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Voxson H305 repair
Voxson H305 repair
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Old 12th February 2006, 02:37 PM   #1
AnthonyPT is offline AnthonyPT  Australia
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Hi tried a new thread but had to settle for this one !
Post would not work

I have been refitting an old Voxson amp from Italy.
I replaced all the rotten wire and all the electrolytics.
The output transistors are BDY24Bs. It is a Voxson H305
50w into 8 ohms. To my surprise and delight the amp fired
up on both channels without initial problems. However after about five minutes the BDY24b (2nd to left on the picture decided to get super hot).
The owner (a friend) is thinking it is in the too hard basket.
The amp seems to have zero biasing adjustments and I wonder
if it could be just the age of the BDY tranny & it needs replacing.
So where do I go from here?

1 Anyone have a H305 schematic for this unit.

2. A list of voltage checks to compare the channels.

3. A OZ source of a few more BDY24Bs

4. If the tranny is oscillating where to look in the circuit
for problems. ( It plays on both chanels ok )

I build speakers and chipamps and in the past found my old
Ravenbourne and Ravenbrook amps a bit of a challenge to fix.

Please help please !



Basic view of amps interior showing output BDY24b trannies.
Attached Images
File Type: jpg h305hot.jpg (22.5 KB, 187 views)
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Old 12th February 2006, 02:47 PM   #2
anatech is offline anatech  Canada
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Location: Georgetown, On
Voxson H305 repair
Hi AnthonyPT,
Split this out for you.

Your bias appears to be the three diodes near the heatsink and a resistor that will be in series possibly. You may find it in parallel depending on the output / driver configuration.

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Old 12th February 2006, 03:14 PM   #3
edl is offline edl  Hungary
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Dear Anthony,

BDY24B's are TO3 packaged NPN bipolar devices with the following ratings:
Vceo-max: 90V
Ic-max: 6A
Pd: 85W
Ft: 10Mhz

As you can see, it is not too hard to subtitue them - if they already passed.

Let's measure the followings:
-is PSU OK?
-how much DC-offset are measuring at the output? It shouldn't be more than +/-100mV.
-how much is the output devices idle? Let's measure the voltage on the emmiter resistors (I think they are the big green ones on your photo), then divide that voltage with the value of the resistor. It need to be between 10-100mA.

About find out oscillation:
-is the resistor of the Boucherout-cell (it's a serial resistor-capacitor on the output of the amplifier) hot? If yes, than the amp oscillating.

We are waiting for the results.
Then we can proceed.

Best regards,
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Old 11th July 2006, 12:42 PM   #4
segale is offline segale  Australia
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Location: Melbourne
I have a H305 schematic if your still need it.
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Old 8th October 2008, 07:43 PM   #5
doubleteo is offline doubleteo  Greece
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Hello segale.

Would it be easy for you,to send me the H305 schematic?
I've been looking for it,for quite a while now.
My email, is doubleteo@windowslive.com
Thank you in advance
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Old 1st May 2012, 05:46 PM   #6
br1zapp is offline br1zapp  Italy
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Originally Posted by segale View Post
I have a H305 schematic if your still need it.
Hello my friend, do you still have the schematic?
Can you send it to me?
I have a friend who is desperately looking for it!
Many thanks in advance.
I am a retired chemical engineer who deals with Voxson Sonar 8-track car radios....with the same problem of rotten wires!
Many thanks in advance
Bruno Zappaterra
email: br1zapp@libero.it
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Old 2nd May 2012, 06:47 AM   #7
br1zapp is offline br1zapp  Italy
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Join Date: Feb 2012
To the administrator.
I would kindly ask your help...to try and find once for all this schematic of the Voxson H305 amplifier.
Yesterday I have tried to send an email to both segale and doubleleo (the only 2 persons who say in the thread that they have the schematic...!) but their email addresses...do not work...maybe they changed them...
As I think that diy should have their addresses too or could get in touch with them, I ask please your help.
Many thanks in advance
Bruno Zappaterra, Ferrara, Italy
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Old 2nd May 2012, 06:51 AM   #8
pinkmouse is offline pinkmouse  Europe
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Voxson H305 repair
Sorry, we have no more info than you. Both members haven't visited here for a very long time so may have moved on.
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