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


    My M125 project

    Share
    avatar
    corndog71

    Posts : 668
    Join date : 2013-03-19
    Location : It can get windy here

    My M125 project

    Post by corndog71 on Wed Mar 21, 2018 11:05 am

    So last year I bought a used pair of M125 amps.  I've been itching for these amps ever since I discovered VTA and this forum.  As much as I can appreciate the compact and heavy guage stainless steel chassis, layout-wise it left a lot to be desired.  So I downloaded Front Panel Express' app and went to work.  So far I have produced the first plate and am blown away by the finished product!  I especially love the matte finish which leaves no fingerprints!
    I'm still waiting on parts to come in and eventually I'll have to order some tubes.  It'll be a few more weeks before I can get them up and running but I couldn't wait any longer to share the pics.

    VTA M125 125 watt amplifiers - stock by Rob C, on Flickr

    It started with a sketch. by Rob C, on Flickr

    Untitled by Rob C, on Flickr

    594F3F6C-C12C-4650-B36A-2CA7ECC7A1D0 by Rob C, on Flickr

    388A0B27-344B-414F-84D8-DC6FB15702EC by Rob C, on Flickr


    Custom VTA M125 by
    Rob C
    , on Flickr


    Last edited by corndog71 on Mon May 14, 2018 9:59 am; edited 1 time in total
    avatar
    Roy

    Posts : 178
    Join date : 2018-01-14
    Location : Netherlands, Europe

    Re: My M125 project

    Post by Roy on Wed Mar 21, 2018 11:29 am

    *like* Very Happy
    avatar
    cci1492

    Posts : 192
    Join date : 2016-05-09
    Age : 57
    Location : Bergen County NJ

    Re: My M125 project

    Post by cci1492 on Wed Mar 21, 2018 1:11 pm

    It's a thing of beauty!
    avatar
    10-E-C

    Posts : 199
    Join date : 2014-02-12
    Age : 64
    Location : upper east tn

    Re: My M125 project

    Post by 10-E-C on Wed Mar 21, 2018 3:34 pm

    Just an observation, seems to me the signal tubes should be as far away from the transformers as you can get for noise reduction.
    avatar
    pedrocols

    Posts : 115
    Join date : 2014-11-24
    Location : Western MA

    Re: My M125 project

    Post by pedrocols on Wed Mar 21, 2018 7:08 pm

    So it looks like is now twice as big.
    avatar
    bluemeanies

    Posts : 258
    Join date : 2015-02-09
    Age : 68
    Location : Folsom Pa.

    Re: My M125 project

    Post by bluemeanies on Wed Mar 21, 2018 8:08 pm

    What you did takes a lot of talent...in that respect I applaud but I have to agree with 10-E-C...especially the tube in between the transformers...rectifier tube I imagine.
    Heat and more Heat not a good mix.
    Besides why fix something that's not broken? I can understand if you wanted wood not liking the industrial look but changing the design to look like a shuffleboard?
    avatar
    cci1492

    Posts : 192
    Join date : 2016-05-09
    Age : 57
    Location : Bergen County NJ

    Re: My M125 project

    Post by cci1492 on Wed Mar 21, 2018 9:13 pm

    This one has the signal tubes by the transformers:

    avatar
    corndog71

    Posts : 668
    Join date : 2013-03-19
    Location : It can get windy here

    Re: My M125 project

    Post by corndog71 on Thu Mar 22, 2018 9:19 am

    bluemeanies wrote:What you did takes a lot of talent...in that respect I applaud but I have to agree with 10-E-C...especially the tube in between the transformers...rectifier tube I imagine.
    Heat and more Heat not a good mix.
    Besides why fix something that's not broken? I can understand if you wanted wood not liking the industrial look but changing the design to look like a shuffleboard?

    Ever seen a Dynaco MK4?  Mine is a similar layout with regards to the PT, rectifier, and OT.  I also added extra vents alongside the power transformer.  The output transformer produces no heat by itself and I figured it would be relatively benign to the driver tubes.  I could be wrong and won't know for sure until I get it up and running.

    It's a lesson learned either way that things don't always look the same when going from paper to real life.

    IMG_6461 by Rob C, on Flickr


    Last edited by corndog71 on Thu Mar 22, 2018 5:47 pm; edited 1 time in total
    avatar
    cci1492

    Posts : 192
    Join date : 2016-05-09
    Age : 57
    Location : Bergen County NJ

    Re: My M125 project

    Post by cci1492 on Thu Mar 22, 2018 10:05 am

    A photo of the wiring available yet?
    avatar
    deepee99

    Posts : 2000
    Join date : 2012-05-23
    Location : Wallace, Idaho

    Re: My M125 project

    Post by deepee99 on Thu Mar 22, 2018 10:37 am

    cci1492 wrote:A photo of the wiring available yet?
    Guess that would be my question to an otherwise elegant design. Bob L's stock amps are set up to eliminate the long wire runs which generate crud. I know of a couple of VTA builders who don't even run the AC switch up front. They put it the switch on the back, next to the IEC, or not at all. John Bedini didn't even install a power switch on his best amps; you had to put one in the power cord.
    avatar
    corndog71

    Posts : 668
    Join date : 2013-03-19
    Location : It can get windy here

    Re: My M125 project

    Post by corndog71 on Thu Mar 22, 2018 11:06 am

    I haven't started soldering yet. Hopefully this weekend. Stay tuned!

    Yeah, I prefer to have the power switch close to the power inlet and main fuse to keep that wiring as short as possible. I did make one mistake with the power inlet. I like using Neutrik PowerCon connectors because they're locking and make a very secure power connection. Unfortunately, I forgot to fix the mounting screw locations before ordering the plate (I had it fixed on the 2nd plate) so the jack is not square with the plate. I could drill new holes to make it square but I'm afraid of damaging the plate or the finish. The 2nd amp will have this fixed.

    One issue I have to deal with is most of the wires coming off the transformers were cut for the original chassis. So I have to add extensions to many of the wires. I've worked hard to balance between keeping things as tidy as possible while giving the tubes room to breathe.
    avatar
    Roy

    Posts : 178
    Join date : 2018-01-14
    Location : Netherlands, Europe

    Re: My M125 project

    Post by Roy on Thu Mar 22, 2018 11:31 am

    Relatively thin  and anodized aluminium presents two problems to drill through - it is  pretty hárd surface so the drill bit needs to be top notch and sharp. And the edges of the material will warp causing the drill bit to drag into the edges which will not give a nice neat hole..

    Posted a trick some time ago with a link to a youtube vid  'old machinist trick' which solves the latter issue https://www.youtube.com/watch?v=4HOxfZKIZQk  more of an issue for larger holes though - holes for mounting bolts or screws not so much but  it still helps with coolant application

    For the first - really good bit suitable for the job, lots of coolant applied and   low rpm..

    Making the punch for the spot to drill a brass hammer helps a lot - it delivers a 'dead' punch no bounce so the punch is true
    avatar
    Roy

    Posts : 178
    Join date : 2018-01-14
    Location : Netherlands, Europe

    Re: My M125 project

    Post by Roy on Thu Mar 22, 2018 11:51 am

    https://cubesfortubes.de/shop?lang=en

    nice place that has transformer covers if you need em - for magnetic shielding and looks ^^
    avatar
    deepee99

    Posts : 2000
    Join date : 2012-05-23
    Location : Wallace, Idaho

    Re: My M125 project

    Post by deepee99 on Thu Mar 22, 2018 2:59 pm

    Roy wrote:https://cubesfortubes.de/shop?lang=en

    nice place that has transformer covers if you need em - for magnetic shielding and looks ^^
    I'd prefer to have as much free air around my xformers as possible, if your cat will permit it.
    avatar
    bluemeanies

    Posts : 258
    Join date : 2015-02-09
    Age : 68
    Location : Folsom Pa.

    My m125 project

    Post by bluemeanies on Thu Mar 22, 2018 10:23 pm

    corndog71 wrote:
    bluemeanies wrote:What you did takes a lot of talent...in that respect I applaud but I have to agree with 10-E-C...especially the tube in between the transformers...rectifier tube I imagine.
    Heat and more Heat not a good mix.
    Besides why fix something that's not broken? I can understand if you wanted wood not liking the industrial look but changing the design to look like a shuffleboard?

    Ever seen a Dynaco MK4?  Mine is a similar layout with regards to the PT, rectifier, and OT.  I also added extra vents alongside the power transformer.  The output transformer produces no heat by itself and I figured it would be relatively benign to the driver tubes.  I could be wrong and won't know for sure until I get it up and running.

    It's a lesson learned either way that things don't always look the same when going from paper to real life.

    IMG_6461 by Rob C, on Flickr


    I wish nothing but success but personally I don't like the elongated look....but that is me. It's your design and what makes you happy is the most important.
    Sincerely, blue
    avatar
    corndog71

    Posts : 668
    Join date : 2013-03-19
    Location : It can get windy here

    Re: My M125 project

    Post by corndog71 on Sun Apr 01, 2018 2:35 pm

    Got the first one wired up and ready for tubes!


    Custom VTA M125
    , on Flickr


    Custom VTA M125 guts , on Flickr


    Last edited by corndog71 on Wed Sep 12, 2018 7:27 pm; edited 2 times in total
    avatar
    deepee99

    Posts : 2000
    Join date : 2012-05-23
    Location : Wallace, Idaho

    Re: My M125 project

    Post by deepee99 on Sun Apr 01, 2018 5:25 pm

    Corndog, lookin' good.
    avatar
    corndog71

    Posts : 668
    Join date : 2013-03-19
    Location : It can get windy here

    Re: My M125 project

    Post by corndog71 on Sun Apr 01, 2018 7:32 pm

    Thanks! I’m crossing all of my fingers it sounds as good as it looks.
    avatar
    cci1492

    Posts : 192
    Join date : 2016-05-09
    Age : 57
    Location : Bergen County NJ

    Re: My M125 project

    Post by cci1492 on Mon Apr 02, 2018 10:37 am

    So it looks like you did away with the little driver board?
    avatar
    deepee99

    Posts : 2000
    Join date : 2012-05-23
    Location : Wallace, Idaho

    Re: My M125 project

    Post by deepee99 on Mon Apr 02, 2018 12:47 pm

    corndog71 wrote:Thanks!  I’m crossing all of my fingers it sounds as good as it looks.
    It will. No doubt there. Give the tubes and caps a little time to air themselves out.
    avatar
    corndog71

    Posts : 668
    Join date : 2013-03-19
    Location : It can get windy here

    Re: My M125 project

    Post by corndog71 on Mon Apr 02, 2018 1:24 pm

    cci1492 wrote:So it looks like you did away with the little driver board?

    Yep, I prefer the simplicity of point to point wiring. I never cared for the exposed circuit board look.

    avatar
    Bob Latino
    Admin

    Posts : 2684
    Join date : 2008-11-26
    Location : Massachusetts

    Re: My M125 project

    Post by Bob Latino on Mon Apr 02, 2018 2:43 pm

    corndog71 wrote:

    Yep, I prefer the simplicity of point to point wiring.  I never cared for the exposed circuit board look.


    Point to point is fine if you know what you are doing on wire routing. It is simpler for the average amp builder to use a driver board. Also, you won't run into strange hum issues using a driver board since the wire routing/layout of the driver board is a factor that has been proven to give no detrimental interactions.

    Bob
    avatar
    corndog71

    Posts : 668
    Join date : 2013-03-19
    Location : It can get windy here

    Re: My M125 project

    Post by corndog71 on Wed Apr 04, 2018 1:58 am

    Just so you guys know, I'm not knocking the M125 design nor any of the classic Dynaco amps. I still appreciate them for all of their well-deserved glory.

    I've only been playing with tubes for the last 20 of my 46 years. Everything I've learned has brought me to this point and I'm the first to admit there's still more I don't know about tube amps and electronics in general. I've had no formal training. Just reading a lot in books and forums, building kits and circuits from scratch and asking lots of questions. I still struggle with understanding ohm's law and its application.

    Looking at the competition I find there's plenty of flexibility in the design of a tube amp. All I wanted to do was be creative and give these amps a little makeover. It's been a real challenge.



    avatar
    corndog71

    Posts : 668
    Join date : 2013-03-19
    Location : It can get windy here

    Re: My M125 project

    Post by corndog71 on Sun Apr 08, 2018 10:09 pm

    Well, whenever you go off script you’re bound to discover new problems.  When rearranging a tube amp into a custom layout it’s ridiculously easy to make mistakes.  Before putting any power into it, I thought I had everything down.  I’d let it sit for a day or two and then take another look.  I also keep a drawing that I compare to the schematics because it helps me wrap my brain around everything.  

    Nevertheless I still made mistakes.  Missed a wire here, and connected a wire or cap to the wrong tube pin there.  Rinse and repeat.  This morning I was feeling confident and decided to give it a test.  I only have three 6550’s so half-power it is.  I checked the heaters with the driver tubes first and things seemed to be ok.  I even checked one side of the octal sockets with my meter and they were good.  

    I shut it off and plugged in a pair of the 6550’s and turned it on.  One side started lighting up but not the other side.  Then all kinds of noise poured out of my test speaker and I shut it off.  Let it cool down a bit, swapped the tubes to make sure it wasn’t a bad tube.  Same side wasn’t lighting up and then the noise came again and this time it blew the cathode fuse. Shut it down, pulled the power tubes and flipped it over to see what I missed.  Ugh!  Totally miswired one of the power tubes.  I forgot to rotate it in my drawing from an earlier version.  I can’t believe I missed it!  I would’ve caught it had I check all of the sockets during the heater test.

    I fixed the socket and decided to give it another shot.  Started it up and checked the bias.  Bias was good but then more loud noise kicked in.  Out of curiosity I flipped it to triode mode and the noise stopped.  Checked voltages and everything seemed good.  I plugged my iPad into the input and played a song and it worked!  Flipped it back to ultralinear and loud noise again.  Triode mode works fine.  Voltages from the output transformer plate and screen taps are right on.  I suspect I damaged the tubes.  Have you guys encountered this?  I was going to get new tubes anyway.  

    For what it’s worth, the drivers seem unaffected by their proximity to the output tranny.  In triode mode with the input shorted there’s just a hint of noise from the speaker which I have to put my ear up against to hear.
    avatar
    corndog71

    Posts : 668
    Join date : 2013-03-19
    Location : It can get windy here

    Re: My M125 project

    Post by corndog71 on Wed May 09, 2018 9:46 pm

    Well, after a few miswires and head scratching and a little help from Roy I finally got these babies up and running! They are dead quiet until the music starts playing. Building mirror image amps is a sure way to test your sanity!


    Sponsored content

    Re: My M125 project

    Post by Sponsored content


      Current date/time is Wed Sep 19, 2018 1:40 pm