Doubling capacity of first filter cap

[GERPUD]

I've replace both 12ax7 and still getting the same hum...

[matt h]

(deleted)

[Jana]

Since it is a single ended amp, there isn't any hum canceling in the power amp.

The simple fix for your hum problem is to add a choke and a cap BEFORE the existing B+ tap for the OT. You need a choke that can handle the current—a 250ma. choke of about 4 to 10 henries would be good. The first cap can still be a 47uf. Your hum will drop out of the floor with this.

Do this before you try elevating heaters, messing with a humdinger, etc.

[GERPUD]

To be able to mess with a "humdinger", I would need to know what is his favourite habitat and what it eats in winter. I'll then be able to build the right trap to capture the beast
I have know idea what is a "humdinger"....

Filtering the B+ of the OT makes sense:
When adding 47uf at first cap, the hum decreases.
When adding 47uf to the second cap, there was no difference.
The B+ of the OT is right after the first cap...

Physically, it is not really easy on the PCB the add a choke on all power before B+ of the OT.
Would it work if I'm putting the choke only on the OT tap?

[V2]

In the stock amp, the B+ for the power tube anode is likely taken from that first reservoir capacitor (stock: 47uF).

If I understand correctly, you added a second 47uF in parallel to the reservoir cap, and the B+ for the power tube anode is taken from there.

Beyond that point, there is a resistor that follows and another filter cap that follows that resistor; B+ for the power-tube screen is taken from that filter cap.

in that configuration, the B+ to the tube anode is still very noisy; the power to the screen is less noisy but could be better.

So Matt suggested that instead of having two parallel 47uF for the first power supply node (to anode), you add a resistor in between the two on the 'hot' power line. If it is only 100 ohms (and 5 or 10 watts), it won't drop much voltage. It will, however, clean up the power to the anode and screen a lot. You will get less 120Hz buzz (which isn't a problem for you anymore) and less hum and buzz from other sources that are common in a single-ended amp.

[ampgeek]

LOL! And you probably wouldn't want to eat that beast or use its hide for anything anyway!!

Here is the basis of the humdinger for your reference. In essence, it is an approach for elevating the filament circuit reference in non-cathode biased power amp applications.

Good luck!
Dave O.

[matt h]

(deleted)

[GERPUD]

I was trying to see where to put the "hum balance pot" until I realised that I do not have heater taps. The PT secondary is only 190-0-190. No heater tap...

Any other solutions?

The guy from RAT valve that solve all the problem of this amp was talking about:
- OT to close of PT
- Ground loop problem ( some way related to the "jumper")
- Not enough filtration

I asked him what did he do but I had no answers...

So I get I need more filtration before the first resistor.
I have no idea of what a ground loop is
No idea of the relationship of OT and PT...

I could place a choke in the back with the PT and OT, but I have to figure how to connect it before the first resistor...

[matt h]

You definitely have heater taps--without something powering the heaters, the tubes would not function. at all.

Per most standards, look for a pair of green wires, twisted together, coming out of the PT. Eventually, they'll connect to pins 2 and 7 on your power tube (and 4/5 and 9 on your preamp tubes).

[GERPUD]

There is two red and two green. That's it.
Two red are 190vrms each
The two green are 0V, both. So they must be the center tap.

[sluckey]

The two green are 0V, both. So they must be the center tap.

Put one meter probe on one green wire. Put the other meter probe on the other green wire. You should have 6.3VAC.

[GERPUD]

Nope.
0V From Green to Green.
0V from Green#1 to ground.
0V from green#2 to ground.
190VRMS from red to green
190VRMS from red to ground.

So : No heater tap.

[Meat&Beer]

[johnnyreece]

Do you get 190V between both greens and reds? I'm assuming you get 380 red to red? What about resistance between the greens?

[tubeswell]

What sort of amp is it? Can you post a schematic?

Single-ended amps are prone to mains frequency hum riding on the signal unless you have whole-of-supply choke filtering