not using it but it looks nice on the shelf with all the knobs polished. I have a nice 11 x17 schematic also. Forget which site I got it off of it was on my old computer before it crashed. There was everything Kenwood for free.
Click to expand...
I have one I’m repairing now. After cleaning the controls it seems pretty good, am going to do a second clean. Are there any transistors in this that are known to go bad?
 
Theo A said:
I have one I’m repairing now. After cleaning the controls it seems pretty good, am going to do a second clean. Are there any transistors in this that are known to go bad?
Click to expand...
None that I found, sold the 8011 also. Should have just kept it.
 
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