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    Proposed Mark III Layout

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    TN Allen

    Posts : 124
    Join date : 2013-01-01

    Re: Proposed Mark III Layout

    Post by TN Allen on Sun Mar 22, 2015 11:41 am

    MontanaWay wrote:
    TN Allen wrote:Before looking more carefully at the Tubes4hifi MK3 photos and noticing the quad capacitor is 80-40-30-20, I bought a quad capacitor similar to what was used in the original MK3, 30-20-20-20. I'm wondering What advantage the 80 & etc capacitor provides over the original?

    a lot of components used in the original Dynaco amps as well as preamps were a compromise, mainly based on cost savings. The 30-20-20-20 is probably absolute minimum. Going somewhat higher, ie 80-40-30-20 gives the amp more 'stored energy', having to rely less just on the transformer to power the unit.
    Of course, having said that, there is a limit too, going to high is no good either. I would NOT use the 30-20-20-20 in this amp, so you'd be better of getting the 80-40-30-20, get the higher voltage unit too, costs a but more, but gives you that margin, especially during power up!

    MontanaWay,

    Thanks. This one: http://www.dynakitparts.com/dynakit-products/capacitors/MULTI-ELECTROLYTIC-C

    MontanaWay

    Posts : 781
    Join date : 2014-02-06
    Age : 58
    Location : Brookings, Oregon

    Re: Proposed Mark III Layout

    Post by MontanaWay on Sun Mar 22, 2015 11:43 am

    TN Allen wrote:
    MontanaWay wrote:
    TN Allen wrote:Before looking more carefully at the Tubes4hifi MK3 photos and noticing the quad capacitor is 80-40-30-20, I bought a quad capacitor similar to what was used in the original MK3, 30-20-20-20. I'm wondering What advantage the 80 & etc capacitor provides over the original?

    a lot of components used in the original Dynaco amps as well as preamps were a compromise, mainly based on cost savings. The 30-20-20-20 is probably absolute minimum. Going somewhat higher, ie 80-40-30-20 gives the amp more 'stored energy', having to rely less just on the transformer to power the unit.
    Of course, having said that, there is a limit too, going to high is no good either. I would NOT use the 30-20-20-20 in this amp, so you'd be better of getting the 80-40-30-20, get the higher voltage unit too, costs a but more, but gives you that margin, especially during power up!

    MontanaWay,

    Thanks. This one:     http://www.dynakitparts.com/dynakit-products/capacitors/MULTI-ELECTROLYTIC-C

    yup, thats the animal! Smile cheers

    TN Allen

    Posts : 124
    Join date : 2013-01-01

    Re: Proposed Mark III Layout

    Post by TN Allen on Sun Mar 22, 2015 12:15 pm

    Thanks again, tna

    TN Allen

    Posts : 124
    Join date : 2013-01-01

    Re: Proposed Mark III Layout

    Post by TN Allen on Mon Apr 06, 2015 9:22 am

    I have a few more questions before I start making the layout and parts permanent. I'd appreciate any responses.

    sKiZo suggested that if I might want to use a GZ37 in the future, and that I should leave enough space for this larger tube. Would the GZ37 be suitable for the mono amp? At around $150 from TubeDepot, I might pass on it, or wait to use it in another stereo amp.

    If I want to eliminate the 5AR4, and a solid state rectifier in the tube socket, could someone recommend a circuit for a hardwired SS rectifier.

    Can the quad-capacitor be located inside the chassis?

    The tube spacing remains a dilemma, looking at the original design, and various other KT88 amp designs, spacing is close, really close in some cases. Is there evidence this does require replacing tubes more frequently?

    I checked the temperature half-way between the EL34s on the ST70, it's about 98-100F, close to the surface 180F, and between the output transformer and tube about 80F. Extrapolating from these temperatures, would spacing at 1/4-1/2 the distance be a significant problem? I realize the heat would dissipate more slowly with closer spacing, but wonder how much this would affect tube life and performance?

    Here are two photos of the tube socket pockets I'll probably mill in either Corian, or the copper-nickel plate. The only drawback to the Cu-Ni is that the top plate would way about 10lbs, the Corian only 2. I do like the look of the Cu-Ni, but would need a wheel barrow to move it around.

    corndog71

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

    Re: Proposed Mark III Layout

    Post by corndog71 on Mon Apr 06, 2015 11:35 am

    I think this is one of those areas that you just have to make the call yourself. I've seen a lot of both instances (close vs far spacing) to think it's more of an aesthetic choice.

    So be creative. Make it look how you want.

    A simple solid state solution is to use a pair of UF4007 diodes with each diode's non-banded end going to one of the PT red leads. The banded ends come together and start the B+ to the first power supply cap.


    sKiZo

    Posts : 1308
    Join date : 2013-04-01
    Location : Michigan USA

    Re: Proposed Mark III Layout

    Post by sKiZo on Mon Apr 06, 2015 3:46 pm

    TN Allen wrote:sKiZo suggested that if I might want to use a GZ37 in the future, and that I should leave enough space for this larger tube. Would the GZ37 be suitable for the mono amp? At around $150 from TubeDepot, I might pass on it, or wait to use it in another stereo amp.

    I got a NOS for $99 (Canadian military markings) and also got a good used 1950's Mullard for about the same. Consider that they may be the last rectifiers you need to buy as they're built strong, and also that you'll not brown out when driving them hard - always a possibility with a GZ34. Then again, the WZ68 copper cap is strong as well and a whole lot less. Your call ... I just like the big bottles. I'm also firmly convinced they sound better.

    Can the quad-capacitor be located inside the chassis?  

    Yup ... and seeing as how a pic is worth a thousand words ...



    The mounting strap is just some flashing tin doubled up and wrapped around the can. How well the case is grounded can make a big difference in how quiet the amp is. You can get a real tight fit if you're careful. I might look into changing out to a wider strap with a dual point mounting and add dielectric grease for improved ground sometime down the road. No rush as there's no noise now, but it couldn't hurt, and I've got a couple other tweaks I want to do anyway.

    The tube spacing remains a dilemma, looking at the original design, and various other KT88 amp designs, spacing is close, really close in some cases. Is there evidence this does require replacing tubes more frequently?

    Heat is a killer. How much heat you get depends on ventilation and how hard you drive the tubes. Add some vents around each tube ...



    That creates a chimney effect that will draw cooler air up from underneath IF you allow for adequate internal venting as well - air's gotta come from someplace.


    TN Allen

    Posts : 124
    Join date : 2013-01-01

    Re: Proposed Mark III Layout

    Post by TN Allen on Wed May 06, 2015 10:59 am

    I've made some progress on this amp project recently. The plate is heavy, but not nearly as heavy as the transformers. I milled one in Copper-Nickel, another in 1/2" Corian. But will probably use the first. Micro-phonics should not be a problem.



    In locating the sockets for the KT 88s, I can have these with both of the pin orientation slots(is there a better term for these?) facing left, right or opposing. In other words, the tubes can be in the same orientation, or mirrored. Is the tube orientation critical?

    DarthBubba

    Posts : 81
    Join date : 2012-05-05

    Re: Proposed Mark III Layout

    Post by DarthBubba on Wed May 06, 2015 5:45 pm

    TN Allen wrote:Here are two photos of a revised layout, ...  but would like to keep the layout reasonably compact. I'd appreciate any further comments or suggestions.


    I'd swap the rectifier and quad-cap locations.  That would give the rectifier, solid state or hollow-state, more breathing room.

    Just my $0.02, and worth every penny you paid.

    nmchiefsfan

    Posts : 33
    Join date : 2012-03-21

    Re: Proposed Mark III Layout

    Post by nmchiefsfan on Wed May 06, 2015 10:38 pm

    If you are going to locate the quad cap underneath, would it not be easier to use discreet components?

    TN Allen

    Posts : 124
    Join date : 2013-01-01

    Re: Proposed Mark III Layout

    Post by TN Allen on Sat May 09, 2015 10:35 am

    nmchiefsfan wrote:If you are going to locate the quad cap underneath, would it not be easier to use discreet components?

    I already have the quad capacitor and other parts, so, I think I'll use these.

    TN Allen

    Posts : 124
    Join date : 2013-01-01

    Re: Proposed Mark III Layout

    Post by TN Allen on Sat May 09, 2015 11:04 am

    Before I make any of the underside of the Mark 3 amp permanent, I wondered if anyone has alternate suggestions I should consider or use. The first photo is with everything in place, but loose, the second shows the parts removed that cover the holes for the transformer wires. These parts would be set off the plate far enough to run the transformer wires without crowding.

    Also, is there a place I can connect the 2.1-3.5 V LED, preferably on the PCB? Thanks for any suggestions or concerns, I appreciate the assistance.




    TN Allen

    Posts : 124
    Join date : 2013-01-01

    Re: Proposed Mark III Layout

    Post by TN Allen on Sun Jan 24, 2016 6:48 pm

    After several months on other projects, I'm ready to wire this amp. I have the Dynaco manual download, the supplemental sheet for the quad cap. from Dynakit Parts, and the instructions for the tubes4hifi PCB. Are there other schematics I might download and use?

    TN Allen

    Posts : 124
    Join date : 2013-01-01

    Re: Proposed Mark III Layout

    Post by TN Allen on Sun Feb 14, 2016 1:08 pm

    I started with the PCB from VTA and transformers from Triode, the quad-capacitor from Dynakit Parts, consequently I don't have an old MKIII to follow for the wiring, but have the VTA MKIII instructions and the original Dynaco Instructions download. Rather than risk real damage to what I have, and possible electrocution, I thought I'd ask for help, and will appreciate any offered.

    I think I have most of this figured out, the connections from the transformers to the tube sockets seem clear, but I may well not have the rest of the connections correct. My questions regarding these are:

    1. Does the Red-Black wire from the Power Transformer connect to the Bias eyelet on the VTA PCB?

    2.The quad-capacitor pins are designated as 1-4 on the VTA MKIII sheet, how do 1-4 relate to the square, triangle, half circle and circle, or the capacitor values?

    3. Which of the tubes should be designated V1 on the VTA sheet? I assume this is important for connecting to the V3 & V4 OUT eyelets on the PCB.

    4. Is the extra wire from the 16 ohm Output transformer to connect to the NFB eyelet on the PCB.

    5. Can the instructions for assembling a new MKIII using the VTA PCB be downloaded, if so, where?

    Here is a link to a Flickr photo of the amp so far:  https://www.flickr.com/photos/68227271@N04/25024347595/in/datetaken/

    I left the choke out, but it fits in adjacent to the Output connections. As I wrote above, any suggestions will be appreciated.

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