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    Mk IV rebuild question

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    lagunamike

    Posts : 7
    Join date : 2015-09-18

    Mk IV rebuild question

    Post by lagunamike on Wed Oct 07, 2015 3:16 pm

    New here and just getting started on some working Mk IV's after completing a new build (from an unbuilt 1976 PAS3 kit) PAS3 with the ZMods and upgrade supplies. I can only find new design Mk IV boards on Curcio's site. Are there any others?? Also - dumb question - what do you all use to polish old Dynaco chassis???

    stewdan

    Posts : 160
    Join date : 2010-03-07
    Age : 78
    Location : Houston Texas

    Re: Mk IV rebuild question

    Post by stewdan on Wed Oct 07, 2015 3:36 pm

    Hi --- Roy at the Tubes4HiFi website used to have VTA Mk4 Boards available, but I don't see them listed now. You might send a message to Roy at info@tubes4hifi.com and see what he says.
    Stew

    lagunamike

    Posts : 7
    Join date : 2015-09-18

    Re: Mk IV rebuild question

    Post by lagunamike on Wed Oct 07, 2015 3:46 pm

    Thanks stewdan. I know that Mk IV's are very similar to half of a ST-70, and I could probably make my own boards from Bob's designs for them, but Curcio's kits and capacitor replacement boards are reasonable and are drop in.

    PeterCapo

    Posts : 380
    Join date : 2008-12-05

    Re: Mk IV rebuild question

    Post by PeterCapo on Wed Oct 07, 2015 7:11 pm

    Dynakitparts.com has fresh MKIV PC boards.  Shannon Parks of Parks Audio has his "Poseidon" board that I believe fits the MkIV (as well as the MkIII).  Triode USA also has a board for the MKIV.

    As far as polishing an old Dynaco chassis, I’d use polish very sparingly, carefully and only as a last resort.  Flitz liquid polish for instance comes with a warning saying not to use it on electroplate like the old Dynacos had.  Assuming polishes are generally similar, I’d opt for a soapy washcloth first, then automotive paste wax.

    lagunamike

    Posts : 7
    Join date : 2015-09-18

    Re: Mk IV rebuild question

    Post by lagunamike on Wed Oct 07, 2015 9:31 pm

    Peter, thanks for the reply. I had already checked dynakitparts and triode. Dynakitparts only has the stock boards for the IV. Triode only shows their boards for the Mk II and III. Not sure the B+ voltages are the same between the III and IV - I know they are between the ST-70 and the IV. I missed the Parks Audio site - very interesting, but is more for the person that likes to take it from scratch a bit more than I wanted. I'll probably go with Joe Curcio's dual triode drop in board kits and cap replacement kits. I want to keep the GZ34 rectifier. I'll post some pics after everything is done.

    As far as polish, I found a general metal polish at a home show that works well. I've used Flitz before and it is a bit agressive. Chrome polish for autos also works well, but has more petroleum in them - so more conductive/flammable.

    Mike

    DynakitParts
    Admin

    Posts : 181
    Join date : 2008-11-30

    Diytube MK IV board

    Post by DynakitParts on Thu Oct 08, 2015 10:37 am

    Mike,
    Shannon Park's MK IV upgrade board is very good...He provides a BOM for all the parts and a manual for installation and setup. Great online support through his DIYtube forum.

    Don't expect much support from Curcio....

    Kevin @ Dynakit

    tubes4hifi
    Admin

    Posts : 1261
    Join date : 2008-11-30

    Re: Mk IV rebuild question

    Post by tubes4hifi on Thu Oct 08, 2015 11:55 am

    I agree with Kevin, don't use the Curcio boards, they are poorly made and poor support.
    I usually send my customers to Shannon Parks site for MK4 boards, unless they want to use my MK3 boards,
    but I have traces where the mounting holes would need to be which would need to be cut, isolated, and jumpered.
    I sold them for a couple years, but selling 1 or 2 pair a year wasn't worth the trouble.
    Here's the link for Shannon's boards . . . . http://www.diytube.com/phpBB2/viewtopic.php?f=11&t=923

    corndog71

    Posts : 444
    Join date : 2013-03-19
    Location : It can get windy here

    Re: Mk IV rebuild question

    Post by corndog71 on Thu Oct 08, 2015 1:53 pm

    I hate to disparage Curcio's MkIV boards as I used them on mine. The PCB quality isn't the greatest out there. Also, If you go with the driver upgrade board AND the cap upgrade board you will have lots of fun integrating the two as Curcio completely failed to consider this in his documentation. Both upgrades assume the amp is stock. I found myself scratching my head a lot during the builds.

    The upside is that Curcio's circuit does sound very good.








    PeterCapo

    Posts : 380
    Join date : 2008-12-05

    Re: Mk IV rebuild question

    Post by PeterCapo on Thu Oct 08, 2015 2:25 pm

    I'm inclined to agree with corndog71 here.  I believe Mr. Curcio's designs are probably very good, but, in my experience, he has not always been as thoroughgoing and communicative as he should be.  I have felt there are certain deficiencies in some of the various documents he has generously made available either on his website or with the items I bought from him.  While this is not necessarily a reason to pass him by, it might be good to be ready to figure some things out if you do decide to use his products.

    This seems as good a time as any to get in a plug for the Dynakitparts board.  Yes, it's the original circuit - but there are many of those who, like me, feel the original circuit is still very much up to the task and should not be overlooked.

    lagunamike

    Posts : 7
    Join date : 2015-09-18

    Re: Mk IV rebuild question

    Post by lagunamike on Mon Oct 12, 2015 2:12 pm

    Thanks to all for the replies and advice. Especially to corndog for the excellent photos - if mine are that "photogenic" when done, I'll put some pics up.

    It looks like I may have made a less than optimum decision - I went with Curcio's stuff, although I could probably still cancel the order. I did have several back and forth emails with Joe about modifying non-stock Mk IV's, and he was prompt to answer. I eventually decided to put my Mk IV's back to stock and check their performance. After 15 years of being idle, they started up, biased ok, and played fairly well.

    I hope this all works out, when I ask for advice, I should probably take it http://illiweb.com/fa/i/smiles/icon_pale.gif . If I'm not happy with the quality of the boards or parts from Curcio, I could send them back and just use the capacitor upgrade with Shannon's input boards.

    I'll post my experiences once the project is complete.

    Mike

    PeterCapo

    Posts : 380
    Join date : 2008-12-05

    Re: Mk IV rebuild question

    Post by PeterCapo on Mon Oct 12, 2015 4:49 pm

    Not too sure why Mr. Curcio’s PCB quality is called into question sometimes.  The only criticism I’ve heard specified from time to time is that his PCBs are single layer and lack plated-through holes.  I do not know from my own observation that this is the case, but I seem to recall reading this.

    I’ve worked on different kinds of PCBs both at home and when I worked in the electronics industry a few years back.  For our purposes here, single-sided boards without plated-through holes is perfectly fine, IMO, if this is indeed the case with Mr. Curcio's boards.  

    Multilayer boards are needed if you are building something with ICs for instance, and you need the layers to fit all the circuitry into the limited space allowed for a single PCB.  You need PTHs to connect the various internal layers of the PCB.  Plated-through holes also allow more contact area with component leads, securing them better.  This is all fine if you’re building a microprocessor-controlled missile subject to vibration hanging under the wing of an F-18 but isn’t really required for tube amps.  Plated through holes can also make rework more difficult.

    The original, 50+ year old phenolic PCBs in the Dynacos were single layer without PTHs for the pads (excepting the eyelets) and are still functioning to this day.  Problem with the original phenolic Dynaco boards is that the pads and traces delaminate easily from the phenolic substrate during rework.  This should not be nearly as much of a problem for any PCB currently in production because, for some time now, the foil layer bonds far better to the substrate.  As long as the pads and traces on Mr. Curcio’s boards do not delaminate easily (seems unlikely they would), his boards should be fine.


    Last edited by PeterCapo on Mon Oct 12, 2015 9:56 pm; edited 3 times in total (Reason for editing : Clarification.)

    boeingpilot

    Posts : 9
    Join date : 2015-06-20

    Re: Mk IV rebuild question

    Post by boeingpilot on Mon Oct 12, 2015 6:03 pm

    My .02....

    I've used both the Curcio and tubes4hifi stuff over the years. Both vendors have been great to answer questions when needed. As for integration of different kits, not a totally unknown situation. My ST70 had the Curcio cap board mod, and then I went for the VTA drive board this year. After conferring with both Joe and Roy, both gave me the same answer of what to change where (there was a resistor change required). It's the nature of the beast, multiple mods have to be thought thru.

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