Values of Filter Caps in the Power Supply?

[rexindigo]

Most of the Guitar Amp designs use much lower Values for the Filter Caps in the Power Supply than the HiFi Builders (22 mF-47 mF) Why is this so and what does this values do to the sound? In my own desing i took what i had lying around and never had any negative "sound reaction".
Can someone help me to understand what changing of these values will do to hum and or sound?

[stokes]

I like using larger caps for the main and screen supply.It will stiffen the response of the amp somewhat particularly the bass,makes it nice and tight.In the old days,guitar amps werent meant to be pushed as hard as we do today.When you crank an older amp the power supply sags a lot from being under-filtered,and the bass is the first to crap out.If you look at modern amps that use solid state rectifiers you will almost always see 100uf for the main supply.Keeps the tone from farting out.

[Enzo]

There is a limit to how much capacitance a tube rectifier shuold see at its cathode. The higher the capacitance, the larger will be the current spikes at each charging cycle - 120 times a second usually. With solid state rectifiers it can be much larger. FOr tube rectifiers, if you need more filtration, add a stage after the first one. That second cap can be larger, but limit the first filter to accommodate the rectifier tube.

Remember too that a guitar amp is NOT hifi and is not in the business of reproducing sound, it in fact is a primary producer of sound and is considered part of the instrument.

A little sag in the power supply is not a bad thing, it adds some compression and lets notes sing more.

[stokes]

The limits for the input cap listed in tube manuals is very conservative.For instance,I have a 5R4 in one of my builds and the manual says 20uf for the input.I did some experimenting with this tube and have a 100uf as the first cap.The amp gets used a lot,probably about 20 hrs a week between both my sons bands and the tube has held up for about a year so far.Couldnt agree with you more on the hi-fi/guitar amp analogy and the power supply sag thing,but many older amps with the 20uf input cap go beyond sag when they are cranked and get quite muddy,of course it is a matter of taste.Putting a 40-100uf in such an amp with a tube rectifier wont eliminate the sag,but to my taste sweetens it up a lot.

[MWJB]

Several builders use 100uf at the main stage with the common tube rectifiers (5Y3, 5U4, GZ34). As Stokes says, the data sheet ratings are on the conservative side. 40-50uf certainly will not be a problem.

[rexindigo]

There is a limit to how much capacitance a tube rectifier shuold see at its cathode. The higher the capacitance, the larger will be the current spikes at each charging cycle - 120 times a second usually. With solid state rectifiers it can be much larger. FOr tube rectifiers, if you need more filtration, add a stage after the first one. That second cap can be larger, but limit the first filter to accommodate the rectifier tube.

Remember too that a guitar amp is NOT hifi and is not in the business of reproducing sound, it in fact is a primary producer of sound and is considered part of the instrument.

A little sag in the power supply is not a bad thing, it adds some compression and lets notes sing more.

This seemes To me the main point: tube rectifiers need lower values! As i build all my amps with Solid State Rectifiers i dont have to care to much, or am i totally wrong? (68mF/400V is what i use right now)

You are very correct about the fact that Tube Guitar amps are a source of sound, i found out after trying out a lot of guitars and other stuff, when i build my first 18watt clone. Suddenly i understood the major contribution to the sound by a good amp. (I had Music Mans and Boogies etc before but this was different, much more intense) Sometimes the simple things are way better than 1000 Options and switches.....

[Bruce / Mission Amps]

It is also about the joules of energy stored and needed through the power supply at high voltage with hollow state gear compared to solid state gear, which I don't think run much more 12vdc to 48vdc, do they?

[stokes]

rexindigo,you can go higher than 68mf,but I think 100-220mf is probably the highest useful value.I say this because I have never seen higher values used in commercialy produced amps,so I assume the designers dont go any higher for a reason.

[jlatrace]

Stokes,
Do you see any issues with going with 80uF at the first fiilter on a 5ar4 rectified 20 watt TW cloned (except for tube rectifier and other tweaks) circuit? I'm having a very small amount of hum that is eliminated by the higher values.
Les

[stokes]

80uf should be fine with the 5AR4.I have a couple of amps with a 5AR4/100uf.Havent had any problems with them.

[jlatrace]

Thanks, I truly appreciate the advice of folks like you and others on this site.