Hybrid amp questions

Tyimo · 25th November 2005, 06:28 PM

Hi!

One familiar of me built the attached amp, but Iam not realy sure that it is working as it is in the schematic.

Could somebody help me to check the schem for errors?

Greets:

Tyimo

anatech · 25th November 2005, 07:17 PM

Hi Tyimo,
Where is the speaker return? Is it a split supply or just 200V? Either way, it doesn't look too stable.

-Chris

nikwal · 25th November 2005, 07:43 PM

i'm no expert, but it looks to me like it could work.. but personally I would look around for a better design.. or at least another design..that one looks a tad sensitive to variations in the tubes, it has no feedback (you might want that). hmm But it could'nt take very long to assemble one of thoose..

jacco vermeulen · 25th November 2005, 07:49 PM

Any idea how many 1302/3281s have to be placed in parallel to get enough output current on 100 volt rails ?

anatech · 25th November 2005, 07:57 PM

Hi jacco,
I don't think very much drive is available from the tubes. Just think how much feedback through the supply there will be. And you'll never get near the rails. It's just wasted heat.

The input appears to be referenced to -100V, therefore it looks like a 200V single ended supply. The bias will not be stable, long term either.

-Chris

jacco vermeulen · 25th November 2005, 08:09 PM

It should, my point was that it only takes a little bit of current and a fast signal to blow the outputs.

Putting drivers between the ECC88 and the output devices, and seperate rails for tubes and bipolars is sensible.
This is a waste of tubes, tube filament powersupply, and heatsinks.

anatech · 25th November 2005, 08:54 PM

Hi jacco,
Whether we go outside SOA or not depends on many things in this circuit. Heck, the ouput cap could short just sitting there depending on where the midpoint settles down to.

An early output death might be a blessing, something will go sooner or later. I agree though, a waste of materials the way it is.

-Chris

Tyimo · 26th November 2005, 08:20 PM

Hi!

Chris: I don't know where the speaker return is and the schem looks a bit strange to me.
I think it has split supply +/- 100V, but I don't understand the grunding point in the circuit too.
I also suspect that the amp is not stable as it is in the schem...
For me the most interesting was the White catode follower in the driver stage.

Greets:

Tyimo

anatech · 26th November 2005, 10:44 PM

Hi Tyimo,
If you look at the diagram, the input signal is referenced to the negative 100V. This is referenced to ground.

The speaker is either referenced to ground or the midpoint of the supply. Either one is risky with the 100V rating of the coupling caps. The current delivered to the speaker will be coupled to the voltage amp stage. This will not sound very good. It may motorboat.

So, have you heard this?

-Chris

sajti · 27th November 2005, 02:27 PM

Hi,

I have the book, which contains this amplifier. Unfortunately there is one mistake in the drawing. There is no -100V. That is the ground. This amplifier works from single +100V power supply. This is the reason for the output capacitor.
So it will works, but there will be problem with the thermal runaway, and with the valve drivers, which are not able to give enough current for the output stage.
So I would use transistor based bias network (Vbe multiplier), and ECC99 in the second stage, with at least 20mA bias. Or driver transistors

sajti

25th November 2005, 07:49 PM	#4
jacco vermeulen diyAudio Member Join Date: Oct 2004 Location: At the sea front, just under Rotterdam	Any idea how many 1302/3281s have to be placed in parallel to get enough output current on 100 volt rails ? __________________ Looks like Sponge Bob has killed another thread.

25th November 2005, 08:09 PM	#6
jacco vermeulen diyAudio Member Join Date: Oct 2004 Location: At the sea front, just under Rotterdam	It should, my point was that it only takes a little bit of current and a fast signal to blow the outputs. Putting drivers between the ECC88 and the output devices, and seperate rails for tubes and bipolars is sensible. This is a waste of tubes, tube filament powersupply, and heatsinks. __________________ Looks like Sponge Bob has killed another thread.

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25th November 2005, 07:17 PM	#2
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi Tyimo, Where is the speaker return? Is it a split supply or just 200V? Either way, it doesn't look too stable. -Chris

25th November 2005, 07:43 PM	#3
nikwal diyAudio Member Join Date: Aug 2005	i'm no expert, but it looks to me like it could work.. but personally I would look around for a better design.. or at least another design..that one looks a tad sensitive to variations in the tubes, it has no feedback (you might want that). hmm But it could'nt take very long to assemble one of thoose..

25th November 2005, 07:57 PM	#5
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi jacco, I don't think very much drive is available from the tubes. Just think how much feedback through the supply there will be. And you'll never get near the rails. It's just wasted heat. The input appears to be referenced to -100V, therefore it looks like a 200V single ended supply. The bias will not be stable, long term either. -Chris

25th November 2005, 08:54 PM	#7
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi jacco, Whether we go outside SOA or not depends on many things in this circuit. Heck, the ouput cap could short just sitting there depending on where the midpoint settles down to. An early output death might be a blessing, something will go sooner or later. I agree though, a waste of materials the way it is. -Chris

26th November 2005, 08:20 PM	#8
Tyimo diyAudio Member Join Date: Nov 2002 Location: Hungary	Hi! Chris: I don't know where the speaker return is and the schem looks a bit strange to me. I think it has split supply +/- 100V, but I don't understand the grunding point in the circuit too. I also suspect that the amp is not stable as it is in the schem... For me the most interesting was the White catode follower in the driver stage. Greets: Tyimo

26th November 2005, 10:44 PM	#9
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi Tyimo, If you look at the diagram, the input signal is referenced to the negative 100V. This is referenced to ground. The speaker is either referenced to ground or the midpoint of the supply. Either one is risky with the 100V rating of the coupling caps. The current delivered to the speaker will be coupled to the voltage amp stage. This will not sound very good. It may motorboat. So, have you heard this? -Chris

27th November 2005, 02:27 PM	#10
sajti diyAudio Member Join Date: Apr 2003 Location: Vác, Hungary	Hi, I have the book, which contains this amplifier. Unfortunately there is one mistake in the drawing. There is no -100V. That is the ground. This amplifier works from single +100V power supply. This is the reason for the output capacitor. So it will works, but there will be problem with the thermal runaway, and with the valve drivers, which are not able to give enough current for the output stage. So I would use transistor based bias network (Vbe multiplier), and ECC99 in the second stage, with at least 20mA bias. Or driver transistors sajti

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