Custom ST-120 in the pipe.

Hi All:
Well finally I got enough pieces delivered to me to start the first amp and give a peek at what is to come so here is the beginnings of my next ST-120 project.
This pic is a mock up just to convey the idea. I am still working on getting the rest of the pieces down to the jungles of Costa Rica.
You can see the driver board is still unfinished and needs some caps and I am also waiting for the arrival of the quad cap and a bias meter.The SCM module as you see here is also incomplete. Mostly done but I still need some caps and a few resistors.
This is under control finally and Roy Mottram is sending some of it to a friend who will bring it down in a week or so.
Right now I am accumulating the funds to buy a transformer set from Bob for the first one and that should be all I need to finish it electronically.
After an email consultation with Bob I decided to use the C-17X chokes on the next ones and they are in the pipe now. The two C-24X chokes in the picture will go into this amp.
I was very happy with the quality of the plates from "Front Panel Express" they did a great job. I bought 5 chassis plates with three slightly differing concepts. All the chassis plates use essentially the ST-70 layout look.
The main difference is that they are a little deeper and bigger overall and some also have a slanted front panel. You can see the cuts for the 90 deg. bend to make flanges for the sides attachment which is still to be done.
After a bit more soldering its into the wood working shop to make the Cocobolo slabs for the sides, front and back.
I have a beautiful Cocobolo log I had sliced into 3" thick slabs and it has been drying out for about 8 months. I think its about ready for the saw and planer. Hope to send some more pics on this part of the project in a week or so.
cheers

Cool! Keep the photos going on the progress!

That's cool. Like the built in Bias Meter Idea. Can't wait to see the cocobolo, one of my favorite woods.

Simply marvelous!!!! I enjoy seeing these projects, keep it coming.

Any updates on this? I'd like to build or buy one of these myself.

Hi:
Yes l would be happy to help you out if I can. I am actually working on building two different ST-120 designs at the moment both with VTA boards and most of the other parts are stock VTA ST-120.
One is the standard nine pin and the other with the new VTA octal board. I also have two different types of chassis already cut out for them.

The one you see here is going to have Cocbolo wooden sides and the other model has an all aluminum chassis.
You can see it on my"Photobucket" page but it is still in it's flat plate form there.
https://s1212.photobucket.com/albums/cc446/baddog1946/

I am about to have that one bent at a shop tomorrow and will post it on the forum in the next few days.
Depending on which one you like I can send you the file for it to have it cut at "Front Panel Express".
You may have to download the free software from them to be able to place an order with this file, I'm not sure about that.
I am not personally interested in becoming the supplier I'm just a fanatic DIY'er but you can get a raw panel in 5-7 days from them if you order using the order option in the free program that you can download from their website and then you can use my file, modify that file or even make your own .
I spent quite a bit of time on these to get them right, starting one from scratch requires a quite a bit of time investment and planning.
The rest of the build parts are all stock VTA ST-120 so everything else can be acquired from Roy or Bob except for the bias meter and the 4PDT triode - ultralinear switch.
Both of them have been very helpful with me on this project so far and I am hoping to pick up the transformers for them from Bob next. If you order the parts from them they will be there for back up and consultation. Give me a few days and I should have some build pics ready to post.
Baddog

Hi All:
Some shots of the preliminary parts layout out on the plate. I am doing it this way with all the rest of the amps as it is very easy to work on it and lets me play around a bit with the parts locations. When everything is just right I will drill the holes I need and bend it into the box format.
I had this one made without the mounting holes so alternate parts could be selected.I am also trying to use as many holes as I can for dual purpose wherever possible like the terminal strips, SCM module etc. and I am leaving enough room in the layout for a delay board as well.
Obviously there is a lot still missing (Transformers) but the look of the front face is of the amp is there and so far there is no crowding of the components which I like.
On Bob's suggestion I am using the c-17x chokes which are a lot bigger physically but still fit nicely on there.
You can also see that I am using some Russian K42 caps on the board (Also a Bob suggestion) we will see how they compare when I get this sucker fired up. I should have two possibly three amps to do a comparison with.
To help with the layout process I printed a few copies of the file I used from Front Panel Express and I am drawing various layouts in pencil on them to see where things might go best.
More to come shortly.
Baddog

Wow! Very exciting. Looking forward to seeing the next steps.

I don't see a hole for the power cord nor (preferably) an IEC power plug hole... or is that the hole next to the fuse?

I don't see a way to switch between the left (1 & 2) and right ( 3 & 4 ) bias readings to the meter! A 4 position rotary would have done that.

There are two mini DPDT switches with on-off-on postions located on each side of the the meter near the bottom of it with numbers to select the tubes individually for bias adjustment. Just move the switch to the desired tube and adjust the corresponding pot(also numbered). A rotary switch is not a bad idea.
Yes the holes are for the fuse and the power cord. I actually prefer the IEC and it is on the last two I had made.
The photo of the back side is a mock up with some parts I had and are not all are the actual parts I am using but you can see the mini switches beside the meter. One is a SPST mini switch I stuck in there for the photo of the front side.

OK, sorry I didn't realize they had a center off position, very nice!

Hi All:
Wow things have gotten interesting with my custom ST-120 project. It has morphed into a whole new ball game.
I had been working on trying to get more watts out of the KT-120 output tubes. The more I got into it the more changes I started to incorporate.
The amp now has deviated from the VTA format to the point it is becoming another amp. I have tried to keep a "Dynaco" look as much as possible even with the changes.

I now have two rectifiers and 2 power supply's and by my calculations it should make an honest 80 watts per channel. Its kind of two 80 watt amps on the same chassis with a common driver board.
To get more power I had to change the power transformer and I have just purchased the following custom toroid transformer with the voltages as listed:

The secondary is 430-0-430 @ 500mA, 70v @ 100mA, 6.3v @ 5 amps, 6.3v @ 5 amps, and 5v @ 5 amps.
Leads exit bottom in two bundles: Primary opposite the secondary windings.

Dimensions:
OD: 138mm x HT: 65mm. Encapsulated into toroid container: OD: 150mm, HT: 90mm.

I'm working on getting the circuit schematic done and hope to have it up here in the near future.

I also had to get yet another chassis made and found a second plate shop "Cam Expert LLC" that does custom plates as good as "Front Panel Express" but cheaper.

They can also etch the back side to 1/2 the plate thickness so bending is very accurate.

As soon as I get my new plate and begin to assemble this baby I will post some photos.


cheers
Baddog