C-lator hum

[martin manning]

The puzzling thing is you have hum with standby off, which opens the HV secondary circuit. Above I suggested disconnecting all secondaries to see if the hum is still there with only the primary connected to the mains.

[bepone]

Yes, I'll power it on and measure VAC on each of the caps positive side and post the results.

ok thx

[bepone]

Screenshot_20240319_125630_Gallery.jpg

What is this, 100R reference to the ground going to the worst electrical point?? 1.st electrolityc cap? this will be removed, and make better. Again we need to correct design online for designer people which doesnt understand anything.

[bepone]

Is this pcb designed on this forum and asian people just proceed with production? Who draw this pcb?

[bepone]

Need to remove all the wires and rebuild all properly.

Point No
1. Heater reference going to wrong point, so 100R need to be removed, will be connected to preamp ground not first filter cap, better the last , or clean gnd like input jack gnd
1a) Heater wires are going too close to signal circuit, need to be relocated (to close to 10M resistor which acting like antenna inserting it back to the circuit)

[martin manning]

Let's review the bidding.

In this configuration you still have hum:

- Cable from amp "preamp out" to C-lator input removed
- Cable from C-lator output to amp "power amp in" in place
- Tube removed from the C-lator
- C-lator main power on, standby on standby

And, the hum is affected by turning the C-lator output level control, but the hum does not go away with the control fully CCW.

Correct?

That is correct.

And there is still hum with the heater circuit disconnected from the PT.

If here is hum with only the primary connected I suspect the problem is in the PT.

[bepone]

Point No
1. Heater reference going to wrong point, so 100R need to be removed, will be connected to preamp ground not first filter cap, better the last , or clean gnd like input jack gnd
1a) Heater wires are going too close to signal circuit, need to be relocated (to close to 10M resistor which acting like antenna inserting it back to the circuit)

2. back of the pots must be grounded - all the metal pot enclosures scratch with the knife and solder and connect to the chassis ground (this can be also major issue)

[martin manning]

2. back of the pots must be grounded - all the metal pot enclosures scratch with the knife and solder and connect to the chassis ground (this can be also major issue)

This is a good point. Could be solved with star washers on the pot bushings making good contact with the chassis. Check to see what's there.

[GAStan]

2. back of the pots must be grounded - all the metal pot enclosures scratch with the knife and solder and connect to the chassis ground (this can be also major issue)

This is a good point. Could be solved with star washers on the pot bushings making good contact with the chassis. Check to see what's there.

I use star washers on all pots and switches. They work to prevent rotation as well as aid in grounding.

However I've noticed the back of some pots have a bit of movement even after torquing the nut. Closer inspection shows its the way they are fastened to the front of the pot-simple bent tabs. On my next build I'll try soldering these tabs in place.

[bepone]

This is a good point. Could be solved with star washers on the pot bushings making good contact with the chassis. Check to see what's there.

No need to do that..long job and complicated..here we see that chassis is powder painted..too much grinding and scratchings needed. We just need to solder the buss wire on the back meta pot enclosures and ground to the signal ground.

[ynor]

Will try your suggestions.

I see that the 2x 100 Ohm resistors are indeed grounded to the first filter cap, as you stated! Should I try grounding to signal ground instead?

I have two cheap DDMs. Both read 5.6 VAC at the PT heaters out (should read 6.3 V) and the HV reads 131 VAC (should read 135 V). Is that within specs? Might be because I measure 230 V at the AC inlet and the PT is marked 240 V?

I have measured VAC on all caps while powered on: 0.0 V. If there is mV > 0.00 (by that I mean more than one decimal), my meters probably can't read it.

[ynor]

Another discovery I just made: Having the top lid over the chassis makes the hum worse. Removing the lid, as in having the top of the chassis makes it hum significantly less, but hum is still there.

[ynor]

Another discovery!!!

When the C-lator is on, there is hum while on both standby or off standby.

When the C-lator is off, the hum is much less.

But when I then remove the C-lators AC mains connected to the wall outlet, there is NO HUM! (disregarding that annoying PT to OT problem, but that's peanuts compared to the C-lators hum).

[ynor]

And: after I moved the reservoar and filter caps groundings, lifting the mains ground now makes it hum less, also when powered off! But not quiet.

[ynor]

And another mystery:

While not connected to anything, the PT of the C-lator vibrates and hums when the lid is on. I can feel the vibrations when touching the chassis. But when I remove the top lid, the PT is completely quiet, as in no vibrations. Why is that?? Putting the lid on makes everything worse: the vibrations appear, and the hum is increased in the amp.