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Harmony H303A safety concerns?

Discussion in 'Amp Central Station' started by ECF, Jun 15, 2007.

  1. ECF

    ECF TDPRI Member

    18
    Jun 3, 2006
    Cape Girardeau, MO
    Hi, I bought a Harmony H303A amp today from the local store and I'm reading that there are considerable safety hazards regarding these amps. It has the original 2-prong cord that I will soon replace, but I also read about needing an Isolation Transformer. Upon inspection, the schematic inside the amp shows that there is apparently an Isolation Transformer already there. Does that mean I'm safe?
     
  2. Rizo

    Rizo Tele-Afflicted

    Apr 28, 2005
    Athens, OH
    I can't help you... but I had a similar experience. A guy I know was in a punch and wanted to sell me his Harmony H303A for $75. The original Jensen speaker was worth that I think.

    Anyway, I posted on an amp forum asking for opinions and I was told the same thing. That there was no isolation transformer and that because of that a 3 prong cord wasn't an option and it was dangerous. So I passed... but I may have been told wrong, who knows. Let's let the experts have a crack at it.

    To be sure, you could always just take it to a tech.
     
  3. ECF

    ECF TDPRI Member

    18
    Jun 3, 2006
    Cape Girardeau, MO
    Thanks. That's what is confusing me, everyone says get an isolation transformer but the original schematic shows that there already is one there. I wonder if they installed one in later models? I guess I'll have to go by a tech and have them look at it just to be safe.

    Thanks again..
     
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  5. Wally

    Wally Telefied

    Mar 17, 2003
    Lubbock, TX
    Whenever I see an amp that uses those tubes, I am wary...Ex: silvertone 1448 -amp-in-the-case" which does not have an isolation transformer. I am sure that other people take the same attitude and maybe to an extreme by thinking that any amp with this tube compliment needs an isolation transformer installed.
    The Harmony schematic certainly does show the isolation tranny. You probably want to change the electrolytics anyway, so a look by a tech is not a bad thing.
     
  6. JohnnyCrash

    JohnnyCrash Doctor of Teleocity

    Mar 12, 2005
    Fullerton, CA
    I love little "pawn shop special" amps like these... I had a chance to grab one from a friend and offered him good money, but didn't want to pressure him. I shoulda pressured him a bit more I guess :(

    Wally's right: new electrolytics and a 3 prong cord would be necessary maintenance... otherwise, how'd she sound?

    Here's the schem:
    http://www.schematicheaven.com/bargainbin/harmony_h303a.pdf
     
  7. ECF

    ECF TDPRI Member

    18
    Jun 3, 2006
    Cape Girardeau, MO
    What are the electrolytics?? Sorry, I don't know a lot about these little things..

    Would it be safe to play it, as it is, through a Whirlwind A/B selector along side my Vibro Champ?
     
  8. Wally

    Wally Telefied

    Mar 17, 2003
    Lubbock, TX
    ECF, words of warning... if you do not understand the safety concerns when working on these amps, then replacing the power cord is a risky venture.
    The electrolytics store voltage. This stored voltage can be harmful?deadly even if the amp is unplugged and even if you are working on the power cord.
    Concerning the elctrolytics, at some age they nolonger filter the AC ripple and/or provide the good steady voltage that is necessary for the amp to yield the tone that it should.
    there are a lot of books out to get one started on the path to understanding amplifiers. Tom Mitchell's 'How to SErvice Your Own guitar Amplifier' is a good basic source in layman's term's. Goodle Aiken Amps and check out his technical info.
    Be careful.
     
  9. teerjerker

    teerjerker Tele-Meister

    224
    Apr 16, 2006
    jersey
    ECF,

    I purchased one of these a couple of months back. I love the little thing. I can't believe something built out of paperboard with a little 6" speaker can sound so good. Really warms a Tele up... if you don't already have an overdrive pedal, get yourself one and play a Tele with the bridge pu through it going into this little guy. What a great sound!

    I've also read the warning about there being no isolation tranny in this amp but mine clearly has one, and all the schematics that I've seen, including the one that is pasted on the inside of my amp has the transformer drawn in the circuit.

    Enjoy!
     
  10. aznrambo481

    aznrambo481 Friend of Leo's

    ECE, the electrolic capacitors are the big, cylindrical things inside. To safely work in a tube amp, KEEP ONE HAND IN YOUR POCKET AT ALL TIMES so you don't zap yourself. The electrolycs' jobs are to make the voltage level after the power transformer. Basically they do that by storing the electicity and letting it out. When you turn off an amp, they retain a charge, sometimes even for months. If you touch the positive end of one of these with one hand, and the metal chasis with another, you are letting all of the electrons escape to ground, straight across you heart. you need to discharge these before you can safely handle them.

    If you are not familiar with a tube amp, I strongly recommend at least reading up on amp construction. I learned the bit i know about tube amps by looking over mods to amps I don't even have :D and trying to get my little head around those weber schematics. I wouldn't feel safe sticking my hand into that. I have heard those caps can explode if put in the wrong way. They also wear out, however I have no idea whether this poses as a danger.

    I know you came to this site to get some encouragement for your project, and to try to figure out what to do next. You should try to have an amp tech show you what to do. Having an experienced professional close at hand can be useful, even for what you may see as a small fix.
     
  11. ECF

    ECF TDPRI Member

    18
    Jun 3, 2006
    Cape Girardeau, MO
    Thanks for all the info guys, but I was never planning on doing any of this work myself. I just wanted to know a little about it before I took it off to a shop.

    But, thanks for all the info, you've all helped out a lot.

    Take Care.
     
  12. zook

    zook Tele-Afflicted

    Aug 6, 2003
    Cochise, AZ
    This is inaccurate information. You can put a three prong cord on anything with a metal chassis. The green wire is attached to the chassis.

    It is chancy without an isolation transformer, but as it was commented the amp appears to have one.

    Winnie
     
  13. teerjerker

    teerjerker Tele-Meister

    224
    Apr 16, 2006
    jersey
    Maybe there's no reason to revive this thread, but I just looked at a Harmony 303B on eBay today. I was thinking, "hmm, what's wrong with this picture?" Well, I'll tell you what - there wasn't a little isolation transformer sitting on the top of the chassis. I looked at the picture of the schematic and as far as I could tell it wasn't drawn in, either. My Harmony amp is a 303A, and it does have the transformer. So there's where the confusion is coming from. Apparently Harmony revised the amp later on (?) to save a few bucks, or had a "junior" model alongside the 303A for those who wanted to save a few bucks.

    so...
    303A - safe
    303B - not so safe
     
  14. Wally

    Wally Telefied

    Mar 17, 2003
    Lubbock, TX
    http://schematicheaven.com/bargainbin/harmony_h303b.pdf

    Thanks for the heads-up, Teerjerker. So right you are. The Schematic Heaven scheme for the 'B' model has had the transformer added with a note from whoever modded the schematic about the safety aspect. I suppose this is a case of a company doing things correctly the first time with the 'A' model and then changing things in order to save a buck or two.
     
  15. Rizo

    Rizo Tele-Afflicted

    Apr 28, 2005
    Athens, OH
    A-hah! Ok, so that must have been the one I was offered...
     
  16. Brendan

    Brendan Tele-Meister

    458
    Feb 21, 2004
    Reviving this one again for a question....I own this 303B and have not used it. I cannot see the schematic linked above ( site down), but is that an isolation transformer I see to the right?
    [​IMG]
     
  17. pango_twango

    pango_twango Tele-Meister

    160
    Jul 15, 2007
    Seattle
    It's what the schem refers to as an IT, but it doesn't function as one that would (and should) go between the 120v and the circuit. The 300- series circuits did that; why I don't know. Not a bad idea to put a fuse in there as well. If my guess is right, on yours the 120 goes to the SPST on the back of the Volume pot.

    A lot of the Harmony/Kay/Silvertone circuits on the Schem Heaven site were re-drawn, and improved, by a guy who used to hang out on Stompbox forum (not sure if he still does). :p

    Another example similar to yours, only with the 120v going to the SPST on the Tone pot:
     

    Attached Files:

  18. Jead

    Jead TDPRI Member

    21
    Apr 28, 2010
    New Jersey
    Hi folks - Brand new to the forum and to Harmony Amps. I'm a little confused on the safe/unsafe model. I think, from what I've read, the "A" model is OK. Can I assume this is one of the "safe" amps (after installing a proper power cord)? Is there anything to worry about with the rust on the transformer or the funky looking tube? Thanks in advance. Here's what I'm waiting for:
     

    Attached Files:

  19. Jead

    Jead TDPRI Member

    21
    Apr 28, 2010
    New Jersey
    Anyone? Is there a definitive yes/no on the different models? I'll take a look inside when it arrives, but I do not want to monkey around with it. I'm hoping that it will be very staitforward to swap out the power cord. I guess an inline fuse would be wise??? I'm also interested in a line out jack. I'm not experienced at all with these low watt tubers and any help (besides take it to your tech) would be appreciated.

    Any Traynor YGM-3 people out there?
     
  20. Psyclone

    Psyclone Tele-Meister

    430
    Dec 14, 2007
    Grand Rapids, Ohio
    You know, I've had one of these amps around for a number of years. I generally leave it in the front porch all summer, and use it quite frequently. Now after reading some information here and about the internet, I've come to find that it's a death trap.

    Why do my favorite amps all conspire to kill me?
     
  21. Dan German

    Dan German Poster Extraordinaire

    As I understand it, the H303A (and the H303C--same thing for Canadian market) with the isolation transformer is not a "death trap" assuming you have put on a proper grounded power cord.
     
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