The Dynaco Tube Audio Forum

Dedicated to the restoration and preservation of all original Dynaco tube audio equipment - Customer support for Dynaco VTA tube amp kits, all Tubes4hifi.com products and all Dynakitparts.com products


    Mark III rebuild troubleshooting...no output!!!

    Share

    steve's garage

    Posts : 24
    Join date : 2015-11-01

    Re: Mark III rebuild troubleshooting...no output!!!

    Post by steve's garage on Tue Nov 17, 2015 4:03 am

    Seems like success. Through my stereo amplifier I'm getting great audio and its reasonably loud but not as loud as I expected 60 tube watts to be. I've got it going into an 8ohm 150w rated speaker. If I turn the pre-amp (amplifier technically) up to a certain point I get crackles. Any ideas?

    audiobill

    Posts : 270
    Join date : 2014-03-13
    Location : Philadelphia

    Re: Mark III rebuild troubleshooting...no output!!!

    Post by audiobill on Tue Nov 17, 2015 9:43 am

    There are some great pedal format guitar preamps......

    PeterCapo

    Posts : 386
    Join date : 2008-12-05

    Re: Mark III rebuild troubleshooting...no output!!!

    Post by PeterCapo on Tue Nov 17, 2015 9:54 am

    steve's garage wrote:Eyelet 2 only has one wire connected to it but bias pot wiper(middle lug is connected to the 50uf bias cap.
    My error. The other end of the wire from E2 as well as the lead from the 50uF bias capacitor go to the wiper.


    Congratulations.

    wildiowa

    Posts : 126
    Join date : 2012-03-19

    Re: Mark III rebuild troubleshooting...no output!!!

    Post by wildiowa on Tue Nov 17, 2015 11:08 am

    DUDE!!!! Four pages of troubleshooting and you were plugging your gee-tar directly into the amp??? You need a hot preamp for that!!! The board knows me as the musician guy who used Dynas in bands and PA stuff all through the 60s 70s and 80s and when I saw you were plugging your guitar directly in I knew what was up....and when you get a preamp in front of it you will be blown away. It will kick Marshall or Mesa a$$. Many early builders put stock Mark IIIs directly into their amp heads (Sunn specifically, and a guy here in Omaha who built many locally under the "Furnace" label). And yes, all my Dynas also have 1/4" jacks, much to the disdain and ridicule of hifi purists. Probably wasn't a good idea to ruin the chassis and now I wish I hadn't but it was so convenient on stage to hook up speakers and stuff we drilled it out and went band standard. That hurts the value of the old stuff.

    Have fun the only thing I found in gigging them is it's a hassle to carry them around and takes additional time to set up but holy crap either guitar or bass it is a monster setup. Properly working it will have a ton of gain but you need enough to push it hard with your preamp. Many pedals are made to go directly into a low-gain guitar amp input and you need to jack up the master volume enough to get line level sufficient to drive the Dyna. Since you are using hifi equipment for band use you will need to experiment to get the right balance of preamp input to get the gain and/or overdrive you want. I'd be interested to hear how this progresses.

    PeterCapo

    Posts : 386
    Join date : 2008-12-05

    Re: Mark III rebuild troubleshooting...no output!!!

    Post by PeterCapo on Tue Nov 17, 2015 11:13 am

    GreggW wrote:Sounds like you're using the guitar as a preamp. Many guitar pickups have a very low voltage output.

    GreggW nailed it.

    corndog71

    Posts : 451
    Join date : 2013-03-19
    Location : It can get windy here

    Re: Mark III rebuild troubleshooting...no output!!!

    Post by corndog71 on Tue Nov 17, 2015 12:51 pm

    steve's garage wrote:Seems like success. Through my stereo amplifier I'm getting great audio and its reasonably loud but not as loud as I expected 60 tube watts to be. I've got it going into an 8ohm 150w rated speaker. If I turn the pre-amp (amplifier technically) up to a certain point I get crackles. Any ideas?

    What's the sensitivity of your speaker? Ultimately you need a preamp to give the amp a good clean signal to work with.

    PeterCapo

    Posts : 386
    Join date : 2008-12-05

    Re: Mark III rebuild troubleshooting...no output!!!

    Post by PeterCapo on Thu Nov 10, 2016 9:19 pm

    Earlier in this thread there was discussion of the proper orientation of the diode and the meaning of the "+" in earlier versions of the Mark III schematic.  I wanted to follow up on this to report that my interpretation of the "+" in the schematic was incorrect, referring to Post n°19 and especially Post n°28.

    At the same time, it is correct that the red/black lead goes to the diode's cathode.

    For the correct interpretation of the "+" on the schematic, have a read here: http://audiokarma.org/forums/index.php?threads/st-70-selenium-rectifier-vs-diode-polarity-enigma.741937/

    Apologies for the error.

    Sponsored content

    Re: Mark III rebuild troubleshooting...no output!!!

    Post by Sponsored content Today at 11:55 am


      Current date/time is Tue Dec 06, 2016 11:55 am