First Timer...Seriously

When I was younger I dabbled in remote control model construction, which involved some very minimal soldering.  Currently I am a dentist so I have the hand skills...BUT...I just got my ST-120 kit from BOB and it is going to be an adventure to say the least!

Last night I began my work with about 1.5 hours to attach everything to the chassis.  The only problems I ran into so far are
1. A missing nut to hold on the fuse holder (which I should be able to grab from Radio Shack)
2. The quadrouple section filter capacitor, with the mounting pins twisted 1/4 turn, doesn't seem that tight to the chassis, it wiggles a little. I attempted to trist the pins a little more but almost broke one off so I stopped!
3. Any advice on soldering?  I am far from an expert...

Any advice on #2 and #3 would be appreciated.  Also, I love Bob's instructions thus far and I not having trouble following them, but would also like to understand WHAT each component does and why it is wired the way it is.  Any good resource to learn that?

Photos to come...

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PeterCapo wrote:2. With a set of whatever kind of pliers you can fit in there (robust needle-nose or whatever), twist the tabs lower down, closer to the chassis – that is, don’t grab them at the tip.  You shouldn’t have to do more than ¼ turn.  To shore-up the ground, run (solder) a short piece of wire from the twist-tab to the adjacent star grounding lug.

3. Apply heat from the soldering iron tip to where the different surfaces being soldered come into contact and apply solder either there or to the opposite side.  The key is to heat both/all mating surfaces that need to be soldered and applying solder to the mating surfaces.  Wipe the soldering iron tip often and keep it “tinned” with fresh solder before making a connection.  Large diameter solder is harder to work with.  I suggest something in the range of 0.02” or 0.03”, but different diameters are available at Radio Shack, so experiment and see what is more comfortable for you to work with.

Thanks Peter, I will try twisting closer to the chassis to see if I can tighten it down. Seems odd that all the components are screwed in so securely to the chassis yet that quad capacitor is so flimsily attached!

Thanks for the soldering tips. I have .050 now but have some Kester 44 .032 on the way which comes highly recommended. May wait for that before I get to the tough stuff.

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PeterCapo wrote:Kester solder is real good.  You can do a good job with other solders, but in my experience Kester flows and sets-up better.  If I recall, we used Kester eutectic (63/37) at Raytheon in the missile sub-assemblies because it is stronger - not really a requirement for audio, unless we’re planning on strapping our Stereo 70s under the wing of an F-18.  Then again, I have seen cracked solder on tube socket lugs, so a eutectic blend here might be advantageous over time, especially for active tube rollers.

The twist-tab multi-section can is a classic design.  They have always been that way in the original Dynacos and, I believe, in a lot of other gear.  It would be good to get those tabs tighter, but running that short length of wire to shore-up the ground is important, regardless.

I am assuming that ground connection will be somewhere in the future instructions from Bob, correct?

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I just finished my 70 last night and fired it up. I found the soldering got progressively better as the project moved along. Youtube is YOUR FRIEND, watch some videos. Also, I used Kester eutectic .032 and it was much better than something else in .050 I had laying around. I also tried whenever possible to tin both pieces before I put them together and that made a huge difference. I bet my next build will be nicer, if I decide to tackle a pre-amp.

Here is a nice video of a guy assembling a kit of a different vendor: https://youtu.be/s5rWCEux_BI He explains and shows nicely how soldering is done. Hope this link is not inappropriate. Otherwise pls delete this entry. I have no relation with that vendor (but have also bought their products in the past).

Enjoy your ST120. I built a ST70 and could not be more satisfied with it.

Michael

So, like ... what's the reasoning behind the additional ground? Noise drain? Doesn't seem like there's any internal electrical connection to the can.

I didn't solder a tab, but I figure I get a decent enough ground for that via the clamp ...



I will add that to my "to do" list next time I get in there though. Doesn't seem like it'd hurt any, but not sure how it will help.

Laminarman wrote: I found the soldering got progressively better as the project moved along.  

You forgot to mention the part about how you backtracked the earlier connections to bring them all up to the same stellar standard you achieved with practice ...   

sKiZo wrote:

Laminarman wrote: I found the soldering got progressively better as the project moved along.  

You forgot to mention the part about how you backtracked the earlier connections to bring them all up to the same stellar standard you achieved with practice ...   

   Now if I did that I wouldn't have an excuse to build something else, would I???

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Waiting for my helping hands and .032 solder before I continue. It is very hard to solder the connections without some sort of helping hand!

Anyone have a good resource to read up on how these babies actually work, such as what each component is for, etc.?

On some of the older Fender amps it is a typical practce to solder the lugs to the chassis for securing the cap can and for proper grounding. An 80 watt with 1/4-inch chisel tip were a must for this application since the chassis acts as a large heat sink.

Besides the need for the hefty soldering iron and tip is there any specific reason this is not sugggested?

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[/quote]Cost: running a short length of wire is a lot cheaper and easier.  I always like to keep an eye toward rework, too; if you think it would be hard soldering those tabs to the chassis, wait until you need to replace the quad can after that.

I mean, I'm sure it's doable, but it seems to make extra expense and work and might possibly damage the chassis (?) and other parts - who knows how that much heat applied to the chassis could affect the quad cap (new one) or other parts.  I would question whether those twist tabs were really meant for soldering.[/quote]

I would agree running the short length of wire is a lot cheaper and easier but for those folks who have the tools and have been doing it for a while as a general practice for guitar amps it begs the question why not for this application. I have replaced 2nd, 3rd and who know 4th generation quad caps on an amp with soldered tabs and it isn't much of an issue especially with a higher wattage and chisel tip soldering iron. Actually after the first replacement it seems future changes are easier. With a good amount of older solder on the chassis helps with the reheat and reflow.

As you noted it could possibly scar the chassis. For most guitar amps, the chassis is hidden by the cabinet so a bit scaring will not be noticed, whereas on a nice shiny Dynaco, etc. with the cage removed it could show up on the exterior.

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Hi..
Just my two cents on this...Sure it's possible to solder one or more of the can capacitor mounting
tabs to the original Dynaco chassis and I have seen this done. But try doing this to either Bob's or my (Dynakit) stainless steel chassis...Not going to happen unless you Mig or Tig this....Another option would be to stick weld this but expect a lot of weld splatter and surface penetration.

Kevin

So this weekend I spent a good amount of time on the St-120 and I am about 99% done, ready to power it up, adjust, and get to listening!

Any tips with regard to pre-initial startup?

Also, I feel like I got so into the build that I finished it faster than expected, and I truly enjoy building it. How do you guys continue to get to build these things once one is done?

"How do you guys continue to get to build these things once one is done?"

Oh oh!  You've got the bug!  Since my first st70 build I have built another st70, a monoblock push pull for my youngest son and helped my oldest build a Millett DCPP amp.  I've also built three guitar amps (including one that I designed myself) and several guitar pedals.

Anyone need some solid state amps???? I've got several for sale!

DrZ123 wrote:So this weekend I spent a good amount of time on the St-120 and I am about 99% done, ready to power it up, adjust, and get to listening!

Any tips with regard to pre-initial startup?

Also, I feel like I got so into the build that I finished it faster than expected, and I truly enjoy building it.  How do you guys continue to get to build these things once one is done?

Before adding any power. check every solder joint.  Lightly tug on the wires to make sure they're secure.  Check all of your grounds with your meter for continuity.  

Know if you miss something and it doesn't work, that you're not alone and it happens to the best of us.  Be safe and patient.