Rivera Thirty Twelve (R30) super Hum!

[Enzo]

IC2 is a negative regulator, it has a different pinout from the positive ones. If IC2 were dead, you wouldn't have half the heaters working

[Helmholtz]

IC2 is giving different basic diode checks then 1 and 3. Just where it’s at in circuit maybe? Only without output it seems.
may not be the cause of noise. Maybe just failed?

IC2 is a negative regulator. so different inside from IC1 and IC2 .

Look for lots of ripple at IC1/IC3 inputs (+24V), i.e.considerably more than at IC2 input. If so, C11 may be bad.

[Indyryder02]

Ok. Yeah just threw me cause I didn’t visually see anything on its output via the scope. It’s putting out negative voltage like it’s supposed to.

yes. Definitely have more ripple on IC1&3 inputs than on 2.
It certainly does look suspect C11. It’s new and feel I had this issue before replacing the caps. So of course skeptical.

[Indyryder02]

So this is probing the open tops of C11 and 12.
1st pic is C11 which matches inputs of IC 1&3
2nd pic is C12 which matches input of IC 2.

[Indyryder02]

Thank you all so much for your wisdom and help.
This is the only place I’ve ever been able to get help.
I’m truly grateful for this brain trust and wealth of information and experience!

[Helmholtz]

C12 side looks good/normal, C11 side looks awful. With that kind of input the positive regulators will have a hard time to put out a smooth voltage (dependig on load current).

What is the voltage scale?

[Indyryder02]

Sorry, you mean on the scope for that pic?
2V per div.

[Indyryder02]

I didn’t realize I could probe the top of caps like these actually.
Voltages too. Is the open end of these caps attached to the positive side then? Seems I learned this before..

[Enzo]

C12 and C11 should look the same, other than polarity. C11 is not working. Either it is bad, or not soldered in well, or installed backwards.

[Helmholtz]

Sorry, you mean on the scope for that pic?
2V per div.

So the voltage is varying by around 10V?

What is the minimum voltage (DC level, DC coupling)?

Yes, definitely C11 is not doing its job.

[Indyryder02]

Sorry. Im
afraid I don’t quite understand the last question.
I usually have the scope AC coupled when I’m probing.
And not sure what you mean by the minimum dc voltage here?

but yes I’d say there about 10v difference in the scope readings.
actual DC volt readings of the tops of the caps is about 18v c11 and -24 c12

[Helmholtz]

Sorry. Im
afraid I don’t quite understand the last question.
I usually have the scope AC coupled when I’m probing.
And not sure what you mean by the minimum dc voltage here?

That's why I said DC coupling. You can use a (calibrated) scope to read DC levels in DC coupling. I'm curious if the voltage across C11 drops below 18V.

[Enzo]

Your regulator IC to put out the 18vDC needs to have at least 20vDC going in. WHen you lose filtration like that, the voltage on that input side falls below that 20v every half cycle. And that ripple passes through to the output. At the bottom of those valleys on the scope, the regulator has no way to keep the voltage at 18 when the input is only ikje 12 or something.

The reason your DC readings are 24v for the good rail and only 18 for teh "bad" rail is that the unfiltered DC averages less than teh 24v it wants to be.

There are many ways to look at it. Helms mentions scope on DC, so if you set the scope to DC coupling and look at the whole +24v supply, you would notice the big gaps in the smooth DC dues to the lack of filtration. If you set the scope on AC coupling and see 10v of AC ripple, you can infer the effect on the DC supply. If you measured that 18vDC there, if you flip the meter over to AC voltas you would see a substantial amount. Over on teh good 24v rail you would see little AC ripple.

[Indyryder02]

You guys are the best! Seriously!
So looks like the negative of C11 wasn’t connected to ground.
(pad had lifted even though it soldered to it. Double sided ♂️ looked perfects fine visually, not until I desoldered I realized the pad was then loose. Knew it’d be something dumb in the end. )

so now if I test voltages on top. C11 shows about 38mv as it’s grounded now. And still have the -24 on the other side.
i only had about 16v at pin 4 of v1 where it should have been 18. Now I have the 18 again. So that would have been another clue.

scope wise. All the first three valves heaters are quiet and show nothing now.
C11 is the same on top. (Quiet) C12 shows about the same ripple it did before. And this is also seen on pins 9 and 5 of v4 and pins 9,4, and 5 of v5. V5 being stronger about 2v v4 down to 1v per div.
It’s pretty quiet now. I’d say acceptable.
it has just a slight hum left to it now.
this ripple I’m seeing on the following valves is normal I’d assume? I’ve never really probed heaters for noise before much. Only for cathode to heater shorts etc.
I once again learned so much from this mishap!
can only learn so much from books. Experience is equal to or greater than in some respects.
Can’t tell you how much I appreciate the help and education!
I’ve donated to the site and will again for sure.

[g1]

I didn’t realize I could probe the top of caps like these actually.
Voltages too. Is the open end of these caps attached to the positive side then? Seems I learned this before..

The can of a radial capacitor is insulated from both of it's leads. What you measure on the can is incidental and not a reliable reading.
However, in this case, what you saw at the can of C11 lined up with it being missing it's ground connection.