HELP with 5F1 BUZZ !!!

[worth]

I've built many 5F1s' ... THIS one has a nasty buzz , NOT hum , when the volume is above 7 with nothing plugged into the input jack. The buzz increases in volume with the volume pot . It also increases in volume when the guitar volume is turned up. The buzz sounds exactly like a transformer that is near flourescent lights, or other equipment.... It's not near ANYTHING that would cause this.  I've checked/ moved every ground, changed coupling caps, changed the volume pot. This amp differs from the stock 5F1 in that I've paralleled two 6V6s' and have a small choke, ( 4 henry 50 ma. )between the rectifier and the B+ to reduce noise. This is my usual set-up , nothing new. The PT is a Hammond 270FX, and the PT is aDoberman/ Heyboer 20W SE. Looking at the photos... the Champ was a LOT more attractive before I started tearing it apart to find the problem.

[TubeGeek]

Just a thought...have you tried other tubes?

[worth]

Yes.. that was the first thing I did, because I suspected the 12AX7. I also tried other 6V6s'. NOTHING changes the character of the buzz.

[Willabe]

Are you sure that the switch on the input jack is making a connection to the jacks hot (tip) when nothing is plugged in?


           Brad      

[worth]

Yes , in fact , I changed the jack in my frenzy to find the buzz.. I've looked  at everything.

[stratele52]

With the 12AX7 remove , do you have the  buzz ? If yes you probably need shielded wire between input jack and 12AX7 and also between volume wiper and 12AX7

[worth]

OK .. the MOST puzzling thing is that the buzz is there with NO guitar plugged in , but rises  with raising the amps' volume ... then WITH a guitar plugged in , the buzz continues to climb even more when turning up the guitar volume. As I said before.. this a buzz that we've all heard when the amp is near certain equipment , or lighting. I have 4 Champs sitting next to the noisey one , that are VERY quiet.

[worth]

I have shielded wire on both input and grid ...I usually DON'T shield the input.. but , In my INSANE CLOWN POSSE search for the buzz.. I did this time.

[stratele52]

I had understand that the amp make the buzz without guitar .That is why we have to work on thew amp only.

 Why don't you answer at my question about the 12AX7 ?

[worth]

NO 12AX7, NO sound at all .. let alone buzzing. That's really not a good test.

[stratele52]

Ok buzz is comming from or before  the 12AX7, No choice this is very simple amp

1- Do you have a 'scope to read signal at 12AX7 pin 2 and 7 ? Probably not , can you use an AC voltmeter ?

2- Can you read what is riples ( AC ) on 12AX7 pin 1 and 6

3- How many DC volts on 12AX7 pin 1 and 6

4- And maximum B+

[stratele52]

On a new built 50% chance are mechanical problem and 50% electrical.

It is not easy to fix an amp who had never work well without seeing it.

Some close up of the 12AX7 socket and wire around could help

[worth]

Pins 1/6 150V DC .. 0V AC.... B+ is 320V DC. It's not a wiring error.

[worth]

Hey guys.. I know amp noises are pretty low on the 'interest scale" so.. If this were YOUR amp , and you had exhausted all possibilities.. what would you do about this buzz ?!!

[Willabe]

Did you remove the paint off the chassis where you bolted the grounds and jacks? If not then your ground might not have a good connection.

Your choke might be too small at 50mA. IIRC, don't most SE 6V6's pull 40mA to 50mA a piece? Your choke is feeding the plate node not the screen? Should be 100mA for 2x6V6. 

I wouldn't trust the heater wires going so close to the tip of the speaker jack.

The OT wires should be twisted together.

The heaters CT green/yellow should be twisted with the heater wires.

The PT high voltage CT should go directly to the reservoir filter caps ground end and then to chassis ground.

(If you have a feed back loop the OT secondary, speaker jack ground, should be grounded with the stage where the FB goes. No FB then it should be grounded with the 6V6's cathode ground. This is if you have isolated/insulated jacks.)

                

                      Brad    

[stratele52]

Hey guys.. I know amp noises are pretty low on the 'interest scale" so.. If this were YOUR amp , and you had exhausted all possibilities.. what would you do about this buzz ?!!

I  said you have forget one or some possibilities. Somthing you don't know, you did not see.

What else ?

[stratele52]

Did you remove the paint off the chassis where you bolted the grounds and jacks? If not then your ground might not have a good connection.

Your choke might be too small at 50mA. IIRC, don't most SE 6V6's pull 40mA to 50mA a piece? Your choke is feeding the plate node not the screen? Should be 100mA for 2x6V6. 

I wouldn't trust the heater wires going so close to the tip of the speaker jack.

The OT wires should be twisted together.

The heaters CT green/yellow should be twisted with the heater wires.

The PT high voltage CT should go directly to the reservoir filter caps ground end and then to chassis ground.

(If you have a feed back loop the OT secondary, speaker jack ground, should be grounded with the stage where the FB goes. No FB then it should be grounded with the 6V6's cathode ground. This is if you have isolated/insulated jacks.)

                

                      Brad    

+1 Brad- stratele52


it is not a wiring error  - worth

[labb]

Chop stick hard on the volume pot. A bad pot could cause this.

[Willabe]

Have you seen this from Merlins site? It's on grounding. Might be helpfull?

http://www.valvewizard.co.uk/Grounding.html


              Brad     

[worth]

I always use the same choke for the 5F1... never had noise issues. As for grounds, I've moved all of them, with no improvement. I've already replaced the volume pot.

Chop stick hard on the volume pot. A bad pot could cause this.

[Willabe]

This amp differs from the stock 5F1 in that I've paralleled two 6V6s' and have a small choke, ( 4 henry 50 ma. )between the rectifier and the B+ to reduce noise.

I always use the same choke for the 5F1... never had noise issues.

If I'm understanding you correctly, the choke you always used was with 1 6V6, not with 2 6V6's?

For a PSE, 2x6V6 Champ with a 50mA choke feeding the B+ plate node, that is too small, it will burn up. You doubled the current draw from the choke. The amp is trying to pull 80mA to 100mA through a 50mA choke.

As for grounds, I've moved all of them, with no improvement.

How?

Just moving them might not change a thing as far as buzz or noise. Each tube stages ground should go to the B+ filter caps ground that's feeding it. Merlin give a very good explanation on grounding.

And did you remove the paint from the chassis where your grounds and jacks are? Looking at your photos it doesn't look like you did. If you don't have a good ground connection to the chassis it's gonna buzz.

You can't depend on the star tooth washer to cut through the paint to the chassis to make a good enough ground. Even if you have gotten away with it before that doesn't mean you always will.

I'm still suspect of the heater wires being so close to the speaker jack tip.

You asked what would you do if it where our amp and these are some of the things I would do/try.    


                  Brad      

 

[stratele52]

Pins 1/6 150V DC .. 0V AC.... B+ is 320V DC. It's not a wiring error.

You must have AC on the 12AX7 , no AC no sound , no buzz

No need to have volts , check for millivolts

[worth]

I disconnected the choke, and used a 100 ohm resistor in it's place.... no change. I have everything in the output section, ( filter caps for that stage, PT center tap, cathode cap/resistor, ) grounded together. I have the pre-amp stage, ( pre-amp filter cap, volume pot, cathode cap/ resistor) grounded together at the front of the amp.  By moving the grounds, I mean that I've jumpered them to known solid grounds, such as the ground wire on the power cord. I've moved the speaker jack, and jumpered it's ground to the output stage.. still no change. I've also jumpered different filter caps across the existing ones.. nothing. The amp sounds like a Champ should, except for this irritating buzz that probably no one except the builder would notice.. but it shouldn't be there , and it's driving me to drink.

[stratele52]

So the buzz is not loud almost no buzz !

I was thinking is loud.

Ans what about  close up photo of the 12AX7 socket/ wiring I ask you ?

[Willabe]

The chassis safety ground wire from the power cord is the noisiest ground in an amp. Nothing else should be grounded with it.

I still think it would be very helpful to you to read Merlins grounding info. It's clear with good drawings.

The 1'st filter cap (reservoir cap) and PT CT should be tied to each other, with nothing else and then run a wire to the the rest of the power amps output section grounds. Merlin, KOC's TUT books and many others swear by this wiring connection. It lets the heaviest currents circulate by them selves and not modulate any of the other grounds.

What about the chassis paint?    

And have you tried to move the heater wires away from the speaker jack?

If the buzz is not very loud any or all of these might make a difference.


                   Brad      

[worth]

Well the buzz IS loud to me.. and it doubles when the guitar volume is increased. Pictures are coming shortly.

[Willabe]

Does your B+ PSU have;

1. SS diodes/choke/filter cap

or

2. SS diodes/filter cap/choke/filter cap


                Brad      

[worth]

V1 socket pics. Brad the order is .. SS diodes-47uf cap-choke-B+ 47uf cap

[Willabe]

Did you use a different, smaller chassis on this build? And is the PT bigger. You said that the OT is bigger.

Maybe you reached the limit on space without buzz?

                  Brad      

[worth]

The chassis is larger than my last Champ build , which is VERY quiet. Could the buzz be caused by a bad PT or OT ?

[Willabe]

What are the 6 diodes for on the little board on the side of the chassis? The 4 small ones are for the B+?

What are the 2 larger diodes for?


                     Brad      

[worth]

They're Zeners to drop the voltage... I've already bypassed them to see if there's something going on with that. What about a bad rectifier diode ?

[stratele52]

Thank's for the pictures , this help

1- What is the shielded wire with 33 K ? I did not see that 33 k on schematic ? Is is the negative feedback ?

2 - Where are the shiedld wires comming from the input jack ?

3 - And where is the shielded wire going to pot 's wiper ?

[worth]

The 33K is the grid resistor from pin 2 to the input jack.. I used only one input , so I used 33K instead of 68K. The other shielded wire is on pin 7 to the volume pot.

[Willabe]

You could try and replace the black wire that goes from the 1'st stages plate to the .02 coupling cap to the X end of the volume pot with a piece of shielded wire? That run is kinda long.

What do you think stratele?


                  Brad      

[worth]

That wire is only about 2 -1/4 inches... and doesn't appear to be sensitive .

[stratele52]

wort, sorry if you answer to this , I'm not sure ; Do you have a heater 's center tab to ground or just 2 wires ?

[stratele52]

You could try and replace the black wire that goes from the 1'st stages plate to the .02 coupling cap to the X end of the volume pot with a piece of shielded wire? That run is kinda long.

What do you think stratele?


                  Brad      

+1000  congrat Brad

Or you put the cap directly ont the tube pin , no more than 1/4 inches long wire.

[Willabe]

Sorry looks like 5" or 6" in the pic.

I like to put the coupling/tone caps right on the pots/controls with as short as possible of a lead on the pot side. You could try and do that and see if it helps? Just use the pot to hold 1 end of the cap and use the 2'nd/furthest eyelet to hold the other end. Run the plate wire to that eyelet, now you don't need shielded wire.  


                   Brad    

[stratele52]

That wire is only about 2 -1/4 inches... and doesn't appear to be sensitive .

if you put the metal end of a "long " scredriver on this wire and tap , you'll probably hear the sound in the speaker . Too long this wire could act like an antenna

[Willabe]

wort, sorry if you answer to this , I'm not sure ; Do you have a heater 's center tab to ground or just 2 wires ?

I think he has the heaters CT elevated on the power tubes cathode R?


               Brad    

[worth]

wort, sorry if you answer to this , I'm not sure ; Do you have a heater 's center tab to ground or just 2 wires ?

I think he has the heaters CT elevated on the power tubes cathode R? Yes.. heater CT is grounded through the cathode resistor.

Sorry looks like 5" or 6" in the pic.

I like to put the coupling/tone caps right on the pots/controls with as short as possible of a lead on the pot side. You could try and do that and see if it helps? Just use the pot to hold 1 end of the cap and use the 2'nd/furthest eyelet to hold the other end. Run the plate wire to that eyelet, now you don't need shielded wire.   I'll try anything at this point. I usually mount the components on the pots for Blackface-type builds.


                   Brad     

I'll


               Brad     

[worth]

I mounted the .02 cap from V1 plate directly to the volume pot with about 1/4" from the cap to the pot eyelet..... No change. Getting bored yet ?

[Willabe]

Getting bored yet?

No.      

I still think you should read the Merlin grounding info. I could take a 1/2 hour to an hour to make a drawing of a wired ground, not random ground, for your amp, but Merlins info is already drawn.   

Your chassis small and the iron is big, your volume pot is very close the the OT, so....     

I'm not saying you can't find/fix it but IIWM, I'd try to clean up every thing I could as far as "good lead dress practice" and with a wired ground/galactic ground. Now that's just me.

It might be 1 thing or a few adding up together.       

You've built on smaller chassis with the amp being very quite, but this amp has twice the current so the EMF is going to be a little larger? They are all shielded, that's a big pluse.

Is that a steel or alum. chassis?

The 3 OT wires on the outside of the chassis should be twisted tightly together, if their all from 1 side of the OT. Are those the secondary fly leads? There also run right by the choke...   

Did you try pushing the heater wires away from the speaker jack?

And what is the switch on the back of the amp?


              Brad      

[Willabe]

I can't realy tell from the pic. what pin #'s they are but is that black wire at 12:00 laying on the socket pin at 11:00?

Also it looks like at least 1 of the screen grid R's is very, very close to the control grid pin on the output tube sockets?


               Brad    

[stratele52]

I mounted the .02 cap from V1 plate directly to the volume pot with about 1/4" from the cap to the pot eyelet..... No change. Getting bored yet ?

Not bored .

[stratele52]

I can't realy tell from the pic. what pin #'s they are but is that black wire at 12:00 laying on the socket pin at 11:00?

Also it looks like at least 1 of the screen grid R's is very, very close to the control grid pin on the output tube sockets?


               Brad    
 

It its a wire from pin 8 close to pin 7 IMO

[Willabe]

So cathode wire across grid pin on the driver triode, which would have the FB loop applied to the cathode, if he's using it?

Take a look at the screen grid R.     


              Brad     

[Willabe]

What happens if you pull 1 of the 6V6's and leave the other 1 in, no more buzz? Put that 1 back and try pulling the other 6V6, no more buzz?


                Brad     

[SleepLess]

Hi.
I can see you've used AES vintage wire, which to my opinion is very bad because it can easily be cut through when you use a cutter or sharp knife. I would really move the wires around hard to see if you don't have a half-cut one. A bad wire could cause hum because of the voltage not passing through it correctly...

Trust me about these AES wires, I bought a good dozen of 50ft spools from them and they ended up in the trash after a full Super Reverb build with them and wire problems...