• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

OTL, continued...

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#65
Richard,
How about having 2 sides and taking the output across the cathodes?
Click to expand...
Absolutely.🙂 That would work fine.

As would, arranging for the cathode to be at zero volts, through some power supply trickery.😉 But then one might consider the power supply caps to be in series with the speaker / load.😱
But aren't they always..😕

Just my little bit of mischief - in Franks absence someone must😎

Cheers,
 
#67
CAPS

Hi,

As would, arranging for the cathode to be at zero volts, through some power supply trickery. But then one might consider the power supply caps to be in series with the speaker / load
Click to expand...

The PSU caps of all anode loaded stages are in series with the output stages,which is not the same as having the output cap in series with the signal path however.

That doesn't mean the PSU caps' quality does not reflect on the signal outputs' quality either.

In fact I always say one listens to a PSU,not an amplifier.

I'm back,😉
 
#68
Sematics

Frank,

The PSU caps of all anode loaded stages are in series with the output stages,which is not the same as having the output cap in series with the signal path however.
Click to expand...
I don't believe that's what I said.😉
I said:
But then one might consider the power supply caps to be in series with the speaker / load.
Click to expand...
Which I believe to be the case.
The only difference between Joel's output cap, and a PS smoothing cap, is the latter has some extra stuff hanging off it, which will hardly help.

Cheers,
 
#69
YEP.

Hi,

The only difference between Joel's output cap, and a PS smoothing cap, is the latter has some extra stuff hanging off it, which will hardly help.
Click to expand...

Given an OTL output stage, one may say the PSU caps are in series with the speaker load (to me they are, no matter how you turn them).
As they are on so many other occasions anyway.

Saying that this has the same deleterious effect as running the signal straight through an electrolytic cap is a bit of an overstatement IMO.

Which brings me to square one:all psu components are in the signal path.

The tricks to minimize the effects I'll try to explain in the PSU thread.

Cheers,😉
 
#74
Hello,

could someone please post here or send me the schematic (with components values) of a good OTL design (such as GRAAF GM-20 or Atma-sphere stuff)?
Click to expand...

Well, this one uses the same output tubes 🙂 .

Also, does anyone tried this version, any comment on sound ?

Best regards,
Kristijan Kljucaric
http://web.vip.hr/pcb-design.vip
 

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#75
AT LONG LAST...

Hi,

Pardon my sarcasm on the first bias supplies.
Honestly they showed a lack of understanding beyond (my) belief.

What you present is a bias supplly allowing you to corrrect some inballance at least.

This is exactly what _arg and myself have been discussing off "forum" for a while.

The Cufioli circuit may seems complex,in reality it is made complex for no reason at all.

With all OTL circuits,pay attention to the PSU.

Cheers,😉
 
#76
Hi!
I am interested to build an OTL amp (to have one as tube sound refernce amp with the legendary full bodied mid-range and velvet vocals ) and I am planing to build the attached schem. Would you tell me your oppinion and suggestions about it?
Thanks!
 

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#77
Hi,

EC360 I dont think is a very common tube and can be difficult to source.

Where did you get the schematic? It is not possible to get 20W from only 4 of these tubes especially with only +- 70V anode voltage. The EC 360 is only specified to max 250mA current which doesn't take you very far, you need ~2.5A peak to get 20W. The 6C33C can give you this current but then you need a voltage of ~140V minimum.

Regards Hans
 
#79
Hi Hans!
Thanks for the answers!
Here in Hungary some people built it already and it works. I try to get contact with them for more info. I think the schematic comes from an amp "cookbook", but I would like ask here some international tube guru for oppinions. I read the EC360 can easily work on such a low voltage and with 200mA. May be the 20W output is a dream, but the main question is: could this circuit work or is there any error?
Thanks!
 
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