Hey its been a while since i posted here and I thought I'd better give this some closure.

Turns out I had two main sources of hum and it had nothing to do with the heater circuit. A good way to eliminate problems in the heater circuit is to run them of a six volt battery - if the hums goes away there is a problem with the heater circuit (It didn't go away in my case).

Problem 1. insufficient filter caps - need to add an extra cap (I think this is now standard on the kits) - I've actually now have five 22mfd caps in my amp

Problem 2. there is a small hum created by the power transformer and output transformer being too close together. You can hear this hum as soon as the power is turned on (its created by the magnetic field from the power transformer cutting through the windings of the output transformer). Its noticeable but not too loud.

G'day elegy

Its about 340mm long and 170mm wide. I made my cabinet 210mm wide to protect the knobs etc that protrude out from the chassis.

The chassis is about 65mm high and 145mm to the top of the big valves. I made mine about 180mm high to provide a bit of cooling space.

Hope this helps

Hi again,

Thanks for your post. You raise some good points and really I think we are talking about the same thing. My limited understanding is that keeping the heater wiring twisted simply cancels out any electromagnetic fields that would otherwise be produced by the pulsating current flow.

For this to work properly the current needs to be equal in both wires. I think this more difficult on my ceriatone because it doesn't have a centre tapped winding for the heater supply (not sure if Fender does this too).

As for the circuits on the web page - I can follow the circuit (to create it) but I can't really explain how it works to reduce the hum. But I am hoping to find out.

I'll let you know how I get on. Cheers>

G'day Hired Hand - you sound a little defensive?

The tech doesn't like the way the heater circuit is balanced through the cathode resistor/capacitor. He reckons it should go straight to ground or better still to ground though another voltage divider circuit.

I've tried connecting it straight to ground but this is actually worse. I'll try the other circuit when I get a bit more time.

There is a bit if information at this site
http://www.netads.com/~meo/Guitar/Amps/Kalamazoo/Mods/hum.html

I made the amp myself - i have an electrical background but this is my first build. Everything else on the amp works great. The hum isn't major but it is annoying.

A few other owners have reported similar things.

Cheers

I've got some unwanted hum on my recently built kit. Its not all that loud but still quite noticeable.

I think its power supply related as it continues even if I remove the preamp valves.

An amp tech told me that there is a simple fix (and that there is glaring problem with the ceriatone circuit)but I am determined to try and fix it myself rather than send it to him.

Anybody else have and solve this problem.

THanks

Well done Winston,

I just went with a kit from Nik. I was interested in hearing that you added another filtering stage - any chance you could share that with me? (That is where you added the additional cap and resistor)

I have some AC hum that I assume your mod would fix. I know a few others that have a similar problem.

Thanks