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Old 14th May 2010, 03:25 PM   #1
diblet is offline diblet  United States
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Default looking for help diagnosing volume loss on tube amplified reel to reel player

i have a fujiya fl-555 (schematic attached) that i am having problems with.

the recorder's volume is very low even at maximum setting.

it was working fine, until during recording, the unit suddenly (and consistently) lost a lot of its gain. this happens both in play and record mode. when playing or recording you can hear things out of the speaker only faintly - and the sound does taper with the volume pot. tapping the wires/joints at the play/record head results in a proportionately quiet buzz as well so it seems to just be a gain/amplifier issue.

it is almost as if everything is working properly only on a much, much quieter level.

_

things i have tried already:
cleaning contacts
checked input and output jacks to ensure they are closed/working
changing to all new tubes

started checking entire circuit for cold joints / continuity
_



does anyone have any ideas as to what might be the issue here?

i have attached a schematic - hopefully it will help diagnosing the issue here...

thanks in advance to everyone for your time + help ... its greatly appreciated

Click the image to open in full size.
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Old 14th May 2010, 03:28 PM   #2
alejo is offline alejo  Argentina
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use insolate transformer. connect to wall can kill you.
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Old 14th May 2010, 03:51 PM   #3
diblet is offline diblet  United States
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thanks for the warning/concern. i don't work on it or have it open while it is plugged in - and i make sure i completely drain all the caps before touching anything.
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Old 14th May 2010, 07:55 PM   #4
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Check that you don't have an open .005 coupling capacitor. Make sure you have about 100 V out of the rectifier. See that there is screen voltage on the output tube, say around 70V. Cathode bypass capacitor on 12AV6 might be open.
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Old 19th May 2010, 03:04 PM   #5
diblet is offline diblet  United States
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awesome, thanks for the ideas bob - i'll be checking these tonight

i have been planning on doing a recap anyway - i'll just order up some replacement caps and do them all - so i can rule them out completely

this will be my first total recap - any advice or suggestions? from what i understand is with electrolytic capacitors find either the same or higher cap/volt ratings - and with ceramic find a value within 20% of the original

also, my experience with electronics has been towards computers, so i am used to ordering from digikey - are there better places to get caps from?

thanks
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Old 19th May 2010, 10:11 PM   #6
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Digikey has some of the parts that work well for tube audio (higher voltage), but if you want an easier path try Antique Electronics Supply. Also others will have suggestions.
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Old 19th May 2010, 10:29 PM   #7
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Quote:
Originally Posted by diblet View Post
thanks for the warning/concern. i don't work on it or have it open while it is plugged in - and i make sure i completely drain all the caps before touching anything.
Is one side of the mains really connected to the mic jack?
How do you make sure it's not the live side?

Holy Moly!!
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Old 19th May 2010, 10:37 PM   #8
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Wow - this is a very good point. I have worked on AC/DC radios in the past, but nothing that I was going to put my mouth next to.
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Old 19th May 2010, 10:47 PM   #9
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Quote:
Originally Posted by firechief View Post
Wow - this is a very good point. I have worked on AC/DC radios in the past, but nothing that I was going to put my mouth next to.
The centre pin of the monitor out is also connected via the transformer...

...that thing is deadly if you plug it on the wrong way round!
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Old 21st May 2010, 04:41 AM   #10
diblet is offline diblet  United States
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Quote:
Originally Posted by firechief View Post
Digikey has some of the parts that work well for tube audio (higher voltage), but if you want an easier path try Antique Electronics Supply. Also others will have suggestions.
just checked them out - they look great, thanks for the suggestion!



Quote:
Originally Posted by Globulator View Post
The centre pin of the monitor out is also connected via the transformer...

...that thing is deadly if you plug it on the wrong way round!
cripes, i guess people were tuffer in the 60s? is this something that should cause me to abandon to unit? that would be quite a shame, but i suppose it beats dying...

Last edited by diblet; 21st May 2010 at 04:58 AM.
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