5F2a choke before or after first filter, and what current rating?

[elipsey]

Last time I put it between the first and second filter, and I really liked the tone and feel, but the amp could have been quieter. It seems like a single ended amp would benefit more from this than a p-p, but I have never tried it.

I have three chokes on hand. The Hammond is the only one with a voltage rating, and 400V seems a bit low... it's also the biggest, like OT sized. Looks kinda funny on a small amp.
Webber: 9H, 120ma, ??DCR
MCI: 4H, 50ma, 150 Ohm
Hammond: 2H, 200ma, 57 Ohm, 400v


Is it significantly quieter to put the choke between the rectifier and 1st filter on your SE amp? Has anyone here tried it?

How do I choose a current rating?

[Tom Phillips]

Choke input filters can be tricky. You must also consider the output voltage you require from the power supply to run your amp. If you simply convert to a choke input filter then your high voltage supply will be some 30% to 40% lower. Are you counting on that?

[elipsey]

Fwiw, my power supply simulator seems to show about half the ripple with the LC filter:



Also, the Weber 5F2H, which has a choke input filter, seems to have a reputation for being pretty quiet:
Re: [Harp-L] Weber 5F2H Harp Amp
Blues Harp Amps: Weber 5F2H Harp Amp

Not really sure if my simulation makes sense, or if half the ripple means half the noise...

[elipsey]

Yeah, that's not a deal breaker by itself. My PT is multi tap: https://taweber.powweb.com/store/022772sch.jpg. I think if I used the 330-0-330 taps I would get a b+ of 350V -ish with the choke input filter, which is a bit low for a princeton/champ, but doesn't seem totally unreasonable to me.

I only want to do it if it's dramatically quieter.

Maybe there are better ways to get quiet, or it's not worth the trade off... I'm kind of meaning to solicit opinions about that, hopefully from someone who has tried it both ways.

EDIT: I should probably add that the guy wants to use it as a recording amp, so trading a little power for lower noise actually makes a lot of sense, as long as the tone is still good.

[Dave H]

Is it significantly quieter to put the choke between the rectifier and 1st filter on your SE amp? Has anyone here tried it?

How do I choose a current rating?

Single ended amps hum too much for me unless there is a Pi filter between the rectifier and OT connection like the 5F2 circuit has. I'd put the choke between the two 16u caps on the 5F2-A to make it like the 5F2 schematic.

I don't know the voltages of the 5F2-A but the 5F2 has 19V across 470R at the 6V6 cathode so the total current from the B+ supply would be 19/0.47 mA + 2mA for the 12AX7 = 42.5mA.

[elipsey]

<---smacks self on head.

Thanks Dave! The first amp I ever built was a 5F2, but at the time I didn't know what PI filter was.

I kind of forgot about this. I switched to a 5F2A tone stack because I though it sounded really dark, and I sort of though of it as a 5F2A after that, but with some hand-wavy difference in the power supply, which I thought didn't matter very much. I though it sounded great at the time, and was plenty loud. I used a Hammond 157R choke on it because the Angela instruments tutorial told me to, so I guess 200ma was enough.

I never knew to measure it's B+, and that amp is long gone now. What was the voltage spec for your transformer, and what B+ did you end up with?

Also, will different inductance values for the choke give me a quieter amp, or does it not matter once you are filtering below the frequencey of rectifier noise?

[Dave H]

My single ended amp is a modified Valve Junior. It hummed and the B+ was far too high so to kill two birds with one stone I used a PI filter with a 1k 7W resistor replacing the choke. It worked great. All the hum is gone and the B+ is now 300V which is fine for an EL84 (or 6V6) with a 5k OT. Your PSU simulation has the B+ at around 400V so you could also try a resistor PI filter.

[elipsey]

nice.

I've heard some people say that the choke stiffens the amp, but I don't really get how that would work since class A amps don't have sag by definition, right?

[R.G.]

I've heard some people say that the choke stiffens the amp, but I don't really get how that would work since class A amps don't have sag by definition, right?

Right. I've heard people claim they can hear the oxygen content in copper wires by listening to sound going through it, too; and that either gold-plating the AC wall plug or hard-wiring the amp to the AC mains in the wall makes an audible difference in the sound.

There is no limit to the self delusion of the human mind.

[jpfamps]

nice.

I've heard some people say that the choke stiffens the amp, but I don't really get how that would work since class A amps don't have sag by definition, right?

If you are using a pentode there is the possibility of sag if the screen supply doesn't hold up under drive even in class A operation.

Of course whether this is audible is another matter.....

[uneumann]

If you are using a pentode there is the possibility of sag if the screen supply doesn't hold up under drive even in class A operation.

Of course whether this is audible is another matter.....

I added at Hammond 193H choke to a univalve. It feeds the OT on this SE amp that I run with a variety of tubes. I did it for hum, but I kept it for tone. I can't say exactly why it impacts the tone - I never did any measurements or tests to figure out why. I liked the end result so I just play it. Its my favorite "small" amp.

See https://sites.google.com/site/string...valve-mod/modc for details

[echuta13]

Maybe it would be better to say that while an SE amp cannot by its nature sag, it can be made stiffer? A couple of ways to approach this may be to add a choke, bump up the power filter cap sizes, or increase the size of the cathode bypass cap on the output tube. This is more of a feel effect than a tonal one btw. My $.02 is that I would only put enough filtering in an amp to make it quiet and that's provided that you have already eliminated all of the other hobgoblins of noise in the other areas of your amp beforehand.