Getting the hum out of a 65 Vibro Champ

[dude]

I searched the hum issues in BF Champs and found the filament wiring to be first choice cause. As I see the chassis is used for a ground.


I assume just lifting those filament grounds and running a two wire filament supply to the heaters as in Fender bigger amps would be the first place to start, using two 100K R off the two legs of the pilot light for a ground. I didn't seem to find any other issues in the search that would cause this hum which is basically pretty loud at idle.


I did change the cathode caps on the 12ax7 to 2uf and 1K5, didn't change much else except put the NF on a switch, of course I drilled no holes in the chassis (easily back to original). Added a bigger OT too.  Just too much hum for recording. 


al 

[labb]

 two 100K R   
You do mean 100 R, right?


Something you might want to check would be the PS caps. Also take the center tap of the filament supply to the Cathode of the Power tube for some heater DC elevation.

[sluckey]

using two 100K R off the two legs of the pilot light for a ground.

That should be two 100 ohm resistors, not 100K.

Adding a 20µF cap and 250Ω/10W resistor between the rectifier tube and the first filter cap will reduce a lot of hum. Even better, use a choke in place of the resistor.

Use a cheap 8" speaker to reduce hum also.

[HotBluePlates]

And you really need to know the hum frequency before you go chasing hum. If the hum in your case is 120Hz, Sluckey's suggestion help & your approach does nothing. If the hum frequency is 60Hz, then vice versa.

[dude]

Yeah, I meant 100 ohm not 100K, thanks.


I did take out the cap can and used single filters (tie-downs no mods to chassis), some say use 40uf for the first one. After the rewired heaters, I'll see how that goes then add the filter and 250 R (reasoning behind this)?


I'm pretty sure it's 60 cycle hum but how do you tell the difference?


What does the extra 20uf and the 250 ohm R do to cut hum...?


Yeah, I could elevate the cathode of the 6V6 too.


Please excuse my ignorance.


I'm very happy with the tone of this Vibro Champ, the OT is older and paper wrapped (probably 10 watts), no rating on it but the math says it's about 10K ohms at 4 ohms.  I'm using a Weber alnico 4 ohm speaker, I've ran the amp with a 10" 8 ohm and no difference in volume but the 8" sounds better.  I probably have a mismatched impedance...?


al

[HotBluePlates]

I'm pretty sure it's 60 cycle hum but how do you tell the difference?

I'm fortunate, in that my DMM (an older Fluke 87III) has a frequency counter. If your meter has such a function, use it (though you will likely have to dig through the manual to find how to use it and its limitations.

If no counter is available, try playing a B-flat on your low E string. 120Hz is an out-of-tune B-flat, while 60Hz is the same note an octave lower (lower than your low E note). Buzzy hum (usually from no heater ground reference) can make it hard to discern the pitch because of all the harmonics of the hum, which is why it sounds buzzy.

What does the extra 20uf and the 250 ohm R do to cut hum...?

Note the output transformer sources B+ from the first filter cap attached to the rectifier output. That is the noisiest B+ in the amp; subsequent series-resistors and filter caps to ground successively remove ripple from the B+, with the preamp getting the cleanest d.c.

A lot of folks here have built Champs over the years, many using heavier OTs and speakers as big as 12". The bigger OT and speaker have better bass response than the Champ's original 8" speaker. As a result, those builders hear hum in their amps that was always there, but which the puny OT/speaker shaved off.

Push-pull amps have no problem attaching the OT to the noisiest filter in the power supply, because the power is fed to the center-tapped primary: hum voltages travel in opposite directions through the primary and cancel. But single-ended amps don't get the benefit of this, and need extra filtering to sound noise-free.

The universal solution has been to add another filter cap to ground before the one feeding the OT, with a resistor or a choke between the new cap and the existing B+ rail. This trims ripple from the power supply before it is fed to the OT. An added C-R or C-L filter is a much better filter than just increasing filter cap values.

A lot of folks never realize that hum in their Champ is mostly a power supply issue, and that the heaters are rarely a problem. But they jump to solutions they've read about elsewhere, never realizing the original Champ was hamstrung by the weak bass response of a small OT and speaker, which reduced any hum to "acceptable level".

[xm52]

This amp is great for recording and can be made to be dead quiet.

You didn't mention it, but the heater wires should be tightly twisted. You can fly them over the top of the tube sockets. Also tightly twist the green pair of heater wires from the power transformer. The 100 ohm pair making up the artificial center tap mounted on the lamp holder is a good idea. So is changing the cap can if necessary.

Other things that you can consider:

-Push back the input jacks and tone pots. Clean the chassis contact surface with a product such as Deoxit. A bad ground will cause hum.
-Check all the grounds from the brass jack plate to the chassis.
-Installed a three conductor power cord.
-Remove the so called death cap, the blue 0.047uF, on the primary of the power transformer.
-Use a shielded wire running from the input jack to the grid of the 12AX7. Ground one end of the shield. I like to do it at the input jack end.
-Replace the two 68K and one 1M carbon composition resistors on the input jack with metal film resistors.
-The top inside of the cabinet usually has a screen which acts as a noise shield for the open face of the chassis. If it is missing, staple a sheet of aluminum flashing in place or install a layer of aluminum tape. Both are available in the roofing department of a hardware store such as Home Depot. The metal sheet can be cut with heavy scissors or scored with razor knife and bent to break it.

[mresistor]

HPB - Interestingly, I built a 65 VC clone a while back in a vintage reproduction chassis and eventually sold it. It was in a 12" cabinet with a 12" alnico speaker.  I used Classic Tone iron and it had a lot of hum and nothing I tried (tips as mentioned above) worked to reduce it until I added another R-C B+ node on the PS as you mentioned. I've built many of these amps and this particular one just had a lot of hum. It was not due to being able to hear the hum better through a 12" speaker, it hummed nicely through a stock 8" as well.  Later, the owner called back and wanted me to install an oversize MM OT. It was monstrous!  It was so big it had to be shifted towards the pre-amp side of the amp, and angled slightly,  to clear the speaker. After install the amp sounded spectacular. But, at that point I decided to pull that extra R-C filter B+ filter node to see if re-positioning the OT farther away from the PT would make a difference. I guess it did because it was then dead quiet without the extra filter node. I attribute the change to the OT moved farther away, but it could also be a combination of new iron too. The wiring was basically identical inside the chassis. Of course not many techs/owners are going to want to modify a stock VC this way. But I do believe it is another solution. 


The MM OT was the American Pro Series F-CHMP-OM

[dude]

I opened the Vibro Champ to make some changes suggested, first to rewire the filaments.


I noticed I wired three power filter caps in place of the cap can, first one 33uf and two 22uf.I separated the grounds keeping 33uf 2nd 22uf grounded at the main ground, leg of the PT. The preamp grounded down to the brass plate.


I do have the first filter, 33uf, right after the 5Y3, so that looks good. The original PT has no ground for the filaments, no 100 ohm R's either. I'll fix that.


I noticed I had three 15 or 10 volt Zeners in series to main ground at PT, I guess I was dropping voltage. Been a while since I had this amp opened and didn't remember. I checked the B+, it's 374v, screens 367v and preamp 231v, does this seen about right? taking out the Zeners would raise the B+ about 25volts so is 400ish too high for one old stock 6V6...?


I guess I could add a choke and take out the Zeners but  don't have a choke.


I do have some odd frequencies on the low E string as HBP mentioned, so since I have a 33uf right off the rectifier, but no 250 ohm R id that OK, if the hum is related to 120v frequencies?   


What is the proper B+ for a BF Vibro Champ< with original PT?


al
 

[mresistor]

I o

I do have the first filter, 33uf, right after the 5Y3, so that looks good. The original PT has no ground for the filaments, no 100 ohm R's either. I'll fix that.


I noticed I had three 15 or 10 volt Zeners in series to main ground at PT, I guess I was dropping voltage. Been a while since I had this amp opened and didn't remember. I checked the B+, it's 374v, screens 367v and preamp 231v, does this seen about right? taking out the Zeners would raise the B+ about 25volts so is 400ish too high for one old stock 6V6...?


I guess I could add a choke and take out the Zeners but  don't have a choke.


I do have some odd frequencies on the low E string as HBP mentioned, so since I have a 33uf right off the rectifier, but no 250 ohm R id that OK, if the hum is related to 120v frequencies?   


What is the proper B+ for a BF Vibro Champ< with original PT?


al

A Vibro Champ doesn't use an artificial center tap on the filaments. What you meant to say was Center Tap on the filament winding, and it doesn't have that.  Your 6.3 vac filament winding has one side which is ground and the other is 6.3 vac. NO 100 ohm resistors in this amp.

Your B+ looks OK. Bear in mind that with todays wall voltage going as high as 123-124VAC the VC B+ could go higher. But it's not a problem really. You could take out the zener(s) and wire in that extra filter node off the rectifier, by adding another cap and a resistor. I forget what resistance I used, probably 250 Ohm 2-3 watt. The extra filter will also drop some voltage to bring B+ down some. You can add resistor or choke. B+ for the plates would still be taken from the same node, which would now be the second node.


heres the schematic of the AA764 VC      http://el34world.com/charts/Schematics/files/fender/Fender_Vibrochamp-AA764-schematic.pdf

[mresistor]

Here's a pic of one of my champs, actually its a 68 Bronco that I received gutted so I built a new amp inside the chassis.   This has the extra R-C filter node off the rectifier and you can see I used a 250 ohm 7 watt wire wound resistor, brown one. I also like to add a screen resistor to lower the screen voltage below the plate voltage. Since you are not using a 4 section cap can you will have to add another 20uf capacitor. 

[mresistor]

Here is another  with an extra R-C node implemented without a cap-can. 

[mresistor]

Also, as has been mentioned to me here, notice those notes on the schematic that says voltages + or - 20%. (top right)  That means that the B+ could be  anywhere from 284 VDC to 426 VDC.
So if it were me I'd pull the zener(s) out.

[mresistor]

OK I was assuming he is using the original PT which has no center tap on the filaments. If however he is using a replacement PT with center tap on the filaments, then of course adding the two 100 ohm resistors off the pilot lamp is a good idea.  I've never done that in my Champs, but might consider it. Another thing you can do to elevate heaters when using a center tapped filament winding is to tie the center tap to the cathode of the 6V6. I did this on the amp in the second pic I posted.

[dude]

OK I was assuming he is using the original PT which has no center tap on the filaments. If however he is using a replacement PT with center tap on the filaments, then of course adding the two 100 ohm resistors off the pilot lamp is a good idea.  I've never done that in my Champs, but might consider it. Another thing you can do to elevate heaters when using a center tapped filament winding is to tie the center tap to the cathode of the 6V6. I did this on the amp in the second pic I posted.

I am using the Original PT, they have no "filament CT". I have an older paper wrapped single-ended "OT" of about 10 watts replacing the 5 watt original which produced just a lot of distorted bass at anything over 6 on the volume.


Just have the hum issue, I have the amp opened now but didn't do the new filament wiring yet. Just getting a plan together first.


Are you saying one way to solve the problem is to move the OT away from the PT? (it's not much bigger than the original but sounds great) I can't do that, this is a non-messed 66 VC with original chassis and I don't want to drill any holes. I did the cap can replacement just like you're second pic but did but have only three P filter caps and can be put back to a new original cap can, easily.


I take it your suggestion is: take the Zeners out, put a 10W, 250 ohm (that's the wattage I have on hand) in series from the rectifier, add a 20uf cap after that 250 R and ground it to same leg on PT as the other P caps. If the filament change doesn't do the trick, I'll add the cap off the rectifier?


I did add a screen resistor, and used a 500 ohm cathode biasing R (two 250's in series) I like to use what I have on hand.


Making the bias hotter using a 470 ohm, not much from 500, how would that affect the tone?


al


   

[dude]

using two 100K R off the two legs of the pilot light for a ground.

That should be two 100 ohm resistors, not 100K.

Adding a 20µF cap and 250Ω/10W resistor between the rectifier tube and the first filter cap will reduce a lot of hum. Even better, use a choke in place of the resistor.

Use a cheap 8" speaker to reduce hum also.

Does the cap go after the 250 ohm R or right on the rectifier pin?

[sluckey]

The cap goes right on the rectifier pin. And one end of the resister also goes right on the rectifier pin, with the other end going to the original first filter cap.

[mresistor]

You know Sluckey,  I suppose that the ground side of an original filament winding without center tap could be elevated by terminating it at the 6V6 cathode. Never tried it though.

[mresistor]

Are you saying one way to solve the problem is to move the OT away from the PT? (it's not much bigger than the original but sounds great) I can't do that, this is a non-messed 66 VC with original chassis and I don't want to drill any holes. I did the cap can replacement just like you're second pic but did but have only three P filter caps and can be put back to a new original cap can, easily.

I take it your suggestion is: take the Zeners out, put a 10W, 250 ohm (that's the wattage I have on hand) in series from the rectifier, add a 20uf cap after that 250 R and ground it to same leg on PT as the other P caps. If the filament change doesn't do the trick, I'll add the cap off the rectifier?

I did add a screen resistor, and used a 500 ohm cathode biasing R (two 250's in series) I like to use what I have on hand.

Making the bias hotter using a 470 ohm, not much from 500, how would that affect the tone?
 

I would not move the OT.
I would take the zeners out.
I would check bias and make sure I am not exceeding 70% of max dissipation which is around 10 watts.
After checking bias you may have to change the 500 ohm to a higher ohm resistor to get the desired result.
But since max dissipation for a 6V6 is 14 watts, it's your tube and your call.

[mresistor]

Tone is a subjective quality, it is in the ear of the beholder, what you like may not be what I like. So, experiment with it within the parameters of the amp, and find that sweet spot that you like.   
Cheers.

[dude]

Are you saying one way to solve the problem is to move the OT away from the PT? (it's not much bigger than the original but sounds great) I can't do that, this is a non-messed 66 VC with original chassis and I don't want to drill any holes. I did the cap can replacement just like you're second pic but did but have only three P filter caps and can be put back to a new original cap can, easily.

I take it your suggestion is: take the Zeners out, put a 10W, 250 ohm (that's the wattage I have on hand) in series from the rectifier, add a 20uf cap after that 250 R and ground it to same leg on PT as the other P caps. If the filament change doesn't do the trick, I'll add the cap off the rectifier?

I did add a screen resistor, and used a 500 ohm cathode biasing R (two 250's in series) I like to use what I have on hand.

Making the bias hotter using a 470 ohm, not much from 500, how would that affect the tone?
 

I would not move the OT.
I would take the zeners out.
I would check bias and make sure I am not exceeding 70% of max dissipation which is around 10 watts.
After checking bias you may have to change the 500 ohm to a higher ohm resistor to get the desired result.
But since max dissipation for a 6V6 is 14 watts, it's your tube and your call.

Thanks, just suggesting a hotter bias as the schematic shows a 470 ohm and usually a 500 ohm is used. I had a friends Tweed Princeton copy I fixed for him, that schematic had a 500 ohm bias R, I tried a 470 and it sounded better with the 500 ohm. I didn't do the math as dissipation of a watt or two isn't much and he was usings a JJ 6V6. But like you say tone is in one's own ears.


Thanks for the info, I appreciate everyones two cents,
al   

[dude]

The cap goes right on the rectifier pin. And one end of the resister also goes right on the rectifier pin, with the other end going to the original first filter cap.

I thought that and should have known that, otherwise I would just have had two caps next to each other with nothing between. I see now that the filter is filtering the rectifier tube, helping to take the ripple and hum out. I remember using a P filter cap off the standby switch once to get rid of the pop in another amp when switching on/off, it worked. 


HBP explained how to tell the difference between 120 and 60 cycle hum, I understand 60 cycle hum, but not up on actually what 120 cycle hum is.... Seems like double 60 cycle. Guess I need to do some research.


Thanks for your help, I'll post the results tomorrow when I'm finished.
al 

[HotBluePlates]

... HBP explained how to tell the difference between 120 and 60 cycle hum, I understand 60 cycle hum, but not up on actually what 120 cycle hum is.... Seems like double 60 cycle. Guess I need to do some research. ...

You're already aware the wall outlet is 60Hz, and since the filament wiring is just stepped-down wall voltage it is also 60Hz.

Each half-cycle of the wall voltage, the full-wave rectifier has one of its two diodes conducting the voltage supplied by that half-winding of the high voltage secondary. Since there are 2 rectified pulses leaving the rectifier each cycle of the wall voltage, the output frequency is doubled to 120Hz.

So if you hear 120Hz hum, you know it's something B+ related. If you hear 60Hz hum, it's either heater-related or associated with the wiring from the wall to the power transformer.

[mresistor]

Checking bias is easy on a Champ or class a SE amp,  you need a multi meter and a calculator.


1. Using a voltmeter check the voltage on the 6V6 cathode pin 8 to ground, write it down.
2. Divide that voltage value by the cathode resistor resistance to get the current value that is going through the cathode resistor
3. Multiply the cathode resistor current you just obtained times the plate voltage. (plate V derived by measuring plate to cathode voltage between pin 3 and 8)
what you get is your power reading in watts, but there is some current going into the screen so this value is slightly overstated... a good thing and we  dont worry about it


if this figure is higher than 14 watts   then you need to change the cathode resistor to a higher ohm value. Then recheck.  I like 10-11 watts in my champs/vc

[dude]

You know Sluckey,  I suppose that the ground side of an original filament winding without center tap could be elevated by terminating it at the 6V6 cathode. Never tried it though.

You can elevate the heaters without a filament CT. Run the artificial ground, the two 100 ohm R off the 6V6 filaments and ground them to the power tube 6V6 cathode. That will work, I've done it. Bruce at Mission amps goes this on his 5E3 kits.


al

[labb]

Just for info, you can bias a single ended amp up to 90% of rated dissipation with out problems.

[dude]

Thanks again for all the help from everyone here.


I'm making some changes now but noticed that the tremolo isn' t working properly.  Such a simple trem circuit, I plan on checking all R's and tremolo caps, not much. When first turning on amp the tremolo works but is weak, after a minute or less it's not working, jack is fine, pedal is working.


I don't have any ceramic caps the right values, can I used Mallory's disc caps (coupling caps), white and yellow ones?  I would think so but just checking as I never seen them used in a tremolo like the VC.


al

[Willabe]

I don't have any ceramic caps the right values, can I used Mallory's disc caps (coupling caps), white and yellow ones?

Yes.

I would think so but just checking as I never seen them used in a tremolo like the VC.

It was probably the price why they mostly used ceramic caps in trem circuits.

[sluckey]

Trem needs a strong tube. First thing I'd do is swap V1 and V2, or just put a known good 12AX7 in V2 socket.

[dude]

Trem needs a strong tube. First thing I'd do is swap V1 and V2, or just put a known good 12AX7 in V2 socket.

OK, I'll try a known good 12AX7 first, thanks.


BTW, I notice that the "original" VC PT (1966) has a yellow with green stripe wire that has been cut and covered with old looking shrink wrap. I'm thinking is a bias tap and this PT was used for a princeton too....? The wire is a little thicker than the 5v rectifier heater, slightly. Any info on what this wire is?


al

[sluckey]

Princeton didn't use a bias tap. Use your ohm meter to find which windings have resistance readings to the mystery wire.

[HotBluePlates]

BTW, I notice that the "original" VC PT (1966) has a yellow with green stripe wire that has been cut and covered with old looking shrink wrap. I'm thinking ... this PT was used for a princeton too....? ...

Yes, the same PT was used in the blackface Champ, VibroChamp, Princeton and Princeton Reverb.

[dude]

All done, all hum is gone. It was the original filament wiring using the chassis as ground.


I lifted the artificial ground (100ohm R) to the 6V6 cathode. No hum, dead quiet, just barely able to tell the amps on.


The hardest thing was getting the pilot light socket out, one of the tabs was soldered to the socket. With the tilted blackface frame chassis getting that big nut off is almost impossible, must be some kind of special wrench...? I used standard filament green cloth solid wire, I guess 20 or 18 gauge, hard to work with as it's pretty thick.


It's completely stock except the OT is slightly bigger about 10watts and I used 2.2uf cathode caps on the two 12AX7's, maybe a coupling cap from .047 to .022. Sounds great and learned a few things.


The tremolo is much better with a known good 12AX7 but still is kind of weak, just not sounding as good as a year ago, thanks Sluckey for the tip.  I'll change out those old ceramic caps, I wasn't going to waste the Mallories I have on hand and their not radial either. I'll order some from Doug once I see what else I might need.


Thanks again for all your help,
al   

[dude]

I can't find any info on the voltage requirements for the three tremolo caps in the Vibro Champ.


Says at top of schematic all caps 400v unless marked but I don't think that applies to the three ceramic caps, .02, .01, .01.


What is the voltage for these caps?   Also, I have a small .022 cap, orange but not an orange drop that has no voltage written on it only:
       
         ic
      .022k
      400 T          Is this cap rated at 400v?


thanks, al

[mresistor]

It says "unless specified"  not marked. And the notes refer to the schematic. So unless the schematic says something different, all caps are at least 400v rated.  That would include the three ceramic caps in the vibrato ciruit.  Most of the time I see ceramics rated even higher. I think I have 1Kv rated in mine. 


You can also replace one to the .01 caps with a .02 to slow the oscillator down which to me gives the speed pot more range.

[mresistor]

You can elevate the heaters without a filament CT. Run the artificial ground, the two 100 ohm R off the 6V6 filaments and ground them to the power tube 6V6 cathode. That will work, I've done it. Bruce at Mission amps goes this on his 5E3 kits.

al

-5E3 is a push-pull amp.  Why go to all the bother to add 100 ohm resistors, when all you have to do is terminate the ground side of the filament transformer to the cathode of the 6V6? The filaments will now be elevated because the current will be passing through the 470 ohm resistor to ground. The same path the  6V6 cathode uses to go to ground. Or alternatively, current will be flowing from ground through the 470 ohm cathode resistor to one side of the filament winding, thus elevating it above ground. 


(OK   sorry   pay no attention to the above I had my head stuck somewhere and got mixed up when I stated this. I was thinking of taking the center tap of a filament winding and connecting to the 6V6 cathode )

[sluckey]

Why go to all the bother to add 100 ohm resistors, when all you have to do is terminate the ground side of the filament transformer to the cathode of the 6V6? The filaments will now be elevated because the current will be passing through the 470 ohm resistor to ground. The same path the  6V6 cathode uses to go to ground. Or alternatively, current will be flowing from ground through the 470 ohm cathode resistor to one side of the filament winding, thus elevating it above ground.

I'd like to see a schematic for what you described.

[dude]

You can elevate the heaters without a filament CT. Run the artificial ground, the two 100 ohm R off the 6V6 filaments and ground them to the power tube 6V6 cathode. That will work, I've done it. Bruce at Mission amps goes this on his 5E3 kits.

al

5E3 is a push-pull amp.  Why go to all the bother to add 100 ohm resistors, when all you have to do is terminate the ground side of the filament transformer to the cathode of the 6V6? The filaments will now be elevated because the current will be passing through the 470 ohm resistor to ground. The same path the  6V6 cathode uses to go to ground. Or alternatively, current will be flowing from ground through the 470 ohm cathode resistor to one side of the filament winding, thus elevating it above ground.

I'd you look at the VC schematic you posted above, one leg of the filament from the PT is grounded at the pilot light, each tube filament is soldered to ground. This works because the 8" speaker and small OT won't create hum. I still have the 8" speaker but a bigger OT, not much but big enough to cause 60 cycle hum. I agree I could have not used the two 100 ohm's as long as I lifted the ground, in this case the 470 ohm R in the 6V6 cathode, so I have 570 ohms rather than 470. I'd still have to redo the filament wiring so the chassis plays no part in the wiring. Bruce at Mission amps uses the two 100 ohm artificial CT, lifted at the 6V6 cathode, I don't think PP or single-ended has anything to do with filament wiring.


But if you're saying I didn't need the two 100 ohm's because I lifted the ground with the 470 ohm R, I think your right. I didn't think of this and just used the 100 ohm's.   

[mresistor]

I'd like to see a schematic for what you described.

Yeah, me too...   What was I thinking?!? I got a little mixed up there.  It would not work because one side of the filaments at the tube sockets are still grounded; Had my head way up there with that one, You have to have the center tap on the filaments to do this as in my amps above, and then take the center tap to the 6V6 cathode .  (this reminds me I need to seek every opportunity to shut up)


Bruces 5E3 filament wiring in the schematic is pretty interesting. He has tied the 100 ohm resistors to the cathode bias, and at a point that is already above ground.  I suppose the two 100 ohm resistors provide balance to the heater string.

[dude]

I noticed something in the Mission Tweedy Amp Layout two posts up.

The first three power filter are all grounded at the same point on brass plate shouldn't the last one (pre-amp filter) be grounded down near the inputs? 

Just like to know.

al

[HotBluePlates]

I noticed something in the Mission Tweedy Amp Layout two posts up.

The first three power filter are all grounded at the same point on brass plate shouldn't the last one (pre-amp filter) be grounded down near the inputs? 

Sometimes close enough is close enough.

The Mission layout matches a tweed Fender layout, except for a couple added touches.