• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Do I NEED to bring up an old amp on veriac?

For the most part, none and none Trom.

I do have a Fluke DMM, a veriac that doesn’t work, an o-scope I don't know how to use, and a signal generator that I've never turned on....I just think it looks cool.

However, I've built every non-stock piece in my system pictured below.
 

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djn said:
So after I fire it up on the bulb and let it run like that for a while, is it good to go from there on?
Two most likely outcomes from this:
1. it will work fine
2. it will blow an electrolytic which could have been rescued if you reformed it properly first

What I often do is fire up briefly using a lamp limiter. Only let it run for a few seconds, then switch off and listen for hissing noises and use your nose to look for burning and use your eyes to look for bulging/leaking etc. If it survives a few seconds operation, then give it a few seconds more. This is a very rough and ready way to reform an electrolytic which was not too bad to start with. It won't work with a cap which needs full reforming, but that needs more knowledge and care.

A variac is not too helpful as, unlike a lamp limiter, it does not restrict the current and gives no indication of problems.
 
I don't understand the reluctance by some who regularly work on electronics to purchase basic tools and learn to use them. You should be able to buy a good variac for less than $100. I have several all bought on epay for less than $100. The work great for slowing down floor fans in the summer so that you don't have a gale blowing over the bed.
 

rayma

Member
2011-04-29 8:37 pm
Hi,

I don't know what kind of signal generator you have or oscope but...hooking up the signal generator to the scope will start to give you an idea of how the controls work on both the signal generator and the scope.

There is little to fear from messing around with these two tools. The signal generator is not so hard to figure out. The scope is a bit more of a hill to climb.

If you have a manual on the scope read it. If not read through a simple Tektronix scope manual which is easy to find on the internet. Also any simple signal generator manual will give you a pretty good idea of how they work.

I would be glad to get you started if you need some help.

If what you have is older analog stuff even better. The newer digital stuff is in some ways less user friendly and normally has more complex functions.

As far as the old amp goes the light bulb idea will keep you out of most serious trouble and as far as old electrolytic go, they most likely need to be replaced any way so having one fail is not the end of the world to begin with.

Use normal common sense and be prepaired to turn the power off quickly. Fire is always a possibility so be prepaired to deal with that issue in the unlikely event it should happen. Eye protection is a good idea also.

Here is a short video I made on the subject.

https://www.youtube.com/watch?v=s7Pwdt27EN4

Cheers,

Billy
 
I recommend replacing the electrolytics and probably coupling capacitors before going very far. Not likely to be in good shape. I don't subscribe to the reform electrolytic cap notion, it doesn't seem to work on more than a very small % of caps, usually the longer life types found in Mac gear and similar. The exception might be on very low hour gear where there is some chance the caps might have some service life left and will reform successfully.
 
Here is a list of changes a guy on AK made to his AA32. Do these changes look reasonable?
I did have a list but did change things around a bit and my ordering is a little confusing even to me. What I can tell you is this....
The best place for most of the smaller films and resistors is Capacitors, Resistors and Schematics for Tube Radios / Electronics Most specs were very close to original.

justradios.com
1. Resistor Kit #7 504 Metal Oxide (Flame Proof) This kit was about 60.00, but eliminated an exhaustive listing of each resistor. All you will need is there and you have lot's left over for another project. Worth it.

2. All Tubular Axial and Mica Caps and lytics x 2 33uf 350V. Barely $15.00 and there. Just look at the values on these in the amp and if anything go up in values especially go up in the voltages as you will not have much choice there. That is almost true of all caps in this amp.

tubesandmore.com
3. Can Cap Multi-Section 1 x 40/40/40/40 350uf closest I could find, but works well. $34.00 Most expensive single unit in the amp.

4. Orange Drops 716 series 600V (I originally got theses from just radios and theirs were too large. 8 x .002 600V (716P600V223J) and 9 x .1uf 600V (716P600V104J)

5. Sprague Atom 4 x 50uf @ 50V

Parts Connexion
6. Obligatto Gold Premium Films 9 x 0.1uf 630V (This is where you need to make a call) I tried these and am very happy with the results. What is also good is they are small and will take some heat. You know it is tight under the tray so be careful on size.

7. 2 x 100K 1 Watt Film resistors - Audio Note - These are low ESR and needed. A bit pricey at $10.00 each.

This is by no means a 100% list as I may have missed something so please check everything. I would recommend the build manual which is available and frankly was worth the $19.00 for me.

Let me know how you proceed, but the places mentioned above will take a lot out of your research.