C-lator hum

[martin manning]

I'm pretty sure those resistors are 100 Ohm. Is that consistent with the 50 Ohm readings I have at the heater pins?

Yes, sorry. When you made those measurements you were essentially measuring 2x 100Ω in parallel since the heater winding resistance is very low.

[ynor]

Just to be sure, can you disconnect one of the heater wires coming from the transformer? You still have a load and chassis connection via the 2x 50Ω balance resistors.

Tried. Still hum.

20240318_200211.jpg

[martin manning]

Rats. Disconnect all of the secondary wires from the transformer, the top four lugs. That leaves only the primary connected, and the core via its mounting bolts. This would be a first step toward taking the PT out of the chassis as sluckey suggested earlier. Turning the return level full CCW should ground out the "power amp in."

[ynor]

Rats. Disconnect all of the secondary wires from the transformer, the top four lugs. That leaves only the primary connected, and the core via its mounting bolts. This would be a first step toward taking the PT out of the chassis as sluckey suggested earlier. Turning the return level full CCW should ground out the "power amp in."

I could try that, but while you were writing I did this:
Moved the PT to the right, by rotating and flipping it on its head and grounded to the chassis with the red wire. Don't think that made any difference either. What do you make of that?

20240318_203049.jpg

[martin manning]

If the hum were induced by the magnetic field around the transformer that should have changed something. Try disconnecting all of the secondary leads. I'm thinking what you are hearing is coming from the AC power, which often has 2nd and 3rd harmonics from other equipment on the lines. I'm not sure how it is getting into your power amp, though. Maybe through the anode resistor and coupling cap? That might mean the power supply filters are bad.

[ynor]

If the hum were induced by the magnetic field around the transformer that should have changed something. Try disconnecting all of the secondary leads. I'm thinking what you are hearing is coming from the AC power, which often has 2nd and 3rd harmonics from other equipment on the lines. I'm not sure how it is getting into your power amp, though.

Yes I think the magnetic field explanation is weakened by this test. I will continue tomorrow and try your suggestions then. I really appreciate your time and efforts, all of you

Also, the amp itself without the C-lator has some annoying hum that I think is coming from a noisy PT leaking to the OT. Aside from vibrating laminates, the speakers hum even if the amp is in standby. When the speaker cable is unplugged (in standby), the hum in the speakers disappears and the vibrating laminates are the only noise left. Could it all be connected?? The fact that the C-lator makes the same hum on other amps or on its own speaks against.

[ynor]

Maybe through the anode resistor and coupling cap? That might mean the power supply filters are bad.

That might be examined when I get my "super advanced " $80 handheld multimeter/oscilloscope, I guess?

[ynor]

Double post...

[martin manning]

Maybe, at least you will be able to see where there is noise voltage. Turning the standby on standby disconnect one side of the HV secondary, so maybe disconnecting the other side won't do anything. Anyway, let's see if the hum is there with only the primary connected. Did you try lifting the earth ground on the C-later AC power already?

[ynor]

Did you try lifting the earth ground on the C-later AC power already?

Yes I did unmount the AC power grounding from the chassis.

[bepone]

I could try that, but while you were writing I did this:
Moved the PT to the right, by rotating and flipping it on its head and grounded to the chassis with the red wire. Don't think that made any difference either. What do you make of that?

20240318_203049.jpg

ok leave the transformer there.. we need to fix 100 Hz component.. some mistake is on the pcb.. can you make picture of pcb traces below rectifier, and all main capacitors?
pls also draw the schematic of rectifier how it is now, from pcb connection..

also you need multimeter with AC voltage, to touch every electrolityc capacitor + pole and read how much it is there, write the findings here.

this is most important now, all the other things and ideas pls dismiss they are not important now.

this AC voltage will show residual ripple, and on electrolytic cap suplying the ECC83 tube MUST BE 0mV!

this according to my assumptions will not be 0, and you are inserting AC ripple voltage from supply directly in signal chain.

[ynor]

ok leave the transformer there.. we need to fix 100 Hz component.. some mistake is on the pcb.. can you make picture of pcb traces below rectifier, and all main capacitors?
pls also draw the schematic of rectifier how it is now, from pcb connection..

Here is the layout of the C-lator, from their website. Note that the grounds are not shown in this layout, and I have the 240 V version. Note that I bought this new and prebuilt from C-tone and they have sold many of these units as a commersial product without these problems. However, they have changed the layout some recently as the PT is now inside the chassis while it previously was outside on every other I've seen.

Clator-PCB-Layout.jpg

I can take more pictures later today. However, the circuit board is not a regular PCB with visible traces (they are transparent) so I don't know excatly how to visualize this in photos. An example is shown below (from my previous photos).

[ynor]

Screenshot_20240319_125630_Gallery.jpg

[ynor]

Although they are not easy to see, I can measure those traces on the board with a DMM to comfirm that they correspond to the layout provided.

[ynor]

also you need multimeter with AC voltage, to touch every electrolityc capacitor + pole and read how much it is there, write the findings here.

this is most important now, all the other things and ideas pls dismiss they are not important now.

this AC voltage will show residual ripple, and on electrolytic cap suplying the ECC83 tube MUST BE 0mV!

this according to my assumptions will not be 0, and you are inserting AC ripple voltage from supply directly in signal chain.

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