OT: Getting rid of the buzzzzzz in my Kalamazoo Model 2

[milkwasabadchoice]

I have this amp and I love the tone, but it has, I think a,  60 cycle hum, but i dont know for sure.  The volume control does not effect the hum, what does this mean? I think I need to repace the filter caps. The filter caps are in an all in one container.  I have read about replacing them with like 20/30/40uf caps, but will this help?

Thanks for your help,
Jason

[barret77]

filter caps, certainly. The hum is the same whenever the volume, 90% of blown filter caps. You can replace them by individual spragues, since the multisection will be too expensive, and the voltage/capacitance can be slightly larger (not smaller) with no tone differences...

of course, I'm not exactly the amp genius, but I guess this is right.

[petemoore]

I don't know exactly either, about the microfarads...I suppose it depends on the application [ITC  :lol: Capplication]. I think I would try matching the farad values.
 Lowering voltage rating on a cap is a general No NO! for replacing caps in amps, higher voltage rating or same is good.

[milkwasabadchoice]

Thanks for the help guys.

-Jason

[niftydog]

Check for DC voltage present at the speaker connections. That could cause some nasty buzzes and hums.

As for upgrading cap sizes, you'd want to make sure you were upgrading the RIGHT caps. Only the power supply ripple filter caps can be upgraded probably, and even then it's not a great idea because you don't know if the other componenets are up to the extra stress. Larger caps take more oomph to charge up.

[milkwasabadchoice]

What if there is DC voltage at the speaker? WHat do I di to get rid of it?

[niftydog]

if there is chances are there's a dodgey DC blocking cap somewhere. Couldn't tell you anymore without a schematic.

[powerplayj]

Is this the model without the three prong plug?  If so, would adding a ground help?  My buddy has one and it is a sweet little find that loves single coils.  The ebay price keeps going up as well as I hear many people are finding these handy for studio use.

[lovekraft0]

Here's the schematic

It's a pretty simple amp- it probably does need filter caps (see this page), and I'd rewire the power transformer circuit to keep from getting fried (here). That should clear up your hum problems, and help reduce the risk of electrocution (something I try to avoid at all costs).  

[niftydog]

righto. If the output transformer is working correctly, there'll be no DC on the speaker. (I didn't realise it was a tube amp!)

[KMS]

I have this amp and I love the tone, but it has, I think a,  60 cycle hum, but i dont know for sure.  The volume control does not effect the hum, what does this mean? I think I need to repace the filter caps. The filter caps are in an all in one container.  I have read about replacing them with like 20/30/40uf caps, but will this help?

Thanks for your help,
Jason

New filter caps on old amps will always make the sound better.   Humming is a classic sign of bad filter caps, real bad, like shorted out completely.  Take a 10K 1/2 watt resistor, or a household light bulb about 45 watts or more and connect one lead to ground of the chassis and the other to the positive side of each stage of the filter caps for about 30 seconds.  If you think you might get shocked use insulted gloves etc, but if you look at the voltage rating on the caps I think you will find that you’re not talking about that much voltage, best to be careful any way.

If you use the light bulb you should see it light up and then slowly dim out to nothing.  If you don't see any light from the light bulb, then the cap is shot, noda, zilch, wasted, totally shorted out and thus you found part of your problem.

If you use the resistor, then you should see an arc or a spark when you make the final connection to de-energize the cap.  No spark? Then you have a dead cap.

You should also connect a third prong ground to the chassis and be sure that you have a real ground (copper rod inserted into the soil outside the house) connected to the third wire buss bar in your electric service box.

Is this a DC power supply?  Most amps are DC (solid state that is) however I don't know that much about tube amps.  Easy to find out. Just look at the circuit and follow the leads from the filter caps, if they connect to 4 diodes in a criss-cross connection, then you have a DC power supply for your circuit and thus you shouldn't worry about getting DC voltage in the circuit, as you showed concern about that.

If the filter caps are shot, then replace them with larger value caps.  You won't find matching caps, guaranteed. The voltage rating can be as high as you want and the uF can be up to 3 times as high and won't hurt anything, except other weak caps and components on the board.  Best to replace all the caps on the board, high voltage, but keep the uf close to original on the rest of the board. Don't be surprised if an input tranny or tube blows, just replace it, it was bad anyway.

Does the amp have power trim for the volume, base, treble, reverb, etc?

This should be easy to see. Look at the volume control and if it is connected to the input (guitar jack) directly then you don't have power trim.  If not, then you have power trim (nice unit) and thus you have a secondary power supply, probably 24 volt DC.  This could also be a source of noise and if it is solid state then the secondary power supply probably has a shot tranny in right now from the primary voltage peaks due to the shorted out filter caps.

How do I know all this?  I just got done rebuilding my amp because I had the same problem you have now.
My amp works better than ever, sounds great.  Cost me $51 in parts, and I tripled the uF on the filter caps.   450watt Peavey, 1972, Module 800 with the booster stage, solid state.
Good Luck

[milkwasabadchoice]

Thanks for the help in the long reply. Im getting ready to try the light bulb test and I'll let you know how it turns out.

Thanks again,
Jason

[milkwasabadchoice]

Ok, another question.  A friend of mine has a Kalamazoo Model 2, and loves it. Want he wants is to keep the same tone, and double the power output to make it louder.  The catch is he wants me to do it!  Do I just clone the whole circut and use a output transformer twice the origanal size? Can you even get the same tubes anymore to go in the clone of the origanal? What kind of transformers would I use?

Thanks for any help,

Jason