Forums :: Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives :: Books
Support This Site: Contributors :: Advertise


It is currently Dec Wed 13, 2017 12:43 am


All times are UTC [ DST ]





Post New Topic Post Reply  [ 159 posts ]  Go to page 1, 2, 3, 4, 5 ... 8  Next
Author Message
 Post subject: Clever 6V6 audio amp with two novel circuits
PostPosted: Oct Sat 14, 2017 8:14 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 21235
Location: Haledon, NJ, usa
I stumbled on this DIY 2-tube amp while web browsing last week. I am a bit intrigued by the novel design and by the fact that the author claims only 0.8% distortion.
The two novel circuits are:
Both direct coupling of the preamp as well as cathode follower output.

I am drawn to the simplicity of the design using only 2 tubes per channel. So I'm thinking about building it just for the fun of it and because it's not a big project.

I'm curious about the performance claims and wonder if it really is as good a performer as described.
So I was hoping to pass this circuit link to the rest of you guys to offer some feedback input pros/cons about the whole idea before I jump into it.

Since the original circuit is from way back in 1949 maybe there are things the industry has found out since then that, nowadays might make this idea not so worthwhile to build.

http://diyaudioprojects.com/Technical/P ... Amplifier/
Image
----------------

Today... just to help enlighten myself a bit;
....As an initial bench experiment to test the cathode follower output idea, tonight I decided to try modifying a regular AA5 radio ( Bendix 526).

So I removed the 150 ohm cathode bias resistor on the 50L6 and then I found an OT with a 19:1 winding ratio.
19 x 19=361
361 x 4 ohms= 1440 ohms reflected.

The DC resistance of the primary is 170 ohms so it's close enough to the proper cathode resistor to properly drop 5.5v on the cathode to set idle current to about 32ma.

I removed the standard speaker and ran B+ directly to the plate. Then I connected another 4 ohm speaker to the 2ndary of the OT.

I works quite well.... sounds good with pretty normal volume.
The cathode is +5.5v .... so w/ 170 ohm primary, it's 32ma zero signal current.

If I make a triode out of the 50L6 and tie the plate and SG together ... the bias voltage goes up to 7v with current at 40ma

Sound good either way.

So I realize my test was not to replicate the exact circuit ... but just to let me see that it WILL work quite nicely w/o the load on the plate.

So I'd like to hear some of your thoughts on this amp.

_________________
To be a man, Be a non-conformist, Nothing's sacred as the integrity of your own mind.
-Emerson


Last edited by Pbpix on Oct Sat 14, 2017 9:08 am, edited 1 time in total.

Top
 Profile  
 
 Post subject: Re: Clever 6V6 audio amp with two novel circuits
PostPosted: Oct Sat 14, 2017 8:51 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 16812
Location: Albuquerque, NM 87123
I'm wondering why his current readings are that precise, as this article seems to be from the 50s or 60s. I didn't see any wattage output ratings, so his claim of .8% distortion is meaningless. Maybe I missed something.


Top
 Profile  
 
 Post subject: Re: Clever 6V6 audio amp with two novel circuits
PostPosted: Oct Sat 14, 2017 8:59 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 21235
Location: Haledon, NJ, usa
Johnnysan wrote:
I'm wondering why his current readings are that precise, as this article seems to be from the 50s or 60s. I didn't see any wattage output ratings, so his claim of .8% distortion is meaningless. Maybe I missed something.

Here he states:
"The output of the amplifier is approximately 4.5 watts. While this figure may seem low to those accustomed to dealing with amplifiers having output of 20 or more watts, it is entirely adequate for home use when an efficient speaker system is used. "

_________________
To be a man, Be a non-conformist, Nothing's sacred as the integrity of your own mind.
-Emerson


Top
 Profile  
 
 Post subject: Re: Clever 6V6 audio amp with two novel circuits
PostPosted: Oct Sat 14, 2017 11:25 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 16812
Location: Albuquerque, NM 87123
The RCA manual says that you will get 8% distortion at 4.5 watts with a 6V6 (class A1). If simply using a cathode follower circuit would yield 1/10 the amount of distortion then that type of circuit would be common as dirt.
I'm not convinced. When you build the circuit, post the results here.


Top
 Profile  
 
 Post subject: Re: Clever 6V6 audio amp with two novel circuits
PostPosted: Oct Sat 14, 2017 3:28 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 21235
Location: Haledon, NJ, usa
Johnnysan wrote:
The RCA manual says that you will get 8% distortion at 4.5 watts with a 6V6 (class A1). If simply using a cathode follower circuit would yield 1/10 the amount of distortion then that type of circuit would be common as dirt.
I'm not convinced. When you build the circuit, post the results here.

Of course... where else would I post it?

Does that 8% value apply to pentode mode only?
Here he's using the 6v6 in triode mode.

When he makes reference to his 0.8% distortion claim it's while he's describing the gain of 115 in the 6sj7 and being direct coupled.
But I don't know how to calculate distortion at all.

Can you enlighten me a bit on how.

_________________
To be a man, Be a non-conformist, Nothing's sacred as the integrity of your own mind.
-Emerson


Top
 Profile  
 
 Post subject: Re: Clever 6V6 audio amp with two novel circuits
PostPosted: Oct Sat 14, 2017 3:42 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 794
Location: Jackson, TN
Look's like an interesting project.

Will you be able to measure distortion and frequency response?

Look forward to reports.

Tim


Top
 Profile  
 
 Post subject: Re: Clever 6V6 audio amp with two novel circuits
PostPosted: Oct Sat 14, 2017 3:54 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 21235
Location: Haledon, NJ, usa
I don't know how to measure distortion so perhaps someone can explain it .

The author claims 0.8% here:
"inasmuch as these two tube elements are connected directly together). With 73 volts at the plate and 55 volts at the screen of the 6SJ7, a voltage amplification of 115 can be obtained at only 0.8 percent distortion. "

Also with the primary winding of the OT acting as the cathode bias resistance we are using 100% degenerative feedback.

The author states:
"The cathode-follower output, in addition to its simplicity, provides both improved high and low frequency response, damping out of all the peaks in both the output transformer and speaker, less distortion, and 100 percent degenerative feedback."

_________________
To be a man, Be a non-conformist, Nothing's sacred as the integrity of your own mind.
-Emerson


Last edited by Pbpix on Oct Sat 14, 2017 3:59 pm, edited 1 time in total.

Top
 Profile  
 
 Post subject: Re: Clever 6V6 audio amp with two novel circuits
PostPosted: Oct Sat 14, 2017 3:56 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 21235
Location: Haledon, NJ, usa
Perhaps 'Flipperhome' can chime in here and shed some light to help explain how the author might have arrived at his figures?

_________________
To be a man, Be a non-conformist, Nothing's sacred as the integrity of your own mind.
-Emerson


Top
 Profile  
 
 Post subject: Re: Clever 6V6 audio amp with two novel circuits
PostPosted: Oct Sat 14, 2017 5:20 pm 
Member
User avatar

Joined: Dec Mon 29, 2014 9:39 pm
Posts: 3393
Location: Los Angeles
I am looking to build another amp. Instead of remodeling a previously built 6V6 for my Cousin, this looks like just the thing.
This will be after I finish the 300b.

_________________
John Smith, over and out.
If I did something right, I made a mistake.


Top
 Profile  
 
 Post subject: Re: Clever 6V6 audio amp with two novel circuits
PostPosted: Oct Sat 14, 2017 6:06 pm 
Member
User avatar

Joined: Dec Mon 29, 2014 9:39 pm
Posts: 3393
Location: Los Angeles
As you could figure, I would like a tone amp added.
Here is the tone section from the Little Prince. Thanks Flip.
But, would like to swap the tubes for 12AX7,s. Also louse
the low gain buffer for an additional 12AX7 amplifying stage.
Attachment:
Baxandall%20Tone%20Control%20w-Vol-Bal%20v3[1].jpg
Baxandall%20Tone%20Control%20w-Vol-Bal%20v3[1].jpg [ 114.86 KiB | Viewed 873 times ]

_________________
John Smith, over and out.
If I did something right, I made a mistake.


Last edited by john8750 on Oct Sun 15, 2017 4:46 am, edited 2 times in total.

Top
 Profile  
 
 Post subject: Re: Clever 6V6 audio amp with two novel circuits
PostPosted: Oct Sat 14, 2017 8:08 pm 
Moderator

Joined: Jan Thu 01, 1970 1:00 am
Posts: 36066
Location: Livermore, CA
Peter

Your 6V6 circuit is connected as a triode cathode follower. Circuit wouldn't add much distortion but also doesn't have any voltage gain.

_________________
Norm


Top
 Profile  
 
 Post subject: Re: Clever 6V6 audio amp with two novel circuits
PostPosted: Oct Sat 14, 2017 9:36 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 21235
Location: Haledon, NJ, usa
Norm Leal wrote:
Peter

Your 6V6 circuit is connected as a triode cathode follower. Circuit wouldn't add much distortion but also doesn't have any voltage gain.

Thank you Norm:
So... I guess you are saying that since it's operating as a triode the 0.8% distortion is probably accurate?

I realize it doesn't have any voltage gain Norm, but t he author claims 4.5 watts.
So if that low 0.8% distortion is real ...then I'd probably be fine with 4-1/2 watts for my living room.

Currently I'm extremely happy with my existing 6V6 PP UL amp.

http://pbpix.com/amp/6v6%20-%206AQ5%20pp-amp-T.png

.... and I doubt that I'm getting more than about 5 or 6 watts out of it.

_________________
To be a man, Be a non-conformist, Nothing's sacred as the integrity of your own mind.
-Emerson


Top
 Profile  
 
 Post subject: Re: Clever 6V6 audio amp with two novel circuits
PostPosted: Oct Sun 15, 2017 2:09 am 
Member
User avatar

Joined: Nov Sat 26, 2011 4:09 am
Posts: 8070
Location: Texas. USA
Pbpix wrote:
Perhaps 'Flipperhome' can chime in here and shed some light to help explain how the author might have arrived at his figures?
Since he doesn't say I can only speculate but imagine it's a 2'nd harmonic calculation from the 6SJ7 plate curves. It's interesting to note that this circuit burns off 25% more power just to get the 6SJ7's screen voltage.

Btw, his claim of 4.5 Watt appears to be based on the 6V6 datasheet typical at 250V but that's pentode mode and his is running triode mode. I don't see any way it's even going to approach that much power. Probably more like 2 Watt.


Top
 Profile  
 
 Post subject: Re: Clever 6V6 audio amp with two novel circuits
PostPosted: Oct Sun 15, 2017 3:45 am 
Member

Joined: Apr Thu 14, 2016 8:25 pm
Posts: 282
Location: pensacola fl
It is possible to have low distortion due to the fact both stages have negative feedback. The output stage has 100% feedback so no voltage gain but current gain is possible.


Top
 Profile  
 
 Post subject: Re: Clever 6V6 audio amp with two novel circuits
PostPosted: Oct Sun 15, 2017 5:49 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 21235
Location: Haledon, NJ, usa
Flipperhome wrote:
Pbpix wrote:
Perhaps 'Flipperhome' can chime in here and shed some light to help explain how the author might have arrived at his figures?
Since he doesn't say I can only speculate but imagine it's a 2'nd harmonic calculation from the 6SJ7 plate curves. It's interesting to note that this circuit burns off 25% more power just to get the 6SJ7's screen voltage.

Btw, his claim of 4.5 Watt appears to be based on the 6V6 datasheet typical at 250V but that's pentode mode and his is running triode mode. I don't see any way it's even going to approach that much power. Probably more like 2 Watt.

Thanks Flip:
You know.. I was studying that 6sj7 SG supply myself last night trying to figure out why those two resistors (R3, R5) are 10 Watts.... I was thinkiing what a waste of power...
But then I suddenly realized... it's the current path for the cathode and the plate current.
The 45ma plate current comes up the cathode by way of those screen grid resistors up through R3 then R5 and on up the cathode....from B-.
So is that being wasted or just the the same 45ma the tube has to draw for zero signal bias at quiescence?
Is there a better way?

_________________
To be a man, Be a non-conformist, Nothing's sacred as the integrity of your own mind.
-Emerson


Top
 Profile  
 
 Post subject: Re: Clever 6V6 audio amp with two novel circuits
PostPosted: Oct Sun 15, 2017 7:11 am 
Member
User avatar

Joined: Nov Sat 26, 2011 4:09 am
Posts: 8070
Location: Texas. USA
Pbpix wrote:
Flipperhome wrote:
Since he doesn't say I can only speculate but imagine it's a 2'nd harmonic calculation from the 6SJ7 plate curves. It's interesting to note that this circuit burns off 25% more power just to get the 6SJ7's screen voltage.

Btw, his claim of 4.5 Watt appears to be based on the 6V6 datasheet typical at 250V but that's pentode mode and his is running triode mode. I don't see any way it's even going to approach that much power. Probably more like 2 Watt.

Thanks Flip:
You know.. I was studying that 6sj7 SG supply myself last night trying to figure out why those two resistors (R3, R5) are 10 Watts.... I was thinkiing what a waste of power...
But then I suddenly realized... it's the current path for the cathode and the plate current.
The 45ma plate current comes up the cathode by way of those screen grid resistors up through R3 then R5 and on up the cathode....from B-.
So is that being wasted or just the the same 45ma the tube has to draw for zero signal bias at quiescence?
Is there a better way?
Well, "better" is debatable but the conventional cathode resistor to ground would dissipate only around .6 Watt.


Top
 Profile  
 
 Post subject: Re: Clever 6V6 audio amp with two novel circuits
PostPosted: Oct Sun 15, 2017 9:46 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 21235
Location: Haledon, NJ, usa
Flipperhome wrote:
Well, "better" is debatable but the conventional cathode resistor to ground would dissipate only around .6 Watt.

Well.. yes of course... but this design is direct coupling so the 6V6 grid needs to be at the same voltage as the 6sj7 plate (+73v)... yet it must still be 12v less-positive than the cathode (+85v) of the 6V6 to set the bias.
So I mean... is there another, better ( less wasteful) way to achieve this?

_________________
To be a man, Be a non-conformist, Nothing's sacred as the integrity of your own mind.
-Emerson


Top
 Profile  
 
 Post subject: Re: Clever 6V6 audio amp with two novel circuits
PostPosted: Oct Sun 15, 2017 11:26 pm 
Member
User avatar

Joined: Nov Sat 26, 2011 4:09 am
Posts: 8070
Location: Texas. USA
Pbpix wrote:
Flipperhome wrote:
Well, "better" is debatable but the conventional cathode resistor to ground would dissipate only around .6 Watt.

Well.. yes of course... but this design is direct coupling so the 6V6 grid needs to be at the same voltage as the 6sj7 plate (+73v)... yet it must still be 12v less-positive than the cathode (+85v) of the 6V6 to set the bias.
So I mean... is there another, better ( less wasteful) way to achieve this?
Is there another way to configure the circuit so the circuit configuration is exactly the same? Probably not.


Top
 Profile  
 
 Post subject: Re: Clever 6V6 audio amp with two novel circuits
PostPosted: Oct Sun 15, 2017 11:43 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 21235
Location: Haledon, NJ, usa
Flipperhome wrote:
Pbpix wrote:
Flipperhome wrote:
Well, "better" is debatable but the conventional cathode resistor to ground would dissipate only around .6 Watt.

Well.. yes of course... but this design is direct coupling so the 6V6 grid needs to be at the same voltage as the 6sj7 plate (+73v)... yet it must still be 12v less-positive than the cathode (+85v) of the 6V6 to set the bias.
So I mean... is there another, better ( less wasteful) way to achieve this?
Is there another way to configure the circuit so the circuit configuration is exactly the same? Probably not.

I meant is there a way to be able to reconfigure it so that "the circuit configuration is effectively the same" ?

Well.. how do other direct coupled circuits do it?
Do they have to "float" the previous driving stage?

_________________
To be a man, Be a non-conformist, Nothing's sacred as the integrity of your own mind.
-Emerson


Top
 Profile  
 
 Post subject: Re: Clever 6V6 audio amp with two novel circuits
PostPosted: Oct Mon 16, 2017 12:04 am 
Moderator

Joined: Jan Thu 01, 1970 1:00 am
Posts: 36066
Location: Livermore, CA
So you don't think direct coupling is something new check this schematic: (Model H)

http://www.nostalgiaair.org/pagesbymode ... 018419.pdf

_________________
Norm


Top
 Profile  
 
Post New Topic Post Reply  [ 159 posts ]  Go to page 1, 2, 3, 4, 5 ... 8  Next

All times are UTC [ DST ]


Who is online

Users browsing this forum: Exabot [Bot] and 8 guests



Search for:
Jump to:  


















Privacy Policy :: Powered by phpBB