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The Dynaco Tube Audio Forum

Dedicated to the restoration and preservation of all original Dynaco tube audio equipment - Customer support for Tubes4hifi VTA tube amp and preamp kits and all Dynakitparts.com products


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HarryY
StevieRay
Peter W.
New2Tubez
Mr C
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    Starting My ST120 Build.

    Mr C
    Mr C


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    Post by Mr C Wed Aug 14, 2019 4:35 pm

    UPS delivered the ST120 yesterday evening. I've unpacked it and set up my workstation. I started assembling the chassis and at the moment I'm on the SCM. So any tips and suggestions, things to look out for, things to be aware of etc. will be greatly appreciated. I work slow so this may take a couple of weeks or so. I'll post my progress here and any questions I may have.

    Mr. C
    Mr C
    Mr C


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    Post by Mr C Wed Aug 14, 2019 11:57 pm

    I did some of the chassis, switch, sockets, speaker posts, fuse. Soldered up the SCM. I need to paint the transformers so I stopped on the chassis. Looking around I dont have any paint so tomorrow I'm off to the hardware store. I started on the driver board in the mean time. Soldered the pots and transistors in. Fitted the tube sockets but I'm going to call it a night.
    Mr C
    Mr C


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    Post by Mr C Thu Aug 15, 2019 6:30 pm

    Finished up the driver board today. It actually went pretty quick once I got started. It looked a little overwhelming when I laid out all the bags. Each step in the instructions is in it's own bag and labeled so it looked like a lot. Took me maybe 3 hours. And I work slow. I got some paint and sandpaper for the transformer this afternoon. The bench is a bit messy after that. I need to pick up the tools and clean up the mess before I do anymore.
    HarryY
    HarryY


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    Post by HarryY Fri Aug 16, 2019 12:27 am

    I would suggest running some emery cloth or fine sandpaper on the terminals of the
    quad cap before installing it. (Mine was a little reluctant to have the solder flow well on it.)

    When you mount it get a grip closer up to the chassis and twist the tabs just enough to hold it tight.
    I believe the instructions said 1/4 turn twist but I only needed to twist about 1/8 turn.

    I also added a couple extra jumpers from the tabs on the can to better ground it.
    In total I have one jumper to each of the ground lugs on the main grounding point next th the quad cap and I ran
    another to the tube socket closest to the quad cap (V7) (The same lug the ESL reduction cap connects to on V7)
    I figured since  that's the main power supply cap it would be worth making sure it was well bonded to the chassis.

    Mr C
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    Post by Mr C Fri Aug 16, 2019 2:03 pm

    Thanks Harry. Thanks. I'm at a standstill for a couple of days, I'll definitely look at an extra ground for the quad cap. It's not in the chassis yet. I probably wont get back to it till early next week.
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    New2Tubez


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    Post by New2Tubez Fri Aug 16, 2019 2:37 pm

    Don't know if you've seen any of the soldering videos on the web but the NASA avionics ones, though tedious, were helpful for me. I didn't follow these to the letter but did end up with good clean connections:

    https://www.youtube.com/watch?v=0SnOW2VdCTI

    I wiped everything down w/ 99% isopropyl before soldering. The quad cap wasn't too bad for me but the gold speaker terminals took some time. The alcohol is also good for removing the rosin with a stiff bristled acid brush and kimwipes.
    Mr C
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    Post by Mr C Fri Aug 16, 2019 5:35 pm

    I remembered the alcohol after I had already got aways into the board. I worked for a defense contractor in my younger days. The technicians in the labs always had alcohol on their bench. I remembered they'd dampen a pad and wipe things down before and after they soldered. I have some 99% on my bench now and was wiping the flux off then looking at my joints with a loupe. I went over a few solders that looked a little iffy. Funny, they where some of the first ones I did. The video was a great refresher and reminder.
    HarryY
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    Post by HarryY Fri Aug 16, 2019 8:43 pm

    You may want to consider adding the stepped attenuator if you didn't order it along with the kit.

    Mr C
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    Post by Mr C Sun Aug 18, 2019 2:37 pm

    So far I have most the chassis hardware in and got started on the wiring. I left off at step 10 on the instructions. Today I'll QA everything I did yesterday then keep going. This seems the most time consuming part so far. Trying to keep it neat and not too amateurish looking. Wink I looks pretty good so far. Clipping the wires, as my friend Bob Vila always says.. Measure twice, cut once. You have to extend the wires on the second choke. I used the wire clipped off the first choke to extend them and it came out nearly perfect.
    HarryY
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    Post by HarryY Sun Aug 18, 2019 3:37 pm

    Mr C wrote:-- snip --

    I used the wire clipped off the first choke to extend them and it came out nearly perfect.  

    I did the same thing and used some black heatshrink on it, hid the splice nicely.

    Mr C
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    Post by Mr C Sun Aug 18, 2019 4:15 pm

    HarryY wrote:You may want to consider adding the stepped attenuator if you didn't order it along with the kit.


    I didnt get one. Most I listen to is vinyl and I figured I'd get a good preamp down the line. I can always get it later.
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    New2Tubez


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    Post by New2Tubez Sun Aug 18, 2019 4:21 pm

    Mr C wrote:
    HarryY wrote:You may want to consider adding the stepped attenuator if you didn't order it along with the kit.


    I didnt get one.  Most I listen to is vinyl and I figured I'd get a good preamp down the line.  I can always get it later.

    I do the same and after a year, still only have a phono pre. This won't be fun to install later.
    Mr C
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    Post by Mr C Wed Aug 21, 2019 2:14 pm

    I made it through the "Wiring" section. It went okay. The instructions where great, I did a QA on the wiring and every thing looked good as per the instructions. I got started with "Installation of the VTA driver board" section. I'm just a couple of steps in on page 10 now. There is 1 bag of parts left! The 10 ohm 2 watt resistors.
    Mr C
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    Post by Mr C Thu Aug 22, 2019 1:58 pm

    I guess I hit a milestone yesterday! Finished up the installation of the DB and the last bag of parts got installed. There are no more parts to go in! Well, one, the power cord. Not much left it looks like. Just connecting the DB and testing. Today I'm going to QA the last section I did before I go any further.
    Peter W.
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    Post by Peter W. Thu Aug 22, 2019 2:48 pm

    I will render opinion here, and not specific to the very fine amp you are building, but to the species in general.

    a) Power Amplifiers are best when they are only power amplifiers. Adding attenuators to them becomes useful *only* when one is using only line-level sources with no on-board attenuators.
    b) For the same reason, I am best-described as 'unsure' of the Triode-Switch option. Why would I go out and purchase a prize bull, then emasculate it?

    I have several times discussed the virtues of a pre-amp that includes some level of gain, and the pre-amps I have on-line include those that will make up to 14 volts (vs. the typical 2 volt nominal "line out" level) out. This will exploit the maximum headroom possible from an amp - and when the amp is tube, the issues with hard clipping are eliminated or reduced.

    So, I see no downside to not installing the attenuator, now or ever. As an example, my most complicated system includes: Power-amp, pre-amp/tuner (Revox A720), equalizer, HD tuner, Cassette, RtR, and two (2) turntables. The pre-amp becomes a wire-management tool and traffic-cop as much as anything else. An amp-based attenuator is kinda-sorta silly in that set-up. Note that the A720 allows balancing the inputs - so that there is no perceived level difference when switching components.
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    Post by HarryY Thu Aug 22, 2019 6:22 pm

    If you have not done the tube rectifier diode mod (AKA Yellow Sheet Mod)you may want to include it
    Mr C
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    Post by Mr C Thu Aug 22, 2019 7:38 pm

    Thanks Peter. That was my thoughts as far as the attenuator. I haven't looked real seriously at preamps yet. I'll use the pre out on the Marantz 2245 for the time being.

    Harry, Thanks. Looks simple. I'll see what I have for diodes.
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    Post by Mr C Thu Aug 22, 2019 7:57 pm

    I made the last solder connection. The power cord to switch. Next section is "Initial Startup". Essentially it's all together. I cant really call it finished till it's turned on and tested. So is there anything I should do in the initial startup? I had thoughts of going through my DBT first time I turn it on. So what are the odds of this thing firing right up? Say, out of 100 kits sold, how many people have problems, how many fire right up? I'm a little afraid to plug it in. Neutral
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    Post by New2Tubez Thu Aug 22, 2019 8:10 pm

    Mr C wrote:I made the last solder connection.  The power cord to switch.  Next section is "Initial Startup".  Essentially it's all together.  I cant really call it finished till it's turned on and tested.  So is there anything I should do in the initial startup?  I had thoughts of going through my DBT first time I turn it on.  So what are the odds of this thing firing right up?  Say, out of 100 kits sold, how many people have problems, how many fire right up?  I'm a little afraid to plug it in.  :|  
    I was the same. I waited almost a week. Ultimately it was either going to work or not but it did and sounded great! My first real soldering project in about 25 yrs.
    I had it plugged into a power strip just in case. I eventually got a variac as the wall current is 122 to as high as 129vac which is a bit much.
    It'll smell a little for a few hours. I miss that smell...
    Good luck and let us know how it sounds.
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    Post by StevieRay Fri Aug 23, 2019 8:45 am

    Plug it in, turn it on, but have a multimeter ready/set/go before that.

    Find the check list that came with the amp instructions, that lists all the voltages for testing, and their ranges.  Find these test points ahead of time.  Be aware of safety. Clip the multimeter ground lead somewhere, and use one hard to probe around.  Be careful not to short points together with the test leads!  Especially be careful probing around the printed circuit board!!

    if all checks good, proceed to checking and doing a preliminary bias setting for each tube -- these would be incorrect during your preliminary voltage checks, because it had never been done.  Make sure you fire it up with all bias pots counterclockwise, and make sure the amp has a load -- a speaker connected, or I like to use some 20W 8-ohm resistors.

    NOTE:  If any tube doesn't bias, turn the amp off immediately and figure it out.  Maybe even come back tomorrow and figure it out, after studying the schematic and putting some thought into it.

    When I fired mine up, one tube wouldn't bias.  I turned the amp off and started checking, looking back especially on the PCB.  After looking over the schematic for the bias circuit, then the PCB, after about 15 minutes I discovered a resistor in the bias circuit that I failed to solder on one end.

    Otherwise, that's the only problem I had -- perfect from the start.

    Note that I use a Weber WS-1 with thermistor built-in, and a time-delay board.

    Cheers and good luck!!
    Mr C
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    Post by Mr C Fri Aug 23, 2019 1:56 pm

    I plugged it in last night and went through the initial startup. The tubes glowed. I let it warm up a bit and set the bias. No problems. The bias set to .500 and was pretty steady. Dead quite. I hooked it to the preout of the Marantz this morning and threw in a CD. It started to sing! Sounded wonderful even through the little desktop speakers. I'm thrilled. What a wonderful kit! The instructions where great. Fairly easy to assemble. After every couple of pages I went back went through it again. After I finished I went through the entire instructions again. I didn't find any mistakes. YEA!! Thanks Bob!
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    Post by Peter W. Fri Aug 23, 2019 2:05 pm

    Excellent outcome!
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    Post by HarryY Fri Aug 23, 2019 5:03 pm

    Mr C wrote:I plugged it in last night and went through the initial startup.  The tubes glowed.  I let it warm up a bit and set the bias.  No problems.  The bias set to .500 and was pretty steady.  Dead quite.   I hooked it to the preout of the Marantz this morning and threw in a CD.  It started to sing!  Sounded wonderful even through the little desktop speakers.  I'm thrilled.  What a wonderful kit!  The instructions where great.  Fairly easy to assemble.  After every couple of pages I went back went through it again.  After I finished I went through the entire instructions again.  I didn't find any mistakes.  YEA!!  Thanks Bob!


    I'm glad to hear it came to life nicely for you.

    They really do sound nice.

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    Post by Dogstar Tue Sep 03, 2019 12:05 am

    How about posting photos? Internal and external please.
    Mr C
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    Post by Mr C Thu Sep 05, 2019 11:47 pm

    I'll have to figure out how to host photos first. We'll see

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