Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: dude on July 10, 2018, 03:23:12 pm
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Building another 6V6 plexi from Sluckey's and Hoffman's schematic posted here. I took the time to have faceplates designed from some free software online, just printed on thick paper and used thin plexiglass to cover, looks great. Second time around with same chassis I won't make the same mistakes as the first, well hopefully :icon_biggrin: .
Anyway, rather than drill out the square old cap can holes for a new round can, I asked before if these old metal cans can be reformed. I assume a variac used to bring up the voltage to 118v over 24 hours, slowly would work...? Is is worth the risk in reforming these old cans? Have to use a can, room is tight, these AO-43's are narrow.
The Hammond cans have an AO part number, don't know the make but look like Mallory's. They have two 50ufs tabs each, for four caps and case is ground. Just wondering to save a lot of work and time if I could reform and use them, I make these Plexi's so 6V6, 6L6s and EL34s can be used, is 50uf too high for the first stage preamp E cap? Use a 5AR5 or 5U4 (PT can handle 5U4)
Any insight would be helpful, as once a bd is in, "major work" to redo the chassis for modern round cap can holes. Note, square is too small to take a modern cap can.
al
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Text is in italian, but you can easily read the photo
http://www.radioedintorni.it/Radiomeccanico/RadioRestauratore/CondVitone.html (http://www.radioedintorni.it/Radiomeccanico/RadioRestauratore/CondVitone.html)
EDIT: English versions
http://www.albertkreuzer.com/can.htm (http://www.albertkreuzer.com/can.htm)
http://metro706.hostmetro.com/~archradi/restoration/electrolytics.html (http://metro706.hostmetro.com/~archradi/restoration/electrolytics.html)
Franco
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Thanks Kagliostro, I was able to translate, good idea to keep the vintage cap can look. I could probably open the can and use it but I'm not concerned about vintage looks.
The more I think about it, the work involved if the cans fail. Probably foolish to try to use a 50 year old E cap can whether or not it reads good and reformed.
Best bet is probably to cut the chassis enough for two JJ cans to work. Last AO-43 I use one JJ can and two axial caps inside on standoffs, none on the BD. But took up wanted room, way too crowded too.
One question is 32uf too high for the preamp filtering, calls for 16/20uf.
al
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One question is 32uf too high for the preamp filtering, calls for 16/20uf.
no
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I've had good luck using old cap cans in an AO-44 and AO-63. Caps work fine but I would not trust them anywhere except in my shop.
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These AO-43 chassis conversions are for gigging friends. I'll just use two new cans 32/32. Thanks, all.
al
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Found a deal on 50/50uf @500 cans, $5 each. Any problem using these for a 6V6 Plexi first two E caps, 32/32 can for PI and preamp? Using 5AR4 or 5U4GB and diodes.
al
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50uf is a bit high for the 5U4GB (rated 40uf max) or even 5AR4 (60uf max). You wouldn't be the first person to push/exceed those ratings, but you wouldn't be the first to experience a failed rectifier tube either.
Series diodes go a long way towards protecting the tubes from arcing, though.
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An in-rush current limiter placed between the rectifier and the first cap may be worthwhile if you push the limits on capacitance.