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    Mismatched Mono Block Pair, Need Advice

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    freakmech

    Posts : 4
    Join date : 2012-12-09
    Age : 42
    Location : Maryland

    Mismatched Mono Block Pair, Need Advice

    Post by freakmech on Sun Dec 09, 2012 11:30 pm

    Hello, new to forum though Ive been reading for a few weeks. I recently have been interested in building a small, low watt tube amp to compliment some other DIY goodies ive been building. DAC, modded PS1 CD player, Overnight Sensation speakers etc... All this gear is based around my workshop/ computer usage. I build a lot of electronics, mostly guitar and home audio related. Ill admit ive never built any tube gear although I have repaired some tube gear, namely guitar amps. Im not entirely comfortable working on high voltage gear but would like to build an amp as im very confident in my skills.

    Anyhow, I was looking online for a small tube amp kit 5-10 watts. Then I remembered that a few years ago my brother gave me a pair of Dynakit mono-blocks and a McIntosh Record Compensator that were saved from Katrina flooding down in new Orleans were I once lived. I stored them away after a brief look at them because at the time I was not at all comfortable working on them. Deadly voltages were something I was not fond of. I completely forgot about them until coming across a kit on Ebay while searching for a small tube amp kit. So I pulled them out and started researching them which brought me here.

    From what I can determine, though looking very similar, I actually have an "early?" big board Dynakit MkII and a MkIII. Im looking for advice as to what to do with them. Im tempted to convert them to matching MkIII's. However Im not sure if this is kosher. I have respect for vintage gear and would hate to hack these up. At the same time I have them and would like to put them to service.

    So far I have determined these things:

    I. I need to see if the transformers are still working. I have not plugged them in as I do not want to charge the caps if im going to be working on these in the near future.
    II. If transformers do work, probably will need to replace everything but the tranns and chassis
    III. If im going to replace most every thing, im ok with updating boards and upgrading to cap boards.

    So with that being said, any advice on where to start? Should I build them as two MkII's or two MkIII's? Should I sell them to someone that might do better at restoring them? Should I try trading them for something better suited like a ST-35 or SCA-35?

    Again, im just looking for advice, Thanks in advance. will post pictures in a few minutes. These things are really dirty.


    Last edited by freakmech on Mon Dec 10, 2012 2:42 am; edited 1 time in total

    freakmech

    Posts : 4
    Join date : 2012-12-09
    Age : 42
    Location : Maryland

    Re: Mismatched Mono Block Pair, Need Advice

    Post by freakmech on Sun Dec 09, 2012 11:43 pm






    freakmech

    Posts : 4
    Join date : 2012-12-09
    Age : 42
    Location : Maryland

    Re: Mismatched Mono Block Pair, Need Advice

    Post by freakmech on Mon Dec 10, 2012 1:59 am

    Hate to clutter the forum but im really thinking a ST-35 is what im looking for. Im interested in a kit, either the Triode kit or Dynaparts kit. Any preference? Would be willing to sell my mono-blocks and McIntosh C-8 if anyone willing to make offer. Obviously im looking to sell at a price close to what a kit will cost. Though, im not against the idea of getting these monos running.

    rmyauck

    Posts : 9
    Join date : 2012-02-18

    Re: Mismatched Mono Block Pair, Need Advice

    Post by rmyauck on Thu Dec 13, 2012 10:28 am

    Down load the manuals from this site , and I think you can upgrade the Mark II to III. Even with highly efficient speakers the added headroom can be nice for music peaks in highs and lows plus the added bandwidth at normal listening volumes.

    Anyway easy to work on amps and not costly to rebuild. Just be careful to discharge caps and only work with one hand in there if powered up.

    Best to recap at the least so you don't risk the Trans. and check resistor values as some drift.

    Also clean tube pins and sockets and other connections.

    With today's higher line voltages try to set the bias as low as you can go where it still sounds good for best output tube life.

    Diode mod listed above is a good one with newer faster UF4007's for a few cents more!

    Google mark III rebuilds also.

    Randy

    GP49

    Posts : 735
    Join date : 2009-04-30
    Location : East of the sun and west of the moon

    Re: Mismatched Mono Block Pair, Need Advice

    Post by GP49 on Thu Dec 13, 2012 2:25 pm

    It is not difficult to rebuild Mk II to Mk III, unless you need a 4Ω tap, which is not present on the Mk II output transformer.

    You are planning a total rebuild, anyway. You need to adjust some values in the power supply and add the Mk III choke. Rectifier changes from 5U4 to GZ34/5AR4. With these changes, higher-voltage power supply electrolytics will be required (but you're not using the old quad cap anyway, are you?). Output tubes change from EL34 to 6550, KT88, etc., and the cathode resistor for biaset changes. A comparison of the two schematics will tell the tale.

    Problem is, the EL34 SOUNDS different from the 6550 and KT88 types. I like it better. So after doing the upgrades on my Mk II, I went back to the EL34s. All else was already rebuilt and remains that way; a different
    bias adjustment setting was the change accompanying the EL34s.

    Lman

    Posts : 1
    Join date : 2012-12-21

    Re: Mismatched Mono Block Pair, Need Advice

    Post by Lman on Fri Dec 21, 2012 5:43 pm

    I've rebuilt amps in the same condition as your amps and, if I were you, I would sell the monoblocks and purchase the ST-35 kit. Easier for you and the ST-35 is a great amp.

    freakmech

    Posts : 4
    Join date : 2012-12-09
    Age : 42
    Location : Maryland

    Re: Mismatched Mono Block Pair, Need Advice

    Post by freakmech on Fri Dec 21, 2012 6:21 pm

    Lman wrote:I've rebuilt amps in the same condition as your amps and, if I were you, I would sell the monoblocks and purchase the ST-35 kit. Easier for you and the ST-35 is a great amp.

    I appreciate everyones input but im kind of thinking about going this route. The ST35 is really what im looking for wattage wise. Its for a small system in my workshop.

    rmyauck

    Posts : 9
    Join date : 2012-02-18

    Re: Mismatched Mono Block Pair, Need Advice

    Post by rmyauck on Sat Dec 22, 2012 6:49 am

    One thing with the extra power you will get the headroom and extra bandwidth over a low power amp! Even with efficient speakers it will still be noticeable. Keep them for the house!

    For more info on ST-35 check out diytube.com site for Triodes's version. Dave Gillespie's EFB mod is a must for tube life and sonics!

    Randy


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