6LU8 Push-pull power amp and other builds

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6LU8 Push-pull power amp and other builds

Postby tony » Tue Feb 15, 2011 1:43 pm

Hi all,

inspired by this article on the net, http://www.veiset.net/6LU8/index.html i decided to build myself one, i have ordered about 700 pcs of these $1 tubes from Roy and Dale Rogalski of http://www.vacuumtubes.net/ now it's time to put them to good use:

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the 6LU8 is like a 6V6 and 1/2 of 12AT7 placed in s single 12 pin compactron envelope, i wanted to use the 21LR8 at first but then the novar sockets had issues, they were loose, i found out that they were intended for tubes like the PL504 which had thicker pins.....oh well.....here is the link for the 6LU8: http://frank.pocnet.net/sheets/123/6/6LU8.pdf

so i designed all the irons needed, the power transformers, filter choke and output transformers, the 2 output transformers used Edrel's RM20 cores which like his more expensive Z11's had the same 0.35mm thikness, Deeco Irons were then used for the power transformers and filter choke, deeco iron has a thickness of 0.5mm....

pics of the irons and some parts:

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the power supply used the 3DG4 tube,http://frank.pocnet.net/sheets/093/3/3DG4.pdf it is likewise a hybrid rectifier using solid-state bridge, a toggle selector switch is used to select ss only rectification if desired.....the advntage of a hybrid is that being a full bridge rectifier transformer heating is way much lower than if staright full-wave is used using tube rectifier only......design and construction of the power transformer then becomes easier and cheaper....
Last edited by tony on Sat Dec 17, 2011 7:44 am, edited 1 time in total.
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Re: 6LU8 Push-pull power amp

Postby tony » Tue Feb 15, 2011 1:49 pm

construction pics:
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Re: 6LU8 Push-pull power amp

Postby tony » Tue Feb 15, 2011 1:57 pm

testing:

i used another set of speakers to test whether the polarity of the output transformer was correct, there is a 50-50 chance you will get it, but upon power up motorboating happened so i had to power down and reverse the plate lead connections to the right one.....after that, the amps was dead quiet, no hum, no hiss no noise.....i tested the amp and found out that the sensitivity was quite low, so i hooked up the 7N7 preamp to get a more decent volume.....later on i found out that i connected 470ohms feedback resistor instead of 4.7k so gain was really low....

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Re: 6LU8 Push-pull power amp

Postby hypertriode » Tue Feb 15, 2011 4:08 pm

NICE, Tony! 8) :clap:
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Re: 6LU8 Push-pull power amp

Postby docsialu » Tue Feb 15, 2011 4:25 pm

congrats sir tony, pede ba magpagawa nyan? :clap: :clap: :clap:
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Re: 6LU8 Push-pull power amp

Postby doasmarx » Tue Feb 15, 2011 4:32 pm

docsialu wrote:congrats sir tony, pede ba magpagawa nyan? :clap: :clap: :clap:


plus one
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Re: 6LU8 Push-pull power amp

Postby tony » Tue Feb 15, 2011 4:50 pm

hypertriode wrote:NICE, Tony! 8) :clap:



thanks Rene, i just want to keep those tubes alive.....
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Re: 6LU8 Push-pull power amp

Postby tony » Tue Feb 15, 2011 5:13 pm

docsialu wrote:congrats sir tony, pede ba magpagawa nyan? :clap: :clap: :clap:



pwede naman.... :)
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Re: 6LU8 Push-pull power amp

Postby ojof00l » Tue Feb 15, 2011 5:51 pm

dalawa na pala ang pila ? :D

mas ok "never-heard",low-profile tubes na pwede pala sa audio. mura na, marami pa!
pahinga muna sa tubo pero kung may babalikan 6bm8 at yung horny ni mang gerry

congrats!
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Re: 6LU8 Push-pull power amp

Postby tony » Tue Feb 15, 2011 5:57 pm

ojof00l wrote:dalawa na pala ang pila ? :D

mas ok "never-heard",low-profile tubes na pwede pala sa audio. mura na, marami pa!
pahinga muna sa tubo pero kung may babalikan 6bm8 at yung horny ni mang gerry

congrats!


rene, yung 6BM8 triode pentode din katulad ng 6LU8, 9 pin nga lang....na kay gerry pa rin yung 832 pp amp nya, sabi nya sa akin nung isang araw...
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Re: 6LU8 Push-pull power amp

Postby docsialu » Tue Feb 15, 2011 6:03 pm

tony wrote:
ojof00l wrote:dalawa na pala ang pila ? :D

mas ok "never-heard",low-profile tubes na pwede pala sa audio. mura na, marami pa!
pahinga muna sa tubo pero kung may babalikan 6bm8 at yung horny ni mang gerry

congrats!


rene, yung 6BM8 triode pentode din katulad ng 6LU8, 9 pin nga lang....na kay gerry pa rin yung 832 pp amp nya, sabi nya sa akin nung isang araw...



pwede ba yan gawing single ended sir? ilang wpc?
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Re: 6LU8 Push-pull power amp

Postby tony » Tue Feb 15, 2011 6:07 pm

docsialu wrote:
tony wrote:
ojof00l wrote:dalawa na pala ang pila ? :D

mas ok "never-heard",low-profile tubes na pwede pala sa audio. mura na, marami pa!
pahinga muna sa tubo pero kung may babalikan 6bm8 at yung horny ni mang gerry

congrats!


rene, yung 6BM8 triode pentode din katulad ng 6LU8, 9 pin nga lang....na kay gerry pa rin yung 832 pp amp nya, sabi nya sa akin nung isang araw...



pwede ba yan gawing single ended sir? ilang wpc?



parang El84 kapag ginawang single ended.....2 watts per bottle...meron akong 6P15P at 6H23.....pwede ring 6J32/EF86....
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Re: 6LU8 Push-pull power amp

Postby obi » Tue Feb 15, 2011 8:34 pm

congrats sir tony! :)

700 pieces? bawal mag hoard hehe

interested din sana mag pa gawa kung pwede.

thanks

ps ano sir yung power output in PP mode?
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Re: 6LU8 Push-pull power amp

Postby tony » Tue Feb 15, 2011 8:54 pm

obi wrote:congrats sir tony! :)

700 pieces? bawal mag hoard hehe

interested din sana mag pa gawa kung pwede.

thanks

ps ano sir yung power output in PP mode?


nasa 10 to 12 watts......pero in terms of volume kasing lakas sya ng Sure T-amp ko na rated at 200 watts....
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Re: 6LR8 as Alternative

Postby tony » Tue Feb 15, 2011 9:06 pm

Squirrelnutzipper wrote:Very, very cool Tony. You should have enough tube stock to supply the entire world's needs for the next century! By the way, why did you decide on the 6LU8 with the duodecar 12 pin socket? Isn't the 6LR8 the same electrically but with a more common 9 pin socket? I assume the price was better on the tubes you got.


my first choice was the 21LR8, i already built the power transformer for them.....but then i found out that the 9 pin novar sockets that i have did not fit, so i had to make another traffo to be used for the 6LU8's..both tubes were listed for $1.....

in 6 years of working in Russia, i have ammased a stockpile of 944 tubes out of which about 700 came from the Rogalski's, but these are the kinds of tube that are virtually unknown to the audiophile world, that is why i got them very cheap.......
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Re: 6LU8 Push-pull power amp

Postby obi » Tue Feb 15, 2011 9:16 pm

tony wrote:
obi wrote:congrats sir tony! :)

700 pieces? bawal mag hoard hehe

interested din sana mag pa gawa kung pwede.

thanks

ps ano sir yung power output in PP mode?


nasa 10 to 12 watts......pero in terms of volume kasing lakas sya ng Sure T-amp ko na rated at 200 watts....


thanks for the very prompt reply sir tony.

reason i asked is yung speakers ko are rated at 12w max. baka ma overdrive, or worst, masunog.

thank you

ps sir, pwede mag request ng quote? thanks
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Re: 6LU8 Push-pull power amp

Postby bonghiskan » Wed Feb 16, 2011 12:38 am

Great project you got going there Tony, keep it going man :clap: :clap: . I like the way your turning those plentiful and forgoten tubes into useable entertainment equipment. Good insight Bro, looking forward into the listening impression :geek: .

Bong
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Re: 6LR8 as Alternative

Postby tony » Wed Feb 16, 2011 7:14 am

Squirrelnutzipper wrote:
tony wrote:
Squirrelnutzipper wrote:Very, very cool Tony. You should have enough tube stock to supply the entire world's needs for the next century! By the way, why did you decide on the 6LU8 with the duodecar 12 pin socket? Isn't the 6LR8 the same electrically but with a more common 9 pin socket? I assume the price was better on the tubes you got.


my first choice was the 21LR8, i already built the power transformer for them.....but then i found out that the 9 pin novar sockets that i have did not fit, so i had to make another traffo to be used for the 6LU8's..both tubes were listed for $1.....

in 6 years of working in Russia, i have ammased a stockpile of 944 tubes out of which about 700 came from the Rogalski's, but these are the kinds of tube that are virtually unknown to the audiophile world, that is why i got them very cheap.......

Maybe the sockets you had were Magnovars? I think that these were most commonly used in Russia?


i got my sockets from seller zhang_sheng, an ebay seller......it is quite difficult to get tubes from Russia IME, it took about 9 months for the 6C33 tubes to arrive at my door.....
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Re: 6LU8 Push-pull power amp

Postby tony » Wed Feb 16, 2011 7:15 am

kalantog wrote:Great project you got going there Tony, keep it going man :clap: :clap: . I like the way your turning those plentiful and forgoten tubes into useable entertainment equipment. Good insight Bro, looking forward into the listening impression :geek: .

Bong


thanks, i have several other tube projects lined up and i am very sure you have not seen those tubes before........
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Re: 6LU8 Push-pull power amp

Postby bonghiskan » Wed Feb 16, 2011 8:26 am

tony wrote:
kalantog wrote:Great project you got going there Tony, keep it going man :clap: :clap: . I like the way your turning those plentiful and forgoten tubes into useable entertainment equipment. Good insight Bro, looking forward into the listening impression :geek: .

Bong


thanks, i have several other tube projects lined up and i am very sure you have not seen those tubes before........


Yes Tony, there is very litte supply of pre-cold war Russian tubes out here. There are a bit of English with no counterpart, and some McMurdo surplus (naturally cryoed :D :D ) transmitter tube but very tricky to source out.

It would be very interesting to see obscure tubes used in an amplifier. Keep it up bro.

Bong
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