How many new builds startup without issue

[Planobilly]

Hi Guys,

I have not built a lot of amps. Perhaps ten or so at this point. About half have some small startup issue. 99% of the issues turn out to be a wire I left out or reversed wire on the output transformer. I have had zero issues with hum or noise caused by lead dress. Zero issues with bad solder joints.

Zero components failures I guess due to the fact I measure every resistor and cap before I install it. Of course there is the typical tune up, bias setting sort of thing.

What is your experience been with new builds?

Cheers,

Billy

BTW...hum is a good thing!! It tells you screwed up...lol

[PRR]

I may be weird. I'd never build a non-trivial circuit all-at-once. Everything can be broken into stages which can be debugged separately.

Also I'm often being creative (or crazy) and know I do not know what I am doing. If the focus is a power amplifier, I may tack-up the essentials powered from another source, and see if it smokes. With a more certain path I may wire line cord, PT, check for AC, diodes and caps, find DC, heater lines and see filament light. Then amplifiers stages front-back or back-front depending which way seems clearer. Check DC bias on each stage as it finishes.

Yes, I have got 98% done and then saw my big OOOPS! 6-part system and at the very end I realized the meter would not interface right. But since all the pieces were working separately, it was not hard to devise and test a fix.

[tubeswell]

Generally, the more amps you build, the less startup issues you tend to have, tho' the number of issues with each successive build approximates a poisson distribution (statistically speaking), and so there is a small likelihood, that even with vast experience at amp building, you will make a cock-up now and again. So you can never be too thorough in your checking.

[alerich]

I may be weird. I'd never build a non-trivial circuit all-at-once. Everything can be broken into stages which can be debugged separately.

+1 on this. I always build the power supply, bias supply and power amp first and get that powered up and idling correctly before I move on to the preamp.

I am 3 for 5 to date. The two that didn't fire up correctly the first time were a Vibro Champ (my first build) with the wrong value resistor at the grid of the 6V6 (took a while to find that) and a 100 watt SLO clone that I had wired the signal from the PI to the power amp in such a fashion that it was canceling itself out (rookie mistake - first quad tube 100 watt build - took a long time to sort that one out). I don't count OT primary wiring polarity as a mistake since that is largely a coin toss.

If it fires up the first time you know how to wire a circuit from a schematic/layout. If it doesn't and you have to fix it, you learn how to troubleshoot and repair. Both have value.

[eleventeen]

"If it fires up the first time you know how to wire a circuit from a schematic/layout. If it doesn't and you have to fix it, you learn how to troubleshoot and repair. Both have value."


Very true.


I do the same as alerich. I wire up the heaters, test 'em, see if tubes light up. Wire up the P/S, see it if works. Not necessarily in that order. Plus, I will know that the P/S, if unloaded, will put out significantly higher volts than when under load. Then bias. Arguably, it is very not smart to fire up a power section with the operation of the bias section untested/unconfirmed. When the bias is going, I confirm the range and crank it as negative as it will go. For a -50 volt design objective, I want to be able to ramp the bias up to negative 75 volts or neg 70 volts. I want to be able to pretty much shut down the output section. I ALSO want the bias NOT TO BE ABLE to go under say 30 volts. THat way, no matter how absent-minded I may be, I cannot crank it so low the output tubes blow up.  So unless I am building a specific design, my first sub-project is to get the bias to range higher than I will want and lower than I want but not able to go too "low".
 
Then I pretty much wire up all the rest. If I have gotten the output bias where I want it AND confirmed the B+ P/S is working, I might stick in the output tubes power up the first few preamp tubes, just to see if I get that golden 1.2-2 volts on the cathodes. I might not.

[Planobilly]

Hi,

Thanks for the feedback.

For me, what ever startup issues there are get fixed in a few minutes without burning anything up. I install and test the power transformer first and test all the tube sockets for correct voltages. After I have the rest of the amp built I install the reciter tube first do some checks, then the preamp tubes, then the output tubes. I check all the plate voltages first. If there are no high voltage issues it is pretty hard to burn anything up.

If I have the output transformer wires reversed that is apparent the second you turn on the standby switch and a quick fix because I have left enough lead to reverse the wires.

Normally for me, if I have an issue, it is because I forgot a ground wire somewhere. I am sure I could get to near 100% correct startup if I took the time to mark every wire on the schematic.

Then there is the case of perplexing issues. I just finished a Mojotone 18 watt clone. Everything started up without issue except.......

The low input jack works fine with a signal generate at any reasonable mv level. The jack works when I plug in a CD player. I see the signal on my scope. Inject a 30mv 1000hz signal and plug into the top jack and I see the normal signal at the grid. Plug into the bottom jack and the signal is attenuated in a normal manner. When I plug in the guitar in that jack I get no signal. This is going on as I write this. I need to go find the issue before I start writing a bunch of four letter words...lol

Cheers,

Billy   

[PRR]

Don't over-look the parts you are overlooking. Bad guitar cable?

[Planobilly]

first thing I checked!!

Billy

[vibrolax]

I've built a dozen or so amps / preamps.  Only one (#2 I think) had a problem bad enough to blow a fuse on the variac.  Never smoked a resistor, or hooked up an electrolytic capacitor the wrong way.  I destroyed one small output transformer breadboarding an early project, not sure how.  I always test the power supplies before connecting them to the load. Before powering up, I make sure all ground terminals have low resistance to the single chassis ground point and that all power rail terminals have high resistance to ground.  On one preamp channel I forgot a tone stack ground that made the tone stack not work.  I generally check off each wire and component on my layout printout before power up.  I might have made one socket wiring error on an early build, but I caught it before power up.  I bring up everything slowly with the variac, first without tubes, and then with recto tube only, then with the rest.  On fixed bias builds, I adjust it to max negative voltage.

A bad solder joint or two have made it into several of my builds.  One took me almost 10 years to find...there was this subtle fizzy sound on note decay....made me think the design was somehow defective.  During the process of replacing the input jack, I found the bad joint on the shielded input wire.

I've never used a pre-existing layout because I actually enjoy the process of creating a Hoffman-style layout from scratch.  They are just so darn logical and systematic!  Once or twice I've laced the buss wire around the wrong set of turrets (caught before installing components).  If I ever wanted to build something that already had a Hoffman layout, I'd probably use it.

For several of my early projects, I built a prototype board and installed it in scrap chassis just to hear if it was worth building in a pretty box.  For many of my later projects, after I make my layout from the schematic, I'll make a pspice schematic from the layout and simulate it with LTSpice.  I like to see all the node voltages, currents, and signal levels coming out right before I build.

Now I have fair confidence everything will be functional on the first try.  I publish build documentation for each project on my website, which is my way of giving back for all the information I've obtained from the internet.  I've been doing more complete docs on later projects.  It all seems worth it when builders send me pictures/clips of their clones/adaptations of my projects.

Checking the design and layout before building, and checking the build before power up can be a drag, but I find rework to be a bigger drag, and ruining more expensive things like chassis and transformers is worse.

[drgonzonm]

Does any one use a check list?  When I was designing pools, I always used one, really cut the errors down.  Building an amp, is more complicated than designing pools.

If you are using a checklist please share.  Thanks. 

[labb]

Schematic, layout and a color marker save me a lot of headaches.

[jim]

 For me it is always a very simple issue that keeps an amp from working--usually an unsoldered eyelet or a missing jumper.  Almost never a bad part.   Then  there is always something you overlooked in your excitement to finish the build.  Even though it might work from the onset you still rework it to be quieter...more gain, T,M, or B etc.  When are we ever really done with it?    Jim

[Planobilly]

Well Jim...It is easier to get "done" when you build the amps for other people. Somehow they never want to let me keep their cool amp and take it to the gig to play...lol

If I really like the kind of amp I am building it is a lot easier to take the time to check every single detail. I just finished the third baseman in the last month...so I am kinda burned out on building that model. The good news is all three started up without issue.

A written check list is actually a good idea.

Billy

[macula56]

I also tend to go with the "build the power supply, bias supply and power amp first" group. That way if I do have any problems with the rest of the circuit I can rule out power problems. I built my last 4 like that and had zero problems.