Looking to apply some T.L.C (Heath TA-16)

[DBK]

I have another post about my heathkit TA-16. But in this post i was hoping to get some responses about what caps and or resistors and what not i should replace with new ones. possibly a picture showing me some in detail. i can solder just fine but i am an amp newbie and i got this amp to essentially learn how to repair/upgrade/mod with out ruining something expensive or what not. any help is greatly appreciated.

Thanks.

[R.G.]

That's an oldie!

First thing to do: replace every single electrolytic (polarized) capacitor in the box. Don't sweat replacing resistors until you find one bad.

Of particular interest are C104, the main DC power supply filter cap, and C22, the output speaker capacitor. Replace both of these with a capacitor of at least 4700uF and at least 50V ratings. For the others, replace them with the nearest standard value, which may be larger (e.g. 4700uF replacing 4000uF, 2.2uF replacing 2uF) and at least as large a voltage rating. More volts is OK too, but over 63V rating does you no particular good.

Take good digital pictures before you change something. You can delete the photos later if you want, but it gives you a good way to figure out what you did later. The digital camera is a vastly underappreciated tool for electronics work.

[52 Bill]

I'm with R.G. here, the electrolytic caps are suspect, especially in the signal chain.

What is the reason for your want to change components? Bad sound? Reliability? Soldering practice?

Do you have the schematic for this amp? How about the assembly manual? Both of these items will help you to better understand the circuit and how it works.

The output section of this amp uses a mix of Silicon NPN and Germanium PNP transistors. Not uncommon for the time when this was developed, but often an overlooked detail when repaired by modern techs.

[DBK]

I'm interested in having some fun tinkering and learning at the same time. its a pity i didn't get to build it when it was new. Mainly I'm not sure that I am going to do a lot. I'm just wondering about things to do to it to make its sound a little cleaner at higher volumes. and fixing the tremolo unit. As it is i put some higher wattage speakers in it and i can turn it to volume 4 with out an incredible amount of breakup. but if i go past 4 the amp starts cutting out and over fuzzing. if i use the amp at volume 2 and say pump it up with full volume pedal effect it gets very loud and sounds good but if i click off the chosen effect there's a huge volume dump. I have a schematic which is kind of hard to understand but i sort of do from guitar diagrams. its a bit more complicated. i don't have a manual but i do desire one. i just cant afford the 25$ for one online right now.

[52 Bill]

Do you have any test equipment? A basic multimeter? Capacitor tester? Do you have enough basic skills and confidence to work on an amp while it is plugged into the wall?

You can find resources online to learn what the symbols on the schematic mean, as well as basic test procedures, like transistor checking.

If what you are saying about using a pedal is that it will play loud and clear with the pedal acting as a boost, then it would seem that the power amp section is working fine and you can investigate the pre-amp circuits for the distortion problem.

[DBK]

I do have some test equipment but probably not the right kind for this. Ill look into buying the right ones you've listed so far. if there's anything else other than those and the manual let me know please. you've been a great help 52 Bill. As well as you R.G. i am sure ill be back with more questions in the coming days. Thanks again.

[52 Bill]

You don't need to go overboard with test equipment, a good multimeter and a decent soldering iron and desoldering system will be more than enough to get started.

Modern meters will now include functions like capacitance and frequency as well as transistor gain. A decent soldering iron with temperature control and interchangeable tips will make your life a whole lot easier. And either a solder sucker or a solder wick will help make part removal much easier with less damage to the pc boards that you will be working on.

[Mark Hammer]

I just picked up one of these over the weekend, ironically. The tolex was kind of dirty, the PCB needs to be hosed down (though I'm using Q-tips and alcohol instead), the wiring is getting kinda crunchy, the jack for the reverb had broken and needed replacement (now replaced), and the reverb pan needed some serious work with rust remover, but it works reasonably well. The grill cloth on mine had been replaced with nylon screening. I'm swapping that for some lovely woven cane material I bought locally that comes very close to the cane material old Mesa Boogie used for their earliest models. The tolex cleaned up very nicely, using some car vinyl cleaner and a stiff (nylon) bristle brush.

The first thing I noticed on mine was the hiss. I read on someone else's web page that they had replaced the input transistor (Q1 and Q2) with a 2N5088 instead of the 2N3391 that it came with. I figured I'd go one better and stuck a 2N5089 in there instead. The hiss is completely gone now.

The higher value electrolytics will be the next things to get replaced so that both hiss AND hum will disappear.

I installed a bright cap on the volume pot of the normal channel, but think I will now install it on both normal and reverb channels, and make it switch selectable. happily, there is plenty of room for installing toggles on the faceplate where the pots mount. I started out with a .01uf cap on the volume pot, but think I'll make it selectable between .01uf, .022uf and none, since I have a bunch of on-off-on toggles sitting around. A value of .01uf gives audible brightness and sheen with single coils, though I suspect it will deliver a much less audible effect with humbuckers (hence the option for .022uf). Certainly the use of a bright function benefits greatly by the transistor swap since one would normally be turning the treble down to make the hiss tolerable. Now I can crank that treble, and enjoy every ice-pick-through-the-forehead moment of it. Somewhere, Johnny 'Guitar' Watson is saying "Did I just hear my name called?".

The turnover frequencies for the tone controls are easily modified by switching one cap for each of them. Obviously not the same as having a 4-5 band graphic on board, or sweepable midrange, but can provide more tonal flexibility for minimal cost and no substantive change to the circuit. Probably the more useful case would be modding the bass control (C101/102).

I'm planning on dickering around with the reverb circuit. Specifically, I find that I like to shave some of the bass off the driving signal so that it provides more of an ambient shimmer than an explicit Dick Dale "doyoyoing". That will likely entail playing with the values of C23 (.22uf) and C25 (.47uf).

The speaker wires could be a little thicker, and I hope to run some 16g (or thicker) lamp cord from the PCB to the speakers instead of the thin stuff there now. When the amp expects to see a 4ohm load, you don't need to add a half ohm, or whatever, from the connector cable.

Mine came with the lower back panel, but not the upper one that goes immediately behind the amplifier portion, so I'm going to have to fabricate one. I might make it extend a little lower than the original to provide some a little closer to a closed back (though not entirely), since this may double as my bass amp. And I suppose some feet, or maybe even casters, might be useful to add.

Finally, this thing desperately needs a real power cord, rather than the skimpy lamp cord and polarity-flipper it came with. I would like to put those days of tongue-to-mic electrocution behind me.