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EL34 schematic confusion

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#262
#263
ah, that one, it used the 6sl7 as input differential amp with a pentode ccs, while the 6sn7 as another gain stage due to the feedback networks.

waynes design acomplishes the same and you get to save two tubes in fact, a 7pin pentode and a 6sl7.

the third one uses a pentode in the input in lieu of the 6sl7.
 
#264
navin

Look for the "Winged C" logo on the tube itself and on the box/carton.
 

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#265
navin, I purchased a matched quad of "Winged C" Svetlana's back in June of this year and I have no complaints. Still going strong and have great sound IMO. What I meant by escaping fron reality was escaping INTO the music! 😀 😉

Wayne
 

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#266
Tony said:
waynes design acomplishes the same and you get to save two tubes in fact, a 7pin pentode and a 6sl7..
Click to expand...

the 7 pin pentode is for rectification so that is not really counted right? so really I save 1 tube per amp.


cogsncogs said:
navin
Look for the "Winged C" logo on the tube itself and on the box/carton.
Click to expand...

Alas no C of any kind on my tubes. Should have got EH instead and saved S$8! my tube has a "S" logo instead.
 
#267
I'd just like to point out that this is my circuit, not Jojo's. The reasons for using both halves of the 6SL7 are to give an all-balanced circuit and to allow the use of local (or 'partial' if you prefer) feedback over both the driver and output stages, rather than just the OP stage. This enables a much larger amount of NFB to be applied, without placing impossible demands on the driver. An all balanced circuit is immune from power-supply hum. For a detailed discussion of this topology, see this thread
 
#268
ray_moth said:
I'd just like to point out that this is my circuit, not Jojo's. The reasons for using both halves of the 6SL7 are to give an all-balanced circuit and to allow the use of local (or 'partial' if you prefer) feedback over both the driver and output stages, rather than just the OP stage. This enables a much larger amount of NFB to be applied, without placing impossible demands on the driver. An all balanced circuit is immune from power-supply hum. For a detailed discussion of this topology, see this thread
Click to expand...

sorry ray moth. I guess since JoJo was discussing it I got confused.

I guess it's time to learn more.

meanwhile i have a few questions for wayne...

My OPT has 4 and 8 ohm taps. the speaker being used in UL is 4 ohms. should the Fb (R24) be connected to the 4 ohm tap or 8 ohm tap? What is the value of R24?

To convert the ckt to Triode all I got to do is connect the 470ohm (R20/21) to the anode. right?

what are the advantages of having a triode input v/s a pentode input (like using an EF86)?

What Q1 can I use. In any case the KSC 945Y is also not available here so i'd need a subsitute for that. MJE?

All Resistors I assume are 1W except R10 which is 0.5W and R4/5 that are 2W. right?
 
#269
My OPT has 4 and 8 ohm taps. the speaker being used in UL is 4 ohms. should the Fb (R24) be connected to the 4 ohm tap or 8 ohm tap? What is the value of R24?
Click to expand...

R24 should be connected to the 4 ohm tap. The value of R24 will be determined experimentally to give 775mV to 1V input sensitivity and as well as any other HF compensation components the may be needed. Here is where you need some test equipment like a scope, DMM, signal generator, 4-8 ohm dummy loads, disposable speakers etc.
Now if I had the same output tyrannies and if I were to be building the same amps, I could give you some values for R24 and other HF compensation components. But you would still need to have the aforementioned test gear. 😉 :smash: I would guess that you could start out with a value of 10k for R24 and then adjust the values using 40Hz, 1kHz, and 10kHz square wave and adjust R24 @10kHz for a good looking square wave, with min ringing. 40Hz signal for LF tilt and LF stability and parasitic oscillations. 30-40Hz would be good for testing OPT core saturation, and so on. I wouldn't start to build an amp w/NFB without the test gear I've mentioned.

To convert the ckt to Triode all I got to do is connect the 470ohm (R20/21) to the anode. right?
Click to expand...

Yes

What Q1 can I use. In any case the KSC 945Y is also not available here so i'd need a subsitute for that. MJE?
Click to expand...

The KSC945Y aka 2SC945 (Japanese) is one of the most widely used small signal transistors on earth! You can find them just about anywhere, VCR's, TV's, Hi-Fi equipment etc. Just about any hi gain small signal transistor will do with around 50V or higher ICBO, VCE, with a hFE of 200 and up.

Sorry I have go to hospital ASAP, so I finish this when I get home

Cheers
Wayne 😉
 
#270
cogsncogs said:


R24 should be connected to the 4 ohm tap.... Here is where you need some test equipment like a scope, DMM, signal generator, 4-8 ohm dummy loads, disposable speakers etc....I would guess that you could start out with a value of 10k for R24 and then adjust the values using 40Hz, 1kHz, and 10kHz square wave and adjust R24 @10kHz for a good looking square wave, with min ringing. 40Hz signal for LF tilt and LF stability and parasitic oscillations..... I wouldn't start to build an amp w/NFB without the test gear I've mentioned.

The KSC945Y aka 2SC945 (Japanese) is one of the most widely used small signal transistors on earth! You can find them just about anywhere, VCR's, TV's, Hi-Fi equipment etc.
Click to expand...

So what may be a good idea is to use a 5K resistor and 10K pot in series for R24 and adjust the pot. What say?

I got a basic scope and DMM but no dummy loads (I got some 10 ohm 10W resistors maybe I can parallel 2 to make 5ohms 20W?) and definitely no disposable speakers. I could get a pair of 10W fullranges out of an old TV will that do?

and maybe I can look arond the same TV or accompanied derelict VCR for 4 2SC945!

Take your time Wayne. Remember I am in no hurry. Besides family comes first! Hope your mom is feeling better today.
 
#272
So what may be a good idea is to use a 5K resistor and 10K pot in series for R24 and adjust the pot. What say?

I got a basic scope and DMM but no dummy loads (I got some 10 ohm 10W resistors maybe I can parallel 2 to make 5ohms 20W?) and definitely no disposable speakers. I could get a pair of 10W fullranges out of an old TV will that do?

and maybe I can look arond the same TV or accompanied derelict VCR for 4 2SC945!
?
Click to expand...


yes, a series combination will do, then get the neared standard value resistor once you get it right.

a full range speakers will do.

you can also use 2sc1815 in place of 2sc945, incidentally, 2sc945 can be found on pc psu boards.
 
#274
Tony, I'd have to do some load line analysis to tell whether or not you'll get enough swing for scree drive. But the 6CM7 sure looks like a good candidate tube for the application- rated max B+ at 500V is a good thing. Screen drive typically calls for 150V or more of swing.
 
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