i have a little bit of confusion with the conversion.
in the original design the audio is fed to the grid.
according to the pinout and the datasheet i have on the 12SA7GT pin 2 where he wants the audio taken in should be the ground for the heater.
1 and 2 are wired to the cathode and screen?
btw the datasheet i got is : http://tubedata.itchurch.org/sheets/127/1/12SA7.pdf
unless anyone has a reason to change it i think the pinout should be
1,2 -> 3
5,6 -> 4,5,8
3,4 -> 2,7
7->6
Thats triode mode right?
in the original design the audio is fed to the grid.
according to the pinout and the datasheet i have on the 12SA7GT pin 2 where he wants the audio taken in should be the ground for the heater.
1 and 2 are wired to the cathode and screen?
btw the datasheet i got is : http://tubedata.itchurch.org/sheets/127/1/12SA7.pdf
unless anyone has a reason to change it i think the pinout should be
1,2 -> 3
5,6 -> 4,5,8
3,4 -> 2,7
7->6
Thats triode mode right?
What made you pick a 12SA7? Thats really not suited for driving headphones. Something like this will work much better.
http://retro-forum.com/download.php?id=37595&sid=36bc03b03e8ebe1dae86ca383a0b33d3
http://retro-forum.com/download.php?id=37595&sid=36bc03b03e8ebe1dae86ca383a0b33d3
I bought these sockets from tube depot
http://www.tubedepot.com/sk-8pinb.html
the pins were so tight i thought i was going to break the tube tyring to force ythem in there so i took a flat head and roated it inside the hole to spread them back out wich was WAY too loose.
in the end had to untwist and remove all the pins, take a pair of pliers (i used snap clamps as its what i had handy) then twist and close the gap until it was snug on the pin then stick them back into the ceramic socket. Seems like a bit of work anyone know of any better made sockets for my next project?
http://www.tubedepot.com/sk-8pinb.html
the pins were so tight i thought i was going to break the tube tyring to force ythem in there so i took a flat head and roated it inside the hole to spread them back out wich was WAY too loose.
in the end had to untwist and remove all the pins, take a pair of pliers (i used snap clamps as its what i had handy) then twist and close the gap until it was snug on the pin then stick them back into the ceramic socket. Seems like a bit of work anyone know of any better made sockets for my next project?
Progress
Now that i have all the pieces and have worked the bugs(theoretically) out of my PSU, I started to put things together.
Control Placement:
Wet Paint:
Now that i have all the pieces and have worked the bugs(theoretically) out of my PSU, I started to put things together.
Control Placement:
An externally hosted image should be here but it was not working when we last tested it.
Wet Paint:
An externally hosted image should be here but it was not working when we last tested it.
I havent had time to do much more work.
The tin pan thing didnt work, The paint bubbled and when i sanded it no more hotter then it got it just warped all to peices.
Glad i wasnt baking bread.
Anyhow ive changed to a cherry box got the tube sockets mounted, All thats left is wiring them into the circuit and finishing the power supply.(i dont suggest Building your own. 48 is an odd voltage.)
The tin pan thing didnt work, The paint bubbled and when i sanded it no more hotter then it got it just warped all to peices.
Glad i wasnt baking bread.
Anyhow ive changed to a cherry box got the tube sockets mounted, All thats left is wiring them into the circuit and finishing the power supply.(i dont suggest Building your own. 48 is an odd voltage.)
Question about output caps
Hi,
Early 2009, I found the schematic and was all jazzed. And then, finding a 19j6 was impossible to find. Or the prices were outrageous. So, I found 6J6's all over the internet and I have about a dozen NOS tubes in hand.
Ok, so now that I'm getting serious on building it, I figured the only route I want to go with this for now is to get a small xformer for the filaments and use a pair of LM317's as the CCS. Quick, dirty, and not so expensive.
My question concerns C3 and C5. Is 150 uF something I should not tweak? I thought about using Nichicon KZs or similar. But 63V is spec'd and my choices are slim. If I could go to 220 uF, I might have better choices. Does anyone know how Peter Millett calculated that value of capacitance?
Thanks for your input in advance!
Hi,
Early 2009, I found the schematic and was all jazzed. And then, finding a 19j6 was impossible to find. Or the prices were outrageous. So, I found 6J6's all over the internet and I have about a dozen NOS tubes in hand.
Ok, so now that I'm getting serious on building it, I figured the only route I want to go with this for now is to get a small xformer for the filaments and use a pair of LM317's as the CCS. Quick, dirty, and not so expensive.
My question concerns C3 and C5. Is 150 uF something I should not tweak? I thought about using Nichicon KZs or similar. But 63V is spec'd and my choices are slim. If I could go to 220 uF, I might have better choices. Does anyone know how Peter Millett calculated that value of capacitance?
Thanks for your input in advance!
C3 and C5 can be anything from ~100uF and up. Basically this and the headphone impedance sets the low frequency response limit of the amp. Even lower if you only use high-impedance headphones. 220uF is fine.
The HeadFi thread on this has more info than you'll ever want to know...
Millett "Starving Student" hybrid amp - Head-Fi: Covering Headphones, Earphones and Portable Audio
Pete
The HeadFi thread on this has more info than you'll ever want to know...
Millett "Starving Student" hybrid amp - Head-Fi: Covering Headphones, Earphones and Portable Audio
Pete
Peter,
Thanks for the direct link and the quick response! I now have some reading to do. BTW, I live in Texas too and I AM A TEXAN!
Very cool to know I am not fenced in on the output caps. Now I have to wonder how the Russian variant sounds (6N15P). Those can be had for dirt cheap, of course. Get 'em while you can, I guess.
Wavebourn, your comment about using light bulbs popped into my head, but I've never played with bulbs before. I suppose if bulb resistance is temp dependent, then voltage across the bulb filament affects what one would measure in circuit. I may give that a try soon in this circuit and dump the LM317 CCS. It would look pretty cool with some bulbs in the circuit. Heckuva conversation piece, for sure!
Thanks for the direct link and the quick response! I now have some reading to do. BTW, I live in Texas too and I AM A TEXAN!
Very cool to know I am not fenced in on the output caps. Now I have to wonder how the Russian variant sounds (6N15P). Those can be had for dirt cheap, of course. Get 'em while you can, I guess.
Wavebourn, your comment about using light bulbs popped into my head, but I've never played with bulbs before. I suppose if bulb resistance is temp dependent, then voltage across the bulb filament affects what one would measure in circuit. I may give that a try soon in this circuit and dump the LM317 CCS. It would look pretty cool with some bulbs in the circuit. Heckuva conversation piece, for sure!
Last edited:
heres some progress updates...
Holes drilled for sockets, volume, and headphone jack. (ceramic sockets)
test fit of the tubes. I came up with the nifty mounting trick for the headphone and the volume pot. I took two metal washers the headphone jack fit through the hole of the firt one and i drilled the second hole out a little bit bigger for the pot. then i found a second washer that had the same hole size and the panel nut for the headphone jack and i glued that to the first washer so the jack is flush with the washer then i used the samesize on the pot and i dropped them into the holes and glued to the wood.
here it is mostly assembled (no power supply)
heres the backside, i Installed a half amp breaker since the circuit is 450ma (fuses seem costly if i screw up) theres a hole for the power cable and the rca jacks are on the far side. sadly though this box is big. If i finish my next design and there is enough room it and the next design will go into the same chassis as my lm3876 amp.
My plans are this since i am a student it means i have a low budget. Im building a set of brynn horns (frugal horn spawn) instead of the fostex driver im using a set of pioneer full range drivers. their cut off is 13khz. the speakers max handling is 60 watts RMS. the lm3876 has a max output of 58watts RMS with 0.06%THD so theyre a dam good match.
Next im still working on a small hybrid OTL amp (something similar to this amp) except its going to use a new production 807 and two buz901 fets per channel. its output should be about 16 watts RMS this is enough to drive a set of tweeters that will make up for what the pioneer is lacking. to prevent the common band spl increase common with multiway speakers im designing a small circuit that detects if a signal is present in crossover feeding both amps if it is then the signal gets inverted and fed to the grid of the 807. This cancels the signal inside the tube (or it could be done in the preamp) so that the tweeter and the horn never produce the same sound. EQ is going to be simple. probably fet based with at minimum an 8band eq. the psychobass enhancer featured on the headwize site and a few other dsp circuits.
An externally hosted image should be here but it was not working when we last tested it.
Holes drilled for sockets, volume, and headphone jack. (ceramic sockets)
An externally hosted image should be here but it was not working when we last tested it.
test fit of the tubes. I came up with the nifty mounting trick for the headphone and the volume pot. I took two metal washers the headphone jack fit through the hole of the firt one and i drilled the second hole out a little bit bigger for the pot. then i found a second washer that had the same hole size and the panel nut for the headphone jack and i glued that to the first washer so the jack is flush with the washer then i used the samesize on the pot and i dropped them into the holes and glued to the wood.
An externally hosted image should be here but it was not working when we last tested it.
here it is mostly assembled (no power supply)
An externally hosted image should be here but it was not working when we last tested it.
heres the backside, i Installed a half amp breaker since the circuit is 450ma (fuses seem costly if i screw up) theres a hole for the power cable and the rca jacks are on the far side. sadly though this box is big. If i finish my next design and there is enough room it and the next design will go into the same chassis as my lm3876 amp.
My plans are this since i am a student it means i have a low budget. Im building a set of brynn horns (frugal horn spawn) instead of the fostex driver im using a set of pioneer full range drivers. their cut off is 13khz. the speakers max handling is 60 watts RMS. the lm3876 has a max output of 58watts RMS with 0.06%THD so theyre a dam good match.
Next im still working on a small hybrid OTL amp (something similar to this amp) except its going to use a new production 807 and two buz901 fets per channel. its output should be about 16 watts RMS this is enough to drive a set of tweeters that will make up for what the pioneer is lacking. to prevent the common band spl increase common with multiway speakers im designing a small circuit that detects if a signal is present in crossover feeding both amps if it is then the signal gets inverted and fed to the grid of the 807. This cancels the signal inside the tube (or it could be done in the preamp) so that the tweeter and the horn never produce the same sound. EQ is going to be simple. probably fet based with at minimum an 8band eq. the psychobass enhancer featured on the headwize site and a few other dsp circuits.
Nope, it's working fine. Check the spelling - lots of people leave off the second 't'.
wow you truely are a genius. thats exactly what ive done.
But no worries i was just wondering if you could take a peak at this schematic.
Most of the info for this design came from three places. Your schematics, a post on tube cad and some threads on this forum.
But no worries i was just wondering if you could take a peak at this schematic.
Most of the info for this design came from three places. Your schematics, a post on tube cad and some threads on this forum.
An externally hosted image should be here but it was not working when we last tested it.
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