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    the safety precautions around high voltages.

is 6J32P equivalent of EF806 ?

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#3
banat said:
what is on your mind ? , to design some hybrid Amp ? 🙂
Click to expand...

Hi Banat ! - yes you are perceptive, I have a hybrid in mind (I am no longer planning to design another SS amplifier - after many years of fun I reached a conclusion with TGM7 & TGM8 although I do have a JLH 1969 still under construction).

Just slowly mulling over tube choices. Priority is linearity in triode-wired operation, but it might also be important to have a good amount of plate current. I have noticed several reports that triode-wired pentodes can be amazingly linear.
 
#4
Have a look at the 6J9P (6Ж9П) in triode connection. It will run quite happily in triode connection at 10mA or so. It is very inexpensive and readily available on ePay.

IIRC in triode connection mu will be around 40.. (Don't quote me as my recollection could be faulty)

Another great choice in triode connection is the D3A running at 10 - 20mA. (mu of up to 80)

These are both quite low noise and linear.
 
#5
Bigun said:
Hi Banat ! - yes you are perceptive, I have a hybrid in mind (I am no longer planning to design another SS amplifier - after many years of fun I reached a conclusion with TGM7 & TGM8 although I do have a JLH 1969 still under construction).

Just slowly mulling over tube choices. Priority is linearity in triode-wired operation, but it might also be important to have a good amount of plate current. I have noticed several reports that triode-wired pentodes can be amazingly linear.
Click to expand...

Bigun

For your consideration read this OTL old article from Mr. J.Futterman ,on my post # 852 : http://www.diyaudio.com/forums/tubes-valves/189282-vacuum-tube-otl-power-amp-86.html,
It is interesting that simple OTL amp is designed almost as some SS amp , with high OLG , high GNFB , and resulting relative low output impedance , but at that old time normally executed only with tubes since silicon power tranzistors not exist .
It is interesting that Futterman OTL amp have almost same internal electronic architecture as JLH 1969 SS A class singleton CFB amp , where GNFB is returned to low impedance node of input emitter ( cathode ) , middle stage is bootstrapped phase splitter , and output SEPP power stage consist from same sex N type BJT power devices ( tubes) .
Any way I think that this concept have some sonic potential , firstly from very good distributed THD spectrum .
And here is what I have on my mind , here is my concept schematic of hybrid Amp based on Futterman OTL amp , with tubes front end , where input signal is directly attached on G1of high gain pentode VAS , followed with DC coupled buffer / CF driver stage ,and further followed with AC coupled common source SS AB class OPS which consist of well known Hitachi lat. Fet`s complementary pair .
Question : what do you think ?
BTW , regardless to this concept check Russian 6C45PI triode , it is very linear high gain tube , which can be better choice for tube VAS than any pentode .
 

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#6
Hi Kevin,

The 6J9P does look nice, also the 6J5P. One thing about the EF806 is that it is still in current production (JJ) and I wonder if there is an advantage in using a tube in current production.

Hi Banat,

I think the JLH 69 was itself inspired by tube amplifiers, so why not allow some ideas with tubes to be inspired by JLH 69!

I think your design looks very interesting. Using cathode follower to drive the FETs is a good way to deal with the need to drive gate capacitance. I have no experience of it, but I prefer to avoid capacitors or inductors in the signal path within the gnfb loop. Using LatFETs makes biassing simple too.
 
#9
Hi AJT - thanks for that - sounds like I should not worry about using older tubes.

Hi Banat, I wonder if you should think about the power-up carefully, what happens when tubes are not conducting and what happens if B+ is up before FET supply. I suspect you want to add some diodes around the circuit to provide some protection against accidental wrong-power up.

I'm not sure what else needs to be thought about, it is a circuit I haven't seen before - it will be fun to experiment with it !
 
#10
Bigun

I think that if both PSU ( B+ for tube front end and bipolar B+ / - for SS OPS bridge ) become instantly power up nothing will happen , no thump on effect , since driver CF cathode res. is still on ground potential , and that driver CF cathode need several seconds of time to pass until become warm and start to conduct , and to rise up on some positive potencial against ground .
BTW , I think that both gate`s coupling caps need to be in range of 0,1uF to max 0,22uF , low leakage high quality ones , MKP types , with 400VDC or more of working voltage .
Actually here I need to correct calculate RC time constant of that resistive high impedance bias network altogether in relation with chosen coupling caps values , just to avoid generation of blocking distortion and to determine low freq. roll off point .
any way I need time to experiment with this relative simple Amp circuit .
 
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#12
Bigun said:
Since your output stage has gain, you could try wiring the input pentode in triode mode, connect screen to plate instead of B+. The feedback factor will be less but it might sound very nice.
Click to expand...

Very Good Point ! :up:

I`m almost forgot that this type of PP OPS it is with certain level of voltage gain to ,
but since I have bunch of NOS noval based double triodes it will be interesting to try them here , I think E80CC is good candidate here , any way I will go first with some ECF82 where VAS will be connected as high gain pentode , than later rewired as triode .
BTW , my intention is to made B+ PSU for suplying tube front end with some standard EZ80 rectifier tube , followed with very simple designed CRC filter PSU , where last C ( 47u ) is in parallel with two 5W series connected Z diodes as simple , cheap & effective B+ regulator .
 
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#14
Bigun said:
People do say that a tube rectifier is the way to go for the best sound and since it is only going to deliver relatively low current for the input stage you can lavish some attention on it.
Click to expand...

No difference between tube rectifier and SS rectifier if B+ filter /regulator is designed well , actually I think that from economic side of view tube rectifier is worst solution than SS rectifier .
 
#18
maton00 said:
that is a good hybrid diagram it is not like the purists ones running 2A of quiesent current for 10 watts of power
Click to expand...

Hi maton00 !

It will be definitely AB class hybrid Amp , much closser biased to economic class B , with no more of around max 25 W dissipation at idle per Amp chassis , I need no more than 20 -25W / 16 ohm / Ch. of max output power , actually max. around few Watt`s per channel for my normal everyday music listening is just OK for me .

Best Regards !
 
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