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  • February 2, 2016 at 9:40 am in reply to: Sovtek Amps Anyone? #121251
    MrHaroldA
    Member
    Quote:
    Behind the first two pre tubes, there is what looks kind of like (but they’re not) two more tube covers. But I don’t believe they’re tubes. I doubt they are, at least. But I don’t KNOW, so that begs the first question: What the hell ARE those things? (I’ll try get pics hosted and posted)

    Those are the preamp filter capacitors C3 and C5 and should be present on all MIG60’s. Can you please post some pictures of your amps?

    November 24, 2014 at 10:24 pm in reply to: Sovtek Amps Anyone? #120409
    MrHaroldA
    Member

    [img]https://scontent-a-ams.xx.fbcdn.net/hphotos-xaf1/v/t1.0-9/10462819_677174669021703_7300845913027503504_n.jpg?oh=cc7331d3e5924d7cc4c8fb335fc033cf&oe=550C28FA[/img]

    … and I recently bought a MIG60 ;)

    July 30, 2013 at 9:37 am in reply to: Wanted Sovtek 2×12 #119290
    MrHaroldA
    Member

    Same here, but preferably in Europe.

    (yeah, old topic)

    March 25, 2013 at 12:27 pm in reply to: Sovtek Amps Anyone? #118869
    MrHaroldA
    Member

    I’ve ordered an upgrade output transformer at IGPW, hoping to fix the “nasal” sound of my Sovtek MIG50.

    I also made a schematic for it, since the old one was unreadible and has some different values on it than mine. Unfortunately, my serial number sticker is also unreadible, so I don’t know which version I have.

    Link to the schematic

    After tracing my head (pun intended) I changed the 47nF in the tonestack (blue) to a more Marhally 22nF (green) to get loads of extra lows and mids!

    tonestack.png

    My MIG50 is now almost at “pexi spec” for only a few bucks and some hours of spare time ;)

    March 19, 2013 at 12:46 pm in reply to: Sovtek Amps Anyone? #118851
    MrHaroldA
    Member
    Quote:
    Unfortunately I intruduced a bit of hum with the master volume, which I hope to solve by using shielded wire, which will cost me some top highs …

    Fixed that pretty fast after reporting it: I used the ground from the pilot light which added the hum. Switching the ground to that of the middle pot resolved all humming issues!

    Quote:
    I was wondering if anyone has the Sovtek catalogues somewhere (for download?) as I guess this won’t be my last Sovtek amp!

    Still looking for that catalogues! ;)

    November 14, 2012 at 10:32 am in reply to: Sovtek Amps Anyone? #118393
    MrHaroldA
    Member

    A fan here! ;)

    I got my Sovtek MIG50 only a few months ago, but I like it! I guess it’s one of the first series, set up as a modded Super Bass clone with the shared cathode on V1 (802R/220uF) and 100nF PI coupling caps. I measured 511V DC on the output tubes!

    I already did the following:
    * added a simple prePI master volume
    * rewired the power amp (cut away more than 1m (3′) of wire and used 18AWG)
    * changed all open jacks to cliffs
    * replaced all pots with Alpha’s (no drilling needed!)
    * removed the two 1nF bright caps
    * internally jumpered the inputs

    Unfortunately I intruduced a bit of hum with the master volume, which I hope to solve by using shielded wire, which will cost me some top highs …

    I was wondering if anyone has the Sovtek catalogues somewhere (for download?) as I guess this won’t be my last Sovtek amp!

    January 14, 2009 at 10:57 pm in reply to: Help needed identifying a Small Stone (v2/v3 mix?) #90726
    MrHaroldA
    Member

    This could be useful, but I’ll first try to place a good opamp or jfet based buffer before the SS…

    Quote:
    From R.G. Keen

    The loss of volume when engaged is correctable in the Issue J Small Stone
    by changing the gain of the two-transistor preamp at the input of the circuit.

    There are two 4.7K resistors at the emitters of the input transistors. One
    (R7) goes to ground from the emitter of Q1, the second (R42) connects the
    emitter of Q2 to the emitter of Q1. Those two resistors set the feedback gain
    of the two-transistor compound.

    Increase the 4.7K between the emitters (R42) to increase the gain. Start with
    10K. Be aware that this will affect the stage biasing, so the headroom may
    be affected; I don’t think this will really be a problem.

    The silly thing *ought* to have included a JFET buffer in front of it for
    buffered bypass and a bit of gain in the first place.

    January 14, 2009 at 8:54 am in reply to: Help needed identifying a Small Stone (v2/v3 mix?) #90693
    MrHaroldA
    Member

    @Fender&EHX4ever;and Ned Flanders:

    Did you fix the volumedrop on your Small Stones?

    January 13, 2009 at 8:15 pm in reply to: Help needed identifying a Small Stone (v2/v3 mix?) #90656
    MrHaroldA
    Member
    Quote:
    What’s the date code on the pot? I’d like to add it to my list.

    Here ya go: v3_issue_h_pot_.jpg

    And the bottom of the PCB:

    v3_issue_h_bottom_.jpg

    I just purchased the schematic from RonSound, so soon I’ll be able to tell if this really is an ‘Issue H’ Small Stone…

    January 13, 2009 at 12:20 pm in reply to: Help needed identifying a Small Stone (v2/v3 mix?) #90623
    MrHaroldA
    Member
    Quote:
    RonSound is me.

    Oops! ;)

    Well, I just thought that if the schematic was present in the public domain, I don’t have to pay for it. I also thought that if it turns out not to be an “Issue H”, I’ll have absolutely no use for the schematic…

    January 13, 2009 at 12:02 pm in reply to: Help needed identifying a Small Stone (v2/v3 mix?) #90620
    MrHaroldA
    Member

    Hey, just a crazy thought: there are “F” markers on the PCB… This won’t have anything to do with an “Issue” of some kind? ;)

    January 13, 2009 at 12:00 pm in reply to: Help needed identifying a Small Stone (v2/v3 mix?) #90619
    MrHaroldA
    Member
    Quote:
    It’s likely an Issue H board (5 op-amps / 4 transistors). Essentially, it’s the same as the Issue J, just earlier by a year or 2. The burned resistor is a 47 ohm.

    What’s the date code on the pot? I’d like to add it to my list.

    Does anyone have a schematic of the Issue H? http://www.ronsound.com has one, but they want $5 for it…

    I’ll have a look at the pot code this evening and try to get better pictures of the front and bottom of the PCB.

    Thanx for the help so far!

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