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


    Futuristic ST-120 ?

    Share

    baddog1946

    Posts : 304
    Join date : 2010-02-03
    Location : Costa Rica

    Futuristic ST-120 ?

    Post by baddog1946 on Sat Oct 08, 2011 9:34 am

    Hi all
    I am doing my Christmas shopping and considering giving an amp kit to my son. A ST-120 came to mind immediately. After cruising the net for alternatives I finally decided that it was still the best bang and quality for the buck and will be ordering one in the next couple of weeks. However I had some thoughts about these amps after looking at the other competitors and the differences.
    The ST-120 is still the best option technically but the only place I had some second thoughts was in the cosmetic area.
    When you really think about it and read Bobs advertising, these amps bear only a passing resemblance to the originals internally and look quite different externally as well if all the mods are included such as the volume attenuator,triode switches, larger transformers and the coppertop rectifier.
    It made me wonder why Bob continues to make the chassis so true to the original format and does not implement a few technically sensible changes like making the hole for the old stereo-mono switch round for tidier attenuator mounting and the power cord hole square so it can take an IEC module and dare I say it make the bias setup like the M-125 mono blocks and eliminate those gaping holes in the front of the chassis. At least offer it as an alternative. Those thick stainless chassis are almost impossible to cut or drill neatly and how do you eliminate those big holes for the bias check??

    I know that it would deviate from the original but I have built two of these amps already and both times I would have preferred to have had these simple mods instead of the original existing situations with the obsolete square switch hole, gigantic octal base holes and separate cord and fuse holes. Since the amp is highly modified from the original I think that some minor improvements in these areas could be allowed nostalgia aside.
    These amps took the technical steps ahead in almost every way and a few minor adjustments to the looks seems innocuous enough to me and would enhance the amp's looks not to mention being able to use modern parts. I hope I haven't offended the die hard retro gang here.
    In any event I am still convinced of their quality and performance otherwise and will always have one in my stable. No offence Bob. Look for my order shortly
    Baddog1946

    Bob Latino
    Admin

    Posts : 2411
    Join date : 2008-11-26
    Location : Massachusetts

    Re: Futuristic ST-120 ?

    Post by Bob Latino on Sat Oct 08, 2011 3:02 pm

    Hi Baddog,

    The design concept behind the VTA ST-70/ST-120 was to make the amp LOOK LIKE an original ST-70 yet SOUND LIKE a modern high quality tube amp. Sort of like a '57 Chevy with a modern motor under the hood.

    Re: adding a IEC AC power connector. This is easier said than done. Right where the AC cord comes in you have about 3/4 of an inch of space inside before you bump into the bottom cover of the power transformer which drops down into the chassis almost an inch. An IEC connector sets into the chassis 3/4 inch to an inch and would bump up against the bottom cover of the power transformer. OK - Lets swap places with the fuse post - No - the fuse post sticks in even further (about 1.5 inches). About the only solution is to swap the AC switch with the line cord input and then place an IEC connector where the switch was. This can be done ..

    Re: the octal tube sockets on the front. They keep the amp looking original. If you machine some holes there on the chassis here for bias test pins like on the M-125's, then the bias test pins stick into the chassis about 3/4 of an inch and will bang into the two front Russian PIO caps. Yes - you can lean the front Russian PIO caps WAY back and get barely enough clearance. The Russian PIO caps cannot be put on the driver board top because the the chassis is in the way on what would be the outer solder connection.

    RE: the stereo/mono cutout and the stepped attenuator. The attenuator fits fine in the stereo mono slot and may be moved up or down slightly if desired. The black knob covers the outline of the stereo/mono slot and the slot is not visible when the knob is on there.

    I have had people ask me to offer TWO chassis - one original and one modern for the VTA ST-70/ST-120. This sounds good but I can get a better price from the chassis manufacturer on 100 pieces of the original chassis than I can on 50 original and 50 modern chassis. It's is a matter of $10 to $12 on the prices I get on these chassis ... I would have to raise the price of the kits to cover the extra chassis costs. Another thing is that every now and then I get a request from a customer to sell him an extra chassis for his OTHER ST-70 that he already has. I can ship it along with his ST-70/ST-120 kit in the same box. He wants a chassis that looks original because he is going to rebuild his old ST-70 and wants it to look "original".

    I guess it all boils down to a person's individual preference. I respect Baddog's opinions and his right to express them on this or any other forum but the chassis for the VTA ST-70/ST-120 amp kits will not be changed. If a customer wants to drill holes for his input jacks to be put on the back of the amp (and a couple of customers have done this) - well - he bought the kit - he owns it and can do anything he wants with it .. The VTA ST-70/ST-120 amp kits may also be purchased WITHOUT a chassis if you want to design your own layout and make up your own chassis. This is a lot of work but some customers have done this ...

    Bob

    tubes4hifi
    Admin

    Posts : 1286
    Join date : 2008-11-30

    Re: Futuristic ST-120 ?

    Post by tubes4hifi on Sat Oct 08, 2011 8:04 pm

    It's very simple to add a nice machined aluminum or wood front panel to an ST70 or ST120 amp, with small holes for bias test pins

    anbitet66

    Posts : 132
    Join date : 2009-12-23
    Location : Valley Stream, NY

    Re: Futuristic ST-120 ?

    Post by anbitet66 on Sun Oct 09, 2011 8:40 am

    With apologies to Bob,

    Baddog,

    What you are looking for is acutally available: http://triodeelectronics.com/st70chassisnew.html

    I'd rather use a repro chassis, but for those who want to upgrade the chassis as well, this should fit the bill as to "modern" spacing of the inputs, as well as binding posts for the speakers, and includes a cutout for an IEC connector and plug, etc...

    Tony

    Bob Latino
    Admin

    Posts : 2411
    Join date : 2008-11-26
    Location : Massachusetts

    Re: Futuristic ST-120 ?

    Post by Bob Latino on Sun Oct 09, 2011 9:02 am

    Re: Triode's chassis - things to keep in mind ..

    1. It is made of the thinner 18 gauge stainless steel not the 16 gauge as found on the VTA amp kits
    2. No place to put a stepped attenuator
    3. No original Dynaco silk screened markings on the front and rear face
    4. No quad cap cutout which means that you must use an under chassis quad cap replacement board which Triode just happens to sell ... hmmmmm ...
    5. It's not really usable with the VTA driver board because there are only TWO points (holes in the chassis) to measure bias. The VTA driver board needs four places to check bias. If this chassis were to be used with the VTA driver board you would have to either (1) drill two more holes to allow you to measure bias OR (2) take off the bottom cover and measure bias off pin 8 of each output tube every time you want to check or change the bias.

    Bob


    Last edited by Bob Latino on Mon Oct 10, 2011 5:33 pm; edited 1 time in total

    baddog1946

    Posts : 304
    Join date : 2010-02-03
    Location : Costa Rica

    Re: Futuristic ST-120 ?

    Post by baddog1946 on Sun Oct 09, 2011 2:29 pm

    I already rejected the Triode option for the same reasons Bob mentions. Too bad the VTA chassis option is such a hassle and expense. Looks like I will have to stay with what we have.

    bcinnamon

    Posts : 26
    Join date : 2011-05-07

    Re: Futuristic ST-120 ?

    Post by bcinnamon on Sun Oct 09, 2011 9:29 pm

    You can improve the aesthetics a lot with some careful paint work. I got great results by sending the chassis out to get powder-coated charcoal gray (afterwards you’ll need to file paint away inside to get a good ground connection where needed to the chassis). You can also experiment with different paint for the transformers and quad cap. I tried black engine paint and gold engine paint, but got the best looks with copper Rustoleum ultra high heat paint on the transformer bells and black on the plates — pretty good match with the glow from the tubes. The stepped attenuator and gold binding posts (all from Bob) also give the amp a much more contemporary look.

    My only “futuristic” request is a remote control stepped attenuator.

    Bob Latino
    Admin

    Posts : 2411
    Join date : 2008-11-26
    Location : Massachusetts

    Re: Futuristic ST-120 ?

    Post by Bob Latino on Mon Oct 10, 2011 5:29 pm

    Hi Barry,

    Your ST-120 is one of nicest "custom" ST-120's I have seen. You did a great job on customizing the amp. Below is a composite photo of the front and rear of Barry's ST-120 amp. Barry, maybe you can comment in more detail on the custom details of your amp?

    Bob



    bcinnamon

    Posts : 26
    Join date : 2011-05-07

    Re: Futuristic ST-120 ?

    Post by bcinnamon on Mon Oct 10, 2011 8:30 pm

    Hi Bob -

    All I did was some careful painting and upgrades — the design and sweet sound is all yours. The gold binding posts and attenuator (both from Bob) are a nice aesthetic and performance touch.

    I called around to local paint shops to find a place that would powder coat the chassis (this is the same finishing technique as factory audio equipment). I had my choice of colors, so I picked charcoal black to blend in. Cost was $125 and it took them one day to paint. The result was very uniform and scratch resistant. This scratch resistance was evident because it was difficult to file off the paint on the inside of the chassis where grounding points were located.

    There are not a lot of controls or adjustments on the amp that require explanation – so the look can be kept pretty clean. Even my family’s cat can figure out that the tubes are hot, the on/off switch is obvious, and the attenuator should be cranked all the way clockwise to “11”. But just in case, I made some white on black labels to identify the bias pins, bias voltage, speaker terminal impedance and proper attenuator setting.

    The two tone paint on the transformers took a bit of extra time (mainly because I screwed up) -- but the results are good enough for the living room. The first evening I sanded down transformers, cleaned off the dust, covered the wires with plastic wrap, then covered the transformer plates with masking tape. The second evening I carefully sprayed three coats of gold (generic) high temperature engine paint on the bells, painting right over the transformer screws (about 30 minutes between each light coat). The third evening I peeled off the masking tape from the plates, masked the bells, then sprayed three coats of black Rustoleum high temperature engine paint on the plates. I also sanded down and painted black the bakelite mounting plates for the RCA jacks and speaker jacks since these are exposed. I sanded down the quad cap and painted that black, too (I resisted the temptation to paint red doors and other colors black). The fourth evening I removed the masking tape from the bells — along with much of the (crappy) gold paint. So much for generic paint. I spent the rest of that evening sanding off the gold paint to get back down to smooth, bare metal. The fifth evening I sprayed on copper ultra-high heat Rustoleum paint. I was very happy to begin assembly the next evening when I found that the copper paint adhered well, and the black paint on the plates did not peel off with the masking tape.

    The rest of the assembly was textbook Bob. Since the top of the power transformer is copper (and not black), I probably sacrifice a very small amount of heat radiation capability. I’ve had no problems with tubes blowing or overheating — just the normal family strife about music tastes and volume levels. My wife likes the black look better than the stainless steel look, when the amp is on the glow from the tubes matches the copper paint, and my friends just assume that it’s a new design amp.

    tubes4hifi
    Admin

    Posts : 1286
    Join date : 2008-11-30

    Re: Futuristic ST-120 ?

    Post by tubes4hifi on Tue Oct 11, 2011 2:03 pm

    nice looking amp Barry,
    for some other alternatives, here's a couple photos of other ST70s I've built in the past . . . .





    Last edited by tubes4hifi on Wed Oct 12, 2011 8:58 pm; edited 1 time in total

    Tom

    Posts : 166
    Join date : 2011-04-04

    Re: Futuristic ST-120 ?

    Post by Tom on Wed Oct 12, 2011 9:01 am

    ^^Dang show off! Razz

    Those are Beautiful!
    You've about doubled my interest in this project. Very Happy

    Tom

    Posts : 166
    Join date : 2011-04-04

    Re: Futuristic ST-120 ?

    Post by Tom on Thu Oct 13, 2011 12:23 pm

    Roy,

    On the upper photo, named ST80A, share some info on how you positioned the circuit board?

    Upside down and hanging from the cover with the sockets on the backside (topside)?

    Moved the caps back and side to side with some insulation on the leads; or, are they where the board would place them.

    I'm really likeing that setup!

    Smile

    tubes4hifi
    Admin

    Posts : 1286
    Join date : 2008-11-30

    Re: Futuristic ST-120 ?

    Post by tubes4hifi on Thu Oct 13, 2011 10:46 pm

    Tom, the board is done as normal, except only tube sockets and bias pots on top side, all other parts on bottom side,
    suspended 1/4" below the top plate, very simple, I've probably build a dozen amps like that.
    there's a couple more similar ones shown here, some of this stuff is REALLY OLD:
    custom stuff

    Tom

    Posts : 166
    Join date : 2011-04-04

    Re: Futuristic ST-120 ?

    Post by Tom on Fri Oct 14, 2011 11:41 am

    Thanks Roy and WOW! Some of those are real beauties!

    You'd do well to advertise some of those setups better.
    No offense intended to the purists,
    but the ST-70, -120 have that look that,
    well,
    only an engineer could love?

    Very Happy Tom

    baddog1946

    Posts : 304
    Join date : 2010-02-03
    Location : Costa Rica

    futuristic ST-120?

    Post by baddog1946 on Fri Oct 14, 2011 5:59 pm

    Hi All:
    This thread has become interesting. It has gotten 500+ looks in less than a week. It clearly demonstrates the interest in the subject of alternate formats for the ST-70/120 amps.
    Maybe there "is" enough interest by some of us to get into trying something different looking. We already have a proven topology in the VTA boards etc.

    Here a suggestion on how it might be done.
    I have been fooling around with a program called "Front panel Express" which is a chassis design program by a company that will build your custom chassis design.
    This is a very innovative program in that it lets you do all the design work and they fabricate it to your specs. Small learning curve as well.
    Of course if you get fancy it will cost you but I came up with a beautiful design for an ST-120 type amp and the cost was under $200 with laser cut aluminum parts and etched labeling.
    You can get the individual panel cost estimates right on the program as you go along so you know where the cost is right away and when you have what you want send it in for fabrication.

    It is free to download from:www.frontpanelexpress.com/.


    I hope some of the forum members find this interesting enough to try one out too. Hell maybe someone will come up with a design a bunch of us will want.
    Its easy to print the drawings of your design and post them. That could be a lot of fun in itself. I hope this stimulates everybody's DIY genes and we see some great ideas in the near future.
    cheers
    Baddog1946

    tubes4hifi
    Admin

    Posts : 1286
    Join date : 2008-11-30

    Re: Futuristic ST-120 ?

    Post by tubes4hifi on Sat Oct 15, 2011 11:22 pm

    excellent program and vendor for those not in the state of Washington, I've been using their program for 6 or 7 years, but
    don't actually have them do panels for me as I'm a resident of WA state and therefore have to add 9.5% sales tax to their prices.
    So I have a place in New Jersey 2000+ miles away do my panels for me using the same program files!!

    baddog1946

    Posts : 304
    Join date : 2010-02-03
    Location : Costa Rica

    Re: Futuristic ST-120 ?

    Post by baddog1946 on Sun Oct 16, 2011 9:00 pm

    Hi Roy:
    I agree with you the "Front panel express" program is excellent not to mention easy to use. I think it could prove to be very useful to members who may want to do a custom faceplate for their ST-70/120's.

    A good way to clean up the bias sockets! A new faceplate could be a cheap and easy mod and lend a very professional personalized look to any ST-70/120 the new faceplate is an idea you suggested in the commentary on one of your own designs photos.
    I just checked the faceplate on a chassis I am doing for an ST-120 project and it was only $45.00. Considering the quality of the finished product that would seem a reasonable cost.

    Since it can be mounted right on to the existing chassis with a couple of existing screw holes or even with some epoxy or polyurethane glue the original amp remains basically unaltered and the faceplate can still be removed so the amp keeps its original condition value.
    This may also be a good option for the member who wants to mount the bias meters on his amp.
    cheers
    Baddog

    davidness

    Posts : 39
    Join date : 2010-09-15

    Re: Futuristic ST-120 ?

    Post by davidness on Mon Oct 17, 2011 9:49 am

    tubes4hifi wrote:excellent program and vendor for those not in the state of Washington, I've been using their program for 6 or 7 years, but
    don't actually have them do panels for me as I'm a resident of WA state and therefore have to add 9.5% sales tax to their prices.
    So I have a place in New Jersey 2000+ miles away do my panels for me using the same program files!!

    I've never known a state that requires sales tax on items meant for resale.

    Sponsored content

    Re: Futuristic ST-120 ?

    Post by Sponsored content Today at 10:05 am


      Current date/time is Tue Dec 06, 2016 10:05 am