Old Univox restoration project

Discussion in 'Shock Brother's DIY Amps' started by backalleyblues, Jun 4, 2009.

  1. backalleyblues

    backalleyblues Friend of Leo's Silver Supporter

    Posts:
    3,168
    Joined:
    Nov 5, 2006
    Location:
    Jacksonville, FL, USA
    Hey gang!

    Picked up an old Univox U-45B (10 watts, 12" Jensen spkr) last weekend (yeah it kinda followed me home!!!). Anyways, the poor thing is in need of some rehabbing. It appears the chassis is completely original, including tubes and caps, and will likely need replacing. So my questions are:

    What would be a good cap for the power supply in this puppy? It takes 10uf for the pwr supply @ 300 volts. Most of the caps I've seen available are 450 volts, I don't think this is a real problem, though. The thing is, are Sprague Orange Drops really worth all that extra coin? Especially in the pwr supply?

    In a related note above, what's everybody's opinion on signal caps? Obviously this is not a high end amp, and probably wouldn't sound right with a mish-mash of low and high end parts in there. A little guidance here would be great...

    Tubes are weird in this amp-12AX7, 2x 6BM8, and a 6X4. Most likely, the rectifier is going (getting lots of pops and voltage drops) but I'm going to replace the whole lot. Which brings me to my final question: Which is the best place to do "all in one" shopping on the 'net? Don't feel like ordering from 3 different places (and pay shipping charges 3 times) if I can get everything in 1 shot... hopefully ordering all of this this weekend, so I can work on this by july 4th, when I go on vacation...

    Thanx in advance for your replies!!!

    Franc Robert
     
  2. marshman

    marshman Poster Extraordinaire

    Posts:
    5,037
    Joined:
    Feb 1, 2007
    Location:
    SE PA
    Well, I get all that sort of stuff from Antique Electronics Supply (AES) http://www.tubesandmore.com/ and though I don't order tons of stuff, they do ship pretty quickly. I think MOJO http://www.mojotone.com can handle your needs as well, though I've no experience with them.

    The 6X4s are, in my experience, pretty common/cheap on the hamfest market (I have a few downstairs if you get desperate), and the 6BM8s are uncommon, which would also work in your favor.

    I'm told that the Sprague Atoms (the big power supply caps) are engineered to look like 'the filter caps of yore' eg, waaay bigger than they need to be with modern manufacturing techniques, so maybe you can get smaller sized ones to fit the space. A fair few folks like to replace old caps with one the next 'size' up for better filtering and bass response...I guess that'll depend on wether you're dead set on accurate restoration or just getting it back into fighting trim.

    Good Luck!
     
  3. shadowfan

    shadowfan Tele-Meister

    Posts:
    203
    Joined:
    Dec 13, 2008
    Location:
    Atlanta, GA US
    Hi:

    No problem in using higher voltage caps in a power supply; even somewhat higher, within reason, capacitance is OK too.
     
  4. backalleyblues

    backalleyblues Friend of Leo's Silver Supporter

    Posts:
    3,168
    Joined:
    Nov 5, 2006
    Location:
    Jacksonville, FL, USA
    OK, what I have learned and done so far-

    Called my local guit-shop, they're able to order me the 6BM8 tubes (they're an Electro-
    Harmonix dealer, and E-H is making that tube) so this opens up a LOT more possibilities as to where to order...

    So far, I'm leaning towards Angela, they've got tested UOS 6X4 tubes @ $2.00 each, and have all the caps needed at a reasonable price (Nichicons, and several others). Figure I'll order several of the 6X4s, being that cheap... even the new ones are only $8, so maybe I'll get one new and a couple UOS...

    I want to get this amp "in fighting trim" for at least recording and low volume practice, so I'm not really into boosting the filter caps' values. On the plus side, even with the original 2-prong cord, it was dead quiet, no hum or hiss at all until I cranked it, even then it was nothing bad. This amp has a real nice old blues tone to it-haven't plugged my lap steel into it, but I'll lay odds I can get instant Elmore James with the steel (I was able to get Robert Nighthawk tones with my telly!).

    Soooo, get the caps and tubes replaced, check the resistors for drift, then let'er rip!!!

    Thanx,
    Franc Robert
     
  5. Twangthang

    Twangthang Tele-Meister Silver Supporter

    Posts:
    203
    Joined:
    Jun 6, 2005
    Location:
    Long Island, NY
    I have the exact same amp

    My brother found it on his garbage run about 15 years ago... The amp had no tubes and I used the cab as an extension for a while and then stopped using it... I broke it out this past year and was able to purchase the tube on fleabay (NOS) for about $30...
    Before I start fooling with it I need fix a few things... I have a schematic but the value of the fuse is not there... Wondering if you could supply that info for me. Also the pot for the tremolo is missing and it looks like the previous owner bridged the positive and neutral wires together... I would like to get that repaired before I power it up.
    I have seen one You tube clip with this amp and it sounded pretty nice.

    Cheers
    Jim
     
  6. backalleyblues

    backalleyblues Friend of Leo's Silver Supporter

    Posts:
    3,168
    Joined:
    Nov 5, 2006
    Location:
    Jacksonville, FL, USA
    I couldn't tell you off-hand what the fuse value is, but I doubt it's higher than 1 amp slowblow... the pot for the tremolo is a 1meg

    interesting thing when I cracked open the amp this evening to confirm all the cap values-ALL the signal caps (except one disc cap) were oil-in-paper caps (Atlas Capacitor)... reading up on them, these have become kinda holy grail pieces for tone. Might explain why this thing sounds so good...:)

    Franc Robert
     
  7. mojo2001

    mojo2001 Tele-Holic

    Posts:
    687
    Joined:
    Feb 5, 2008
    Location:
    DC
    I have seen lots of those plastic wrapped Japanese oil caps in hi-fi gear. They sound great if in good order, but most of them are leaky as can be. They are not well sealed like the mil-spec glass to metal seal American or Russian surplus types.

    So, be sure to check the grid side of the coupling caps for + DC squeaking through. It should measure 0 DC at the grid. Then check them again after you put a few dozen hours on the amp because this problem can get worse with some use.

    Just putting that comment in there for consideration.
     
  8. backalleyblues

    backalleyblues Friend of Leo's Silver Supporter

    Posts:
    3,168
    Joined:
    Nov 5, 2006
    Location:
    Jacksonville, FL, USA
    Thanks mojo for that info.

    I looked at them closely for leaks last night, and didn't see any, but I will check them as well with my VOM when I pull the chassis (ordered my filter caps and the 6X4 tube from Angela this AM).

    Franc Robert
     
  9. mojo2001

    mojo2001 Tele-Holic

    Posts:
    687
    Joined:
    Feb 5, 2008
    Location:
    DC
    I am referring to electrical leaks, rather than physical leaks--although both are possible (and interrelated).

    Basically, paper caps without a mylar layer will develop leakage paths due to moisture getting into the cap through small openings, like where the leads get in or where the fiber insulator meets the case. Thus they become high level resistors at DC instead of infinite ohm devices and enough DC can squeak through to cause problems.
     
  10. backalleyblues

    backalleyblues Friend of Leo's Silver Supporter

    Posts:
    3,168
    Joined:
    Nov 5, 2006
    Location:
    Jacksonville, FL, USA
    Understood mojo, I wasn't sure how to check caps, but you explained that nicely. Once the parts all get here... :)

    Franc Robert
     
  11. mojo2001

    mojo2001 Tele-Holic

    Posts:
    687
    Joined:
    Feb 5, 2008
    Location:
    DC
    Yeah, the way to test caps is keep the B+ side connected to voltage and disconnect the other side from circuit.

    Measure for + DC voltage appearing between loose cap lead and ground...should be NONE.

    A cap should BLOCK DC and let only AC through.

    Depending on the actual hookup, you can usually do this with caps in place. A high value resistor between grid and ground won't affect the test.

    If one or two volts leaks through to the grid side of a power tube, it will still "work"...might even give a funky vintage sound. Every yellow Astron cap on the planet leaks and they can still sound good. But if it gets up to where it affects bias, that is a problem...this is why leaky caps cause excessive current draw & red plating.

    Grid bias is negative. A positive voltage on the grid lowers bias, working the other direction from a cathode bias resistor, and causes tube to draw more current.

    And one or two volts leaking through to a 12AX7 grid wildly affects bias, so that ain't good at all.
     
  12. JohnnyCrash

    JohnnyCrash Doctor of Teleocity Gold Supporter

    Posts:
    11,044
    Joined:
    Mar 12, 2005
    Location:
    Fullerton, CA


    450 volts is fine. As far as the capacitance value, it depends on how much the 6X4 rectifier can deal with. I'm sure it can handle bigger than 10uF, but not sure how much more. I'd feel safe with a 20uF, but not so safe with a 47uF or 50uF.

    Increasing the first filter cap can help tighten up bass and reduce a little bit of noise.

    Orange Drops are coupling (or signal) caps. Sprague's Atoms are their electrolytic filter caps. Atoms are ridiculously large and way too expensive. Illinois or other brands are plenty good, smaller, and cheaper.





    I've used a mish-mash of high and low end parts on a few amp builds. The difference isn't as big as you'd think.

    Still, uniform cap brands looks nicer, makes ordering easier, and can help when trying to figure out what value is what.

    The usual suspects for CC's are Mallory or Orange Drops. Some folks say OD's sound a bit brighter than Mal's. I disagree, they're about the same.

    SoZo's are premium and not so huge of an improvement that I'd say go that way either. On the plus side, if I remember correctly (its been about 2 months since that build), they mark the outside end of the foil for even better performance.

    Can't go wrong with OD's, Mal's, SoZo's or other brands. It depends on how much you want to spend - again, the difference isn't night and day, its more subtle. If this is to be a live amp, go with the usual suspects - if this is for recording, you might want to invest in premium caps.





    TubesAndMore.com - they've always been the best in my book. Other great places are HoffmanAmps.com, Turretboards.com, and a few other places (though I don't think they sell tubes, so TAM is the place!).
     
  13. mojo2001

    mojo2001 Tele-Holic

    Posts:
    687
    Joined:
    Feb 5, 2008
    Location:
    DC
    There are scads of 10uf @ 350V/400V caps on ebay for around $1 apiece, but they are radial.

    Look for Elna, Nichicon, Chemicon, etc.

    I usually look for 105 degree C rated caps...this is an indicator of a higher grade cap designed for switching power suppies (low ESR, good HF performance, and longevity).

    Personally I think the Atoms are a bit of a rip but they do fit nicely in vintage amps looking for axial caps. Most of the modern Japanese radials will be higher grade parts overall.

    Now, whether you actually want a really high performance electrolytic cap in guitar amps sound-wise is another story for another thread.
     
  14. backalleyblues

    backalleyblues Friend of Leo's Silver Supporter

    Posts:
    3,168
    Joined:
    Nov 5, 2006
    Location:
    Jacksonville, FL, USA
    Well, spent a little time going through the amp this afternoon with my VOM...

    Found a number of signal caps that tested with less than infinite resistance, so methinks these are going bye-bye...

    Double checked the fuse too, twangthang, and it is indeed a 1 amp/250v slo-blo fuse...

    I won't be able to really dig into the amp until after I move in 2 weeks, but I certainly will then...

    Thanx!

    Franc Robert
     
  15. Twangthang

    Twangthang Tele-Meister Silver Supporter

    Posts:
    203
    Joined:
    Jun 6, 2005
    Location:
    Long Island, NY
    Thanks Franc...
    Awesome info in this thread. Until I am done with closing on our new house this project is on hold. I would be very interested in how this works out for you... Please keep posting!

    Jim
     
  16. CAMARA53

    CAMARA53 TDPRI Member

    Posts:
    17
    Joined:
    May 18, 2009
    Location:
    North Carolina
    yes great info, please do let us all know how you make out, I am trying to restore a univox u255r myself replaced all the tubes already, hittin the caps next,wish I was better at reading schematics..I would love a layout of this thing or a couple of hi res pics to follow as it looks like someone was doing a little rewiring or modding or something,I started a thread about it but only 1 reply ;(
    well good luck on yours and wish me luck on mine
     
  17. backalleyblues

    backalleyblues Friend of Leo's Silver Supporter

    Posts:
    3,168
    Joined:
    Nov 5, 2006
    Location:
    Jacksonville, FL, USA
    Well, now that the move is done and vacation beckons (starting Friday!!!) I'll finally be able to get to this project. BTW, Angela gave me sledgehammer service-sent out a tracking # (for the Post Office! Dang!) and got everything within a couple days.

    See ya at the end of this week!

    Franc Robert
     
  18. backalleyblues

    backalleyblues Friend of Leo's Silver Supporter

    Posts:
    3,168
    Joined:
    Nov 5, 2006
    Location:
    Jacksonville, FL, USA
    Alrighty, the update everyone's been waiting for (yeah, right, suuuurrrreeee!):lol:

    Finally got to the amp this afternoon, and redid all the electrolytic caps in it, put in the new/old 6X4 rectifier (left the other original tubes in) and fired it up-

    WOW!!!!:D:D:D

    Thick, gnarly blues tones in this little beast, just now there's more of a "presence" to the sound, as in, it went from a Chihuahua to a Rottweiler. Dead quiet, too, so I'm a real happy camper. This was not without its adventures, though...

    From the pictures, you can see that this was actually a primitive circuit board amp, with a thin brown fiberglas(?) board carrying the traces. Several of the traces started coming up while I was doing the replacement of the caps, mercifully everything held together though (Whew!)...the 10uf 450v caps were radials, just like the originals, but the 100v caps were modern, which was a slight pain to get right for positionings sake. While I had the chassis pulled, I also cleaned it out, tightened things up, etc. and checked various things out about this amp. Some of the more interesting things:

    Speaker is a Jensen C12S, code 220636 (36th week of 1966). Makes this amp a late '66, maybe early '67, and one of the last of that model made. Still in nice shape, methinks I'll keep this in there. If it blows, then I'll get one of Ted Weber's Signature speakers...

    Chassis had a sticker on it (by the mounting holes) that said "Made In Japan"... might explain the Atlas oil-in-paper caps this puppy has...

    While this has a circuit board for the electronic parts, it's all flying leads to the tubes, trannys, etc. Lotsa intricate work in here, especially for such a small chassis (maybe they wired everything first, then installed the board, sockets, etc.?). If this didn't work out I was thinking of dropping a 5E3 circuit in there-glad I don't have to now, it would have been a serious pain to do...

    Anyways, thanks for tuning in!!!

    Franc Robert
     

    Attached Files:

IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.


  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.