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Dyna MK3 Transformers

67.255.90.46
Posted on June 7, 2015 at 11:30:52
mark.korda@myfairpoint.net
Audiophile

Posts: 1253
Location: Maine
Joined: August 16, 2011
 Hi, after years of stalling I'm finally getting to restore a pair of Mark 3's.A couple years ago Bob Latino from the Dyna tube forum gave me some instructions on how to use a multimeter to see if the transformers were okay.The 2 output transformers passed the tests. The power transformers are a little different. I have to apply 120 volts of power to the 2 black wires(primary) of which I have a variac that will handle that. Then I need to measure 2 red wires on the (secondary) which are stepped up to 820 to 870 volts AC. My brand new multimeter from Home Depot, the 48 dollar model is only rated up to 600 volts AC. So here I'm going to stop and maybe bring them to a electriction who might have a higher rated multimeter. The other voltages seem low enough to measure. Is this the correct method or is there another way around this? P.S. When I measure the 800 plus volts I will use every safety precaution in the world as well as looking like the (lineman of the county). Thanks, appreciate any advise......Mark Korda

 

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RE: Dyna MK3 Transformers, posted on June 7, 2015 at 12:53:01
Steve O
Audiophile

Posts: 12381
Location: SE MI
Joined: September 6, 2001
 You can use your 600V rated meter to measure between the CT of the sec and either side of it. This would be a measurement betw one red and red/yel and then the other red and red/yel. In each case you should get ~ 435VAC: 2 x 435 = 870. Since you have a variac, another method would be to apply 60 VAC to the primary and then measure the full secondary (red to red). Since the primary is half voltage, the secondary will be too: 1/2 x 870 = 435. Whatever you choose to do, be safe. If you're not confident, get assistance.

 

RE: Dyna MK3 Transformers, posted on June 7, 2015 at 14:22:26
mark.korda@myfairpoint.net
Audiophile

Posts: 1253
Location: Maine
Joined: August 16, 2011
 Thanks Steve, great ideas and safety is my number one priority upon doing this, thanks Mark K.

 

RE: Dyna MK3 Transformers, posted on June 9, 2015 at 11:27:17
mark.korda@myfairpoint.net
Audiophile

Posts: 1253
Location: Maine
Joined: August 16, 2011
 Hi Steve, I've had these Dyna Mark 3's for ever. They left my possession around 1982 where I took them apart. I traded them to a friend who I later lost track of. He resurfaced later and I got the amps back in a trade and an old Ford Ranger for a paint truck.They stayed in a project box for 15 years in my small cramped studio. I have moved and now I have room for stereo projects.I just used your idea on the variovac only using 20 volts.I did my Jethro Bodine math and both power transformers passed with flying colors, thanks to you, again,thanks! I have thru the times collected every thing I need to make these new,circuit board,chokes,800 volt cap replacement board and even a 2 new,or old packets of hardware from the old Stereo Cost Cutters from Ohio. They bought the last remaining Dyna tube stuff before it was re manufactured again not to long ago. The last hurdle before I have the fun of assembelly is to get the chrome chassis sand blasted and hopefully powder coated a Cleveland Browns orange or McClaren (Can-Am) orange, same color.I think that would look cool with the brown cages. Without a little info and push by you Steve, they might have ended back in the box....I'll have some pics for you....Mark K.

 

RE: Dyna MK3 Transformers, posted on June 9, 2015 at 11:35:00
rickl
Audiophile

Posts: 583
Location: Twin Cities
Joined: February 7, 2002
 Mark, I think you will have fun.

I have 4 Mark IIIs. Two where relatively complete, one was mostly complete and the 4th needed PS iron and a complete rebuild.

Over the last few years I was able to get all 4 working great with new caps, Curcio boards and iron.
looking for some jazz and a little libations - js

 

RE: Dyna MK3 Transformers, posted on June 10, 2015 at 07:38:20
airtime
Audiophile

Posts: 11287
Location: Arizona
Joined: February 4, 2003
 sounds like a very enjoyable project. I had the MKIII with the KT88 tubes. One of my all time favorites!!!!

And I was very sorry I sold them for the silly reasons I did.

One day I would like to get back into a ST-70 kit from Bob Latino

charles

 

RE: Dyna MK3 Transformers, posted on June 11, 2015 at 07:56:39
digepix
 I had a pair of Mk. III's back in the 80's that I got rid of due to parts unavailability like the quad cap. They did sound good and not long after I got rid of them everyone started making parts again. I also had a pair of original PAM 1 mono preamps that I later traded in towards an Audible Illusions 2B. With the new preamp it sounded very good and I should have kept them with my Vandersteens.

 

RE: Dyna MK3 Transformers, posted on June 11, 2015 at 10:55:01
Steve O
Audiophile

Posts: 12381
Location: SE MI
Joined: September 6, 2001
 Good to hear things worked out OK. However.......testing at the low voltages you describe verify the ratios under unrealistic conditions. If they were mine, I'd perform one more test: wire in a 1amp fuse in series with the primary, make sure all secondary leads are separated and not in contact with anything and plug into 120VAC. The test here is that the fuse doesn't blow immediately or after a minute or two. If it passes this test too then you know internal insulation is good at operating voltages. Good luck with your project.

 

RE: Dyna MK3 Transformers, posted on June 11, 2015 at 15:40:09
mark.korda@myfairpoint.net
Audiophile

Posts: 1253
Location: Maine
Joined: August 16, 2011
 Hi Steve, thanks. Besides the 800 plus volts measurements I turned up my variovac to 120 volts on the lower voltages and both transformers were mirror perfect in measures they needed to achieve. Would that be ok? Thanks Mark...Thanks you others for the pep talks...love em!...Mark.

 

If you did that, you're covered. (nt), posted on June 11, 2015 at 18:33:32
Steve O
Audiophile

Posts: 12381
Location: SE MI
Joined: September 6, 2001

 

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