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  1. #1

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    Recently bought a polytone from the early 80's I think. Is very close to mint condition but half way through my 3rd gig with it the stupid thing dies. Very bad smell, fuse blown of course and just blows again when replaced. Assuming it is the power transformer that has overheated? Heard warnings about polytone's reliability before but should have taken them more seriously.
    Anyway, just wondering what to do from here. Have taken to a local guitar shop and the tech will look at it in the next 2 weeks. Assuming it is the power transformer, is it worth getting it replaced? Would it continue to have problems due to its closed back design and having no ventilation? I love the sound of this thing, it is the sound I've been wanting ever since playing jazz guitar. Should I gut it and use it as a 15 inch guitar cab and buy a mambo or similar head?
    Anyway, I know people still use polytones a lot, what do people do to make them more reliable? or are later models more reliable than the older ones?

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  3. #2

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    If it's from the 80s, it's very likely some components ( filter caps) are making the amp overheat & blow the fuse. You can't tell anything until you hear from your tech- it might be worth saving. The closed back design only causes problems in the 8" baby brute model. Power transformers are not available new as far as I know, but might be available on ebay from scrapped amps.

    Someone on the forum said that there are 2 kinds of polytones- those that never work, and those that work for ever. He has a point. Yours might be the second kind.

  4. #3

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    Franz, it blew. You can rule out 'work forever'. Hence, not the second kind but it did work so not the first kind either. Guess it is just a Polytone. It mostly works until it decides not to work...somewhat like me.

  5. #4

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    I've had an 8" Baby Brute for ten years and gigged it under pretty punishing conditions ... no problems. I don't hear negative reviews on Polytone from my many professional friends, except that the company itself provides zero customer service, which has been my experience, too. Other than the fact that some parts are unavailable, which can happen with many vintage amps, IMO, Polytones are as reliable as any other well known brand. I love Fender tube amps, but I've had more trouble with Fenders' reliability than Polytones'. Get it fixed, it probably will last a lifetime with reasonable maintenance.

  6. #5

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    I've never had a problem with my Polytone, which I've had for at least ten years, but then, I don't gig much, so I can't say I've asked a lot out of it....

  7. #6

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    Quote Originally Posted by Jabberwocky
    Franz, it blew. You can rule out 'work forever'. Hence, not the second kind but it did work so not the first kind either. Guess it is just a Polytone. It mostly works until it decides not to work...somewhat like me.
    C'mon Jabs, it was probably lying unused for decades. We all blow occasionally.

    I have a feeling Polytone went out of business with the death of the founder a year or 2 ago.
    I should have qualified my point about baby brute reliability. The others will still work if you leave them on overnight by accident….

  8. #7

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    Steve, maybe your tech can make some sense of these schematics posted here: Amplifier Schematics . Scroll to the Polytone section.

  9. #8

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    Back when I had a Polytone (early MiniBrute II) it had some heat sensitivity- losing volume as it got hot- and the reverb didn't work. I e-mailed them to get a recommendation for a local authorized amp tech in Minneapolis-St. Paul. They sent me the name,I took the amp in and got it fixed for less than $100. The reverb, it turned out, had never been connected (good QC there at Polytone) and there were a couple of caps that had to be replaced. It was a workhorse for years after that and AFAIK the pedal steel player I sold it to is still using it.

    I was never really sure if I liked the sound of that particular amp, at least for my playing, but have heard many people sound wonderful playing through those amps. I recurrently think I should pick another one up.

    My guess is that the OP's amp burned up a cap. It'd be worth having a tech look at it, IMHO.

  10. #9

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    I taught at a music shop from '94-2010, had a polytone minibrute in my room to use. It always worked fine. I remember that amp being in that store back when I took lessons there in the mid 1980s!

  11. #10

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    ike a lot of amps, they do better when not being moved around all the time, but a lot of Polytones tend to break dow when gigged.

  12. #11

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    Can you post a pic of the amp and a pic of the insides?

    Your power transformer is probably fine. A more likely suspect would be a filter cap or power transistor - both easy fixes for a good tech.

    I fixed several polyones in the last year. The circuits are quite simple and easy to work on if you can get the correct schematic. There seems to be a lot of mis-information on the web about repairing these.

    Here's a link to a Polytone rebuild I did.

  13. #12

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    I never had an amp that old that wasn't kind of a pain. I don't think there's anything inherently unreliable about Polytone amps, but if you're going to have an amp that's that old, you'd better have a good amp tech.

  14. #13

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    Quote Originally Posted by Franz 1997
    If it's from the 80s, it's very likely some components ( filter caps) are making the amp overheat & blow the fuse. You can't tell anything until you hear from your tech- it might be worth saving. The closed back design only causes problems in the 8" baby brute model. Power transformers are not available new as far as I know, but might be available on ebay from scrapped amps.

    Someone on the forum said that there are 2 kinds of polytones- those that never work, and those that work for ever. He has a point. Yours might be the second kind.
    I have an 8" Baby Brute that I have used for decades with no problems. I have also owned a number of other Polytones over the years and they have all been reliable. I would try to get it repaired.
    Keith

  15. #14

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    I have 4 Polytones, ranging from a 70s MBIII, to a 80s MBPA, to a 90s MBII. My favorite is an 80s Baby Brute. That 8" speaker in the one cubic foot volume cabinet is the best jazz amp ever. That sealed small cab has heat issues, however. It is a bear to keep the Baby in top kit. The 70s amps, if stored in damp places--basements--are starting to show unreliable IC-PREAMP chips. Moisture infuses right through the chip cases and corrodes the leads. The 70s chips are unavailable but can be subbed with newer op amps and dead bugged into the circuit. Three of my Polytones have been gigged heavily and have never posed any problems.

  16. #15

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    Quote Originally Posted by Greentone
    I have 4 Polytones, ranging from a 70s MBIII, to a 80s MBPA, to a 90s MBII. My favorite is an 80s Baby Brute. That 8" speaker in the one cubic foot volume cabinet is the best jazz amp ever. That sealed small cab has heat issues, however. It is a bear to keep the Baby in top kit. The 70s amps, if stored in damp places--basements--are starting to show unreliable IC-PREAMP chips. Moisture infuses right through the chip cases and corrodes the leads. The 70s chips are unavailable but can be subbed with newer op amps and dead bugged into the circuit. Three of my Polytones have been gigged heavily and have never posed any problems.
    I agree about the baby-brute being a great jazz amp. Mine had heat issues resulting in 2 failures over 25 years, and I recently had the polytone power amp replaced with a 180w class D power amp as used in the mambo amp, retaining the poly preamp and characteristic tone. Now the amp runs very cool, has better headroom, and weighs 15lb.

    Those 70s opamps are still available from chinese sources, although they might be copies or equivalents.

  17. #16

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    Mine has worked without complaint (not that I would be responsive to its complaints, anyways) for 30 years and has done a lot of travelling. It's the most reliable amp I've owned. Just sayin'.

  18. #17

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    heat issues with my 1997 mega brute 8in.
    loses vol and tone 2nd, 3rd set.
    prob buy mambo 8

  19. #18

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    Quote Originally Posted by tucson matt
    heat issues with my 1997 mega brute 8in.
    loses vol and tone 2nd, 3rd set.
    prob buy mambo 8
    I'm a big fan of mambo amps, have used the 8, and still have a 12" model- BUT the mambo 8 really doesn't sound the same as the Poly 8" model ( i.e. baby or mega). The cabinet is considerably smaller than the poly, which makes a big difference, and the tonal response doesn't have the typical polytone 'coloured' sound, which you like or you don't. It's quite different - good, but different, and very neutral-sounding.

    If you like the poly sound, get it fixed. It's not too hard to ventilate the cabinet safely, with a vent in the back panel. If you want a change, try the mambo 8.

  20. #19

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    I was in the process of restoring the fabric on the front of my 1978 102D last year when (while it was on) a great amount of white smoke that smelled bad came out of the holes and it ceased to work. I'm guessing some type of electronic cap(s) burst. I took the back off and besides it being lined with a ton of pink fiberglass getting in the way of everything, the wiring was a MESS. Spaghetti wiring everywhere.

    I'm considering a Mambo in the near future, but I still would like to get the 102D fixed. I'm not sure how much it will cost or if the typical amp repairman around here would be able to fix it. (The page of schematic diagrams posted is great.....thanks!)

  21. #20

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    Sounds from your description like one of the electrolytic caps crapped itself. Happens on amps of age. The circuit on the Polytone is simple. You should be able to find someone to fix it.

  22. #21

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    + 1 on that; but sometimes a blown cap takes an IC with it- happened to me once. Often it's an obsolete 4739 opamp. They can be substituted, but it's a pain & more expense. I always suggest replacing caps before firing an old amp up, on these poly threads.

    The poly wiring is an art form in itself. Still, they are well worth keeping going IMO.

  23. #22

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    +1 on the IC. Happened on my 70s MBIII. A tech can dead bug a suitable op amp right on top of the obsolete IC. This is a permanent fix. Those 70s Polytones sound great because they work the bejabbers out of the speaker. They are running at a 3-ohm load. The amp is really getting it on.

  24. #23

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    I replaced the stock opamps in the preamp section of my MB III with 5534 and 5532. Improved the sound and greatly reduced the background noise. Required some socket rewiring and a minor PCB mod, but was totally worth the effort.

  25. #24

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    Quote Originally Posted by Greentone
    +1 on the IC. Happened on my 70s MBIII. A tech can dead bug a suitable op amp right on top of the obsolete IC. This is a permanent fix. Those 70s Polytones sound great because they work the bejabbers out of the speaker. They are running at a 3-ohm load. The amp is really getting it on.
    Can you elaborate on this? I heard that argument before but never really understood why a lower load would influence tone.

  26. #25

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    You are drawing more power into a lower impedance speaker load causing the amp to work harder. The amp sounds warmer because there is a trifle more the at that power load. Actually, this makes no sense to me electronically but it's the explanation a Polytone dealer gave me in the 70s.
    Last edited by Greentone; 07-22-2014 at 12:13 PM.