6LU8 Push-pull power amp and other builds

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

Postby tony » Thu Jul 03, 2014 5:11 pm

12j5 tube rectified buffer....

those who want to build this, here is the schematic, took me 5 minutes to design...
i can say that the plate characteristics curve were spot on....
operating point is about 6mA at 150 volts plate..
the cathode resistor used 820 ohms, but values from 560 to 1k can be used...

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

Postby tony » Sat Jul 19, 2014 11:16 am

tony wrote:now playing.....amp can still use some tweaks...
EF86 buffered by 6N1P driving the 829b paralleled sections in triode mode

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sad to say, this is a failed design, i can't find tubes that have sections that are equally matched,
and since the cathodes are common to both sections, they do not conduct equally so that
the resulting distortion is audible....i suppose i can tweak this by manipulating filament
voltage to get the transconductance equal on either side, but that will be too much hard work...
so i ditched the septar socket and put in an octal socket instead....
in came the 6AV5 horizontal output tube rated for 11 watts....but in this
amp it is running about 16 watts plate dissipation, 250volts plate at 60mA cathode,
does this ring a bell? yes, it does, it is the operating point for the 2A3....

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the power factor of almost 90% and a power draw of about 80watts...
the power traffo is rated for 180VA, so that the power traffo will be
very cool to touch and will last a long long time....
the high power factor is indicative of a very good power supply...

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for those interested to design their own SET,
this is how i sized the cathode bias resistor:
for triode mode, grid 1 bias is calculated as follows:
Vg = -(Vpx0.6)/mu
mu equals 4.5 and Vp is 250 volts,
so that Vg is 40volts,
looking for 60mA. Rk, the cathode resistor then becomes,
40/60 = 600ohms, this is achieved with a parallel combination of
1k and 1.5k 5 watt resistors, making for a 600 ohm 10 watt
cathode bias resistor....this resistor dissipates 2.4 wattm
so that use of a 10 watt resistor is very much justified...

it would interest you to note the in the actual amplifier,
bias was at 39.5 volts, am i lucky or what? :tmi:
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Re: 6LU8 Push-pull power amp and other builds

Postby tony » Sat Jul 26, 2014 3:57 pm

no tube journey can proceed without transformers,
this is an educational video about making transformers...

http://www.youtube.com/watch?v=s6NyTprQCBI

output and power transformer for a 4P1L parallel SET....
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output and power transformer for 832b amp....
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Re: 6LU8 Push-pull power amp and other builds

Postby camotecue » Sat Jul 26, 2014 9:43 pm

Tony,

Yan na ba yun? Ano driver ng 4p1L?
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Re: 6LU8 Push-pull power amp and other builds

Postby tony » Mon Jul 28, 2014 11:36 am

camotecue wrote:Tony,

Yan na ba yun? Ano driver ng 4p1L?


yup, russian 6zh9 at 6n1p.....
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Re: 6LU8 Push-pull power amp and other builds

Postby tony » Tue Aug 19, 2014 11:34 am

this an 832 pp amp in the works, OPT is 8k a-a to 8 ohms,
concertina drive, 12at7, a line amp using the 12au7 is built in,
and a vsps phono stage, makes this amp a full function integrated amp...

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this is my parallel SET using the 4P1L's, OPT is 2.5k to 8 ohms,
target operating point is 200 to 250 volts at 60mA..
input voltage amp is a 6J9 in pentode mode for more gain,
a 6N1p in a broskie cathode follower config to drive the output stage grids...

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another 6550 pp amp good for about 50 watts per channel..
OPT is similar to A431 without the ultralinear taps, i operate these amp pentode more...
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Re: 6LU8 Push-pull power amp and other builds

Postby camotecue » Tue Aug 19, 2014 12:47 pm

Nice projects to keep the fire burning!
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Re: 6LU8 Push-pull power amp and other builds

Postby tony » Wed Aug 27, 2014 11:51 am

china tube buffer na merong volume control so pwedeng preamp na rin...
intended to mate with my upcoming honey badger build...
uses the 6N3_5670_2C51 tube...

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

Postby nicole » Wed Aug 27, 2014 4:16 pm

Hi Sir Tony..

Tanong lang po sana, ano po pwede replacement ng 50CA10 output tube ng Luxman SQ38F Integrated Amp?

Thanks




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

Postby tony » Wed Aug 27, 2014 5:57 pm

nicole wrote:Hi Sir Tony..

Tanong lang po sana, ano po pwede replacement ng 50CA10 output tube ng Luxman SQ38F Integrated Amp?

Thanks

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meron na ang Shuguang new production tube...

50CA10 din...http://www.leisure-audio.com/Shuguang-5 ... s-p37.html

specs here....http://frank.pocnet.net/sheets/084/5/50C-A10.pdf

mu of 8 means this is easier to drive than a 300b or a 2A3....
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Re: 6LU8 Push-pull power amp and other builds

Postby tony » Fri Aug 29, 2014 10:56 am

if you are put off by the $75 price of the Shuguangs...
the 21HB5 can be used, also a 12 pin compactron tube,
while not a true triode, it can be run as triode...
a little rearrangement of heaters and pin connections and you are good to go,
bias adjustments need also to be done....

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

Postby tony » Fri Aug 29, 2014 3:13 pm

my 832 pp amp lives.....
no global negative feedback...
plate B+ is a bit high at 405 volts, screen at 180 volts...
a slight red plate after 30 minutes so i am going to lose some plate B+
i reckon, about 9 watts per plate ought to do it...
how is the sound? i like it.... ;)
this amp comes with a phono stage built in....

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in all my builds i implement a central ground point

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

Postby nicole » Fri Aug 29, 2014 8:03 pm

Nice amp sir Tony

Cancel ko na lang yung Luxman SQ38FD, rare & pricey yung 50ca10.. Now I'm choosing in between Scott 299D or Eico ST70.

Thanks


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

Postby tony » Sat Aug 30, 2014 7:56 am

nicole wrote:Nice amp sir Tony

Cancel ko na lang yung Luxman SQ38FD, rare & pricey yung 50ca10.. Now I'm choosing in between Scott 299D or Eico ST70.

Thanks


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how much is the luxman? i vote for the eico st70.... ;)
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Re: 6LU8 Push-pull power amp and other builds

Postby nicole » Wed Sep 03, 2014 12:23 pm

Hi Sir Tony,

Luxman SQ38F - 22,000,000 vnd. (around 1,037 usd).. yes now I'm leaning to Eico ST70 match na match siya sa Klipsch Forte II

tony wrote:
nicole wrote:Nice amp sir Tony

Cancel ko na lang yung Luxman SQ38FD, rare & pricey yung 50ca10.. Now I'm choosing in between Scott 299D or Eico ST70.

Thanks


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how much is the luxman? i vote for the eico st70.... ;)
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Re: 6LU8 Push-pull power amp and other builds

Postby tony » Wed Sep 03, 2014 12:25 pm

this my interpretation of how a 6550 amp is built.
pentode operation with G2 regulation, and big OPT's....

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phono stage built in.....
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big filter choke, and generous filter caps makes a very stiff psu..
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Re: 6LU8 Push-pull power amp and other builds

Postby tony » Sun Sep 07, 2014 8:02 pm

designed and built up G2 regulator board using the 2SK3028 mosfet
and 120 volt zeners for a G2 of about 380 volts....

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Last edited by tony on Sun Sep 14, 2014 7:09 pm, edited 1 time in total.
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Re: 6LU8 Push-pull power amp and other builds

Postby tony » Sun Sep 07, 2014 8:02 pm

designed and built up G2 regulator board using the 2SK3028 mosfet
and 120 volt zeners for a G2 of about 400 volts....

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

Postby tony » Thu Sep 11, 2014 5:51 pm

6550 amp completed construction...

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

Postby alexg » Fri Sep 12, 2014 11:54 am

tony wrote:my 832 pp amp lives.....
no global negative feedback...
plate B+ is a bit high at 405 volts, screen at 180 volts...
a slight red plate after 30 minutes so i am going to lose some plate B+
i reckon, about 9 watts per plate ought to do it...
how is the sound? i like it.... ;)
this amp comes with a phono stage built in....

Image

Image

Image

in all my builds i implement a central ground point

Image


Hi Tony, what kind of connector did you use for the 832 top connectors?

I have a bunch of 832s and played with them before.

Thanks.
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