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Old 26th September 2009, 01:49 AM   #31
miklos is offline miklos  Canada
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Thanks Helmuth,
It's running hot, especially in the summer.
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Old 4th February 2010, 05:14 AM   #32
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Quote:
Originally Posted by Helmuth View Post
I cleaned the contacts, some remove the connector and make a sturdy wire wrap.

This is important to be sure of good contact of the +76V
Hello Helmuth, Congrats on a job well done. Boy, do those look nice!
I'm restoring a TA-5650 and only have +58v at the +VDC terminal on
both sides of the power board pin position #61 and #76. The !0,000uf
caps give +49 -49v. Any suggestions? It should read about 76Volts, is
that right? Regards,
Klipschorn dude
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Old 4th February 2010, 09:21 PM   #33
Helmuth is offline Helmuth  Netherlands
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Quote:
Originally Posted by Klipschorn dude View Post
Hello Helmuth, Congrats on a job well done. Boy, do those look nice!
I'm restoring a TA-5650 and only have +58v at the +VDC terminal on
both sides of the power board pin position #61 and #76. The !0,000uf
caps give +49 -49v. Any suggestions? It should read about 76Volts, is
that right? Regards,
Klipschorn dude
Thanks Klipschorn dude witch klipsch do you own?

On your problem I do not understand what you measure. Mine had a open cicuit in the circuit board. there was not contact from the ground of the powersupply to the endstage board.

I would say check the diodes and mass connection.

Your not measuring the wrong pins? The cascade voltage. Of the pre end stage.

Succes
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Old 5th February 2010, 01:56 AM   #34
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Quote:
Originally Posted by Helmuth View Post
Thanks Klipschorn dude witch klipsch do you own?

On your problem I do not understand what you measure. Mine had a open cicuit in the circuit board. there was not contact from the ground of the powersupply to the endstage board.

I would say check the diodes and mass connection.

Your not measuring the wrong pins? The cascade voltage. Of the pre end stage.

Succes
Hello Helmuth. The voltage on R419 -100 and on R414 +69. It originally
starts at +89, then drifts to +69. Big caps (10,000uf) are + and - 48.5
It looks like on end stage board position connection #61 Pin 4+ from
bottom should be +75, It is only 56. any suggestions?
As far as the Klipsch speakers, I own 4 Klipschorns and a RC-7. I've owned
all the Klipsch Heritage line. Loved them all. Happiness always,
Klipschorn dude
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Old 5th February 2010, 05:41 AM   #35
miklos is offline miklos  Canada
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Hi K Dude,
You could try the following:
Mark (for position) and remove all VFet's.
Measure the B2 (+-76V) voltages.
If they are right and symmetrical than something is wrong with the VFet's (check VFet's with a diode checker).
If the B2 voltages are still wrong, check the diodes (D404, D407, D405) and the capacitors (C416, C412, C413) for the +76V and the capacitors (C414, C408, C409) for the -76V supply.
Also you can disconnect the PS from the Power Amp board ,load the B2 supply with resistors and check the + - voltages.
The PS voltages are not regulated, so any unsymmetrical load would pull them out of symmetry.
For example large differences in VFet pinch off voltages or a fault in the driver stage.
I purchased four VFet's from Jims audio in Hong Kong for my TA-4650, the B2 voltages in the amp never equalized. One of the VFet's pinch off voltage is way off from the rest.
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Old 5th February 2010, 06:34 AM   #36
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Quote:
Originally Posted by miklos View Post
Hi K Dude,
You could try the following:
Mark (for position) and remove all VFet's.
Measure the B2 (+-76V) voltages.
If they are right and symmetrical than something is wrong with the VFet's (check VFet's with a diode checker).
If the B2 voltages are still wrong, check the diodes (D404, D407, D405) and the capacitors (C416, C412, C413) for the +76V and the capacitors (C414, C408, C409) for the -76V supply.
Also you can disconnect the PS from the Power Amp board ,load the B2 supply with resistors and check the + - voltages.
The PS voltages are not regulated, so any unsymmetrical load would pull them out of symmetry.
For example large differences in VFet pinch off voltages or a fault in the driver stage.
I purchased four VFet's from Jims audio in Hong Kong for my TA-4650, the B2 voltages in the amp never equalized. One of the VFet's pinch off voltage is way off from the rest.
Thank you Miklos. I will check all of the above. When I bought the amp
all the V-fets were no good. They were removed and power board and
power supply board were recapped and the dreaded diodes on the power
board(end stage as Helmuth calls it-what a nice fella as well) were fixed. Rookie as I am, I was adjusting RT301, RT351 for bias at speaker terminals and then realized duh no power fets installed. I may not have returned the RT301 and RT351 to their original position. Could that have an effect on the + or - 76 volts being correct? I just removed the input connector #6 from the power board and the - voltage at pin 2 from the bottom was -101 at the #61 connector. Pin #4 voltage, counting from the bottom at #61 was now +
120 volts. Just reconnected input(connector #6 to power board) and now
the voltages are back as before: Pin #2 voltage starting at -78 and
climbing all the way to -110 then stabilizing. Pin #4 voltage starts at
+77 and drops all the way down to +59 then stabilizing. I cannot
disconnect the power supply from power board because mine is of the
wire wrap type at the terminals. I hope that I have given you enough
information. I was considering ordering the V-fets from Jim's, but now
from what you told me, doubtful I will await your answer with much
eagerness. Cheers,
K-dude
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Old 5th February 2010, 08:16 AM   #37
miklos is offline miklos  Canada
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Hi K-Dude,
If the output transistors not in the voltages should stabilized around the given +-76V. Try to turn the bias pots to the lowest resistance value, the two pots going in the opposite direction, please check the PCB layout. The wire wrap connections are easy to remove, but later you have to solder them back to the pins.
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Old 5th February 2010, 11:36 AM   #38
miklos is offline miklos  Canada
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The VFet's are now only available from littlediode in England. Here's the ebay ad:
2SK60 Transistor x 1 pieces - - eBay (item 380175321852 end time Mar-06-10 11:00:13 PST)

2SJ18 Transistor x 1 pieces | - eBay (item 400074931993 end time Feb-20-10 01:45:47 PST)

They're pretty expensive and they are made by Hitachi, not Sony. On the ebay ad is no picture.
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Old 5th February 2010, 12:25 PM   #39
Mooly is online now Mooly  United Kingdom
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Has anyone ever done any work on making these amps work with conventional Lateral FETs ?
I'm sure the driver stages and bias generator could be re jigged to work OK.

Or does that defeat the whole object of owning one of these
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Old 5th February 2010, 12:36 PM   #40
miklos is offline miklos  Canada
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"Or does that defeat the whole object of owning one of these"
Yes.
They would become Hitachi amplifiers from the seventies.
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