looking for info, class a ultra linear

a fine line between stupid and clever

looking for info, class a ultra linear

Postby funkmeblue » Wed Jul 09, 2008 2:05 pm

I was hoping someone here might be able to point me in the right direction. I want to build a power amp that is push/pull class A ultra linear that can run 6l6, kt66, and el34's. I just recently built the je labs stereo el34 hifi and was wondering if I turned that power amp into a mono push/pull amp, with those same voltages would if be class A? I plan on using triode electronics dynaclone z565 output. Thanks for your time
funkmeblue
 
Posts: 11
Joined: Tue May 20, 2008 2:56 pm

Postby dhuebert » Thu Jul 10, 2008 7:16 am

Are you sure of your definitions? I don't know of ayone who runs push-pull class A. They say they do but when you look at the circuit it all turns into BS. Maybe someone can enlighten all of us and explain how a push-pull running less than 360 degrees can be class A. I know if the signal is small enough the tubes conduct 360 D but turn the volume up a bit and right away you're into AB. Anyways, your amp will do the job, as for class A tho...

Don
User avatar
dhuebert
KT88
 
Posts: 820
Joined: Thu May 01, 2003 9:26 am
Location: Winnipeg Manitoba Canada

Postby funkmeblue » Thu Jul 10, 2008 4:58 pm

george alessandro makes amps that are push/pull class a, that's all I know about it. So if I use the same voltages and 820 ohm cathode resistor as the JE labs I can turn it into a push pull circuit?
funkmeblue
 
Posts: 11
Joined: Tue May 20, 2008 2:56 pm

Postby TomMcNally » Thu Jul 10, 2008 5:39 pm

I just read about everything I could find on Alessandro's amps on
his website, and other googled sites.

I don't see anything that says his "Class A" amps are push-pull.
I would venture to guess they are paralleled output tubes in
single-ended Class A, and NOT push-pull.

Send some links !

... tom
User avatar
TomMcNally
Darling du Jour
 
Posts: 2729
Joined: Sat Nov 19, 2005 2:19 pm
Location: Northfield, NJ

Postby 6L6/807 » Thu Jul 10, 2008 5:51 pm

Greetings to all,

"Class A" is a definition of the operating point of any valve whether large signal or small signal, and whether single ended or push-pull. It means that throughout the entire intended cycle of operation the valve(s) is never driven into the cutoff region. This is achieved by setting the bias to one half of the cutoff value. All single ended amplifiers must be operated in class A as distortion will be the result of operation in any other class. The limiting factor on power output will, of course, be anode dissipation limits. It is possible to construct a class A push-pull amplifier which is basically two single ended class A amplifiers strapped together in such a way that each valve is driven out of phase with the other but their outputs are additive. In this case, the push-pull amplifier will deliver twice the output power of a single ended amplifier and if one output valve is pulled from its socket the amplifier will still function very well at about half the normal power output.

For all practical purposes, single ended 6L6 family and EL34 valves are capable of about 10 or 11 watts of output so any push-pull amplifier that delivers more than 20 to 22 watts of power is probably not operating in class A.

Since the bias requirements of 6L6 family and EL34 are different, it will be difficult to make an amplifier that can operate either valve in class A without bias adjustment.

Class A - 50% of cutoff, no grid current, single ended or push-pull
Class AB1 - 66% of cutoff, no grid current, push-pull only
Class AB2 - 80% of cutoff, grid current on peaks, push-pull only
Class B - 95% of cutoff, grid current at all times, push-pull only
Class C - RF only, not used in audio

Best,

Wade
6L6/807
 
Posts: 18
Joined: Mon Jul 07, 2008 6:27 am
Location: Oklahoma USA

Postby funkmeblue » Thu Jul 10, 2008 5:52 pm

then why does he have a phase inverter, I have seen pictures of the inside, his blue tick model was reviewed in guitar player a while back, the review is on his site. far as I know they are push pull.
on that note, are you still liking your stereo el34? I have kt66's in mine, like them better and they look real cool
funkmeblue
 
Posts: 11
Joined: Tue May 20, 2008 2:56 pm

Postby TomMcNally » Thu Jul 10, 2008 5:58 pm

Yep, I like my JE Labs EL-34 SE ... using and old pair
of Leslie branded 6550's or Tesla Firecracker EL-34's
in it ... sounds real nice.

Wade - the autobiased amps seem to take any tube
and work well with no adjustment.

Well if anyone has some info or links, pass them
along ... Alessandro's site has very little technical info.
User avatar
TomMcNally
Darling du Jour
 
Posts: 2729
Joined: Sat Nov 19, 2005 2:19 pm
Location: Northfield, NJ

Postby funkmeblue » Thu Jul 10, 2008 6:08 pm

......sooooo can I turn the JE labs stereo into a mono push pull? Even if it's not class A?
funkmeblue
 
Posts: 11
Joined: Tue May 20, 2008 2:56 pm

Postby funkmeblue » Thu Jul 10, 2008 6:26 pm

http://www.alessandro-products.com/revi ... tick.shtml
here is the link to the review of the bluetick.....4 3l34's in class a. I think it's page 4 in a side note that george discusses his output section
funkmeblue
 
Posts: 11
Joined: Tue May 20, 2008 2:56 pm

Postby SDS-PAGE » Thu Jul 10, 2008 6:28 pm

Well, I don't see why not. You got the tubes and chassis punched out. All that you need are puch pull OPTs (dynaclone like you said), new schematics and rewiring. You can do that sort of things (SE to PP and vice versa) to pretty much any kind of amps, not just with JEL stereo.
User avatar
SDS-PAGE
KT88
 
Posts: 865
Joined: Thu Feb 22, 2007 4:41 pm
Location: Brandon, SD

Postby funkmeblue » Thu Jul 10, 2008 6:36 pm

I don't see any othe circuits with an 820 ohm bias resistor. I'm building a whole new amp, like my hifi too much for that
funkmeblue
 
Posts: 11
Joined: Tue May 20, 2008 2:56 pm

Postby SDS-PAGE » Thu Jul 10, 2008 6:59 pm

You can't expect to use same parts for your new build. There will be changes accordng to the schematics. FWIW, I just built a stereo 2A3 with 820 ohms 10W cathode resistors. Have you considered paralleling your output tubes and using lower primary impedance on your OPT to make it a SE monoblock? This will depend on kind of OPTs you have. Some Edcors and Hammond 125ESEs allows for impedance matching.
User avatar
SDS-PAGE
KT88
 
Posts: 865
Joined: Thu Feb 22, 2007 4:41 pm
Location: Brandon, SD

Postby funkmeblue » Thu Jul 10, 2008 7:07 pm

just want a push pull amp that can exept these tubes without being as loud as my trainwreck express I built using 6sl7's. want to go ultra linear because it just sounds really cool. thanks for the help guys.
funkmeblue
 
Posts: 11
Joined: Tue May 20, 2008 2:56 pm

Postby dhuebert » Sun Jul 13, 2008 9:38 pm

As for class A vs AB: Musicians can be very gullible, Not you of course, and class A sounds impressive so amp builders will stretch the truth and say their push pull amps are class A. As I said
if the signal is small enough the tubes conduct 360 D but turn the volume up a bit and right away you're into AB
So amp builders say their amps are class A even though it is only true for a very limited condition, impressing the hell out of non-tecnical types and moving product. Guitar amps and sound reproduction industry in general is very susceptible to sales BS, which I think is likely the case here.

I personally have not seen a push pull amp biased class A at full power, I don't even think it's possible.

Don
User avatar
dhuebert
KT88
 
Posts: 820
Joined: Thu May 01, 2003 9:26 am
Location: Winnipeg Manitoba Canada

Postby Gingertube » Mon Jul 14, 2008 1:48 am

Don etc.,

As was stated above it is perfectly possible to have push pull class A. The Guitar Amp fraternity became very SUS about claims of push pull class A because of the VOX AC30 which claimed to be push pull Class A but was'nt. There is a new AMPEG EL84 Amp which also claims to be Push Pull Class A but since it claims to be able to put out 30 Watts probably is'nt either.

What the VOX was is "Deep Class AB".

All Class AB amps run Class A up to the power level where one output tube cuts off. "Deep Class AB" simply means that the amp has a significant amount of power available before the output tubes are driven hard enough that one starts to cutoff on alternate half cycles, in the VOX AC 30 that happens at about half power. On most guitar amps it happend at 1/10th power or even less.

In a class AB amp the smoothness of that transistion from Class A to Class B as more signal is applied affects its performance.

Why: A Push Pull output transformer has an anode to anode impedance (Raa). This determines the load seen by the output tubes.
When BOTH tubes are conducting then each tube sees a load of Raa/2 but when one tube cuts off the other sees a load of Raa/4. So the loading of the tube changes on peaks of the signal.

One of the benefits of Ultralinear is that it gives a smooth transition from Class A to Class B.

I don't really see that you would get much benefit from full Class A AND Ultralinear but by all means give it a try. This is more suited to HiFI than a guitar amp.

Cheers,
Ian
Gingertube
 
Posts: 245
Joined: Thu Oct 05, 2006 10:27 pm
Location: Adelaide, South Oz

Next

Return to guitar amps

Who is online

Users browsing this forum: No registered users and 13 guests