08-23-2009, 03:53 AM
I've been building a custom "from chassis-up" scratch-build stereo-tube hifi amp the past several weeks in my spare time.
I thought up the tube layout, and applied my ideas in mixing together some of my good vintage-spares parts (all),.. into a orig 1947 RCA roll-over tube cage type orig old auditorium style orig PA chassis I recently acquired.Its a very-cool looking vintage homebrew rig if nothing else I suppose. Heavy duty chassis indeed!
I have the both amps on same chassis working now, and both sounds very good so far with a CD player playing thru it via separate amps 5k audio separate vol, treble, & bass controls, but Ive had to make some mods to get rid of excess distortion in my orig design. Im getting there, but still have very-slight distortion happening.
I also realize that since I basically dreamed-up the overall schematic as a "try-build", Im on my own out in left-field on this homebrew amp project! However, any your thoughts or suggestions would be appreciated in ridding the excess mimimal-distortion in this 2- monoblocks amps on one chassis project! Ive already looked for most obvious solutions, slight minimal distortion still present.
Heres the vintage parts & basic layout I used in this stereo amp project so far. Simple 5-tube lineup( for each individual amplifier) using 2 push-pull audio-tubes output ( ea amp) all on 1 chassis. I have no "hum" probs whatsoever,or any crosstalk,between individual amps, both quiet as a mouse between CD tracks playing thru both the amps out to matched vintage 8 ohm spkrs, both linear audio out trans properly matched in ohms to spkrs. This rig is absolutely " hum-free" & dead silent quiet, between CD player tracks! I used a half-wave AC to DC conversion diode bridge to power all the preamp tubes filaments chain by DC only, negative side chassis ground. The audio out PP tubes are 6.3 ac volt fils only. Both audio trans share the same B+ source.
The overall design is a cathode-biased amp ( all pin # 1 & pin 8 out to ground via (2)- 300 0hm 25 w power resistors worked, with separate 150 uf electrolytics strapped across each appropriately to improve smooth bass-response,for each set of pp output tubes sockets, that will accept any 6CA7/EL34, or 6550s, or 6L6s in push-pull. All work, as Ive subbed them in & out of the circuit. That the "beauty" of a Cathode-biased amp indeed! Most all tubes in this amp interchange, even the phase inverter, a 6SL7 with a 6SN7 ( I havent done that yet), but socket is ready. Going to a 6SN7 is going to lose my overall drive into the output tubes, as reason of my thoughts. In any case, the amps are working very well so for, and stable after many hrs power-up during my build via variac. The whole rig pulls less that 3 amps overall. I balanced the overall chassis DC voltages with the power trans centertap to ground via a 800 ohm 25 watt adjustable power resistor set now at about 150 ohms.
For the preamp tubes, I now have a 6C5 ( replacing my orig 6SJ7 idea front-end tube that was overkill on high-impedance selection) for aligning with a conventional home CD player. Fixed that prob. Bad idea from the getgo!
Now, my tube lineup is as follows,: 6C5 input tube feeds a 6J5 (same tube interchanges with 6C5) and so on on all schematics. That took care of the initial overdrive input (very high distort) prob on my orig design.
Total preamp tubes are now a 6C5, feeding the 6J5, into a 6SL7 phase-inverter setup, then into the pp audio tubes. I used some spare vintage early 1960s matched linear 20 watt audio trans off a old Sherwood S-5000 stereo integrated orig 6BQ5 in pp setup. Im using a heavy spare vintage power trans 450-0-450, 1 5U4 rectifier providing dc to both amps onboard,and main B+ is running consistent 403 vdc, and all 250 volts points out to preamp tubes are spot on using a 2-watt dropping-resistor back to chassis. The dc powered filaments on the preamp tubes ( running + & - ) are also spot on 6.3 volts dc via the high-uf / low voltage electrolytics.
Im almost homefree without any distortion in the circuit on this project! Still has a slight amt, and Ive carefully checked overall voltages! Any ideas?
Thanks in advance!!
I thought up the tube layout, and applied my ideas in mixing together some of my good vintage-spares parts (all),.. into a orig 1947 RCA roll-over tube cage type orig old auditorium style orig PA chassis I recently acquired.Its a very-cool looking vintage homebrew rig if nothing else I suppose. Heavy duty chassis indeed!
I have the both amps on same chassis working now, and both sounds very good so far with a CD player playing thru it via separate amps 5k audio separate vol, treble, & bass controls, but Ive had to make some mods to get rid of excess distortion in my orig design. Im getting there, but still have very-slight distortion happening.
I also realize that since I basically dreamed-up the overall schematic as a "try-build", Im on my own out in left-field on this homebrew amp project! However, any your thoughts or suggestions would be appreciated in ridding the excess mimimal-distortion in this 2- monoblocks amps on one chassis project! Ive already looked for most obvious solutions, slight minimal distortion still present.
Heres the vintage parts & basic layout I used in this stereo amp project so far. Simple 5-tube lineup( for each individual amplifier) using 2 push-pull audio-tubes output ( ea amp) all on 1 chassis. I have no "hum" probs whatsoever,or any crosstalk,between individual amps, both quiet as a mouse between CD tracks playing thru both the amps out to matched vintage 8 ohm spkrs, both linear audio out trans properly matched in ohms to spkrs. This rig is absolutely " hum-free" & dead silent quiet, between CD player tracks! I used a half-wave AC to DC conversion diode bridge to power all the preamp tubes filaments chain by DC only, negative side chassis ground. The audio out PP tubes are 6.3 ac volt fils only. Both audio trans share the same B+ source.
The overall design is a cathode-biased amp ( all pin # 1 & pin 8 out to ground via (2)- 300 0hm 25 w power resistors worked, with separate 150 uf electrolytics strapped across each appropriately to improve smooth bass-response,for each set of pp output tubes sockets, that will accept any 6CA7/EL34, or 6550s, or 6L6s in push-pull. All work, as Ive subbed them in & out of the circuit. That the "beauty" of a Cathode-biased amp indeed! Most all tubes in this amp interchange, even the phase inverter, a 6SL7 with a 6SN7 ( I havent done that yet), but socket is ready. Going to a 6SN7 is going to lose my overall drive into the output tubes, as reason of my thoughts. In any case, the amps are working very well so for, and stable after many hrs power-up during my build via variac. The whole rig pulls less that 3 amps overall. I balanced the overall chassis DC voltages with the power trans centertap to ground via a 800 ohm 25 watt adjustable power resistor set now at about 150 ohms.
For the preamp tubes, I now have a 6C5 ( replacing my orig 6SJ7 idea front-end tube that was overkill on high-impedance selection) for aligning with a conventional home CD player. Fixed that prob. Bad idea from the getgo!
Now, my tube lineup is as follows,: 6C5 input tube feeds a 6J5 (same tube interchanges with 6C5) and so on on all schematics. That took care of the initial overdrive input (very high distort) prob on my orig design.
Total preamp tubes are now a 6C5, feeding the 6J5, into a 6SL7 phase-inverter setup, then into the pp audio tubes. I used some spare vintage early 1960s matched linear 20 watt audio trans off a old Sherwood S-5000 stereo integrated orig 6BQ5 in pp setup. Im using a heavy spare vintage power trans 450-0-450, 1 5U4 rectifier providing dc to both amps onboard,and main B+ is running consistent 403 vdc, and all 250 volts points out to preamp tubes are spot on using a 2-watt dropping-resistor back to chassis. The dc powered filaments on the preamp tubes ( running + & - ) are also spot on 6.3 volts dc via the high-uf / low voltage electrolytics.
Im almost homefree without any distortion in the circuit on this project! Still has a slight amt, and Ive carefully checked overall voltages! Any ideas?
Thanks in advance!!
