Help! I tried to recap my amp!

[Structo]

Soldering looks much better!

You'll have that amp up and running in no time.

[Phil_S]

I think Cornelius was joking, but don't put solder in your mouth. It's poison He's also correct about doing no mods until you have it fixed.

If you're worried about lead poisoning, it hasn't been present in standard soldering tin here in Norway for years; now it's about 95% tin, 4% silver and 1% copper. (RoHS)

So no, i wasn't joking.
That said; if soldering are your job, chewing soldering tin all day would probably not be healthy, even without the lead.

But i'm not worried for that very small amount of time i use my mouth as a third hand.

Cornelius, lead or no lead, I think this is an unwise practice. Please don't suggest to others it is OK. We can disagree without being disagreeable.

I have always managed with two hands. If you tin the wire, it can be fixed in place and it will stay there until you solder it.

[Cornelius]

Warning DocZ!! The amp shouldn't be operated without a load (speaker or artificial) if you have the power tube installed. It will seriously jeopardize your output transformer and power tube among other things.

Hang in there!

Dave O.

Thank you for the warning, I had disconnected everything from the power transformer, except for the filament heaters. So basically I was just using all the tubes as light bulbs. I was told this was ok.

DocZ

Yes, this is ok.
And your soldering looks better. It's the shiny, flowing look of the tin we want to see, not the wrinkled dull look.

And now we're getting rather exited and curious to whether you'll get any sound if you now connect the high voltages and the speaker, with the old preamp tubes in ofcourse.

I suspect that it was bad connection in the sockets that lead to the noise and crackle in the first place, and now that you have removed and inserted the tubes several times, the sockets should have 'cleaned up' a bit. (not that they're clean, but it should be better contacts there...)

[docz]

Ok guys, we have sound again!

But sadly it is still the same story when it comes to the sound.

It powered up, I could now hear a hum, this wasn't there before.
It is not as loud as it used to be.
The scratch/static appears after a couple of minutes and it's pressence changes sporadically
First time I turned on the tremolo button the static disappeared, only to return 30 seconds later.
The static sounds also get into the effects, meaning they probably appear somewhere in the first stage of sound and beeing sent to the effect drivers.

I still can't measure a DC voltage on the caps though, maybe my multimeter is screwed? Or maybe they drain right after I power off? That would be weird wouln't it?

Ok that's the update, any ideas folks? Is it the first preamp tube perhaps?

Doc-Z

[Phil_S]

Ok guys, we have sound again!

Very good news. Your OT is working.

But sadly it is still the same story when it comes to the sound.

I disagree. You have sound. The rest can be fixed.

It powered up, I could now hear a hum, this wasn't there before.
It is not as loud as it used to be.

Hum can be fixed. It would help to know if it is...50 or 60Hz (don't know what you have in Norway for power supply), or 100/120Hz. On the guitar, A below the low E string is 55Hz and the A string is 110Hz. This tells us if it is a power supply problem or filament hum.

The scratch/static appears after a couple of minutes and it's pressence changes sporadically

Opinions will differ here. I would leave this problem for later. Fix the hum first.

First time I turned on the tremolo button the static disappeared, only to return 30 seconds later.
The static sounds also get into the effects, meaning they probably appear somewhere in the first stage of sound and beeing sent to the effect drivers.

I'm not sure what to make of this.

I still can't measure a DC voltage on the caps though, maybe my multimeter is screwed? Or maybe they drain right after I power off? That would be weird wouln't it?

This makes perfect sense. Caps will hold a charge, but some amps discharge quickly.

To measure B+ voltage (DC) at the filter cap, the amp needs to be powered on. Set the meter for a proper DC range...I'll guess ~350V. Red probe to the + side of the filter cap and the black probe to the chassis. See if you can clip the black probe on so you have one hand free. One hand belongs in your pocket when probing a live chassis (not a joke.)

[Aurora]

Hi Docz...how's things going??

Just a few things...
If you haven't done so already, I'd strongly suggest you reconnect your power cord as pr. the picture you have on page 2, where the blue wire goes to the fuse and the brown goes to the switch. As it is in one of your last pictures, one power phase is permanently connected to the power transformer ( as long as your socket is in the wall). The picture on page 2 shows one phase protected by the fuse and the other by the switch, which is in accordance with the schematic. Here in Norway, we generally don't have a neutral - both phases are hot. Only in some industrial areas, and in residential areas built from scratch during the last few years does the norw. power grid carry a neutral. It deosn't really make any difference though - except you should not have the faulty connection.

Also - if you intend to keep on tweeking amps, get some spring loaded hook clips and "banana leads" - in this way you can connect for measurements before powering up - at least until you get the hang of poking around in live HV curcuits

AS for tubes - Motron as I mentioned is located in Vestfossen, which is a bit away from you, but still acccessible if you drive there yourself

[docz]

oh man.. thanks... Well guess I have to re-wire it again.

About the hum, I think it is 50 hz type hum, it is pretty deep. We have 50hz AC lines here I believe.

How do I get rid of the hum? And where do I start to troubleshoot the static? It is hard to describe, it is the kind of noise you get from a scratchy pot on the guitar.

DocZ

[Aurora]

As for the static like noise, - have you tried getting some contact cleaner into the pots and rotate them vigorously?? There's usually an opening around the solder lugs...
What happens if you move the pots? More noise??

If the hum you have is 50 Hz, there's an issue in the signal path, - or from the heaters... if it's 100 Hz it's from the rectifier / filter caps... ( 100 Hz is roughly low F# or G on a normal guitar......)
I assume you have attached a speaker, and hear the hum through the amp/ speaker.... or is it mechanical hum from the transformer?
It's late now, and I'm about to shack in, but does the hum vary with the volume control? If yes - you have switched input jacks, - supposed to ground the input with no jack in.. have you cleaned the switches on the input jacks?

[Phil_S]

Do you get the static when you rotate the pots? I don't think you said.

Group-think here on the 50Hz hum. I think maybe it's time to clip the black wire from the filament lug to the HT CT? I think I'd go for a pair of 100 ohm resistors. one between each filament lug and the CT on the PT? Anyone else?

[docz]

The pots have no effect on the noise. Except for the effect knobs. When I turn them, the noise is sent to the effect like it was a signal. So if I turn the reverb, I get the same noise - only with reverb. Tremolo I get the same noise - but now with tremolo.

I put back all the wires I had removed before I tested it, the black wires and all.

DocZ

[martin manning]

That's great that the effects are working! How about making a voltage chart? Measure and write down the voltage to ground from each tube pin (with the tremolo off). That will get an overall picture of where things are, and if it all looks good then you can chase down the hum.

MPM

[docz]

Yes I will do that, how do I do that? Do I measure AC or DC?

Edit: I didnt' see "ground" in your post until I read it the second time. That means DC right?

DocZ

[Phil_S]

Yes, DC voltage. See if you can get a clip for the black lead. Clip it to the chassis or a chassis bolt. Then you need only one hand to move the red probe from point to point. Skip the heater/filament pins as those are AC and we know that part is working.

[MBD115]

I would like to add - - when you are measuring voltages on the tube pins (or anywhere else for that matter) make very certain you don't touch any 2 things at once and short something out with the probe.

Very carefully only put the meters probe onto "1" thing and make certain it doesn't touch anything else. I say this because a little slip and the probe can short something.

Clipping the black ground lead is important because of the "1 hand in the amp at a time" yes, but it is also important because you can pay 100% attention on the other (the red) lead so as not to let it slip against some nearby item causing a short.

Even better is having clips on both leads. This way you can verify the connection (and any possible shorts) with the amps power off and the caps drained, then, after removing your hand(s) from the amp of course, power it on and get the reading.

And again I would like to say - anytime you are going to stick a hand in there - first check for the presence of voltage with your meter and make certain the caps have indeed drained. Take nothing for granted - especially when dealing with this much voltage. Make certain first.

There is much you can learn about amps by doing this project but I mostly want you to learn how to work safely. That way you can apply what you learn now on future projects.

Good luck with the project -- and be careful

[Structo]

Yes, safety first!
If you are working inside an amp that is not plugged in you know of course the big filter caps can hold a charge.
So discharging them is the first thing to do.

I like to take a test lead with insulated alligator clips at each end and clip one to the plate resistor of V1 and the other to chassis ground.
This drains the caps through that 100K resistor.
Some amps you need to have the standby switch in the play position to completely drain all the caps.
Some amps have balancing resistors on the big caps that double as bleeder resistors once the amp is turned off.
But never depend on that!

Always double check with the voltage meter that the caps are indeed discharged.
You can either leave the test lead clipped to where it is or after the caps are drained, clip it to a big cap + end and the other to ground to keep the caps drained but always remove it before powering up the amp again.

I like to probe the eyelets on the board if at all possible verses trying to touch the probe to the socket lugs.
Just trace the wire to the socket and then touch the prove to the eyelet that has that wire on it.

Sockets are numbered from the inside of the chassis clockwise after the gap on 9 pin tubes and after the locating lug on the octal power tubes.

It is very easy to slip off of a socket lug and short something, making a big spark and melting your probe tip or worse shocking you.

The reason you never want two hands inside a live chassis is because if you get a shock the charge will travel through the one hand and out the other hand and your heart is in the middle of this path.
So the risk of electrocution and death is a real danger here.
Remember you are dealing with over 400v DC and that can be very deadly.

Here is some troublshooting tips for hum.

Excessive Hum

A good way to divide and conquer is to turn the volume control(s). If the hum changes levels as you do this, then the source of the hum is something that affects the stages of the amp before the volume control. A faulty, humming preamp tube can be isolated this way very quickly. Conversely, if the volume control does not affect the hum, the cause is somewhere after the volume control.
Faulty tube
Tubes sometimes develop internal hum, for reasons known only to themselves. Do some tube swapping to locate the problem. Use the volume control test
Severely unmatched output tubes in a push pull amplifier
Push pull amplifiers get by with less power supply filtering because they're supposed to cancel this ripple in the output transformer. The cancellation can be upset by output tubes that use different amounts of bias current, allowing the hum to be heard.
Faulty power supply filter caps
Faulty bias supply in fixed bias amplifiers
A bias supply with excessive ripple injects hum directly into the grids of the output tubes. Check that the bias supply diode is not shorted or leaky, and then bridge the bias capacitor with another one of equal value to see if the hum goes away.
Unbalanced or not-ground-referenced filament winding
Defective input jack
If the input jack is not making good contact to the guitar cord shield, it'll hum. Likewise, if the jack has a broken or poorly soldered ground wire, or not-very-good connection to the grounded chassis, it will cause hum. If messing with the jack changes the hum, suspect this.
Poor AC grounding
In amps with two wire cords, defects of the "ground reverse" switch and/or capacitor can cause hum. A leaky power transformer can also cause this. It's especially bad when the ground reverse mess is already dicey.
Induced hum
Placement of the amplifier near other equipment can sometimes cause it to pick up radiated hum from other equipment. Suspect this if the hum changes loudness or tone when you move or turn the amp. There is usually nothing you can do about this except move the amp to where the hum is less.
Poor internal wire routing
If the signal leads inside the amp are routed too near the AC power wires or transformer, or alongside the high-current filament supply wires, they can hum. Sometimes using shielded cable for signal runs inside the cabinet can help. It is hazardous to do, but you can open the amp up and use a wooden stick (NOT A PENCIL) to move the wires around inside to see if the hum changes. This is hard to do well and conclusively, since the amp will hum more just because it is open. BE VERY CAREFUL NOT TO SHORT THINGS INSIDE THE AMP.
Poor AC Chassis Ground at Power Transformer
A common problem is the main ground point to the chassis. The green wire (you DO have a three wire line cord, don't you?) ground to the chassis, the "line reverse" cap, the CT on the filament windings, the CT on the high voltage windings, and other things associated with power or RF shield grounding are often tied to lugs held under one of the power transformer mounting bolts. If this bolt becomes loose, or if there is corrosion or dirt under the lugs, you can get an assortment of hum problems.
Defective internal grounding
There are potentially lots of places that must be tied to ground in the internal wiring. This varies a lot from amp to amp. If one is broken loose or has a poor solder joint or poor mechanical connection, it can show up as hum. Note that modified amplifiers are particularly susceptible to this problem, as the grounding scheme that the manufacturer came up with may well have been modified, sometimes unintentionally. With the amp unplugged, open and the filter capacitors drained, carefully examine the wires for signs of breakage or mods.
Relay Coil Hum
If your amp is home-built, you may have used an AC-coil relay for some switching functions. If you used the filament AC for powering this relay, you can get an AC hum in the signal path induced from the coil. The cure is to run this relay from DC by rectifying and filtering the filament supply or changing to another type of relay that's less susceptible to causing hum. Of course, for homebuilt amps, there could be many hum-inducing problems.

Go here for more troubleshooting tips.

http://www.geofex.com/ampdbug/ampdebug.htm