Tube Amp Archive

I kept searching to get the last little bit of hum out. It appeared to be
the bias supply after all.

That's just what i wanted to know thanx.

That's just what i wanted to know thanx.

Made a ground reference at 40VDC. There is less hum, still a little bit, but acceptable!!! My AC30 heritage is a lot noisier!!! I gigged it last weekend, before i did the elevated heater ground, with no issues at all. Not even hum, i think. As there was some background noise. I added the elevated he...

I tied them all to ground.

The heaters are full ac right now. The voltage between cathodyne cathode and ground is 40V. I'm thinking of elevating the heaters to a 20V reference. Maybe it could help. At rehearsal the hum is barely noticeable, but at home it disturbs me a little And practice makes perfect, so it has to be solved...

Ok, i've split the busbar in two parts, so i grounded the power bus at the screen side, and the signal bus at the input side. I'm not shure this is the correct way. Then i connected the unused pins of one half of the PI valve, and grounded them. I also scoped the HT at the PI and the recovery stage ...

A coupla things which may or may not help -is there a grid leak resistor on your input triode? It's not shown in the schematic (maybe you put it on the jack and just didn't note it). No, it fell off the printing window, but its there. -have you tried bypassing the effects loop? It's not uncommon fo...

The big caps are all connected via the bus wire, and grounded on one side only, near the input.

The center tap is connected via the standby switch to the bus bar.

I'm going to separate them tomorrow.

Thanx for the reply's. Crossing my fingers!!

I'm not touching anything with my hands! I'm touching it with the cable i've disconnected to see what's happening. No connection = no hum, touched = hum on either sides of that cable. The V3 is removed, so maybe my 50Hz is actually a 100Hz hum? Soundclip is in earlier post. When the 0,01uF cap, comi...

ok, i disconnected the signal wire feeding the PI, no hum at all. V3 is not inserted, but when i touch the contact point with the wire i disconnected, it hums. This is narrowing the problem down to the recovery stage (V3), or the path between the recovery and the PI. But how can this hum exist, with...

I just changed the cap by the same type.

Here are some photo's, and a sound clip.

ok, i've changed the grid leak to 470k with a slight difference. I also replaced the 220uF cap of the bias supply. (It was a bit swollen) No difference. If i turn the heater balance, there is no difference anymore, which excludes the heater coupling. The controls do not alter, or add extra hum anymo...

Ok, i moved my grounding point. With some difference in the good direction.

What is the easiest way to find out about magnetic coupling of the transfo's,

and what is the best remedy to get rid of it?

The transfo's are 12cm apart, and with a different angle. 90°

Thanx for the help already!!!

Ok, i removed the DC-supply for the heaters of V1. Certainly a big improvement!! But still 50Hz. A 20mVpp at the speaker output (not really loud). If the volumes are set to max, there is a noticeable hiss. Now i have an other question. If you have a full bridge rectifier, in parallel with for exampl...