My first guess would be push-pull EL84, but the 5k push-pull OPT's would not be right for that... Any chance of trying to draw a schematic?
Given that it is diy, then a schematic is really needed. Valves are highly likely to be just 12A-7 or EF86 in typical input and driver stages, so look for heater wiring to the normal pins for those valves, and compare to some existing schematics with those valves.
Quite a tidy build. Looks like it might have been a kit. I agree with trobbins here.
btw - Just by looking at the electrolytics, it might be older than you think. I wouldn't want to power it up without going over it very carefully first. Then after going over it, perhaps powering it up only on a variac.
btw - Just by looking at the electrolytics, it might be older than you think. I wouldn't want to power it up without going over it very carefully first. Then after going over it, perhaps powering it up only on a variac.
you dont need the entire schem. Follow the OPTs back to the relevant sockets and then back from there to the relevant cathode resistors. They will give a good indication of bias and hence narrow down the likely suspects in combination with the power rating of the power trannie and choke.
Realistically, EL84 pp powers. The voltage gain stage (middle of front three) is a double triode which means a paraphase or ltp splitter. Doesn't leave many options once you know what the catode resistors are.
Realistically, EL84 pp powers. The voltage gain stage (middle of front three) is a double triode which means a paraphase or ltp splitter. Doesn't leave many options once you know what the catode resistors are.
Let as see:
Pin1-no con.
Pin2-cathode
Pin3-G1/grid
Pin4-haeter
Pin5-haeter
Pin6-no con.
Pin7-no con.
Pin8-no con.
This is not EL84, and no any pentode(no G2-screen connection!), this is output triode!
Only 2 tubes have pinout like this: 6S4 and 6S4A.
Pin1-no con.
Pin2-cathode
Pin3-G1/grid
Pin4-haeter
Pin5-haeter
Pin6-no con.
Pin7-no con.
Pin8-no con.
This is not EL84, and no any pentode(no G2-screen connection!), this is output triode!
Only 2 tubes have pinout like this: 6S4 and 6S4A.
Not a very tidy build... AC wiring is not twisted and inconsistent color coding for the filaments. Note that the power supply uses a full-wave voltage doubler circuit.
It appears that pins 4&5 are filaments on the four output tubes and pin 9 to be the plate to OPTs. It also looks like pins 3,6,7,8 are not connected. Hard to tell with pins 1&2, it might actually be a 12B4A triode. Note the wiring on the power transformer for the filaments... looks like the pair of 6.3V windings are in series with a yellow and blue going to the first output tube pins 4&5, which could be 12.6V.
You will need to trace a few wires out on the three input tubes to see where they go... follow the input wiring from the volume pots on the chassis front to the input tubes, which pins are used as input? Also look for cathode resistors to ground for all tubes and note the values. Some closer and sharper pictures might help as well.
EDIT: Yes, Pin 1 could be a blank and pin 3 could be connected... so a 6S4 might be it, good call.
Regards, KM
It appears that pins 4&5 are filaments on the four output tubes and pin 9 to be the plate to OPTs. It also looks like pins 3,6,7,8 are not connected. Hard to tell with pins 1&2, it might actually be a 12B4A triode. Note the wiring on the power transformer for the filaments... looks like the pair of 6.3V windings are in series with a yellow and blue going to the first output tube pins 4&5, which could be 12.6V.
You will need to trace a few wires out on the three input tubes to see where they go... follow the input wiring from the volume pots on the chassis front to the input tubes, which pins are used as input? Also look for cathode resistors to ground for all tubes and note the values. Some closer and sharper pictures might help as well.
EDIT: Yes, Pin 1 could be a blank and pin 3 could be connected... so a 6S4 might be it, good call.
Regards, KM
Last edited:
Ok, its not tidy built but looks like a kit is what I meant. full wave voltage doubler? ugh. 
Probably best to strip it for parts.
Probably best to strip it for parts.
full wave voltage doubler? ugh.
Yeah, like that junk from Fisher, Marantz, McIntosh...
According to the pinout (only 3 used connections + heaters) and application (5K PP OPT) the output tubes must be very likely 6RA8 (6R-A8) triodes. This tube was only used and manufactured (by NEC only) in Japan and can be found in some old Luxman and Sansui amps. Good luck finding one today ! As far as the other tubes are concerned, tracing down the schematic would be needed for identification, or try looking at old Luxman schematics (especially the kit versions) on japanese websites. The one I found in an old book (model A2500) uses 6AQ8 and 12AU7 as input and phase splitter tubes but yours might be different. Your amp looks like a home built version of one of the many kits Luxman offered in the 1970's in Japan.
Japanese Triode
LUXMAN/LUXKIT A2500‚ÌŽd—l ƒ‰ƒbƒNƒXƒ}ƒ“/ƒ‰ƒbƒNƒXƒLƒbƒg
Japanese Triode
LUXMAN/LUXKIT A2500‚ÌŽd—l ƒ‰ƒbƒNƒXƒ}ƒ“/ƒ‰ƒbƒNƒXƒLƒbƒg
Last edited:
No, sir! Correctly implemented, the "full wave" doubler is an excellent way to obtain a superior, low impedance, PSU. Low copper losses is but 1 feature.
As Mr. Bavis stated, some [😉] "poor" designs used doubler PSUs. The H/K Cit. 2, Marantz 8B, and some McIntosh models are prime examples and those models are some of the very best amps ever made.
Guys,
As the OP is in Japan, he has a fair chance of finding the 6R-8A that's been mentioned. Does anyone have a data sheet link or even knowledge of what the heater draw is? Assuming the Japanese triode is "unobtainium", I'm thinking Octal sockets go in and triode wired 6AV5s get used for the "finals", but sufficient heater current has to be available.
Remember, Sylvania internally trioded 6AV5s to fill a US DoD order for 6B4Gs.
As the OP is in Japan, he has a fair chance of finding the 6R-8A that's been mentioned. Does anyone have a data sheet link or even knowledge of what the heater draw is? Assuming the Japanese triode is "unobtainium", I'm thinking Octal sockets go in and triode wired 6AV5s get used for the "finals", but sufficient heater current has to be available.
Remember, Sylvania internally trioded 6AV5s to fill a US DoD order for 6B4Gs.
Eli, I actully once owned an 8b. It was in a console unit that was put curbside for disposal. The console was damaged beyond repair but I managed to salvage the marantz and speakers. This was back around '84 or '85...
It was a wonderful sounding amp in a time when nobody appreciated such things. I sold it for a tidy profit when in university. I don't think that I would build a clone of it today though. Just being honest.
If you have one of these 'best amps ever' classics at home in everday use then I'm very happy for you. Most music listeners I know have sold off all the 'classic' gear, except for maybe the turntable...
Anyway, this sounds like an interesting project, with strange tubes. I would of course want to get it running befor drawing a verdict.
It was a wonderful sounding amp in a time when nobody appreciated such things. I sold it for a tidy profit when in university. I don't think that I would build a clone of it today though. Just being honest.
If you have one of these 'best amps ever' classics at home in everday use then I'm very happy for you. Most music listeners I know have sold off all the 'classic' gear, except for maybe the turntable...
Anyway, this sounds like an interesting project, with strange tubes. I would of course want to get it running befor drawing a verdict.
Last edited:
If you weren't in Japan I'd buy it. 5K would be good for 4 EL84 / channel if you wanted to install 2 more sockets on each channel. Probably very good transformers. Could make two nice guitar amps.
- Status
- Not open for further replies.