813

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813

Postby tony » Mon Mar 25, 2013 7:53 am

I first saw this tube in 1968 at our Physics Lab at the Rizal High School, and ever-since this tube has become my Holy Grail of sorts.....


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so having bought a quad of these from Gerry Sta Maria, tel. 5237551, for 1500 pesos a bottle,(can also be purchased at Watson's for 3,500 each NOS RCA) i have decided to build a set amp, after my 2A3 set success..

plate curves for the 813...
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from the curves using incremental plate current, plate voltage and grid voltages, tube characteristics were calculated.....
so that near the operating point chosen, 800volts at 100mA plate current, mu = 7, this is better than the mu of 845, GM70 of about 5,
plate resistance was about 1400 ohms, so that a 5k OPT is fine, i choose instead to design my set OPT at 6.6k:6ohm impedance matching.
operating the trioded 813 at higher plate load results in decreased output power, but since i stopped counting watts a long time ago, this is not so much a concern as far as this build is concerned.

power traffos are split into 2, one for plate B+ with unloaded B+ of about 1100volts, with its own 6CK3 damper tubes as a hybrid tube rectifier,
the other power traffo will supply the filament power for the 813, the filaments will be dc and a toggle switch is provided to reverse poalrity so that the filaments wear out evenly ...... this traffo will also supply the front end drive...fixed grid biasing will be used to maximise power output..

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the driver tube will use the 11HM7...http://www.shinjo.info/frank/sheets/049/1/11HM7.pdf
Last edited by tony on Tue Apr 02, 2013 9:55 am, edited 2 times in total.
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Re: 813

Postby 6a3fan » Mon Mar 25, 2013 8:14 pm

Nice project Tony. I myself am scared to build an amp with more than around 450 volts B+.
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Re: 813

Postby tony » Tue Mar 26, 2013 5:13 am

6a3fan wrote:Nice project Tony. I myself am scared to build an amp with more than around 450 volts B+.


thanks 6a3fan.....:D

this 813 tube can dish out a lot of power, a quad operating at 2500volts can put out 1000 watts of audio power......http://www.chambonino.com/construct/const9.html

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Altec Lansing 260 also used a pair of these tubes...... http://www.pearl-hifi.com/06_Lit_Archiv ... _Instr.pdf
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Re: 813

Postby tony » Tue Mar 26, 2013 10:21 am

building the amp...

chassis layout...
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drilled chassis painted silver using hammertone type spray paint...
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sockets, filter caps, parts mounted...
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power traffos mounted, one each for the plate B+ and the other for the filament dc supply and front end psu...tubes likewise fitted....
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as you can see, the OPT's are not yet installed, still to wind them, it is a 6k:6ohm to accomodate either a 4 or 8 ohm and even 16ohm speakers...
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Re: 813

Postby tony » Sat Mar 30, 2013 12:19 pm

update....

2 x 25 amps bridge to supply 10volts dc @5amps to the 813 filaments...

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HV B+, front-end B+ and grid bias supplies done...

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Re: 813

Postby tony » Mon Apr 01, 2013 9:58 am

update....

the two power traffos will be turned on using relays, power status by blinking blue leds for standby, steady blue led for operate mode...

mounting plate done, nibbling tool shown is a handy tool any diy'er should not be without...
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controller board....
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mounted on plate...
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mounting plate on inside of chassis....
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pc assembly mounted...
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Re: 813

Postby tony » Thu Apr 04, 2013 9:25 am

pre-final update.....internal wirings done, remaining step is the OPT....

bias pots mounted on brackets....
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parts for the 11HM7 input tubes mounted on a pcb...
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Re: 813

Postby edrel sison » Thu Apr 04, 2013 1:38 pm

glad to see those siemens 47/250V radial caps put into good use. powering up is nigh, perhaps the 813 glow is in the offing before the weekend.. :) :)
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Re: 813

Postby tony » Thu Apr 04, 2013 5:32 pm

edrel sison wrote:glad to see those siemens 47/250V radial caps put into good use. powering up is nigh, perhaps the 813 glow is in the offing before the weekend.. :) :)


those caps are for the negative grid biasing circuit.....i also used your 330ufd and 150ufd ecaps...the OPT's will start winding this weekend... :D
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Re: 813

Postby tony » Sun Apr 14, 2013 8:13 pm

building the OPT's....
starting the first secondary layer...
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side by side winding ensures no mistakes...
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Re: 813

Postby tony » Tue Apr 16, 2013 12:15 pm

almost there....
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813

Postby s2kov » Mon Apr 22, 2013 1:43 pm

Very nice! :-)
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Re: 813

Postby tony » Mon Apr 22, 2013 3:20 pm

thanks Andy, i am taking my time, i am giving more time for the varnish to completely dry up, about a week or two more... 8)
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