Tube DIY Asylum

Do It Yourself (DIY) paradise for tube and SET project builders.

Return to Tube DIY Asylum

Message Sort: Post Order or Asylum Reverse Threaded

Using 6L6s in Altec 1568a

73.13.182.66
Posted on February 20, 2015 at 11:15:46
baileyler
Audiophile

Posts: 359
Location: Chadds Ford, PA
Joined: January 17, 2007
 I have a pair of Altec 1568a with EL34 in PP.

I remember someone saying they could be modified to run EL34s or 6L6s, I think by adding a cathode resistor (and adjusting bias), but I don't recall (and can't find) any of the details.

Does anyone out there have the specifics on this?

 

Hide full thread outline!
    ...
RE: Using 6L6s in Altec 1568a, posted on February 20, 2015 at 15:48:56
Chip647
Audiophile

Posts: 2649
Location: The South
Joined: December 24, 2012

Certainly looks like the fixed bias adjustment would be plenty.
But why on earth would you not just use EL34 tubes?

 

RE: Using 6L6s in Altec 1568a, posted on February 20, 2015 at 20:18:35
danlaudionut
Audiophile

Posts: 5480
Location: Schenectady
Joined: June 6, 2002
 Chip

I used to like EL34s because compared to
the SS amps that I was using they excelled.
But after trying other tubes the EL34s
were like the bottom of the barrel IMO.
6L6s and their cousin KT66s were king.
With KT88s being power champs
for honorable mention.

DanL



 

What Dan said~nT, posted on February 20, 2015 at 21:50:32
Cleantimestream
Audiophile

Posts: 7550
Location: Kentucky
Joined: June 30, 2005
 ~!
The Mind has No Firewall~ U.S. Army War College.

 

But, but , but..., posted on February 21, 2015 at 06:37:13
Chip647
Audiophile

Posts: 2649
Location: The South
Joined: December 24, 2012
 They are very different tubes. The 6L6 has twice the Plate resistance and puts out half the power as the EL34. If you just swap 6L6 into a circuit designed for a EL34, you are not optimizing the tube. I hate to say it, but you might like the effect this non-optimization has on the sound.

Properly set up, I have no problem with EL34 and would definitely say that they are not the bottom of the barrel. But, hey, it is a free country.

Altec must have been daft to design an amp out of the bottom of the barrel tubes :-)

 

RE: But, but , but..., posted on February 21, 2015 at 09:15:45
danlaudionut
Audiophile

Posts: 5480
Location: Schenectady
Joined: June 6, 2002
 Not if you get 6L6GCs which
most current production are.
Also I always go triode with them
but others use them in UL and
report the same sonic benefits.
I would assume the same
would go for pentode.

DanL



 

RE: But, but , but..., posted on February 21, 2015 at 09:44:02
Chip647
Audiophile

Posts: 2649
Location: The South
Joined: December 24, 2012
 Where you have to look is for a given voltage and current for the 6L6GC and the EL34, then look at the Zout for each, you will see that the Zout for the 6L6GC is over twice that of the EL34 for comparable conditions. They are very different tubes and just because they have the same pin out (more or less) and bias in the same general vicinity, does not mean that they are electrically identical. The circuit that is optimized for the EL34 is not optimized for the 6L6GC. That is all I am saying.

 

RE: But, but , but..., posted on February 21, 2015 at 10:56:03
danlaudionut
Audiophile

Posts: 5480
Location: Schenectady
Joined: June 6, 2002
 No, what you said was ...
"But why on earth would you not just use EL34 tubes?"
And I told you why - better sound.

DanL



 

RE: Using 6L6s in Altec 1568a, posted on February 21, 2015 at 11:41:26
Michael Samra
Dealer

Posts: 36118
Location: saginaw michigan
Joined: January 30, 2005
 They are very different tubes. The 6L6 has twice the Plate resistance and puts out half the power as the EL34

Not true,at least when it comes to half the power.The KT66 has a much lower plate resistance than a 6L6gc and even tho it's still higher than an EL34,on measurement in a circuit that is optimized for EL34s the power loss is measurable but not that noticeable under listening.
I have done this test on a Marantz 8B and when I swept the amp,the response was very flat to 60k with the KT66s and I was down about 6 watts overall but the distortion was lower in the sub 20 cycle region with the KT66s and this was at 1 watt,5 watts,and 10 watts.In the 2khz to 10khz region,the distortion numbers would literally flip between the two tubes at various frequencies but at no time was it ever over .16% in the 1 watt and 10 watt range from either tube.
I understand where you are coming from with the point of logic that a lower resistance tube should perform better especially in a circuit that is optimized for one tube vs the other. This just isn't always the case.
If you look at the 25 watt curves of an EL34 as opposed to a 6L6gc or a KT66,it will explain a lot why many people prefer the 6L6gc and KT66 to the EL34.This is provided the EL34 circuit can swing enough extra voltage to drive either of the tubes..I have two pair of rebuilt and upgraded Altec 1569s and I can run four KT88s in them and make 106 watts at 1 khz.
I think a lot of people like the imaging,focus,and detail at the upper and lower extremes of the 6L6 family of tubes.Where an EL34 takes about 70 volts of drive to reach full power,the 6L6gc and KT66 takes about 90v volts of drive to reach full power.You just need the drive to make it happen and there are very capable EL34 amps that can do this.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken

 

RE: But, but , but..., posted on February 21, 2015 at 12:26:22
Chip647
Audiophile

Posts: 2649
Location: The South
Joined: December 24, 2012
 I said that plugging in 6L6 into an amp set up for EL34 was suboptimal.

You said "Not if you get 6L6GCs which most current production are."

I said that that is nonsense.

You said: I like them better anyway.

To that I say, I am happy for you, but they could be used better placed in a circuit designed for them.

 

RE: Using 6L6s in Altec 1568a, posted on February 21, 2015 at 12:38:18
Chip647
Audiophile

Posts: 2649
Location: The South
Joined: December 24, 2012
 "I understand where you are coming from with the point of logic that a lower resistance tube should perform better especially in a circuit that is optimized for one tube vs the other. This just isn't always the case."

You are saying that a circuit that is optimized for a particular tube will perform better with a considerably different tube type plugged in, one in which the circuit is not optimized for? Your KT66 must be pretty awesome, and will be even more awesome if used correctly.

 

RE: Using 6L6s in Altec 1568a, posted on February 21, 2015 at 12:48:41
Triode_Kingdom
Audiophile

Posts: 10045
Location: Central Texas
Joined: September 24, 2006
 Michael, have you compared manufacturers' data, 6L6 VS EL34? At the lower Z plate loads for which EL34 circuits are often designed, the 6L6 makes much less power. This has nothing to do with available drive voltage, although as you say, that presents another challenge.

 

RE: But, but , but..., posted on February 21, 2015 at 20:09:20
danlaudionut
Audiophile

Posts: 5480
Location: Schenectady
Joined: June 6, 2002
 > The 6L6 has twice the Plate resistance
> and puts out half the power as the EL34.

>> Not if you get 6L6GCs which
>> most current production are.

> The circuit that is optimized for the EL34
> is not optimized for the 6L6GC.

>> (but get) better sound

You may get fewer watts but you get better sound
with either the 6L6GC or KT66 than any EL34.
Hence the response to ...
But why on earth would you not just use EL34 tubes?
Optimize just means the most watts.
6L6 family is much more linear.
KT66 has details and extension that are phenominal.
By comparison the EL34 is just bland.
IMO Sacrifice a few watts for improved sound.

DanL



 

RE: But, but , but..., posted on February 22, 2015 at 01:10:57
Triode_Kingdom
Audiophile

Posts: 10045
Location: Central Texas
Joined: September 24, 2006
 "KT66 has details and extension that are phenominal. By comparison the EL34 is just bland."

You say this is though it's an established fact. Is that true? Is there confirmation of this from an authoritative (commercial or academic) source? Does it apply to EL34s in both pentode and UL mode?



 

RE: But, but , but..., posted on February 22, 2015 at 03:43:34
danlaudionut
Audiophile

Posts: 5480
Location: Schenectady
Joined: June 6, 2002
 DanL



 

RE: But, but , but..., posted on February 22, 2015 at 09:02:09
Triode_Kingdom
Audiophile

Posts: 10045
Location: Central Texas
Joined: September 24, 2006
 So, it's only your opinion and a few anonymous others? I assume David Hafler isn't among them? :)

 

RE: But, but , but..., posted on February 22, 2015 at 09:44:35
danlaudionut
Audiophile

Posts: 5480
Location: Schenectady
Joined: June 6, 2002
 Mine, Mikey and Cleantimestream
I have others that post me off-line
that concur with my assesment.
I will not divulge their identity
because that would be wrong.
You have three here so not
"a few anonymous others".

DanL



 

RE: But, but , but..., posted on February 22, 2015 at 10:56:56
Triode_Kingdom
Audiophile

Posts: 10045
Location: Central Texas
Joined: September 24, 2006
 C'mon, a whole "three people" is enough to make this a fact, not an opinion? OK, whatever you say.

 

RE: But, but , but..., posted on February 22, 2015 at 11:44:35
danlaudionut
Audiophile

Posts: 5480
Location: Schenectady
Joined: June 6, 2002
 Since you have not heard them
(or you would have said so).
My three (plus un-named others)
definitely trumps your "opinion".

DanL

PS Also I not heard ANY dissenting opinions.



 

Sheesh, what does it matter? Everyone I know states 6L6 sounds better than EL34,I DON'T believe in coincidence, posted on February 22, 2015 at 12:21:43
Cleantimestream
Audiophile

Posts: 7550
Location: Kentucky
Joined: June 30, 2005
 ~!
The Mind has No Firewall~ U.S. Army War College.

 

RE: Using 6L6s in Altec 1568a, posted on February 22, 2015 at 13:29:16
baileyler
Audiophile

Posts: 359
Location: Chadds Ford, PA
Joined: January 17, 2007
 Heated discussion, and everyone has their own opinion (which is perfectly OK), but I have more 6L6 types than I do EL34s so I just want to give a few different ones a try (but only the GCs and possibly vintage Genalex KT66).

I gather I am OK with just changing the bias (no mods needed).

If someone can confirm that is the case, then there only remains one question - about what range should I bias the typical 6L6GC?

 

RE: But, but , but..., posted on February 22, 2015 at 14:48:02
Triode_Kingdom
Audiophile

Posts: 10045
Location: Central Texas
Joined: September 24, 2006
 It's not a contest. You presented it as though it was a fact, but apparently it's not. That's all I was asking.

 

I'm holding a 6L6 right now. It doesn't sound like anything. (nt), posted on February 22, 2015 at 14:53:47
Triode_Kingdom
Audiophile

Posts: 10045
Location: Central Texas
Joined: September 24, 2006
 nada aqui

 

RE: I'm holding a 6L6 right now. It doesn't sound like anything. (nt), posted on February 22, 2015 at 21:06:35
danlaudionut
Audiophile

Posts: 5480
Location: Schenectady
Joined: June 6, 2002
 TK

CAUTION
You are starting to sound like a troll.

DanL



 

RE: I'm holding a 6L6 right now. It doesn't sound like anything. (nt), posted on February 22, 2015 at 21:40:09
Triode_Kingdom
Audiophile

Posts: 10045
Location: Central Texas
Joined: September 24, 2006
 No, you just didn't get it. The sound of an amplifier is the product of many things. OPTs, coupling caps, class of operation, driver and output stage operating conditions, power supply, brands and conditions of tubes, etc., etc. I don't believe anyone can say 6L6 amplifiers categorically sound better then EL34s, and I was surprised that you said otherwise as though it's a fact. I'm not criticizing your opinion, but that's all it is - an opinion. Anyway, your inability to reference an authoritative source for this clarifies the issue for me. No need to drag it out.


 

RE: I'm holding a 6L6 right now. It doesn't sound like anything. (nt), posted on February 23, 2015 at 05:22:45
danlaudionut
Audiophile

Posts: 5480
Location: Schenectady
Joined: June 6, 2002
 This is true BUT ...
You will never get a 4 cylinder VW engine
sound anything like the Viper V10.
And you will never get an EL84 amp
sound anything like a KT88 amp.
Tube choice IS the main factor in amp sound.
All other factors influence the sound
but tube choice is the building block.

DanL



 

and so...., posted on February 25, 2015 at 05:32:01
PakProtector
Audiophile

Posts: 12363
Joined: May 14, 2002
 I stick with Thoriated, DH tubes...unfortunately there are no DH tubes with the characteristics of the TV horizontal outputs, and those can sound quite good. 25 watt plates wrapped around a 2.5A cathode are not to be despised....and EL84's make fine signal tubes...:)
cheers,
Douglas

Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.

 

agreed Douglas, hard to beat an 801..., posted on February 25, 2015 at 09:56:30
Cleantimestream
Audiophile

Posts: 7550
Location: Kentucky
Joined: June 30, 2005
 so, I was reading the 3rd edition Radiotron book last night wherein they mention an expensive way to sidestep using feedback for a push/pull Pentode/beam tetrode by redesigning the output transformer... Is that what your latest 813 schemo entails?
The Mind has No Firewall~ U.S. Army War College.

 

RE: agreed Douglas, hard to beat an 801..., posted on February 25, 2015 at 12:48:45
PakProtector
Audiophile

Posts: 12363
Joined: May 14, 2002
 I should look for that, have you a page number?

I do doubt it is what I am running, that being the E-Linear circuit with a LTP attached to 20 or 30% U-L taps on the plate winding. The 813's are going to get replaced with the original 4E27, and whilst I am under the hood, the 6H6Pi-under-FQP1N60 cascode is going to get replaced with a pair of EL84's.

That deals with output Z nicely; the local FB drops the plate Z of the pentodes nicely...which also benefits the low end response. Will probably hook the final's g2 to 20% and the front end LTP to 30%.
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.

 

RE: agreed Douglas, hard to beat an 801..., posted on February 25, 2015 at 17:52:52
Cleantimestream
Audiophile

Posts: 7550
Location: Kentucky
Joined: June 30, 2005
 Page 40, under the heading "Application of Negative Feedback"
The Mind has No Firewall~ U.S. Army War College.

 

err...., posted on February 25, 2015 at 18:04:15
PakProtector
Audiophile

Posts: 12363
Joined: May 14, 2002
 I guess I need to find a copy of Radiotronics 76( 26th May, 1937), pages 42-44...:)
cheers,
Douglas

Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.

 

RE: err...., posted on February 25, 2015 at 21:17:41
Cleantimestream
Audiophile

Posts: 7550
Location: Kentucky
Joined: June 30, 2005
 I didn't have that one either Douglas.

The flywheel discourse DID remind me ... when reading these REAL old Ham books... that the use of three chokes in series {do not recall anything else} could slightly increase the B+. Had I been further along in learning I would have been far more interested, than I was @ the time.

The Mind has No Firewall~ U.S. Army War College.

 

RE: err...., posted on February 26, 2015 at 18:49:23
PakProtector
Audiophile

Posts: 12363
Joined: May 14, 2002
 Looks like a fun treasure hunt; I'd not mind seeing what they are talking about.
cheers,
Douglas

Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.

 

Page processed in 0.037 seconds.

[ Top Top of Page ] [ Contact Us ] [ Support/Wish List ] [ Copyright © 2024, Audio Asylum, all rights reserved ]
[ General ] [ Speakers ] [ Tubes ] [ Vinyl ] [ Digital ] [ Hi-Rez ] [ Video Asylum ] [ Cables ] [ Tweaks/DIY ] [ Music ] [ Films ]