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+11

nmchiefsfan

DarthBubba

zx

turbotoy

Maintarget

Cubdriver

corndog71

Bob Latino

Pat R.

sKiZo

GP49

15 posters

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Proposed Mark III Layout

TN Allen: Posts : 167
Join date : 2013-01-01

Post n°1

Proposed Mark III Layout

by TN Allen Tue Mar 03, 2015 6:23 pm

Here is a photo via Gyazo of an Mark III layout I am considering. If the two transformers are 2" apart, is it likely the interference between the two will sufficiently diminished. http://gyazo.com/36952f6053d347fcfacc7fd77ae320b9

I tried inserting the image using the icon that is two icons to the left of the You Tube icon above, that is in the tool bar.

corndog71: Posts : 840
Join date : 2013-03-19
Location : It can get windy here

Post n°2

Re: Proposed Mark III Layout

by corndog71 Tue Mar 03, 2015 6:56 pm

If you're going to make your own layout then I would highly recommend separating the power tubes and rectifier tube by 4" center to center. This was recommended by the tube manufacturers back in the day. It really does help keep the amp cooler. Bunching everything together only makes everything hotter and heat ultimately degrades everything over time.

I built my own ST120 using a plain Hammond box. Everything but the tubes and the power transformer stay nice and cool.

Proposed Mark III Layout IMG_8733_zps764f64ee

Proposed Mark III Layout IMG_8733_zps764f64ee

GP49: Posts : 792
Join date : 2009-04-30
Location : East of the sun and west of the moon

Post n°3

Re: Proposed Mark III Layout

by GP49 Tue Mar 03, 2015 6:58 pm

I also like the way the fuseholder and power switch are protected between transformers on the above-shown amplifier. Many fuseholders got broken off when mounted on the side of amplifiers where they were vulnerable when being moved, turned up on end for servicing, and such.

TN Allen: Posts : 167
Join date : 2013-01-01

Post n°4

Re: Proposed Mark III Layout

by TN Allen Tue Mar 03, 2015 7:10 pm

I plan to use a solid state rectifier in the 5AR4 socket. Our power fluctuations seem to be a problem for the 5AR4 in the ST70 I upgraded. The rectifier socket and quad cap, would be between the transformers, and choke underneath the chassis. I can move the KT88s further apart, the 12AU7s though are fixed of course.

The chassis will be a combination of wood, Corian, Aluminum, or possibly Cupranickel. I have access to 3/8" plate with a nice pickled finish.

Regarding the fuse holder and switch. I bought a combination fuse, switch and 3 prong IEC connector to mount on the back of the chassis. I agree it's a good idea to protect the switch and fuse holder.

corndog71: Posts : 840
Join date : 2013-03-19
Location : It can get windy here

Post n°5

Re: Proposed Mark III Layout

by corndog71 Wed Mar 04, 2015 2:59 pm

TN Allen wrote:I plan to use a solid state rectifier in the 5AR4 socket. Our power fluctuations seem to be a problem for the 5AR4 in the ST70 I upgraded. The rectifier socket and quad cap, would be between the transformers, and choke underneath the chassis. I can move the KT88s further apart, the 12AU7s though are fixed of course.

The chassis will be a combination of wood, Corian, Aluminum, or possibly Cupranickel. I have access to 3/8" plate with a nice pickled finish.

Regarding the fuse holder and switch. I bought a combination fuse, switch and 3 prong IEC connector to mount on the back of the chassis. I agree it's a good idea to protect the switch and fuse holder.

I eliminated the rectifier socket altogether and just hard wired UF4007 diodes. I've lost too many rectifier tubes over the years and am done with them. I highly recommend the turn-on delay circuit if you go solid state.

I also skipped the PCB and point to point wired the entire driver circuit. I pretty much needed to in order to integrate the rather large power supply caps I chose to use.

TN Allen: Posts : 167
Join date : 2013-01-01

Post n°6

Re: Proposed Mark III Layout

by TN Allen Wed Mar 04, 2015 4:43 pm

I've wondered why the 5AR4 tubes are so easily damaged compared to those I had in my ST 70 during 1968-~1987, when I stopped using it. I upgraded it a couple of years ago, and don't use it much, but have probably used more 5AR4s than I used when I used it daily for nearly 20 years. I finally gave up and now have the solid state rectifier from TubeDepot.

Given I have the transformers in the same orientation, the cores are parallel, will that cause problems?

sKiZo: Posts : 1530
Join date : 2013-04-01
Location : Michigan USA

Post n°7

Re: Proposed Mark III Layout

by sKiZo Wed Mar 04, 2015 6:37 pm

3/8" plate? Is that a misprint?? That's INDUSTRIAL STRENGTH!

Any room to put the choke inside? Less clutter up top, and that would certainly give the transformers room to breathe.

My transformers are pretty tight, but never had any issues. Spacing is pretty much identical to a stock ST120 if I remember right.

Proposed Mark III Layout Chassis-top-fit-02

Proposed Mark III Layout Chassis-top-fit-02

Then again, they DO look like they fit the 4" center to center rule - more like 5". Then again, yet again, that "rule" seems a bit arbitrary based on iron size. The ST120 has some pretty massive iron compared to a lot of amps.

Oh. And ya ... 5AR4's ain't what they used to be. The Chinese ones are downright scary - you can read by the nuclear glow on one of those. I have a sweet little Mullard that doesn't work as hard and drives the amp well. Even better, I went to a Mullard GZ37 big bottle that doesn't even break a sweat. Food for thought - those and the GZ33 are about the same size as a KT88, so plan your layout accordingly if you want to have that option later on.

Last edited by sKiZo on Wed Mar 04, 2015 6:45 pm; edited 2 times in total

Pat R.: Posts : 57
Join date : 2015-02-26
Location : SE Pennsylvania

Post n°8

Re: Proposed Mark III Layout

by Pat R. Wed Mar 04, 2015 6:38 pm

Proposed Mark III Layout 108155c5fe6fc992507d1c4832b4ac42

Here is TN's Image of his proposed layout..

Bob Latino: Admin; Posts : 3276
Join date : 2008-11-26
Location : Massachusetts

Post n°9

Re: Proposed Mark III Layout

by Bob Latino Wed Mar 04, 2015 6:48 pm

TN Allen wrote:

Given I have the transformers in the same orientation, the cores are parallel, will that cause problems?

The power transformer and the output transformers on any tube amp should have the plates of the transformers at right angles to each other. If the plates are parallel then there is the possibility that there could be some "induced" transfer of small amounts of AC current from the power transformer to the output transformer. If you like that custom layout for a Mark III, I would just rotate the power transformer 90 degrees one way or the other.

Bob

TN Allen: Posts : 167
Join date : 2013-01-01

Post n°10

Re: Proposed Mark III Layout

by TN Allen Wed Mar 04, 2015 8:00 pm

Pat R. wrote:

Here is TN's Image of his proposed layout..

Pat R.,

Thank you for posting the photo, that is a great help. I'll work on solving my photo posting problem.

tna

TN Allen: Posts : 167
Join date : 2013-01-01

Post n°11

Re: Proposed Mark III Layout

by TN Allen Wed Mar 04, 2015 10:01 pm

sKiZo wrote:3/8" plate? Is that a misprint?? That's INDUSTRIAL STRENGTH!

Any room to put the choke inside? Less clutter up top, and that would certainly give the transformers room to breathe.

My transformers are pretty tight, but never had any issues. Spacing is pretty much identical to a stock ST120 if I remember right.

Then again, they DO look like they fit the 4" center to center rule - more like 5". Then again, yet again, that "rule" seems a bit arbitrary based on iron size. The ST120 has some pretty massive iron compared to a lot of amps.

Oh. And ya ... 5AR4's ain't what they used to be. The Chinese ones are downright scary - you can read by the nuclear glow on one of those. I have a sweet little Mullard that doesn't work as hard and drives the amp well. Even better, I went to a Mullard GZ37 big bottle that doesn't even break a sweat. Food for thought - those and the GZ33 are about the same size as a KT88, so plan your layout accordingly if you want to have that option later on.

Yes, it is 3/8", that's what is available, it's really nice material, and would make a nice CNC project. I figure it will add about 10lbs. The pickled finish is very attractive.

The transformers are 2" apart, and I'll probably put the coil inside the chassis. I'll rethink the layout to leave room for the Mullard, that seems like a very good idea.

Thank you for the suggestions, tna

corndog71: Posts : 840
Join date : 2013-03-19
Location : It can get windy here

Post n°12

Re: Proposed Mark III Layout

by corndog71 Thu Mar 05, 2015 12:17 am

Just to clarify, the 4" suggestion was primarily for the power tubes.

sKiZo: Posts : 1530
Join date : 2013-04-01
Location : Michigan USA

Post n°13

Re: Proposed Mark III Layout

by sKiZo Thu Mar 05, 2015 9:55 pm

OK, then 4' between power tubes What a Face

What a Face

Pat R.: Posts : 57
Join date : 2015-02-26
Location : SE Pennsylvania

Post n°14

Re: Proposed Mark III Layout

by Pat R. Fri Mar 06, 2015 9:22 am

sKiZo wrote:3/8" plate? Is that a misprint?? That's INDUSTRIAL STRENGTH!

Any room to put the choke inside? Less clutter up top, and that would certainly give the transformers room to breathe.

My transformers are pretty tight, but never had any issues. Spacing is pretty much identical to a stock ST120 if I remember right.

Then again, they DO look like they fit the 4" center to center rule - more like 5". Then again, yet again, that "rule" seems a bit arbitrary based on iron size. The ST120 has some pretty massive iron compared to a lot of amps.

Oh. And ya ... 5AR4's ain't what they used to be. The Chinese ones are downright scary - you can read by the nuclear glow on one of those. I have a sweet little Mullard that doesn't work as hard and drives the amp well. Even better, I went to a Mullard GZ37 big bottle that doesn't even break a sweat. Food for thought - those and the GZ33 are about the same size as a KT88, so plan your layout accordingly if you want to have that option later on.

That's a great looking amp. Can we see the underside?

TN Allen: Posts : 167
Join date : 2013-01-01

Post n°15

Mark lll Changed Layout

by TN Allen Fri Mar 06, 2015 12:17 pm

Here is an image of the layout changed a bit to add spacing between the KT88s, and also between the transformers, there is now 4" C-C spacing for the tubes, and 3+" between the transformers, I prefer to leave these in a parallel as they look better this way to my eye, and I'd also like to try and detect any inductance/magnetic interference, out of curiosity. If it doesn't work, I'll make another plate with the transformers at 90 degrees. With this spacing I can also try a more robust 5AR4, similar to what sKiZo is using, provided I can find one. The quad cap would also be between the transformers.

Proposed Mark III Layout A482ea08a87315a032ed9471f6c43c4a

Proposed Mark III Layout A482ea08a87315a032ed9471f6c43c4a

Pat R.: Posts : 57
Join date : 2015-02-26
Location : SE Pennsylvania

Post n°16

Re: Proposed Mark III Layout

by Pat R. Fri Mar 06, 2015 1:35 pm

TN Allen wrote:Here is an image of the layout changed a bit to add spacing between the KT88s, and also between the transformers, there is now 4" C-C spacing for the tubes, and 3+" between the transformers, I prefer to leave these in a parallel as they look better this way to my eye, and I'd also like to try and detect any inductance/magnetic interference, out of curiosity. If it doesn't work, I'll make another plate with the transformers at 90 degrees. With this spacing I can also try a more robust 5AR4, similar to what sKiZo is using, provided I can find one. The quad cap would also be between the transformers.

Do you know what would really be cool since you like the symmetry of the transformers.. see if you can scavenge a couple of old potted transformers and repurpose the cans!... I've had to unpot a few in the past and it's really not that hard. You just heat them up on your gas grill (put some foil down and face them up) and if you are careful you can pop the old xformers out like a popsicle.. Then sand blast em and repaint em.. Now that would be cool! and if you are really brave you could refill them up with tar and pot your own.

If you were to repot some new xformers you could orient them the so called correct way while still being aesthecially pleasing to you.

Pat R.: Posts : 57
Join date : 2015-02-26
Location : SE Pennsylvania

Post n°17

Re: Proposed Mark III Layout

by Pat R. Fri Mar 06, 2015 1:48 pm

If the symmetry of the Xformers is something the bothers you wouldn't it be neat if you could get ahold of some old Potted transformers and repurpose them.. Perhaps find a few junk ones from an old Heathkit or something like that.. and un pot the old Xformers and use the new ones.. It's not that hard to un pot them. I've done this several times using the gas grill outside.. just put plenty of foil down and heat them up... with oven mitts you can test how it's coming along. If you time it just right you can pull on the old leads and un pot it just like a popsicle from a mold.. The strip/sandblast the cans.. repaint them or even wrinkle finish them! and Voila... symmetry.. as the xformers will be inside and no one will see them.

A couple of these babies from a Heathkit W4 would be sweet.. this one is wrinkle finished.

Proposed Mark III Layout C9c6e9d0e4803845dff881c1554b036f

Proposed Mark III Layout C9c6e9d0e4803845dff881c1554b036f

sKiZo: Posts : 1530
Join date : 2013-04-01
Location : Michigan USA

Post n°18

Re: Proposed Mark III Layout

by sKiZo Fri Mar 06, 2015 5:59 pm

Pat R. wrote:

That's a great looking amp. Can we see the underside?

Oh, go ahead, twist my arm hard enough and I'll post up a couple pics of my "precious" ...

Proposed Mark III Layout Tungsol-kt120s-002

Proposed Mark III Layout Tungsol-kt120s-002

Ow! OW! OK ... here's a nudie!

Proposed Mark III Layout Wiring-done-003

Proposed Mark III Layout Wiring-done-003

Basically an ST120 with a few minor mods ... only major electrical changes were the meters, larger chokes, internal "Y" bridge, bias and volume pots. Also did the thermister slow start and the yellow page mod on the rectifier.

PS ... I HIGHLY recommend Front Panel Express for custom chassis work if you're not a master machinist. CNC on all the exposed holes gives everything a clean look. Free design software, so just do your layout and click the buy button. Bit pricey, but hey, I'm worth it ...

http://www.frontpanelexpress.com/

PPS: 1000 posts ... king me!

Last edited by sKiZo on Fri Mar 06, 2015 8:06 pm; edited 1 time in total

TN Allen: Posts : 167
Join date : 2013-01-01

Post n°19

Re: Proposed Mark III Layout

by TN Allen Fri Mar 06, 2015 6:58 pm

Pat R.,

I was just looking at transformer cases, it appears these are available for about $14/. On the other hand, there is probably a reasonable distance apart that would also solve the problem. I'm more curious about this than concerned about symmetry.

SKiZo, that is a gorgeous amp, nicely done. I teach machine shop at a small engineering school, including CNC use and CAD. I thought I'd do the design and layout.

Within reason, I'd do some design and machining for others on this forum, free.

Cubdriver: Posts : 83
Join date : 2014-01-21
Age : 59
Location : Southeastern Litchfield Co, CT

Post n°20

Re: Proposed Mark III Layout

by Cubdriver Fri Mar 06, 2015 7:44 pm

sKiZo wrote:OK, then 4' between power tubes

THAT'S gonna make for an awkward chassis!

-Pat

Pat R.: Posts : 57
Join date : 2015-02-26
Location : SE Pennsylvania

Post n°21

Re: Proposed Mark III Layout

by Pat R. Fri Mar 06, 2015 9:34 pm

TN Allen wrote:Pat R.,

I was just looking at transformer cases, it appears these are available for about $14/. On the other hand, there is probably a reasonable distance apart that would also solve the problem. I'm more curious about this than concerned about symmetry.

SKiZo, that is a gorgeous amp, nicely done. I teach machine shop at a small engineering school, including CNC use and CAD. I thought I'd do the design and layout.

Within reason, I'd do some design and machining for others on this forum, free.

Where did you find the transformer cases? I'd be interested in that.. On some of the fine amp work done here I would love to see those xformers in a can.. some like the more industrial look of the raw transformer, I kinda like the clean lines of a can.

TN Allen: Posts : 167
Join date : 2013-01-01

Post n°22

Re: Proposed Mark III Layout

by TN Allen Fri Mar 06, 2015 10:20 pm

Pat R.,

They are on a website www.vt4c.com

I'm using a phone and haven't figured out how to provide a direct link.

I also saw many available via ebay, however, they were more expensive.

I think they would be very attractive.

sKiZo: Posts : 1530
Join date : 2013-04-01
Location : Michigan USA

Post n°23

Re: Proposed Mark III Layout

by sKiZo Fri Mar 06, 2015 10:28 pm

Food for thought - heat can be a killer. Some iron runs hot enough without being stuffed in a can, man ...

If you do enclose the Latino or Dynaco iron, I'd consider adding some vent holes at the base and top. I'm sure there's many ways it could look decent if done right.

Pat R.: Posts : 57
Join date : 2015-02-26
Location : SE Pennsylvania

Post n°24

Re: Proposed Mark III Layout

by Pat R. Fri Mar 06, 2015 10:32 pm

sKiZo wrote:Food for thought - heat can be a killer. Some iron runs hot enough without being stuffed in a can, man ...

If you do enclose the Latino or Dynaco iron, I'd consider adding some vent holes at the base and top. I'm sure there's many ways it could look decent if done right.

Thanks sKizo, I'm aware of some of the new iron running hotter than the old.. something that would be addressed for sure. I just think it would be an ultra clean set up with freshly painted cans.. even one with vent holes would look better to me than raw transformers.

PS you want to talk about hot irons.. come have a feel of my Citation II after a hard days work! The PO sold it to me because his wife complained it made the room that they had it hooked up in too HOT! haha.. but ask Jim McShane.. he says it's normal on a Citation II.

Pat R.: Posts : 57
Join date : 2015-02-26
Location : SE Pennsylvania

Post n°25

Re: Proposed Mark III Layout

by Pat R. Fri Mar 06, 2015 10:34 pm

TN Allen wrote:Pat R.,

They are on a website www.vt4c.com

I'm using a phone and haven't figured out how to provide a direct link.

I also saw many available via ebay, however, they were more expensive.

I think they would be very attractive.

Thanks for the site.. it's pretty big and I'll have to look around. If you get to a computer and can send a link to the can page that would be great.. meanwhile I'll keep looking.

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Post n°26

Re: Proposed Mark III Layout

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