6LU8 Push-pull power amp and other builds

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Re: 6LU8 Push-pull power amp and other builds

Postby tony » Sun Mar 17, 2013 1:52 pm

now playing.....2A3 SET, 3 watts output driving my US Audio 90db floorstanders...
D3a triode wired at about 10mA plate current.....
the 2A3 operates with 250volts plate and 60mA cathode for a tube dissipation of 15watts producing a little over 3watts output power....

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Re: 6LU8 Push-pull power amp and other builds

Postby tony » Mon Mar 18, 2013 10:08 am

2nd unit, slightly different circuit...

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Re: 6LU8 Push-pull power amp and other builds

Postby camotecue » Mon Mar 18, 2013 7:54 pm

tony wrote:2nd unit, slightly different circuit...

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Nice!
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Re: 6LU8 Push-pull power amp and other builds

Postby tony » Mon Mar 18, 2013 8:09 pm

thanks Larry, the Tango OPT clone by Mang Rey Luis sounds very good indeed......and the operating point of 250volt/60mA was spot on, the psu squared up right and good....this is a ver heavy amp....and worth the wait, i am glad i finished it finally after finding the inspiration and the courage to proceed... :)

My next SET build is going to be the 813, 900volts at 100mA, fixed bias, driven by a 11HM7 pentode.....i am now winding irons....i woill use the 6BE3 damper diodes for rectification....... 8)
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Re: 6LU8 Push-pull power amp and other builds

Postby tony » Thu May 16, 2013 6:31 am

my 3rd 6V6 pp amp build....

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Re: 6LU8 Push-pull power amp and other builds

Postby tony » Thu May 16, 2013 6:33 am

the 6LU8 tubes which i go for U$1 at Rogalski's now sells for $4..... :(
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Re: 6LU8 Push-pull power amp and other builds

Postby kabubi » Thu May 16, 2013 8:19 am

tony wrote:the 6LU8 tubes which i go for U$1 at Rogalski's now sells for $4..... :(


i think you're part of the reason for adding more premium to this tube :D
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Re: 6LU8 Push-pull power amp and other builds

Postby tony » Thu May 16, 2013 11:10 am

kabubi wrote:
tony wrote:the 6LU8 tubes which i go for U$1 at Rogalski's now sells for $4..... :(


i think you're part of the reason for adding more premium to this tube :D


:rofl: good thing i bought a lot of them to last me a lifetime...but there are still a lot of sleeper tubes there that still sells for $1 and i am keeping my mouth shut... ;) and i have a stash of them that have yet to see action... 8) :lol:
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Re: 6LU8 Push-pull power amp and other builds

Postby tony » Thu May 16, 2013 11:47 am

a neighbor of mine came to the house yesterday afternoon and brought me these tubes....
these are ST bottle tubes and required 4 pin and 6 pin sockets...
a power amp can be made out of a pair, or a nice driver for the GM-70, 845, 211, 813, 300b or 2a3...
i hope there is more where these came from... 8)
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Re: 6LU8 Push-pull power amp and other builds

Postby kabubi » Thu May 16, 2013 12:57 pm

Master Tony, sa gut feel mo, anong mga Tubo ang papantay o hihigit pa sa 12ax7 pag in apply as a phono stage tube?

Salamat ng marami po.
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Re: 6LU8 Push-pull power amp and other builds

Postby tony » Thu May 16, 2013 4:51 pm

kabubi wrote:Master Tony, sa gut feel mo, anong mga Tubo ang papantay o hihigit pa sa 12ax7 pag in apply as a phono stage tube?

Salamat ng marami po.


D3a....http://www.diyaudio.com/forums/diyaudio ... reamp.html
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Re: 6LU8 Push-pull power amp and other builds

Postby tony » Tue May 21, 2013 4:58 pm

some kindhearted members at PDVD donated to me a Luxman LV-103 and an LV105 to play around with....they are Japanese pier units and therefore run on 100 volt mains.....as i am always afraid of Murphy, i decided to convert them to 230 volt mains instead...

both the LV-103 and the LV105 use the 6CG7 tube long tail pair as VAS to drive the lateral mosfet output stage. a separate small power traffo is used to light up the filaments.....since the 6CG7, (a 9 pin analogue of the 6SN7), likes better to run on higher plate voltages, i have decided to replace them with 6dj8 type tube, but this is another story altogether... :D

main power traffos removed:
an angle grinder was used to remove the welds on the side of the power traffos to separate the E's from the I's...prior to grinding these 2 traffos were completely immersed in a tub full of lacquer thinner for 2 weeks.....

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with the coil assembly yanked out of the core, the bobbins were pried open to separate the primary and secondary chambers.....these traffos have completely separate primary and secondary chambers so that only the primary coils is changed...the secondary coil assembly is left untouched...

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so the primary coil is put on my winder to count the number of turns which turned out to be 220 turns of #19 magnet wire, therefore at 230 volts this becomes 506 turns of #23 wire...
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then comes the windup for the 230volt primary...
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once done, installing the E and I's comes next....since i do not have access to tig welding, i decided to do the traditional interleaving, but first the weleded edge must be grinded to make it easy to separate the laminations...

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the E's completed...
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inserting the I's...
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finally inserting the copper banding, mu-metal wrapping and mounting brackets installed completing the job..
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completed traffo is immersed into a tub of clear air drying polyurethane electrical varnish..
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completed traffos ready for action...
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Re: 6LU8 Push-pull power amp and other builds

Postby babydoc » Tue May 21, 2013 7:58 pm

LIKE :D :D :D

... a very informative way of converting power supply. thanks for sharing
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Re: 6LU8 Push-pull power amp and other builds

Postby tony » Tue May 21, 2013 8:36 pm

babydoc wrote:LIKE :D :D :D

... a very informative way of converting power supply. thanks for sharing


thanks, :D.... but wait, there is more.....:D
there is a 2nd smaller traffo and is used to power the tube filaments...
it is likewise converted to 230 volts..
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primary turns are counted on the winder...
there were 1008 turns of #30 wire counted, to convert to 230vac,
i wind 2600 turns of #35 for primary coil..
secondary windings have two coils of 170 turns each of #25 magnet wire..
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winding new primary coil...
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reinserting the E-I's..
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finally putting back the endbells and brackets...
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completed traffo...
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Re: 6LU8 Push-pull power amp and other builds

Postby tony » Fri Jun 14, 2013 3:18 pm

in order to rebuild this amp, first i have to dismantle it...

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start with the handles...
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handles and panel removed...
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the two big caps are removed next, the bypass and bleeders will be replaced with something better...
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this is the central ground point bolted unto the chassis at a single point..
the grounded side of the main filter caps are connected by #8 auto cables, the speaker cables are made of #14 auto cables...
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these are the relay boards for soft starting and speaker protector, the sensor and control circuits are on a pcb at the other side of the mounting bracket...
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traffo, power amp modules stored away for later disposition...
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the chassis, front panel and handle are sent to Golden Diamond Powder coaters in Santolan, Pasig...
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the small parts are to be cleaned and reused as much as possible,
the two big NTK 56,000/80 volt filter caps will be retired and replaced with two Nichicon 105*C
68,000/100 volt caps...
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lucky for me, i did not use he whole of the winding window to build this traffo 20 years ago,
it was originally a 55-0-55 volt traffo, but i was able to drive stereo channels into 250 watts per channel back then...
with the available slack in the window, i was able to squeze in 16 more turns of #14 teflon covered wires for an additional voltage, so that now i have a 65-0-65 volt power traffo..
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Re: 6LU8 Push-pull power amp and other builds

Postby tony » Sat Jun 22, 2013 7:44 am

i added 8 bifilar turns to up the voltage from 2 x 55v to 2 x 65 volts....

i used teflon coated #14 wire for the added turns,
good thing that 20 years ago, i did not use the full winding window,
so today i was able to squeeze in more turns
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since endbells are not available for 2inch cores,
i decided to use "FulaTite" automotive putty to form one.

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angle grinders used to shape the "masilya", then fine grit sandpaper prior to painting...
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gray hamertone painting...
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left out to dry for several days...
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Re: 6LU8 Push-pull power amp and other builds

Postby tony » Sat Jun 22, 2013 7:47 am

last night this came to my door..
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opening the box...

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still going thru the parts to see what is missing...
obviously the amp needs a chassis and a pair of heatsinks..
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Re: 6LU8 Push-pull power amp and other builds

Postby tony » Fri Jun 28, 2013 6:35 am

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Re: 6LU8 Push-pull power amp and other builds

Postby tony » Fri Jun 28, 2013 9:27 am

someone asked me to tweak his 6BQ5 set...
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Re: 6LU8 Push-pull power amp and other builds

Postby tony » Sun Jul 28, 2013 3:46 pm

more traffo builds here...

https://www.facebook.com/tony.tecson/media_set?set=a.601150319906606.1073741835.100000349293477&type=3

here is what happens to an opt winding that has failed...
the opts were from a 6v6 pp amp wherein the windings tested open circuit...

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