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PostPosted: 24 Sep 2009, 16:50 
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I (and not only I) would be very grateful if the scheme of the modified amplifier would be marked by the required voltages and currents! If this is possible - please do!
In the scheme changed nominals of the two resistors (from 33k to 47k and 1,5 k to 1k), in comparison with the original. Perhaps, and the currents have changed? :worried:
I already have many of the components needed to start the assembly, but I can not determine with the nominals of resistors!

With best regards, Yuri.


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PostPosted: 25 Sep 2009, 19:23 
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Hi Yuri, I don;t think this info is available or Dan likely would have passed it along, but I will ask him anyway.

What are you trying to determine?
Cheers

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PostPosted: 26 Sep 2009, 00:49 
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Hi Gio, Hi Yuri,

In the Hiraga class A the front end has zener diodes to "set" the voltage some some of the voltages are the same as the original amplifier.

In the second and third stages of the amplifier I have only changed what is shown on the schematic / text provided.

feel free to ask if you want some more info

-Dan

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PostPosted: 26 Sep 2009, 23:48 
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oh i just subscribed to this topic (finally) i thought subcription was automatic - thanks for the tip Gio

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PostPosted: 28 Sep 2009, 12:44 
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Hi Dan! Hi Gio!
Thanks for the clarification!
Sorry for this late reply, I caught a bad cold and was in bed with a high temperature. :mrgreen:

Now for the currents and voltages is clear, must stand as indicated in the scheme of the magazine.
Output voltage power supplies will I have + - 42 volts (transformers 30-0-30). Do not have any problems with transistors 2SA634 and 2SC1096? After all, they have collector-emitter voltage maximum of 30 volts.

With best regards, Yuri.


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PostPosted: 28 Sep 2009, 20:55 
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Hi Yuri,

Hope you are better now !

The 2SA634/2SC1096 do not see full rail due to the way they are connected.

The transformer i used is 25-0-25 giving approx 35.35V dc,

My advice would be dont use 30-0-30V with the circuit shown as the 2SC1096 2SA634 already run quite hot.

if you use 30-0-30V you will end up with 42.42V dc approx in turn the output stage and the bias must be increased to allow the amp to run in class A and the amp will have to increase in size and heatsinking etc etc.

you could do a few things if you are set on using that 30-0-30V transformer and 2SC1096 2SA634,

Reduce the bias so the amp operates in class A until it reaches a certain output level.

Use different transistors for example BD139/BD140 or MJE340/MJE350 or MJE15034/MJE15035 along those lines

-Dan

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PostPosted: 29 Sep 2009, 07:26 
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Thanks Dan! I'm better!
I am very grateful for the assistance and patience extended to such an amateur like me! But i really want to build this amp, even if will have to overcome many difficulties!

I managed to get the transformers only with the release of 30-0-30V... However, even with excess power (700VA each)... :blush:
I listened to your advice, and replacement transistors 2SA634/2SC1096 on MJE15034/MJE15035!

With best regards, Yuri.

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PostPosted: 29 Sep 2009, 09:40 
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no problems :)

yes 700VA is enough - I am using 500VA and its enough :)

But more is better for some things any how !

-Dan

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PostPosted: 06 Oct 2009, 04:22 
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Hi! :)

I have a small question about Zener diodes are used. A little confusing is that in the modified scheme of the magazine set Zener diodes at 22 volts. In the original scheme on 9 volts! How you think, friends, why there was such replacement?

Sincerely, Yuri.


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PostPosted: 06 Oct 2009, 07:35 
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my understanding is for the 25V rail version the zeners were raised to raise output power by raising input/vas voltage swing

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