Hey everyone Im new here and Im really having a tuff time with this little japanese amp i bought on ebay. So the story I got from the seller was the amp worked prior to him trying to install a new plug and after it was blowing fuses. So I got the amp and he had tried to install another two prong plug which I know is a shock hazzard so i went out to home depot and got a 3 prong and a installed it as well as all new tubes from a local tube shop here in denver. I made the assumption that he had wired the cord correctly so i did the same. Well the amp just keeps blowing fuses and 35w4 tubes so im currious if the plug is wired to the rectifier tube correctly. Im going to post pictures so hopefully you guys can help me out here cause im stuck on this one.
Thanks Guys
http://www.flickr.com/photos/80698781@N00/5688847698/
http://www.flickr.com/photos/80698781@N00/5688847670/
Thanks Guys
http://www.flickr.com/photos/80698781@N00/5688847698/
http://www.flickr.com/photos/80698781@N00/5688847670/
Chris,
I don't see a power trafo in the photos. That makes the amp a DEATH TRAP, unless it's modified. Be grateful fuses and tubes failed, instead of you being killed.
That unit employs a 150 mA. series heater string. Japanese AC mains are lower voltage than those in North America. You need 10 W./150 Ω and 1/2 W./3.3 Ω resistors inserted into the series string to drop 23 Volts.
A $11.41 Triad N-68X isolation trafo from Allied Electronics (stock # 967-9502) will provide the protection necessary.
Replace all caps. in the unit. The 'lytics are undoubtedly bad and all the rest are suspect.
Check all resistors for drift out of tolerance. Replace as needed.
I don't see a power trafo in the photos. That makes the amp a DEATH TRAP, unless it's modified. Be grateful fuses and tubes failed, instead of you being killed.
That unit employs a 150 mA. series heater string. Japanese AC mains are lower voltage than those in North America. You need 10 W./150 Ω and 1/2 W./3.3 Ω resistors inserted into the series string to drop 23 Volts.
A $11.41 Triad N-68X isolation trafo from Allied Electronics (stock # 967-9502) will provide the protection necessary.
Replace all caps. in the unit. The 'lytics are undoubtedly bad and all the rest are suspect.
Check all resistors for drift out of tolerance. Replace as needed.
I’m an ignorant novice. I have recently acquired a 4” speaker attached to a 2x4x6 chassis with a tube complement of two 50C5 and one 12AU6. You can find pictures at https://plus.google.com/photos/1085...s/5691308028790967569?authkey=COGJmPH9-7HfogE How did all that get crammed in there? I guess it is true point to point. I assume it is some type or radio receiver.
Rattling a screw driver grounded to the chassis around to everything that looked like a cap brought no snap crackle or pop. I’m just going to tear the guts out. I want to convert it to a low watt guitar amp. One knob, kind of a combination of these two 1-12AU6; 1-50C5; 1-35W4 http://dogbarkmusic.com/Harm/harmony.pdf http://lectrolab.files.wordpress.com/2010/09/lectrolab_r203_r2.jpg Do you think there is enough room in there?
I plan to use the current cabinet. It is Bakelite. Not too many dials or knobs up front. The tube sockets are riveted in and do not appear scorched or chipped. I know I need to install a 1 to 1 isolation transformer as mentioned in this thread.. I think it will fit on top when all those other things are gone. I plan to put the ot on top too apparently with the core at right angle to the isolation transformer. That makes room underneath.
Assuming the ot and speaker are ok; it seems I can read ohms across the speaker to determine impedance, yes?
I want to put a ¼ out for a speaker cab on the back. Is there one that disconnects and reconnects the internal speaker just by inserting and removing the plug? If yes what is the part #? Where do I find it. I’m not connecting with Google on this question.I've been told one can do it with a shorting jack, but I think it leaves me with the internal speaker in series with the external speaker. I see switching jacks but can't find wiring diagrams.
Any and all advice appreciated. Thanks Rob
Rattling a screw driver grounded to the chassis around to everything that looked like a cap brought no snap crackle or pop. I’m just going to tear the guts out. I want to convert it to a low watt guitar amp. One knob, kind of a combination of these two 1-12AU6; 1-50C5; 1-35W4 http://dogbarkmusic.com/Harm/harmony.pdf http://lectrolab.files.wordpress.com/2010/09/lectrolab_r203_r2.jpg Do you think there is enough room in there?
I plan to use the current cabinet. It is Bakelite. Not too many dials or knobs up front. The tube sockets are riveted in and do not appear scorched or chipped. I know I need to install a 1 to 1 isolation transformer as mentioned in this thread.. I think it will fit on top when all those other things are gone. I plan to put the ot on top too apparently with the core at right angle to the isolation transformer. That makes room underneath.
Assuming the ot and speaker are ok; it seems I can read ohms across the speaker to determine impedance, yes?
I want to put a ¼ out for a speaker cab on the back. Is there one that disconnects and reconnects the internal speaker just by inserting and removing the plug? If yes what is the part #? Where do I find it. I’m not connecting with Google on this question.I've been told one can do it with a shorting jack, but I think it leaves me with the internal speaker in series with the external speaker. I see switching jacks but can't find wiring diagrams.
Any and all advice appreciated. Thanks Rob
Guitar amp thread so it gets moved to the I&A forum where it belongs.your are ok for getting the impedance, add 20%.
Can't tell by the pictures whether you have room for the transformer with the speaker but I would guess it would all fit. The jack you want is a regular switched 1/4" jack like you would use on the input of the guitar amp. The output would be wired to the end terminal of the jack, go through the switch when a plug is not inserted, and the other terminal of the switch would go to the speaker and then to ground.
MONO CHASSIS MOUNT W/ N.C. SWITCH 1/4" JACK | AllElectronics.com
It looks like an old Tube radio , I bought one at a garage sale a while back that I was going to use to salvage the power transformer but after openeing it I saw that it was directly mains powered with no power transformer at all which pissed me off and scared me thinking that they actually allowed this death trap to be sold in a store .......
PS: in Japan they also use a different voltage , generally 100v but 90v in some areas so there might be problems useing it in the US or europe .....
PS: in Japan they also use a different voltage , generally 100v but 90v in some areas so there might be problems useing it in the US or europe .....
It is safe as a radio as there is no exposed circuit for a person to contact unlike a guitar amp which has that darn cord attached to it.
There were a LOT of valve radio 'death traps' sold - some even used special resistive mains leads to drop the mains voltage (so no shortening, or replacing, the mains lead).
But I can't believe a guitar amp was ever made in such a way?.
BTW, I thought Japan had both 120V and 240V mains, depending where you were - it's why Japanese gear was always switchable, even relatively recently (VCR's etc.). Presumably this isn't the case any more?.
Japan has been on 100V mostly 60Hz with some 50Hz areas depending on where you are located for many decades, the switchable mains provision was for exported products. Like the U.S. few products for domestic sale have switchable mains.
I picked up an old japanese tube amp last year that i used for parts and it had a japanese power xformer that had 90v and 100v ac primary taps on the transformer , it had a 235v 35ma, 6.3v 2a, 5v .5a secondary taps ......
when connected to a 115v source it gave me about an extra 25v on the 235v secondary but it made the 6.3v tap too high to use as heaters .......
when connected to a 115v source it gave me about an extra 25v on the 235v secondary but it made the 6.3v tap too high to use as heaters .......
I thought post WWII their infra structure was rebuilt by the USA and UK, each fitting their own mains voltages - and that was the main reason for Japanese equpment having customer adjustable mains switching.
Just my 2 cents, I think you should determine whether (or why) you would want to do a complete tear down and rebuild of this vintage amp. It is not going to be a simple fix.
Safety Number#1 is absolute need to use an isolation transformer& Proper polarized wall plug.
Bleeder resistors should be placed across the power supply cap to safely discharge when the amp is turned off.
You have a dead short situation, and the output transformer also needs to be checked, and all the electrolytic caps replaced. You should probably sketch out the wiring, pull all the components out and verify what is still usable.
I would not even plug in replacement tubes until all supply voltages were double checked as correct at the sockets.
Don't want to be negative about it, but because something is vintage it does not necessarily mean it is of more value or even worth restoring..(IMO)
Safety Number#1 is absolute need to use an isolation transformer& Proper polarized wall plug.
Bleeder resistors should be placed across the power supply cap to safely discharge when the amp is turned off.
You have a dead short situation, and the output transformer also needs to be checked, and all the electrolytic caps replaced. You should probably sketch out the wiring, pull all the components out and verify what is still usable.
I would not even plug in replacement tubes until all supply voltages were double checked as correct at the sockets.
Don't want to be negative about it, but because something is vintage it does not necessarily mean it is of more value or even worth restoring..(IMO)
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