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

[catnine]

A few years back I built a AA764 champ homebrew , wired it the same way ( this is the non trem champ) I used the same values for all the componants .

My question is on a 73 SF champ i had the original cap can was 40/20/20uf so for my build I used F&T electrolytics 47/22/22 uf . The PT is a weber replacement unit as is the OT . I use a nOS 5Y3 and JJ 6V6 and JJ 12ax7.

I was here a few years back asking about the 5Y3 and a res cap of 47 uf being too large , on advice I installed a 47 ohm 3 watt resister in series between the pin 8 of the 5Y3 and the B+ to the fisrt filter cap to protect the 5Y3 from inrush charging the cap.

What other affect will a 47 uf cap have . From what I understand a larger cap holds the voltage longer and can tighten bass response some what.

The amp is quiet , sounds good with no issues from low levels to full up .

[Enzo]

Let me get this straight, you are concerned that 47uf is too large in place of 40uf??

Back in the old days, many electrolytic caps had tolerance ratings of -20/+80%. That means a perfectly good 40uf cap could measure 72uf and be within spec. Or for that matter 32uf would be OK as well. FIlter caps are not even today very precise items. 7uf difference is not worth thinking about. And it is within a 20% tolerance anyway.

A little overload on the rectifier won't destroy the tube instantly. It is like being overweight, it ain't like you are healthy at 180 pounds, and obese magically at 181 pounds. Same with tubes, if the book says 40uf tops, that doesn't mean 41uf is a killer.

[catnine]

Let me get this straight, you are concerned that 47uf is too large in place of 40uf??

Back in the old days, many electrolytic caps had tolerance ratings of -20/+80%. That means a perfectly good 40uf cap could measure 72uf and be within spec. Or for that matter 32uf would be OK as well. FIlter caps are not even today very precise items. 7uf difference is not worth thinking about. And it is within a 20% tolerance anyway.

A little overload on the rectifier won't destroy the tube instantly. It is like being overweight, it ain't like you are healthy at 180 pounds, and obese magically at 181 pounds. Same with tubes, if the book says 40uf tops, that doesn't mean 41uf is a killer.

Well the AA764 champ in the schem shows a 20uf for all three filter caps yet my 73 SF had a 40/20/20 uf cap can and at the time I built this home brew I used what I knew the 73 champ had. I didn't trust the fender schem and the Bronco had the same 40/20/20 uf cap can . I just went with came in my 73 champ as stock , it was never replaced and when I did a recap on the 73 SF I got the same value and brand cap can. I have no idea what the best value is or if it makes all that much difference or if I replace the 47uf filter cap with a 22uf which I do have if that will even make a difference . All I have read is a higher value 1st filter cap will make the amp stiffer and add some bottom end , now if that applies to a SE AA764 champ I really can't say. I can replace it with a 22 uf , it's a lot of work because they are seperate caps and there is not a lot of room to work since it is a narrow panel tweed style chassis. Lets just say It was easy when I built it but now with everything in place you really have to move thing out of the way to remove the cap and replace it.

[Intergalactic Tourister]

Well the AA764 champ in the schem shows a 20uf for all three filter caps yet my 73 SF had a 40/20/20 uf cap can

Fender may have had a surplus of 20uf caps so just decided to throw them in the AA764 to save money. The point is... the caps are about within tolerance- or close enough.

All I have read is a higher value 1st filter cap will make the amp stiffer and add some bottom end

The problem is all your other components... they too are probably all over the place regarding tolerance! To say the 22uf is the cause of a stiffer amp is ignoring the fact that you have other components in play that are upwards of 80-120% off tolerance. That could be making your amp stiffer. Who knows.

But yes I've read the same thing but opposite. Smaller filter cap makes the amp stiffer. I have an old silvertone with an 8uf filter cap. The amp feels stiff to me.

[Intergalactic Tourister]

To say the 22uf is the cause of a stiffer amp is ignoring the fact that you have other components in play that are upwards of 80-120% off tolerance

That is my quote above. Let me put it into some perspective.
What if Fender in the 1950s and 1960s had access to capacitors, resistors, PTs, OTs, from the year 2011. Do you think their values (and tolerances) would be the same as you see on their old schematics? I personally don't think so due to economics, size, and quality of components.

So, maybe you try for yourself both caps 22uf & 47uf. Better yet, try 10uf and 60uf. I'd like to know what you find out.

[Enzo]

Remember that the single ended CHamp is a class A amplifier, so the current draw from the powr supply is more or less constant. NO sag. Stiffness is a measure of sag, which applies to typical class AB push pull amps. A MUCH greater concern in the single ended amp is hum - there is no hum cancellation like in a push pull amp. SO increasing the cap value is one way to fight hum without redisigning the amp or adding expensive chokes. I would suspect that Fender increased the cap size to cut fown on complaints of hum in their amps. I do have a Fender service bulletin in my files regarding Champ hum. It says: a certain amount of hum in a single ended amp is normal. This is not a defect, do not try to "repair" it. SO they were not oblivious to the hum issue.

I have Fender Champ schematics showing both 20uf and 40uf first filters. From different years. Changes like that were made all the time. The Bronco was essentially a CHamp with a tremolo. The AA764 Bronco shows the 20uf, and a later drawing shows 40uf. I would expect the CHamp and Bronco lines to show similar development changes. Heck, look at the old original CHamp with 8uf caps.

[catnine]

I didn't know there were champs with 40 uf and 20 uf depending on the year. I only had access to the fender field guide and a book by G Weber showing the same diagrams so at that point I didn't trust the diagram and went with what fender built my 73 champ with. The rest of the diagram I used and also the type of resisters used and their banded values and the type of caps as close as I could get . the only cap value I did not go by on the diagram was the 20uf res cap . My 73 champ also had a 330pf cap across pins 8 and 5 on the 6V6 socket , that I left off my build and added a 470 ohm screen resister and a 1500 ohm grid. I also did not ground the heaters on one side to the chassis as per the 73 . I did not expect my build to sound just like the 73 , I just wanted to be close . When I got my 73 SF is was all stock .

I did change the 47uf cap for a 30 uf and did hear a loss in bottom as far as what bottom a champ can produce , now I did not measure the caps actual value so the 47uf could have been 60 uf and the 30uf could have been 21uf or the reverse , I have no meter to measure this value I just trust they are within tolerance .

That said , since the 40 uf lasted with the stock 5Y3 in my 73 for decades and I did replace that cap can with the same 40/20/20 and the same brand cap can so if fit and still had no issues then I assume the 47uf (give or take) will be acceptable in my build .

Changing that cap is quite a job , this is a allen amps chassis he used to sell a narrow panel tweed type with not much room to go in there again to test different cap values . I have a the same 30uf and a new 22uf and if there was a way of predicting the outcome if I put in the 22uf then yes it would be worth the effort yet I cannot see how this can be predicted . Bottom line is if the 47 uf I have in the build now will not be an issue and in two years it has not then I assume the 47uf res cap from what I gather in the above responses is acceptable for all practical purposes . Now if the 22uf would be a wiser and better choice then I will go with that.

[Intergalactic Tourister]

All in all I personally think you made a good judgement call based on the info you had.

A long time ago, when I replaced the filter capacitor can in my old silvertone I used the exact same values (one of which was 5uf I believe!). I basically wanted it to sound the same. And doing this told me a lot... because I had a hypothesis going into this. I thought "fresh caps will get rid of the hum better than the original caps." But, "having the same values will keep it sounding original."

Turns out the amp sounded exactly the same- hum and all. I thought at least the hum would be reduced- no. But I'm fine with it. I like how it sounds. But what I think it told me was the values are too low to begin with to make much of a difference. I bet larger caps would lower the hum but could change the sound like you said. A trade-off like almost everything else.

Changing that cap is quite a job... not much room to go in there again to test different cap values. I have a the same 30uf and a new 22uf and if there was a way of predicting the outcome if I put in the 22uf then yes it would be worth the effort yet I cannot see how this can be predicted ..

I thought there was a formula for the B+ and bank of filter capacitors/resistors. That is how designers come up with the value of caps to use. I've looked before but never found clear info on that. Please reply if you find out.

[Enzo]

The lesson there is that hum is not generic. You can increase filter cap value by 100 times and it will do nothing to reduce hum coming from poor grounding or from radiated AC fields or from heater interactions. Each one of 20 sources of hum will have its own cure.

[Intergalactic Tourister]

You can increase filter cap value by 100 times and it will do nothing to reduce hum coming from poor grounding or from radiated AC fields or from heater interactions.

Or like me... increase filter cap value by nil. I didn't expect any hum reduction due to cap value- rather had a hunch replacing 40 year old caps for fresh ones might at least have a slight audible difference. But no.

But they needed to be replaced anyway.

catnine:
Could you maybe use clips to parallel a 20uf cap to the cap you have soldered in the amp. It may be easier this way and you could at least hear the difference of a larger capacitance... to see how it affects the low end.

[catnine]

Or like me... increase filter cap value by nil. I didn't expect any hum reduction due to cap value- rather had a hunch replacing 40 year old caps for fresh ones might at least have a slight audible difference. But no.

But they needed to be replaced anyway.

catnine:
Could you maybe use clips to parallel a 20uf cap to the cap you have soldered in the amp. It may be easier this way and you could at least hear the difference of a larger capacitance... to see how it affects the low end.

There is a formula to determine the values of filter caps at least what a certain rect tube can handle . I had as my first amp a harmony with a 12 inch speaker and a tone and vol control in the back at the top . All I knew is it had tubes and a 12 , didn't know it was a SE amp . That amp was the worst sounding amp for clean tones and had an always present hum . I was only 13 way back then and was happy to just finally have an amp to go with my three PU Harmony Rocket guitar .

I suppose I could clip in the 22uf cap in parallel with the 47uf just to see. if it provides more bass yet I do feel it won't make that much difference since the main problem this amp seems to have is one it is a SE amp and two the speaker is a weber sig 10s ceramic which is considered bright no matter what amp it is powered by.

Most of the old SE amps I had 40 years ago all hummed .

[Intergalactic Tourister]

That is a cool Harmony setup you had.

I suppose I could clip in the 22uf cap in parallel with the 47uf just to see. if it provides more bass yet I do feel it won't make that much difference since the main problem this amp seems to have is one it is a SE amp and two the speaker is a weber sig 10s ceramic which is considered bright no matter what amp it is powered by.

I understand. But it just seems the only way is to try the different caps in your amp. As we've posted there are a lot factors to be considered and your speaker is one of them.

There is a formula to determine the values of filter caps at least what a certain rect tube can handle .

True. But I think you're still within range for 5y3. Enzo made that point as well. I thought you just wanted to know the lowend affects of different caps within the "safe" range for you rectifier tube.

[catnine]

That is a cool Harmony setup you had.



I understand. But it just seems the only way is to try the different caps in your amp. As we've posted there are a lot factors to be considered and your speaker is one of them.



True. But I think you're still within range for 5y3. Enzo made that point as well. I thought you just wanted to know the lowend affects of different caps within the "safe" range for you rectifier tube.

My build sounded just as quiet with the 30uf as it does with the 47uf , who know what it would be with the 22uf . I had two other SF champs one from 1980 and one from 1968. Both of them hummed but then at the time I had them I knew nothing about filter caps . I do know the 1968 had alot of hum and I removed the chassis and saw someone added a huge blue filter cap in place of one in the cap can so it probably needed a recap . I know the 47uf did add a stiffer bottom end , I doubt going higher will change that much if at all.

The main issue I have is this AA764 build does produce highs that bother me where the 73 SF champ I owned and recaped did not have these highs . When I got it the fellow who owned it before put in this Torres mod kit and it made the 73 sound like a OD pedal full on all the time , he supplies the stock parts so I took out the mod kit and the amp then sounded perfect to me. The only thing I did not like was the stock speaker , any bass at all and the speaker flabbed out so I installed a weber sig 8 s alnico and that fixed the flubbing issue and made the amp sound even sweeter.

There are all sorts of mods to change the BF tone stack that may or may not get rid of the highs , I can say the tone stack lift is NOT one of them that I cared for. If your Silver tone hums and has a 5Y3 try a 30uf and see if that curs the issue , wouldn't hurt. It just might get rid of the hum and add a bit of bottom end . You never did say what model the Silvertone is or if it's a SE or push/pull.

[Intergalactic Tourister]

My build sounded just as quiet with the 30uf as it does with the 47uf , who know what it would be with the 22uf .

That was kind of my point when suggesting to parallel a cap with a clip- However, you won't know what a smaller cap sounds like unless you rip yours out and put one in.

The only thing I did not like was the stock speaker , any bass at all and the speaker flabbed out so I installed a weber sig 8 s alnico and that fixed the flubbing issue and made the amp sound even sweeter.

You were referring to your 73 SF above... but that would seem a better place to start in general rather than changing filter caps (in your new build) to dial in a lowend. But I understand you were curious about the idea as well. I am too. But I would personally make adjustments almost everywhere else first before thinking to lower the filter caps.

There are all sorts of mods to change the BF tone stack that may or may not get rid of the highs

I personally wouldn't start at the tone stack- especially if its to spec and you followed the instructions in your build and didn't make a wiring mistake (or wrong cap or resistor value). You could maybe try increasing the cathode bypass resistor, first. But I don't know if you even have one because I don't have the schematic.

If your Silver tone hums and has a 5Y3 try a 30uf and see if that curs the issue , wouldn't hurt. It just might get rid of the hum and add a bit of bottom end . You never did say what model the Silvertone is or if it's a SE or push/pull.

Its the 1482 Twin Twelve. No rectifier tube at all- just diodes.

I can live with the hum really. Plus I completely recapped the amp, changed bad resistors, new rectifier diodes, twisted the filament wires and moved them away from other wires... put new tubes in... then put the old tubes back in.

I left all the ceramic discs in... so it might be them. But I will increase the filter caps in the future sometime... after I've played it a good while.

[catnine]

"Its the 1482 Twin Twelve. No rectifier tube at all- just diodes".
Man is that the piggy back with reverb . If so I had one of those in 1966. Great amp If this is the amp I am thinking of I don't recall mine humming at all, only if I got near it with the guitar.