PP- which input/splitter topology??

AuroraB · 15th February 2007, 06:28 PM

After sarching around for some time, just gathering info, I've decided to do something tubewise for myself.
I have been reparing /servicing tube eqpt. for many years, so I don't expect any serious problems from a strictly practical point of view. For the time being, I'm not in for a lot of experiments. I want to make something with a decent result, for starters, and as "therapy" from other chores. The experiments will have to come later, when I have more time. I've decided for something around 40-60 W or so.. don't need much more.....

I found this one, which looked interesting
http://www.jogis-roehrenbude.de/Lese...uanleitung.htm

which is closely related to this one
http://www.jogis-roehrenbude.de/Vers...ommes/GU50.htm

I think I'll stick to EL/KT tubes tho' - mainly for reasons of easy supply.

But then there's a lot of them out there, ---lots of various topologies. As for OPTs, Lundahl and Hammond are within easy reach..
The output part is fairly easy, but what about the input / splitter part?? Concertina, CCS etc. etc.
Any thoughts about better/worse, characteristics...??
My mains experiences with tube amps, are mostly applications where linearity and distortion are not major factors....

SY · 15th February 2007, 06:52 PM

It's an adaption of a good 1960 circuit, but the 6SN7 is not a great candidate for cascoding. These days we can do better, especially regarding the balance of the phase splitter.

For a KT-series tube, you'll need on the order of 30-40VRMS drive, which can be best achieved by cascaded constant-current-tail diff amps, or something like a Williamson.

If you're adventurous and open-minded, try using a well-wound 1: 1+1 input transformer to get the signal balanced right from the get-go, then use diff amps the rest of the way through.

Johan Potgieter · 16th February 2007, 09:13 PM

Just one thing bothering me in the given GU50 amplifier circuit: Surely R12 and R13 cannot be only 22K? That will give a highly unsatisfactory load to the phase inverter. I would believe that to be a misprint for 220K, but such a value would somewhat exceed the maximum specified for fixed bias operation of the power tubes.

Perhaps phase splitter anode loads of 47K/56K working into 100K grid resistors? Mmmmmm...

ray_moth · 16th February 2007, 10:00 PM

Quote:

Just one thing bothering me in the given GU50 amplifier circuit

One thing bothers me too - GU50 is a mercury vapor rectifier.

Zen Mod · 16th February 2007, 10:05 PM

Quote:

Originally posted by ray_moth

One thing bothers me too - GU50 is a mercury vapor rectifier.

cyrilic GU isn't

AuroraB · 16th February 2007, 10:27 PM

This GU50 is evidently some russian / east German pentode type, which I will not use, mainly for supply reasons, - even if it might be good. I will most certainly stick to some El or KT, - or something very close.
Edit: BTW- the referred german article says tteh GU50 is russian copy of af a "Wehrmacht" type LS50, also known as a former East German tube SRS 552......

Even if there are a few variations, like straight pentode, UL, triode strap etc, the actual output stage is fairly straight forward. Some issues about choosing the correct anode impedance load, perhaps.

The difficulties seems to be in choosing the input/splitter circuit, and this is where I seek the advice. A few months back, I felt like going for a classical Dynaco Mk-III, which I know from a rather famous scandinavian PA setup from way-back-when, but surely something must have happened in the tube world in 40 years???
Any possible links to proven circuits that are reputably better than the Mk-III ??

Johan Potgieter · 16th February 2007, 10:33 PM

Ray,

So what is that doing in the reference of the Grommes 260 or whatever? And I cannot even blame it on my knowledge of German!

I am now retiring to bed (it is about 2:00 in the am here) and shall take a stiff brandy to try drown my inferiority feelings.

Yours liquorly.

AuroraB · 16th February 2007, 10:43 PM

Quote:

Originally posted by Johan Potgieter
Ray,

So what is that doing in the reference of the Grommes 260 or whatever? And I cannot even blame it on my knowledge of German!

I am now retiring to bed (it is about 2:00 in the am here) and shall take a stiff brandy to try drown my inferiority feelings.

Yours liquorly.

Somehow I think the Grommes topology inspired the GU amp. And I kind'a liked the looks of the Grommes ..- I see alu and rack mount boxes every day, and I am totally fed up with them!!
Mahogany and brass will be my choice of materials when I start building!!
Come to think of it---Does anybody know anything about these Grommes amps???

Yours liquorly.....
( I just found some Scotch in my innermost cabinet corner

)

Johan Potgieter · 16th February 2007, 10:44 PM

AuroraB,

Just before drowning the sorrows inflicted by Ray, I cannot now access a particular circuit, but I have been using a pentode input directly coupled to a Schmitt (long-tailed pair), much like the given circuit, for years (decades) now. As you said, there are no particular outstanding circuits, but I found that very reliable and capable of low distortion, though you mentioned that that was not too important.

I hesitate to tout my own circuits around, but could put something on here in the morning that I have used. But others will probably oblige with references; there are many very suitable circuits in this category.

Regards.

SY · 16th February 2007, 10:46 PM

EF86 or 5879? (Let's see how well I know you!)

15th February 2007, 06:28 PM	#1
AuroraB diyAudio Member Join Date: May 2001 Location: Norway, -north of the moral circle..	PP- which input/splitter topology?? After sarching around for some time, just gathering info, I've decided to do something tubewise for myself. I have been reparing /servicing tube eqpt. for many years, so I don't expect any serious problems from a strictly practical point of view. For the time being, I'm not in for a lot of experiments. I want to make something with a decent result, for starters, and as "therapy" from other chores. The experiments will have to come later, when I have more time. I've decided for something around 40-60 W or so.. don't need much more..... I found this one, which looked interesting http://www.jogis-roehrenbude.de/Lese...uanleitung.htm which is closely related to this one http://www.jogis-roehrenbude.de/Vers...ommes/GU50.htm I think I'll stick to EL/KT tubes tho' - mainly for reasons of easy supply. But then there's a lot of them out there, ---lots of various topologies. As for OPTs, Lundahl and Hammond are within easy reach.. The output part is fairly easy, but what about the input / splitter part?? Concertina, CCS etc. etc. Any thoughts about better/worse, characteristics...?? My mains experiences with tube amps, are mostly applications where linearity and distortion are not major factors....

15th February 2007, 06:52 PM	#2
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	It's an adaption of a good 1960 circuit, but the 6SN7 is not a great candidate for cascoding. These days we can do better, especially regarding the balance of the phase splitter. For a KT-series tube, you'll need on the order of 30-40VRMS drive, which can be best achieved by cascaded constant-current-tail diff amps, or something like a Williamson. If you're adventurous and open-minded, try using a well-wound 1: 1+1 input transformer to get the signal balanced right from the get-go, then use diff amps the rest of the way through. __________________ “Listening to records is like ****ing a picture of Brigitte Bardot.” - Sergiu Celibidache

16th February 2007, 10:46 PM	#10
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	EF86 or 5879? (Let's see how well I know you!) __________________ “Listening to records is like ****ing a picture of Brigitte Bardot.” - Sergiu Celibidache

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16th February 2007, 09:13 PM	#3
Johan Potgieter diyAudio Member Join Date: May 2005 Location: Pretoria, South Africa	Just one thing bothering me in the given GU50 amplifier circuit: Surely R12 and R13 cannot be only 22K? That will give a highly unsatisfactory load to the phase inverter. I would believe that to be a misprint for 220K, but such a value would somewhat exceed the maximum specified for fixed bias operation of the power tubes. Perhaps phase splitter anode loads of 47K/56K working into 100K grid resistors? Mmmmmm...

16th February 2007, 10:27 PM	#6
AuroraB diyAudio Member Join Date: May 2001 Location: Norway, -north of the moral circle..	This GU50 is evidently some russian / east German pentode type, which I will not use, mainly for supply reasons, - even if it might be good. I will most certainly stick to some El or KT, - or something very close. Edit: BTW- the referred german article says tteh GU50 is russian copy of af a "Wehrmacht" type LS50, also known as a former East German tube SRS 552...... Even if there are a few variations, like straight pentode, UL, triode strap etc, the actual output stage is fairly straight forward. Some issues about choosing the correct anode impedance load, perhaps. The difficulties seems to be in choosing the input/splitter circuit, and this is where I seek the advice. A few months back, I felt like going for a classical Dynaco Mk-III, which I know from a rather famous scandinavian PA setup from way-back-when, but surely something must have happened in the tube world in 40 years??? Any possible links to proven circuits that are reputably better than the Mk-III ??

16th February 2007, 10:33 PM	#7
Johan Potgieter diyAudio Member Join Date: May 2005 Location: Pretoria, South Africa	Ray, So what is that doing in the reference of the Grommes 260 or whatever? And I cannot even blame it on my knowledge of German! I am now retiring to bed (it is about 2:00 in the am here) and shall take a stiff brandy to try drown my inferiority feelings. Yours liquorly.

16th February 2007, 10:44 PM	#9
Johan Potgieter diyAudio Member Join Date: May 2005 Location: Pretoria, South Africa	AuroraB, Just before drowning the sorrows inflicted by Ray, I cannot now access a particular circuit, but I have been using a pentode input directly coupled to a Schmitt (long-tailed pair), much like the given circuit, for years (decades) now. As you said, there are no particular outstanding circuits, but I found that very reliable and capable of low distortion, though you mentioned that that was not too important. I hesitate to tout my own circuits around, but could put something on here in the morning that I have used. But others will probably oblige with references; there are many very suitable circuits in this category. Regards.

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