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SE 45 active parafeed breadboard ...

24.140.98.34
Posted on May 6, 2015 at 17:16:54
deathtube 667



Got the SE 45 active parafeed circuit wired up on my breadboard tonight.

No problems with center tapped AC heaters despite the bird's nest breadboard presentation.

Subjectively, very enjoyable listening to Altec 811B/808 & Foster 025N03 with this circuit.

I'll get some measurements posted later.

 

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RE: SE 45 active parafeed breadboard ..., posted on May 6, 2015 at 18:54:14
vinnie2
Audiophile

Posts: 4481
Location: North Carolina
Joined: September 28, 2013
 Love those breadboards. Cool.

 

RE: SE 45 active parafeed breadboard ..., posted on May 7, 2015 at 19:20:47
Caucasian Blackplate
Industry Professional

Posts: 8313
Location: Seattle
Joined: June 18, 2004
 What did you end up finding for output transformers?

 

RE: SE 45 active parafeed breadboard ..., posted on May 8, 2015 at 03:47:29
deathtube 667
 Altec 70V Line OPT #15708. 1W primary tap. 8 ohm secondary.

They are a bit larger in size that the original Paramour parafeed OPT if you remember those.

I posted a phase vs. bandwidth plot on the MQ forum sometime ago.


 

RE: measurements ..., posted on May 10, 2015 at 18:46:40
deathtube 667
 Took some basic circuit measurements:

The overall gain is .96

THD% = .91 @ .485W with 1KHz sine input.

Did not have enough voltage output from soundcard to reach 1W.

With signal generator, Power Out before clipping was just over 1W.

I will probably look for a higher gain driver stage than C4S 6SN7 for better level matching in a multi-amp system.


 

RE: measurements ..., posted on May 10, 2015 at 22:19:03
hennfarm
Audiophile

Posts: 535
Location: Oregon
Joined: October 8, 2008
 Looks like a ICT with a full wave tube rect? What's the B+ around 275vdc?

 

RE: measurements ..., posted on May 11, 2015 at 03:35:04
deathtube 667
 B+ on the C4S of the 45's was 500VDC.

The rectifier is a hybrid FWBR.

 

RE: measurements ..., posted on May 11, 2015 at 09:07:29
rage
Audiophile

Posts: 793
Joined: December 17, 2010
 next driver tube for me is EL84 in pentode.

It's going in the 2a3 amp too. At LEAST for a test run and measurements. I suspect it'll kick ass.

How do you like this amp you are running? The breadboard looks cool!

 

RE: 6SL7 C4S driver ..., posted on May 11, 2015 at 17:50:45
deathtube 667
 The 6SN7 was too lazy, not enough gain or jump factor in my multi-amp set up for good level matching.

I set up 6SL7 C4S but got horrid distortion until I realized that I needed at least 2mA bias current for the extended C4S to work properly.

THD = 1.24% at 1W with 1KHz sine input.

Overall gain = 2.5

I realized an improvement of about 1% THD vs. 6SN7/triode 6V6 active parafeed circuit at the same 1W power output.

Not sure that JM or DF will approve of your pentode driver for 2A3.


DT667

 

RE: 6SL7 C4S driver ..., posted on May 11, 2015 at 19:54:23
Tre'
Industry Professional

Posts: 17304
Location: So. Cal.
Joined: February 9, 2002
 "...too lazy, not enough gain or jump factor..."

I would define "not enough gain" as not being able to reach the output power wanted or required for your purposes with the available source signal voltage.

Do you care to define "too lazy" and/or lack of "jump factor"?

I have wondered about this for some time now.

Thanks.

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: 6SL7 C4S driver ..., posted on May 12, 2015 at 15:01:54
deathtube 667
 Archived posts by DF or JM might be a place for you to investigate the concept of jump factor.

 

RE: 6SL7 C4S driver ..., posted on May 12, 2015 at 16:26:51
Mr_Steady
Audiophile

Posts: 2042
Location: North Florida
Joined: August 19, 2014
 So I have a question for you if I may.

When you are getting the sound pressure level you want, and your attenuator is wide open. Do you still have the same headroom as you do when you are getting the same SPL at the 12:00 position?

----------------------------------------------------------------
Big speakers and little amps blew my mind!

 

RE: 6SL7 C4S driver ..., posted on May 12, 2015 at 19:08:32
Tre'
Industry Professional

Posts: 17304
Location: So. Cal.
Joined: February 9, 2002
 Yes.

Headroom has to do with maximum output power not volume control position.

If your system can reach the average SPL you desire at a volume control setting that limits the peak output voltage of the source to something less than a voltage that would drive the output tube to clipping then there is no loss of dynamics.

So 12:00 or 3:00 or wide open, as long as you are getting the average sound pressure level you want and the output tube is not being clipped, even at the peak signal level, then you have enough headroom.

With digital it's cut and dry. My CD player outputs a maximum of 2VRMS (measured).

That is to say, a waveform that reaches digital zero....outputs 2VRMS. The digital system is not capable of outputting any more voltage than that.

If, as in my case, even with the volume control wide open, that 2VRMS (2.88 volts peak) is not enough to drive my output tube to clipping then there is no way I'm "missing" any dynamics.

Having more gain in the driver stage just means that the volume control will have to be turned down more to get the average SPL back down to the same level (where the musical peaks don't clip the output tube).

The relationship between the average level and peak level of the source signal does not change, pre volume control vs. post volume control.

Tre'




Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: 6SL7 C4S driver ..., posted on May 13, 2015 at 06:37:03
Al Noakes
 I always thought that the expression 'jump factor' referrred to the sound of an amplifier using a low slew rate driver tube with excessive gain . This , like 'transfer efficiency' or 'transfer function' was invented by a narcissist . The words 'bullshit' or 'bollocks' seem to be more appropriate when substituted for 'transfer efficiency' or 'jump factor'

Al

 

RE: 6SL7 C4S driver ..., posted on May 13, 2015 at 08:32:14
Mr_Steady
Audiophile

Posts: 2042
Location: North Florida
Joined: August 19, 2014
 Thank you Tre'



----------------------------------------------------
Big speakers and little amps blew my mind!

 

RE: 6SL7 C4S driver ..., posted on May 13, 2015 at 09:57:05
drlowmu
Manufacturer

Posts: 9730
Location: East of Kansas City
Joined: January 10, 2005
 Al,

You are mightily mistaken !!

In about 2011, ( before the Montana Forest Fire that destroyed Dennis' home ) Dennis took his amps to his local University's E.E. Department to be measured, they elected to measure the amplifier on test gear that specifically measured transfer efficiency, and that is precisely how they did it.

The test instrument set up cost around $2,000,000 Al. So...others, real E.E.s, and some Universities, DO use transfer efficiency. You seemingly are simply not aware of this.

I just posted this to set the record straight. Regards,

Jeff Medwin

 

RE: 6SL7 C4S driver ..., posted on May 13, 2015 at 10:34:05
Al Noakes
 What I am aware of is a load of bollocks every time you bring this up . I'm not stupid enough to fall for any of this anecdotal $2,000,000 testrig nonsense without seeing some proof . Also what is 'transfer efficiency' measured in ?

Al

 

RE: 6SL7 C4S driver ..., posted on May 13, 2015 at 10:56:42
LinuxGuru
Audiophile

Posts: 582
Location: European Union
Joined: November 11, 2008
 > Also what is 'transfer efficiency' measured in ?

in kiloBS, megaBS or even gigaBS, depending upon jump factor.

 

RE: 6SL7 C4S driver ..., posted on May 13, 2015 at 14:21:24
Al Noakes
 I would have thought it would be measured in Frakers . A Serious Stereo amp has a transfer efficiency of 1 Fraker , anything else won't even make it to 0.9 Fraker etc etc etc

What makes me chuckle with this whole 'transfer efficiency' 'transfer function' thing is that the losses within the output transformer are not even considered but the external wiring to it is :)

Al

 

RE: 6SL7 C4S driver ..., posted on May 14, 2015 at 08:42:26
deathtube 667
 "What makes me chuckle with this whole 'transfer efficiency' 'transfer function' thing is that the losses within the output transformer are not even considered but the external wiring to it is :)"

Not sure that is a correct assumption.

The OPT winding compliments the unconventional 2A3 operating point DF uses if I remember correctly.

Perhaps either DF or JM will comment further.

 

RE: 6SL7 C4S driver ..., posted on May 14, 2015 at 10:25:25
drlowmu
Manufacturer

Posts: 9730
Location: East of Kansas City
Joined: January 10, 2005
 "What makes me chuckle with this whole 'transfer efficiency' 'transfer function' thing is that the losses within the output transformer are not even considered but the external wiring to it is :)"

Hardly, the equipment allows you to look at any two points in a circuit, and measure transfer efficiency. I am sure the most classic look would be input to output, which includes the output transformer, doesn't it.

This testing was done in the EE lab at Montana State University, in Bozeman MT. Al. They get NASA work, and they have an extensively equipped EE lab. I am sure if you go there, you will see this equipment they used to measure amplification !!!

Regards...

Jeff Medwin , not Pinocchio

 

RE: 6SL7 C4S driver ..., posted on May 14, 2015 at 16:13:48
rage
Audiophile

Posts: 793
Joined: December 17, 2010
 I don't know about transfer function, but I do know Dennis doesn't hack up leadouts on output transformers.

 

RE: 6SL7 C4S driver ..., posted on May 14, 2015 at 23:55:51
Al Noakes
 You really need to use some common sense , stop relying on those two clowns' dogma and go your own way

Transformer winders tend to balance the copper losses between primary and secondary when producing a design . You can reduce losses by using thicker gauge windings but this means less primary inductance or a bigger core . All output transformers have losses , in fact , I believe this is the most lossy part in an SE amplifier . If you have a DCR of 200 ohms in the primary and 0.8 ohms in the secondary then the DCR of the leadouts is irrelevant no matter how thick the wire . So much for 'transfer function' when you consider the DCR involved !!!

Al

 

RE: 6SL7 C4S driver ..., posted on May 14, 2015 at 23:59:35
Al Noakes
 What is transfer efficiency measured in ?

'They get NASA work'

Bollocks...

Al

 

RE: 6SL7 C4S driver ..., posted on May 15, 2015 at 09:27:37
drlowmu
Manufacturer

Posts: 9730
Location: East of Kansas City
Joined: January 10, 2005
 Correct !!

 

RE: 6SL7 C4S driver ..., posted on May 15, 2015 at 10:46:35
Lew
Audiophile

Posts: 10912
Location: Bethesda, Maryland
Joined: December 11, 2000
 I think 'Transfer Efficiency" is a property not unlike what one supreme court justice said about "pornography"; "I don't know how to define it, but I know it when I see it." In the case of TE, substitute "hear it" for "see it". Which does make one wonder just what could have been measured with $2M worth of equipment at Bozeman.

The terms "Transfer Function" and Transfer Efficiency do have definitions in math and physics, but nothing I have read has anything to do with audio.

 

RE: 6SL7 C4S driver ..., posted on May 15, 2015 at 11:12:08
Triode_Kingdom
Audiophile

Posts: 10048
Location: Central Texas
Joined: September 24, 2006
 "what is 'transfer efficiency' measured in ?"

Stench.

 

RE: send in the clowns ..., posted on May 15, 2015 at 17:06:42
deathtube 667
 I've actually learned some good things from JM that I use all the time.

The more I get into higher quality/high efficiency transducers like Altec , the reality of some of his ideas starts to make more sense to me.

I got my rebuilt 414-8B's back from GPA , got the t/s parameters measured and hope to get them in the test boxes this weekend.

My system should take a step forward in efficiency since the 414's measured over 100dB/1W/1M.



 

RE: send in the clowns ..., posted on May 17, 2015 at 03:27:30
Al Noakes
 ' the reality of some of his ideas starts to make more sense to me.'

You are obviously easily influenced by those who shout the loudest . The vast majority of these 'ideas' are based upon junk science , dogma and narcissism . You would be better off finding your own way , you seem stuck on this whole DrLowMu/Dennis nonsense . It's not healthy...

Al

 

RE: you are correct ..., posted on May 17, 2015 at 08:57:04
deathtube 667



I fell prey to the influence of megalomaniacs.

Woe is me.

 

Beautiful Job !!!, posted on June 1, 2015 at 07:21:00
drlowmu
Manufacturer

Posts: 9730
Location: East of Kansas City
Joined: January 10, 2005
 Liked it .

Jeff Medwin

 

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