Doubling capacity of first filter cap

[GERPUD]

Hi,
To get rid of the 60HZ noice issue I have on my amp, I thought that increasing the first filtering cap from 47uf to 94uf (2x47uf) would solve the problem. I've tried quickly it and it works very well.
I now wonder if that can cause any long therm issues.
I read that it can add more load on the PT, that it provides better bass response, but there should have a reason why they put only 47uf.
Is there an other way to get rid of the noise? A choke?
The 60hz hum does not increase when increasing the volume.
There is also higher frequency noises that are less anoying to me, that where still present with the added filtering cap.

[matt h]

(deleted)

[Garthhog]

What type of rectifier is in your amp? Tube rectifiers have a maximum capacitance requirement. I believe the 5U4GB tubes I use are 40uF. The reason for the maximum capacitance is to limit inrush current supplied by the rectifier tubes... too much can quickly destroy a tube.

Ryan

[GERPUD]

It's a very simple Class A tube amp.
Diode rectifier.
There is no heater tap on the PT (200-0-200 only)

Matt h, you're right, the most annoying frequency is 120Hz. So the added Cap is removing 120hz, not 60hz.

I do get 60hz noise with guitar pluged in. Even with humbucker, depending on the orientation of the guitar.

"If you're getting hum that is constant, you're likely looking at transfomer induced hum or needing to deal with the AC Heater situation (be it by elevation, a faux-ct, or a humdinger pot installed)."
Could you explain that? Sorry I don't understand...

So, I read that i may due to the OT to close to the PT.
What is the best way to have a better filtration?
A choke for the whole amp? only of the preamp?

Thanks!!!

[rp]

Tube rectifier? If so I'm not aware of a tube rectifier than can handle more than 60mf. If you have a tube rectifier the datasheet will give you the max first cap value, though I believe that if for the full current rating so depending on your use you can push it some. If ss you are be fine. If it's 120hz hum you could also try adding an extra stage. What's the circuit? Some old designs like from the 50s w/ one cap on everything after the screens really benefit from an extra stage.

[GERPUD]

I have no idea of the circuit.
I'm trying to fix a cheap guitar amp that has several issue: Fender Ramparte.
Anybody else would have sell it and buy a better one.
Instead, I found, with this amp, the opportunity to learn tube amp electronic (with your help of course!).

[Reeltarded]

Is the amp open when it's humming?

Standing close to an amp and being on axis and in plane with the power transformer makes the most hum.

Open amps make noises.

Standing close makes noises.

Combinations make lots of noise.

[Firestorm]

The Ramparte is single ended so it will benefit from the CRC filter Matt suggested. Just put a resistor of say 100 ohms at 5 watts between the anodes of the two 47uF caps. Put the rectifier output to the first one and connect the OT lead and the rest of the HT supply to the second one. It will also help to elevate the heaters by tapping a later point in the HT string (screen supply or later) and voltage dividing it down to 50 volts or so. Connect the heater center tap to that (filter it if you like). The hum that varies with guitar orientation is easy: stand farther away from the amp.

[GERPUD]

In detail:

No guitar pluged:
Little 120hz hum when warming up
Louder 120Hz hum when warmed + higher frequency noise

When I plug a guitar. I get even more higher frequency noise IF I don't touch the strings. If I touch the strings, I do not have additional noise.

I got 60hz because I was too close to the amp. So that is not a real issue. Otherwise, I don't hear the 60Hz.

More capacity on the first cap filter got rid of the 120Hz, but I don't know if it is a good reliable fix, or is there any better solution.

Thanks

[Reeltarded]

When you are plugged in and the guitar is turned up and you aren't touching the stings your guitar is an antenna. That is everyone with passive pickups on a wire.

Ignore that part.

[Reeltarded]

I think we have arrived at some determination that your amp has no problems but you are now chasing physics.

[GERPUD]

But I think there is already a CRC.
From what I see,
Rectifier - 47uF - resistor (2W) - 22uF and (then go to the power tube)
and then it goes through an other 2W resistor (then go to preamp)

There is a weird thing: The first 2W resistor is brown-black-black--gold, which is supposed to be 10ohm+/-5%, but my amp meter is reading 800ohm.

Also, like I said in a previous post in reviewing this amp, they did a correction on the PCB around the 22uF cap. They scratched the ground link that is going under this cap on both sides, and add a wire to jump around it. I don't know if it this ground was connected to this cap under it (I'm not able to see on the other side of the PCB). I had the confirmation of the accredited Fender shop that this "jumper" has been made by fender's factory.

So... is 47uF - 800ohm (2W) - 22uF should be silent enough?
If yes, maybe fender bypassed the second filtering cap for unknown reason and that would be the cause of my annoying hum...


Any clue??

[GERPUD]

"I think we have arrived at some determination that your amp has no problems but you are now chasing physics. "

I don't think I am....
go read my post on this amp
https://tubeamparchive.com/viewtopic.php?t=26675

[GERPUD]

Matt h:
By the way, I did replace the cathode resistor as you recommend me on this post:
https://tubeamparchive.com/viewtopic.php?t=26672

I've put 450ohm, and now, from your calculation, I get 28.5W, which is bellow 30W.
Thanks again!

[romberg]

In detail:

No guitar pluged:
Little 120hz hum when warming up
Louder 120Hz hum when warmed + higher frequency noise

Here is my shot in the dark. The symptoms match almost exactly a minor problem I recently had. I was getting a rather annoying 120hz buzz with nothing at all plugged into the input. I searched quite a bit for possible ways this rectifier ripple could be entering the signal path. Ten minutes playing with my oscilliscope found it.

It was the first 12ax7. Somehow that thing was defective in a way that coupled what little ripple was left all the way at the end of the filter chain into my signal path. It was also adding tons of hiss. Replacing it made all the pain go away.

So, you might try the simple stuff first. Swap out a few tubes and see if the symptoms change.

Mike