chinacave
Its Like a Jungle Sometimes; It makes me Wonder
I am servicing some nice tube gear and tone arms for a pal of mine, retired from the Pro Mastering / recording studio supply / importing / consulting business -
Today I delivered 3 restored Marantz 7c's to him and he put this unit in my car to check out. He MAY have the service info somewhere... the photo below is not mine but is the same version as the one on my bench - cribbed the photo from the web...
1) Can anyone share a schematic of this unit? I have found some similar ones around the interwebs, but it seems there were several / many versions, 6 tubes, 4 tubes per side - different tubes etc.
2) there is a hair-thin wire on each tube from pin #3 to Pin #4 - and also in at least one place on the terminal strips- Acting as a fusible link for safety? Funny thing is that the tube date sheet I have seen for the 6FW5 shows NO connection - nuthin' at pin #4 (?!) - Strike that - #4 IS n/c - but used as a tie point for one of the ferrite-shielded connections to the tube - I noticed in another photo of the underside of a different model the maker included a short length of spare fusible wire for servicing... Interesting - have not seen any indication of it on the other H3 schematics found so far for other versions -
3) 3 Big computer caps here - the speaker outputs are capacitor-coupled through them - 800mfd @200 vdc - and another 400mfd @375 vdc - all are Sprague "computer-lytic" I have seen the warnings on other threads on these amps to FIRST, before anything - (IE especially w/ the OTL amps, ) replace the capacitors before testing. I have repaired / restored many PP tube amps, never an OTL one. So I have the equipment and experience, I think, to slowly bring this up on a variac to A) see if it works and B) possibly 'reform' the caps. This would be for testing only, I have NO intention of playing 40-50 year old gear with old time-bomb capacitors - Is there something unique to the OTL / Futterman circuit that argues against that course of action?
4) Any advice / clues / hints always welcome!
Today I delivered 3 restored Marantz 7c's to him and he put this unit in my car to check out. He MAY have the service info somewhere... the photo below is not mine but is the same version as the one on my bench - cribbed the photo from the web...
1) Can anyone share a schematic of this unit? I have found some similar ones around the interwebs, but it seems there were several / many versions, 6 tubes, 4 tubes per side - different tubes etc.
2) there is a hair-thin wire on each tube from pin #3 to Pin #4 - and also in at least one place on the terminal strips- Acting as a fusible link for safety? Funny thing is that the tube date sheet I have seen for the 6FW5 shows NO connection - nuthin' at pin #4 (?!) - Strike that - #4 IS n/c - but used as a tie point for one of the ferrite-shielded connections to the tube - I noticed in another photo of the underside of a different model the maker included a short length of spare fusible wire for servicing... Interesting - have not seen any indication of it on the other H3 schematics found so far for other versions -
3) 3 Big computer caps here - the speaker outputs are capacitor-coupled through them - 800mfd @200 vdc - and another 400mfd @375 vdc - all are Sprague "computer-lytic" I have seen the warnings on other threads on these amps to FIRST, before anything - (IE especially w/ the OTL amps, ) replace the capacitors before testing. I have repaired / restored many PP tube amps, never an OTL one. So I have the equipment and experience, I think, to slowly bring this up on a variac to A) see if it works and B) possibly 'reform' the caps. This would be for testing only, I have NO intention of playing 40-50 year old gear with old time-bomb capacitors - Is there something unique to the OTL / Futterman circuit that argues against that course of action?
4) Any advice / clues / hints always welcome!
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