One question on fliter cap values on fender AA764 champ build.

[Intergalactic Tourister]

The PT is rated at 100 mA on the HT and a old champ is 70mA plus the PT from weber which is what I got has a 4 amp 6.3 and a 3 amp 5 volt

That is fine. Your PT is rated well above. The old Champ PT is also fine.

[Enzo]

Ok , I don't know what to do , just leave it alone or change the 1st cap to a 22UF that I do have .

Here's the thing. We are having a discussion of the the3ory behind all this stuff. We are discussing practical design considerations, etc etc etc. But really, this is not rocket surgery. This stuff is not critical. Think about the tire pressure on your car. The manual says 32 pounds of air in them. We could discuss what happens to underinflated tires, and overinflated tires. We can talk about how pressure increases as the tires heat up. SOmeone will chime in that for some obscure reason it would be better to inflate the tires with pure nitrogen rather than plain air. But at the end of the day, whatever you inflate them with, if there is within a few pounds of the specified 32psi, the tires will work just fine, you can drive down the road perfectly well and safely.

AMps that are supposed to have no more than 20uf and have 40uf there anyway can be found any day, and at 40-50 years old are still working. Statistically maybe the rectifier tubes have a somewhat shorter life that way. MAybe. Tube last 15 years instead of 18 years. Maybe the tube gets broken before it wears out too. The specs in the tube books are not absolute brick wall specs. If the tube is rated for 400v, it doesn;t explode at 401 volts. All these rules of thumb are flexible.

SO it is interesting to consider these matters, and you certainly won't go wrong by doing it "right." But none of this is chiseled in stone. You are concerned about hum. Good to be concerned. The basic filter of the old stock Fender worked well enough, to improve it took more and more brute force. The change fcrom 10uf to 20uf will make more difference than the change from 20uf to 40uf. The law of diminishing returns. Instead of trying to pound the hum into submission with a huger and huger filter cap, adding another stage of filtration will work better.

Look at the oldest Champs and then look at the progression as the designs got more recent. The original 5C1 CHamp had 8uf caps. Larger caps than that were expensive then. But look at the schematic. Note the first cap - the reservoir cap as some call it - doesn't serve any part of the circuit. The second filter stage serves the power tube plate. Those two stages work better than a single 16uf stage would. Move ahead to the 5E1 CHamp. The resistor betwen filter stages has ben replaced by a choke. That improves filtration right there. Note the plates still drag their current from the second filter stage.

Now progress to the 5F1. OOps, now they are taking the plate current from the first filter node. They increased teh 8uf to a 16uf, but still, the earlier filter system was "better." And the later designs all take the plate supply from the first filter. Cheaper to do it this way.

But if you want to reduce hum, putting two filter stages before the tube will help better than tons of cap.

And of course that will ONLY re3duce hum coming from power supply ripple. It will do nothing for ground related hum, radiated field hum, etc.

[catnine]

Here's the thing. We are having a discussion of the the3ory behind all this stuff. We are discussing practical design considerations, etc etc etc. But really, this is not rocket surgery. This stuff is not critical. Think about the tire pressure on your car. The manual says 32 pounds of air in them. We could discuss what happens to underinflated tires, and overinflated tires. We can talk about how pressure increases as the tires heat up. SOmeone will chime in that for some obscure reason it would be better to inflate the tires with pure nitrogen rather than plain air. But at the end of the day, whatever you inflate them with, if there is within a few pounds of the specified 32psi, the tires will work just fine, you can drive down the road perfectly well and safely.

AMps that are supposed to have no more than 20uf and have 40uf there anyway can be found any day, and at 40-50 years old are still working. Statistically maybe the rectifier tubes have a somewhat shorter life that way. MAybe. Tube last 15 years instead of 18 years. Maybe the tube gets broken before it wears out too. The specs in the tube books are not absolute brick wall specs. If the tube is rated for 400v, it doesn;t explode at 401 volts. All these rules of thumb are flexible.

SO it is interesting to consider these matters, and you certainly won't go wrong by doing it "right." But none of this is chiseled in stone. You are concerned about hum. Good to be concerned. The basic filter of the old stock Fender worked well enough, to improve it took more and more brute force. The change fcrom 10uf to 20uf will make more difference than the change from 20uf to 40uf. The law of diminishing returns. Instead of trying to pound the hum into submission with a huger and huger filter cap, adding another stage of filtration will work better.

Look at the oldest Champs and then look at the progression as the designs got more recent. The original 5C1 CHamp had 8uf caps. Larger caps than that were expensive then. But look at the schematic. Note the first cap - the reservoir cap as some call it - doesn't serve any part of the circuit. The second filter stage serves the power tube plate. Those two stages work better than a single 16uf stage would. Move ahead to the 5E1 CHamp. The resistor betwen filter stages has ben replaced by a choke. That improves filtration right there. Note the plates still drag their current from the second filter stage.

Now progress to the 5F1. OOps, now they are taking the plate current from the first filter node. They increased teh 8uf to a 16uf, but still, the earlier filter system was "better." And the later designs all take the plate supply from the first filter. Cheaper to do it this way.

But if you want to reduce hum, putting two filter stages before the tube will help better than tons of cap.

And of course that will ONLY re3duce hum coming from power supply ripple. It will do nothing for ground related hum, radiated field hum, etc.

The issue with this amp has never been hum . What it is when I first built this amp it sounded fine. I used a F&T 47uf res cap yet I have no way to measure the exact value . Then I got freaked out by issues of stressing the 5Y3 with a large res cap so I rmoved the 47uf and installed a 30uf again give or take . then what happened is I got icepick highs and all I did was repalce the one cap . due to the highs I ordered another 47uf F&T cap yet the highs are still there and the same , again I have no way to measure the value of the cap I trusted it wass close to the stamped value on the cap. For all I know the orig 47 which is now junk if even here because I had to clip the leads since I installed it with the eyelet baord out while building the amp and used the lead of that orig cap to reach another eyelet next to it for ther B+ leads so not to have 4 leads stuffed into one eyelet. So here I am , wish I never replaced the original 47uf whatever cap . even with thr 30uf give or take there was no hum or noise and there is still not. hum is not the issue the icepick highs are and yes I have been told this cannot be yet it is.

So I have one 22uf F&T cap that I got with the other two 22 uf F&T caps that are still in this amp . Now I have no idea if the cap is the problem , it is possible the orig 47uf could have been 25 uf or less or more . I would not know. Now if the 5Y3 is working just to keep the 47uf res cap charged during operation and the amp is working of the cap more than the PT it may be possible this is the reason for the icepick highs . I do know there are duty cycles and the res cap needs the most charge , perhaps I am wrong . So I have options leave it alone and turn the treb pot down which helps or take out the 47uf res cap and install the F&T 22uf cap I have form the same batch that the other F&T 22uf caps came from which have always been in the amp.

Is it possible that the 5y3 is just working more to keep the res cap up because the cap will keep pulling until it is charged.

[diagrammatiks]

tube rectifiers are almost 60 year old technology. There isn't all that much to them.

There's an absolute limit to the reservoir capacitor tat they can handle.

That number is usually max 47-50uf.

going to 22uf might make a difference it might not.

The tube rectifier doesn't care how big the cap is as long as it's under the limit.

I do know this for sure though...the size of the reservoir capacitor is in no way shape or form responsible for the ice pick highs.

not at all. can't be.

[Intergalactic Tourister]

so I removed the 47uf and installed a 30uf again give or take . then what happened is I got icepick highs and all I did was repalce the one cap .

Yeah, that capacitor won't cause icepick highs. For that matter, the whole power supply won't. Go over your components individually... sounds like you may have disturbed something else in your amp.

*It is possible you may have knocked a connection loose somewhere else.
*may have pressed another component to short against another component.
*burned a resistor or different cap accidentally with your solder iron.

[Enzo]

Well possibly the old cap was leaky and the newer caps aloow maybe a lille more B+? Just guessing here. And maybe that allows a litle more gain in the preamp stages. But i have to agree, that size of filter cap shouldn't result in ice picking.

I could be wrong, but I tend to think differnces in the caps that you might hear are less about the capacitance, but more a matter of things like ESR and stuff. If I haven't already mentioned it, I will here, e-caps in the old days comonly had tolerances of -20/+80%. SO a 47uf cap could be all over the map and still be within spec. It just isn't that critical. But as caps dry out over time, they may maintain their capacitance as mesured on a cap meter, but they also tend to grow more and more resistive inside.

[ThermionicScott]

FWIW, I figure you can get away with a higher reservoir cap (say, up to 40-47uF) in Champs and tweed Princeton types since the amp is only drawing about 1/3 of the 5Y3's current capacity, so the spikes aren't going to tax the cathode as much.

Just a shot in the dark: I'd check the negative feedback connection. If it got disconnected somehow, the extra harmonics would give some "edge" to the sound.

- Scott

[catnine]

Yeah, that capacitor won't cause icepick highs. For that matter, the whole power supply won't. Go over your components individually... sounds like you may have disturbed something else in your amp.

*It is possible you may have knocked a connection loose somewhere else.
*may have pressed another component to short against another component.
*burned a resistor or different cap accidentally with your solder iron.

No I have checked everything many times over and check everything when I do any work on the amp just to make certain I have not melted anything . Also I test each circuit and all the resisters and nothing there has changed all the grounds are good .

[diagrammatiks]

enzo's right about the esr rating....

but even then ... you could expect a usable older type electro to have an esr in the high 4 digits mOhms for 22-47uf.

An f&t axial is actually not all that good in regards to its numbers. It rates something like 5000mOhm Esr at 22uf.

there are caps that'll do 300-500mOhm at 22uf...

that being said I still don't see why that would change your high frequency response at all. It will change your bass transient recovery...but ice picky highs are something else entirely.

do you have ceramic caps in the amp? are you sure they didn't overheat?

I mean I understand that you've checked everything but you're still attributing a problem to an impossible cause.

[catnine]

enzo's right about the esr rating....

but even then ... you could expect a usable older type electro to have an esr in the high 4 digits mOhms for 22-47uf.

An f&t axial is actually not all that good in regards to its numbers. It rates something like 5000mOhm Esr at 22uf.

there are caps that'll do 300-500mOhm at 22uf...

that being said I still don't see why that would change your high frequency response at all. It will change your bass transient recovery...but ice picky highs are something else entirely.

do you have ceramic caps in the amp? are you sure they didn't overheat?

I mean I understand that you've checked everything but you're still attributing a problem to an impossible cause.

enzo's right about the esr rating....

but even then ... you could expect a usable older type electro to have an esr in the high 4 digits mOhms for 22-47uf.

An f&t axial is actually not all that good in regards to its numbers. It rates something like 5000mOhm Esr at 22uf.

there are caps that'll do 300-500mOhm at 22uf...

that being said I still don't see why that would change your high frequency response at all. It will change your bass transient recovery...but ice picky highs are something else entirely.

do you have ceramic caps in the amp? are you sure they didn't overheat?

I mean I understand that you've checked everything but you're still attributing a problem to an impossible cause.

No ceramic caps . All I did was remove the 47uf cap and did it carefully and this required the + side which is only soldered to the eyelet and the 1k 3 watt dropping resister and a jumper to an eyelet to the left where the B+ lead form the rect is and the red lead from the OT , I did this to make less leads in an eyelet and easy removal of the caps or resisters. I use a heat sink of a spool of lamp wire with both wires soldered to one alligator clip so as not to over heat anything . The other end on the cap is the ground which is jumpered to the the extra eyelet to it's left and to a lead bolted to the PT stud with a good soldered on terminal end . I checked the 1k after the work and all solder joints are shiny and good and the 1k still measures 1k . This is all I did and all this work is far away from the rest of the board and componants. This is when the increased highs began . I later to tame the highs replaaced the .1 uf and.047 tone caps so see it that would help , I have a SM 250pf treb cap and never changed it. And i never did any work at the pots and there read what they should be. So either the 250pf treb cap all by itself changed value by some freak coincidence or it's my imagination yet after the work my wife asked what I did , why does the amp have so much treb . Yes I have been told the res cap cannot do this , ok fine , yet I ask if this were all you changed and the result were these new highs would you not look at what you just did and suspect that to be the issue ? I don't have the original 47uf cap so if the caps cannot cause highs then I have to suspect the new 30uf and the new 47uf but then what's the point if this is not possibal as the cause , these caps are only 2 years old.

[catnine]

The cap is recharged every pulse- give or take, of course. But if the cap is fully discharged you want it to be able to handle that situation. If the cap is fully charged, somehow, then you'll still be fine.

It is the 60hz (US) pulses. So the B+ going into the reservoir cap is not full on 100%. It is like an incandescent light bulb... try turning it on-and-off as fast as you can flip the light switch. You'll notice that the bulb will never get to its fullest brightness or wattage. This is due to you making it pulsate at the switch. Same concept. The mA draw will not get to its fullest.



If 40mA is the draw... times 5 = 200mA. But it pulsates... and the other filters caps are also supporting the larger one with respect to mA. So I don't believe your calculation takes all factors into account. In other words you have more than one big filter cap in your amp.

Further it depends if the mA is average or peak. I don't have the specs of your amp, but I believe that if 40mA were peak then you'd want about 30% higher rated PT.

enzo's right about the esr rating....

but even then ... you could expect a usable older type electro to have an esr in the high 4 digits mOhms for 22-47uf.

An f&t axial is actually not all that good in regards to its numbers. It rates something like 5000mOhm Esr at 22uf.

there are caps that'll do 300-500mOhm at 22uf...

that being said I still don't see why that would change your high frequency response at all. It will change your bass transient recovery...but ice picky highs are something else entirely.

do you have ceramic caps in the amp? are you sure they didn't overheat?

I mean I understand that you've checked everything but you're still attributing a problem to an impossible cause.

No ceramic caps . All I did was remove the 47uf cap and did it carefully and this required the + side which is only soldered to the eyelet and the 1k 3 watt dropping resister and a jumper to an eyelet to the left where the B+ lead form the rect is and the red lead from the OT , I did this to make less leads in an eyelet and easy removal of the caps or resisters. I use a heat sink of a spool of lamp wire with both wires soldered to one alligator clip so as not to over heat anything . The other end on the cap is the ground which is jumpered to the the extra eyelet to it's left and to a lead bolted to the PT stud with a good soldered on terminal end . I checked the 1k after the work and all solder joints are shiny and good and the 1k still measures 1k . This is all I did and all this work is far away from the rest of the board and componants. This is when the increased highs began . I later to tame the highs replaaced the .1 uf and.047 tone caps so see it that would help , I have a SM 250pf treb cap and never changed it. And i never did any work at the pots and there read what they should be. So either the 250pf treb cap all by itself changed value by some freak coincidence or it's my imagination yet after the work my wife asked what I did , why does the amp have so much treb . Yes I have been told the res cap cannot do this , ok fine , yet I ask if this were all you changed and the result were these new highs would you not look at what you just did and suspect that to be the issue ?

[catnine]

here is the amps chassis

[ThermionicScott]

Could be external to the amp. Have you cleaned your ears recently? Caught or recovered from a cold? Has the humidity/air pressure gone up or down since changing the cap? Still using the same guitar, right?

- Scott