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


It is currently Dec Mon 18, 2017 10:02 am


All times are UTC [ DST ]





Post New Topic Post Reply  [ 159 posts ]  Go to page Previous  1 ... 4, 5, 6, 7, 8
Author Message
 Post subject: Re: Clever 6V6 audio amp with two novel circuits
PostPosted: Oct Mon 23, 2017 10:57 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 21291
Location: Haledon, NJ, usa
john8750 wrote:
Pbpix wrote:
I updated the print to reflect that either 6V6 or the 6AQ5 are interchangeable here.
I tested it with the 6AQ5 and listening to it tonight .. and of course everything's fine.

I modified the 6SH7 cathode resistor.
I also removed the .05 uf input cap because when I connected the Mp3 player output directly, the volume went noticeably up a bit.

BTW: I just went back the last few pages and replaced earlier versions w/this latest one.

The reason is that Google robots grab and post these schematics... and I'd rather let them get only the latest version instead of a bunch with minor early versions that might confuse ppl who copy and try them.
( I know... how thoughtful of me... lol)
Image




Good job peter. What would happen if you remover the other .05 coupler?

Bad news.
That would put 110v DC from the plate of the 6sh7 right on the grid of the 6v6 blasting on bazaaam!!
That cap is there to BLOCK the DC voltage from getting on the grid of the 6V6.

You may see others where they use direct coupling but in those cases the cathode on the 6v6 would have to be raised so as to keep the bias on the grid about 10 more negative than the cathode.

_________________
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 Tue 24, 2017 10:20 pm, edited 1 time in total.

Top
 Profile  
 
 Post subject: Re: Clever 6V6 audio amp with two novel circuits
PostPosted: Oct Mon 23, 2017 11:48 pm 
Member
User avatar

Joined: Dec Mon 29, 2014 9:39 pm
Posts: 3440
Location: Los Angeles
Pbpix wrote:
john8750 wrote:
Pbpix wrote:
I updated the print to reflect that either 6V6 or the 6AQ5 are interchangeable here.
I tested it with the 6AQ5 and listening to it tonight .. and of course everything's fine.

I modified the 6SH7 cathode resistor.
I also removed the .05 uf input cap because when I connected the Mp3 player output directly, the volume went noticeably up a bit.

BTW: I just went back the last few pages and replaced earlier versions w/this latest one.

The reason is that Google robots grab and post these schematics... and I'd rather let them get only the latest version instead of a bunch with minor early versions that might confuse ppl who copy and try them.
( I know... how thoughtful of me... lol)
Image




Good job peter. What would happen if you remover the other .05 coupler?

Bad news.
That would put 110v DC from the plate of the 6sh7 right on the grid of the 6v6 blasting on bazaaam!!
That cap is there to BLOCK the DC voltage from getting on the grid of the 6V6.

You may see others where they use direct coupling but in those cases the cathode on the 6v6 would have to be raised so as to keep the bias on the grid about 10 more negative than the cathode.



It would be about 43volts, but I see your point.

_________________
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 Mon 23, 2017 11:56 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 798
Location: Jackson, TN
OK, this thread looks like a bait and switch., :shock:

What happened to Peter's original scheme?
Cathode OP transformer
Direct coupled

I'd still like to know whether it is practical.

Thanks, Tim


Top
 Profile  
 
 Post subject: Re: Clever 6V6 audio amp with two novel circuits
PostPosted: Oct Mon 23, 2017 11:59 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 21291
Location: Haledon, NJ, usa
john8750 wrote:


It would be about 43volts, but I see your point.

Why 43?
I show the plate as approx 60-110v

_________________
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 Tue 24, 2017 12:22 am 
Member
User avatar

Joined: Dec Mon 29, 2014 9:39 pm
Posts: 3440
Location: Los Angeles
Pbpix wrote:
john8750 wrote:


It would be about 43volts, but I see your point.

Why 43?
I show the plate as approx 60-110v



Oops, correction, it would be 39.28volts.
Just figure the resistance divider of 100k and 560K would be 5.6
220volts divided by 5.6 would be 39.28volts.

_________________
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 Tue 24, 2017 12:23 am 
Member
User avatar

Joined: Dec Mon 29, 2014 9:39 pm
Posts: 3440
Location: Los Angeles
Tkilboy wrote:
OK, this thread looks like a bait and switch., :shock:

What happened to Peter's original scheme?
Cathode OP transformer
Direct coupled

I'd still like to know whether it is practical.

Thanks, Tim



Sorry about the wild ride Tim. Hang in there.

_________________
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 Tue 24, 2017 12:54 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 21291
Location: Haledon, NJ, usa
Tkilboy wrote:
OK, this thread looks like a bait and switch., :shock:

What happened to Peter's original scheme?
Cathode OP transformer
Direct coupled

I'd still like to know whether it is practical.

Thanks, Tim

Hi Tim:
I made a mention a cpl posts back about my progress there.
I'll explain again:
I wanted to build the ckt just as shown in the 1st post using the cathode follower idea.
At first I did not have the correct 6SJ7 tube. So while waiting I decided to first build the basic of the amp as a conventional ckt using a 6SH7 tube.
This works nicely as the latest post shows. (also works fine with 6SJ7 and 6SG7)

When the 6SJ7 tubes arrived I tried to implement just the cathode follower OT part of the ckt but also keeping the 6SJ7 driver as a capacitor coupled.

When I tried this.. it DID work... seemingly very well... but I wasn't getting very much volume.
( I did not have the 6sj7 direct coupled but I don't think that's the cause of low volume.)
So I think the reason is that the original schematic shows 335v for B+ and my testing HV supply can only deliver 220v for B+.

So I am assuming that perhaps the mediocre volume level is due to the low B+.

But I'm also only using a 4k OT instead of 5k - 6k as suggested.
if the primary had the correct DC resistance of about 250 - 266 ohms.
If I had 266 ohms on the primary it should develop a 12v bias developing 45ma.

Right now my primary is about 296 ohms but I'm only getting 9.5v bias. This creates only 32ma instead of the 45ma as indicated on the orig schematic.
So I don't have all the ingredients matching the orig print.

So ... for now I'm going to put the cathode-follower idea on the back burner until I can get my bench test ckt fed by the full 335v.
I will have to build that using a voltage doubler ckt i've used before for approx 300v.... so I'll be experimenting with that first to try to make a good solid 335v.

Perhaps Flip can comment on if he feels that the increased B+ would help bring up the volume to a decent level even though the cathode-follower ckt has no gain to speak of. Typically gain is expressed as less than one..

_________________
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 Tue 24, 2017 1:18 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 21291
Location: Haledon, NJ, usa
john8750 wrote:
Pbpix wrote:
john8750 wrote:


It would be about 43volts, but I see your point.

Why 43?
I show the plate as approx 60-110v



Oops, correction, it would be 39.28volts.
Just figure the resistance divider of 100k and 560K would be 5.6
220volts divided by 5.6 would be 39.28volts.

... uhhh yeah but if it were directly coupled... that 560k resistor isn't there.
But if it were just left there and you pull the .05uf cap... yes. Zap.

_________________
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 Tue 24, 2017 2:56 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 798
Location: Jackson, TN
Thanks for the update Pater.

I suspect that you are right in that the increased B+ may provide more volume, also optimizing bias on the 6V6.

I think it's a cool configuration and am interested in the outcome. Right now I'm not in a position to build another amp, so I must enjoy the experience through other's projects :P

Thanks, Tim


Top
 Profile  
 
 Post subject: Re: Clever 6V6 audio amp with two novel circuits
PostPosted: Oct Tue 24, 2017 5:01 am 
Member
User avatar

Joined: Mar Wed 26, 2008 3:06 pm
Posts: 794
Location: Cave Springs, AR
Tkilboy wrote:
OK, this thread looks like a bait and switch., :shock:

What happened to Peter's original scheme?
Cathode OP transformer
Direct coupled

I'd still like to know whether it is practical.

Thanks, Tim

I understand your question and would also like to see how the original circuit works, but who cares about a coupling capacitor and the location of the OPT as long as it sounds good?? 8) :lol:

_________________
Mark


Top
 Profile  
 
 Post subject: Re: Clever 6V6 audio amp with two novel circuits
PostPosted: Oct Tue 24, 2017 6:33 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 21291
Location: Haledon, NJ, usa
err ducks wrote:
Tkilboy wrote:
OK, this thread looks like a bait and switch., :shock:

What happened to Peter's original scheme?
Cathode OP transformer
Direct coupled

I'd still like to know whether it is practical.

Thanks, Tim

I understand your question and would also like to see how the original circuit works, but who cares about a coupling capacitor and the location of the OPT as long as it sounds good?? 8) :lol:

Well...sure ... if it sounds good.... Great!

The reason we want to know more about how the cathode-follower circuit performed is because the author of the circuit (with the cathode-follower OT )... claimed that in such a position compared to a more conventional arrangement, the author found that he was able to increase the quality with less distortion. (albeit with less gain) So it was the purpose of this thread to try to bench test that and find out more about it.
Along the way the more conventional circuit I built using the 6SH7 proved to also be a great sounding experiment. But its layout is conventional and it was built as an additional fun test while waiting for the tubes to build the cathode-follower circuit.

_________________
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 Tue 24, 2017 4:14 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 12261
john8750 wrote:
Tkilboy wrote:
OK, this thread looks like a bait and switch., :shock:

What happened to Peter's original scheme?
Cathode OP transformer
Direct coupled

I'd still like to know whether it is practical.

Thanks, Tim



Sorry about the wild ride Tim. Hang in there.

I have to agree with Tim, probably every tube manual published from mid '30s has a 6V6/6AQ5 audio amp circuit with OPT in plate... I'd like to see a build with OPT in cathode as well....

Yeah I could build it, mostly too daym lazy...

Tom


Top
 Profile  
 
 Post subject: Re: Clever 6V6 audio amp with two novel circuits
PostPosted: Oct Tue 24, 2017 9:45 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 21291
Location: Haledon, NJ, usa
35Z5 wrote:
I have to agree with Tim, probably every tube manual published from mid '30s has a 6V6/6AQ5 audio amp circuit with OPT in plate... I'd like to see a build with OPT in cathode as well....

Yeah I could build it, mostly too daym lazy...

Tom

Me too Tom:
... I explained where I'm at so far to Tim a few posts above...

Maybe you have some ideas about this?

I wanted to build the ckt just as shown in the 1st post using the cathode follower idea.
At first I did not have the correct 6SJ7 tube. So while waiting I decided to first build the basics structure of the amp as a conventional ckt using a 6SH7 tube.
This works nicely as the latest posted schematic shows. (also works fine with 6SJ7 and 6SG7)

When the 6SJ7 tubes arrived I tried to implement just the cathode follower OT part of the ckt but also keeping the 6SJ7 driver as a capacitor coupled.

When I tried this.. it DID work... seemingly very well... but I wasn't getting very much volume. .. only about 1/2 the volume of what I get w/the conventional ckt.

( I did not have the 6sj7 direct coupled but I don't think that's the cause of low volume.)
So I think the reason is that the original schematic shows 335v for B+ and my testing HV supply can only deliver 220v for B+.

So I am assuming that perhaps the mediocre volume level is due to the low B+.

But I'm also only using a 4k OT instead of 5k - 6k as suggested.
if the primary had the correct DC resistance of about 250 - 266 ohms:
If I had the exact same 266 ohms on the primary as the author suggested, AND 335v B+, it should develop a 12v bias @ 45ma.

Right now my primary DC resistance is about 296 ohms and w/220v B+, I'm only getting 9.5v bias. This creates only 32ma instead of the 45ma as indicated on the orig schematic.
So I don't have all the ingredients matching the orig print.

So yeah, I'm certainly curious and still determined to test this as a cathode-follower.
It's just.. for now I'm going to put the cathode-follower idea on hold a bit just until I can get my bench test ckt fed by the full 335v B+.
Right now I just use my adjustable 220v bench supply.
So in order to do the 335 volts, I will have to build it using a voltage doubler ckt I've used before for approx 300v.... so I'll be experimenting with that rig first to try to make a good solid 335v.

Perhaps you or Flip can comment on if you feel that the increased B+ would be the key to help bring up the volume to a decent level; even though the cathode-follower ckt has no gain to speak of. Typically gain is expressed as less than one..

_________________
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 Wed 25, 2017 12:39 am 
Member
User avatar

Joined: Nov Sat 26, 2011 4:09 am
Posts: 8099
Location: Texas. USA
Pbpix wrote:
...When I tried this.. it DID work... seemingly very well... but I wasn't getting very much volume. .. only about 1/2 the volume of what I get w/the conventional ckt.

( I did not have the 6sj7 direct coupled but I don't think that's the cause of low volume.)
So I think the reason is that the original schematic shows 335v for B+ and my testing HV supply can only deliver 220v for B+.

So I am assuming that perhaps the mediocre volume level is due to the low B+.....
When you put the OPT in the cathode you turn the 6V6 into a triode and that reduces the possible power out by half to a third of what the pentode, in pentode mode, can muster.


Top
 Profile  
 
 Post subject: Re: Clever 6V6 audio amp with two novel circuits
PostPosted: Oct Wed 25, 2017 1:15 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 21291
Location: Haledon, NJ, usa
Flipperhome wrote:
Pbpix wrote:
...When I tried this.. it DID work... seemingly very well... but I wasn't getting very much volume. .. only about 1/2 the volume of what I get w/the conventional ckt.

( I did not have the 6sj7 direct coupled but I don't think that's the cause of low volume.)
So I think the reason is that the original schematic shows 335v for B+ and my testing HV supply can only deliver 220v for B+.

So I am assuming that perhaps the mediocre volume level is due to the low B+.....
When you put the OPT in the cathode you turn the 6V6 into a triode and that reduces the possible power out by half to a third of what the pentode, in pentode mode, can muster.

So do you believe that bringing the B+ up to 335v will help bring up the volume to a more typical level?

_________________
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 Wed 25, 2017 1:27 am 
Member
User avatar

Joined: Nov Sat 26, 2011 4:09 am
Posts: 8099
Location: Texas. USA
Pbpix wrote:
Flipperhome wrote:
Pbpix wrote:
...When I tried this.. it DID work... seemingly very well... but I wasn't getting very much volume. .. only about 1/2 the volume of what I get w/the conventional ckt.

( I did not have the 6sj7 direct coupled but I don't think that's the cause of low volume.)
So I think the reason is that the original schematic shows 335v for B+ and my testing HV supply can only deliver 220v for B+.

So I am assuming that perhaps the mediocre volume level is due to the low B+.....
When you put the OPT in the cathode you turn the 6V6 into a triode and that reduces the possible power out by half to a third of what the pentode, in pentode mode, can muster.

So do you believe that bringing the B+ up to 335v will help bring up the volume to a more typical level?
It'll increase the power output, for sure, but it will still be half to a third of normal power levels. The low B+ just makes it worse.

Note that half power does not mean half volume.


Top
 Profile  
 
 Post subject: Re: Clever 6V6 audio amp with two novel circuits
PostPosted: Oct Wed 25, 2017 1:44 am 
Member
User avatar

Joined: Nov Sat 26, 2011 4:09 am
Posts: 8099
Location: Texas. USA
Pbpix wrote:
....Perhaps you or Flip can comment on if you feel that the increased B+ would be the key to help bring up the volume to a decent level; even though the cathode-follower ckt has no gain to speak of. Typically gain is expressed as less than one..
Output tube 'gain' isn't the issue. It just means there has to be more gain in the preamp going to it.

Raising B+ will produce more power and the power gained is a function of voltage squared, so it's more than simply raising B+ "by 30%" would imply (for those who think 'linear').


Top
 Profile  
 
 Post subject: Re: Clever 6V6 audio amp with two novel circuits
PostPosted: Oct Wed 25, 2017 2:05 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 12261
Think of it like this... Assuming gain roughly equal, with triode making 1w and pentode producing 3W, volume will be same till the limit of triode is reached then it begins to distort, whereas the pentode still has additional undistorted volume available... BUT in triode mode I suspect the gain is somewhat less, so it could require a higher signal input than the pentode...


Top
 Profile  
 
 Post subject: Re: Clever 6V6 audio amp with two novel circuits
PostPosted: Oct Wed 25, 2017 6:08 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 21291
Location: Haledon, NJ, usa
Flipperhome wrote:
Pbpix wrote:
....Perhaps you or Flip can comment on if you feel that the increased B+ would be the key to help bring up the volume to a decent level; even though the cathode-follower ckt has no gain to speak of. Typically gain is expressed as less than one..
Output tube 'gain' isn't the issue. It just means there has to be more gain in the preamp going to it.

Raising B+ will produce more power and the power gained is a function of voltage squared, so it's more than simply raising B+ "by 30%" would imply (for those who think 'linear').

Well I'm listening to it in cathode-follower mode as I type this... but I have to have my Mp3 player up high.
I don't have a perfect 5 or 6 k OT but I tried a few odd PP ones and various secondary taps to get max volume.

This PP one has 330 ohms on 1/2 the primary. So with 230V B+ it creates 12v bias @ 36ma.

You're right about B+. As I vary the B+ up and down from as low as 100v up to 250v .... the volume sounds the same.

My ears are not able to determine if there's any particular improvement in the distortion. So I think it would require some test equipment.

Volume at the moment (w/my Mp3 at max) is what I'd call medium to low by normal listening standards that I'm used to... whatever that might mean.

Image

I placed my 6db passive transformer signal booster between the Mp3 outpt and the amp.
Now.... ok...
Now (using 6SJ7) I get some decent volume and was able to even back off the Mp3 vol control one full notch.
This amp gives the greatest signal to the 6V6 when I use the 6SH7.
So I just popped the 6SH7 back in... with the 6b signal booster too... and now again more volume. Now I can back off the Mp3 volume even 1 more notch.

Ok... I now have the other OT I was using on again the Pt-291 PP.
1/2 the primary on this one is 240 ohms as I remeasure it now.
With 230v B+ I'm getting about 10v bias @41ma

So to summarize:
... using the 6SH7 tube.... and a 240 ohm primary w/230v @41ma volume is good.... but only after I added the 6db passive sig booster to my Mp3 player.

Sounds VERY good! .... now let's try to define "good".
.. at least as nice as the conventional ckt... and if it's got less distortion... only test equip will tell.

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


Top
 Profile  
 
Post New Topic Post Reply  [ 159 posts ]  Go to page Previous  1 ... 4, 5, 6, 7, 8

All times are UTC [ DST ]


Who is online

Users browsing this forum: No registered users and 6 guests



Search for:
Jump to:  


















Privacy Policy :: Powered by phpBB