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    Help with Dynaco MK II wiring

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    Chris Scott

    Posts : 6
    Join date : 2017-05-09

    Help with Dynaco MK II wiring

    Post by Chris Scott on Wed May 10, 2017 6:23 pm

    Hi everyone, brand-new guy here....I have a pr. of MK II units here that I'm reconditioning for a friend. I'm not very good with the tech aspect of these things (assembled and worked on a few guitar tube amps) so go easy on me please ...just a few questions;

    First, is re. the selenium rectifiers - will an N4007 diode be sufficient for this as a replacement? - I read here that "any diode will work", but just want to make certain.

    Next is the 12 ohm bias resistor - will 1/2 watt flameproof be sufficient as well? - I wasn't able to find any precision resistors in this value so I plan to just connect up a 10 and a 2.5 ohm in series - no issues with this?

    And lastly, they came to me in poor physical condition, but in (allegedly) working order, and have had the original common/8/16 speaker terminals replaced with a simple +/- pr. of screw terminals. I'm wondering if someone can supply me with a simple diagram re. how this part should be wired up, just to confirm that how it's currently wired is correct?

    Thanks in advance!
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    j beede

    Posts : 401
    Join date : 2011-02-07
    Location : California

    Re: Help with Dynaco MK II wiring

    Post by j beede on Wed May 10, 2017 9:56 pm

    A 1n4007 is an appropriate replacement for the Selenium stack. It may not be a "drop in" replacement as the operating range of your bias pot may not be wide enough to accommodate the smaller forward drop across the diode versus the Selenium rectifier. Adding another 10KOhms in parallel with the stock 10KOhms to ground in the bias divider may be necessary. Be sure to pay attention to polarity when you replace the diode and the 100µF bias supply cap. The bias voltage is negative.

    Regarding the output transformer wiring... black is common. If the OT is stock, yellow is the 16 Ohm tap and orange is the 8 Ohm tap.

    Bob provides schematics online, have you found one for the MkII?
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    tubes4hifi
    Admin

    Posts : 1364
    Join date : 2008-11-30

    Re: Help with Dynaco MK II wiring

    Post by tubes4hifi on Thu May 11, 2017 9:34 am

    Dynaco MK2 manual is here (along with all the other Dynaco manuals)
    http://tubes4hifi.com/downloads.htm

    Chris Scott

    Posts : 6
    Join date : 2017-05-09

    Re: Help with Dynaco MK II wiring

    Post by Chris Scott on Thu May 11, 2017 1:42 pm

    Hey thanks tubes4hifi and j beede, appreciate the info and links!

    ...oh, and the 12 ohm resistor can be a 1/2 watt as well, correct? - the example shown in some of the photos I've seen looks to be a 1 watt or larger, but as there's no wattage rating called for on the parts chart I thought I'd better ask...
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    tubes4hifi
    Admin

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    Join date : 2008-11-30

    Re: Help with Dynaco MK II wiring

    Post by tubes4hifi on Mon May 22, 2017 8:16 pm

    yes, the 12 ohm can be a 1/2w, or even a 1/4 watt

    Chris Scott

    Posts : 6
    Join date : 2017-05-09

    Re: Help with Dynaco MK II wiring

    Post by Chris Scott on Tue May 23, 2017 7:41 pm

    Thanks tubes4hifi!

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