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Mosvalve 300w 15in combo for 350...good buy?

Discussion in 'Amps and Cabs [BG]' started by irishryno, Jan 16, 2012.


  1. irishryno

    irishryno

    Jan 22, 2008
    Alabama
    I have it on layaway at my favorite music store and they have a great history of taking care of me, and my shoppingwith them. It looks brand new and sounds good, I just want to make sure its worth it. It does have a valve preamp.
     
  2. bongomania

    bongomania Gold Supporting Member Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    Be aware that Tubeworks is out of business, and the last owners, Genz Benz, have very recently said they do not have parts or schematics for many of those amps, and that some of the parts are long-ago discontinued and rare.
     
  3. someparts

    someparts

    Nov 22, 2010
    Ohio
    Around $200-250 would be a better retail price I think.
     
  4. will33

    will33

    May 22, 2006
    austin,tx
    Yeah, I have the 300watt head version of those. Great sounding amp but yes, he said it's the MOSFET's that are no longer made. I'm not tech enough to do this, but there are plenty of techs who probably could figure out a repair using stuff that is in production although, I would imagine it could quickly get more expensive than the amp is worth with the time involved circuit tracing, parts sourcing, making modifications, etc.

    Somebody else in that thread said Genz did send them a schematic a few years ago. There is also supposedly a Tubeworks fan website where people post schematics but even getting one doesn't mean you can get parts. Personally, I think that sucks as they were great sounding amps but that's the way it is. Know this before you buy one.
     
  5. Schematics are available on the web for this amp...just search on RT3300 amp and they'll show up. As I said before and bongomania mentioned, some of the parts are getting hard to find, specifically the power MOSFETS. I found some back a few years ago and bought all they had (there are other amps that use them too, such as Trace Elliot, and I repair amps as a side job so I figured I'd be proactive). You can still find them but you won't find them at your local Radio Shack, that's for sure.
    The P/Ns for the power FETS are 2SK135 and 2SJ50 FWIW....
     
  6. will33

    will33

    May 22, 2006
    austin,tx
    So where would I find them?:D. A set of spares would mean I'll be hanging onto my MosValve for a very long time.
     
  7. 1pair Transistor HITACHI TO-3 2SK135/2SJ50 K135/J50 | eBay

    Ebay is about the only place I've seen them for sale for the past few years. I bought 15 pairs about 8 years ago for $15 a pair from a place like Newark or Allied...I've gone through half of them....I hope I never run out.
     
  8. someparts

    someparts

    Nov 22, 2010
    Ohio
    You've gone through that many? Seems excessive?
     
  9. Not when one fixes amps...Some older Trace Elliots, Marshalls, Peaveys use them. Up until 2 years ago, I was repairing 2-300 amps a year...I took a sabbatical and then throttled back on the repairs...now it's about 75-100 a year :D
     
  10. someparts

    someparts

    Nov 22, 2010
    Ohio
    Whoops, didn't read that you repaired amps. Thought it was for one well-gigged amp.
     
  11. irishryno

    irishryno

    Jan 22, 2008
    Alabama
    I asked the store owner to consider a lower price since I would not be able to readily get parts for repair, not to mention any repairs would have to be done 90 miles away. There is nothing local. My big question I guess would be, would I be willing to bite the bullet and pray this would work for a few years, allowing me to save up for a mesa, which is what I really want. It looks in great condition. and Sounds great. It does have some dust in the pots and could do with a cleaning interiorly. Thank you for all the insight guys. Will keep you guys posted.
     
  12. Consider the fact that it is probably over 20 years old and still works fine...if it was played by the previous owner fairly often, then you can consider it's past the "infant mortality" stage. From here on out, if you take care of it, like keep dust out of it, make sure the fan is clean (and works), and don't play it hard in the baking sun where the temps can soar inside the amp, you should be good to go. The biggest killer of electronics is heat...buildup of heat can be caused by dust caked on heatsinks and/or circuitboards, dirty fans (dust on the leading edges of fans reduces their efficiency by up to 75%), keeping a black piece of electronic equipment out of the direct sun, etc etc...

    Good luck!
     
  13. irishryno

    irishryno

    Jan 22, 2008
    Alabama
    Great news. I spoke with someone at Genz Benz and the sent me the links which I will post now of replacement mosfets. Both companies are in England so I will have to wait and pay more shipping, bout worth it since I now know I can get parts. Also, he made me aware of a hidden problem with the RT 3300. The 5 pins tying the solid state to the preamp tend to break and are hard to notice that a break has occured. He recommends getting a flexible wire soldered in place of the pins professionally and this will relieve most problems with the board. Now for the juicy info. Again, thanx for you help.

    Exicon MOSFETS:


    Lateral Mosfet


    2SJ50=ECF10P16


    2SK135=ECF10N16





    Magnatec MOSFETS:


    Buy MOSFET P-channel MOSFET,2SJ50 7A 160V Magnatec 2SJ50-MAG online from RS for next day delivery.


    Buy MOSFET N-channel MOSFET,2SK135 7A 160V Magnatec 2SK135-MAG online from RS for next day delivery.
     
  14. will33

    will33

    May 22, 2006
    austin,tx

    Awesome info, thanks. And thanks to the folks at Genz for sending it your way, and you for sending it our way.
     
  15. BassmanPaul

    BassmanPaul Gold Supporting Member

    Aug 25, 2007
    Toronto Ontario Canada
    Just as a point MOSFETs in parallel will need to be matched for gate voltage. this allows them all to pass about the same current. If they are not matched you could get the situation where one device is doing more work than the rest.
     
  16. I've run into this with bipolar transistors (hence the need for emitter resistors) but my experience with MOSFETS has been that they can be paralleled up as they tend to share current naturally due to increased resistance of the one which has started to carry extra current. If necessary, you could place a .01 ohm (wattage TBD) in series with each Mosfet to help with any imbalances but I've found that to be unnecessary for the stuff I've built.
     
  17. irishryno

    irishryno

    Jan 22, 2008
    Alabama
    Amp is now parked in the living room and has disturbed the neighbors, so primary functionality test was a success. I have ordered 10 of each and should have them in a couple of weeks. This thing is incredible. The sound and the volume are incredible. Only thing that bothers me is a present hum at volume. It's not my bass, it's quiet on the church pa and on my other amp. Any recommendations?
     
  18. BassmanPaul

    BassmanPaul Gold Supporting Member

    Aug 25, 2007
    Toronto Ontario Canada
    I've never had such a problem with bipolar devices. Matching is a simple procedure and should be done for reliable operation.
     

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