HELP with 5F1 BUZZ !!!

[Willabe]

I keep forgetting this.   

If you have a FB loop disconnect it and see if the buzz goes away. If it does swap the OT primary B+/plate wires and reconnect the FB loop. And double check the FB R's values.


             Brad     

[stratele52]

Can you put a tube shield on the 12AX7  ?..It's so close to magnetic field from transformer

[Willabe]

Can you put a tube shield on the 12AX7  ?..It's so close to magnetic field from transformer

Ah! Yes, +1000.


            Brad     

[worth]

If I pull 1 6V6, the other will red-plate pretty quickly, unless I double  the cathode resistor value. The switch on the back is a negative feedback defeat.. when the NFB is switched out , the buzz is more than doubled. The depth of field in the photos is deceptive.. the wires are not lying on one another. I've really manhandled every wire connection several times.. not a peep. The chassis is a Hammond 20ga. steel, which I've used many times. The AES wire CAN be tricky to cut , but I'm careful, and I really do like this wire... too bad you trashed yours Sleepless , I would have gladly taken it off your hands. What do you guys think about a bad diode causing this buzz ? In my opinion, this noise is not a lead dress or grounding issue.... I've moved every wire, ( which is why it looks a little messy now ) moved the speaker jack, checked every ground with a meter, lifted the board , replaced the input jack and volume pot, and checked all resistor values with a meter. The OT primary is 2.5K , and the secondary is 8 ohms.

[worth]

Ther's only one OT primary wire.

Can you put a tube shield on the 12AX7  ?..It's so close to magnetic field from transformer

No, this ceramic socket doesn't have a tube shield.

I keep forgetting this.    

If you have a FB loop disconnect it and see if the buzz goes away. If it does swap the OT primary B+/plate wires and reconnect the FB loop. And double check the FB R's values.


             Brad      

[stratele52]

Try to put a shield , hold it with your hand if needed , but try it.

There are some shield made for those socket

[Willabe]

There's only one OT primary wire.

Huh? Can't be, has to be a start and a finish to the OT primary wind, so 2 wires. 1 goes to the B+ PSU and the 2'nd goes to the 6V6 plate. You can't run the OT primary and secondary wires together.

What are the 3 wires on top of the chassis in between the OT and choke?

No, this ceramic socket doesn't have a tube shield

Try to put a shield , hold it with your hand if needed , but try it.

There are some shield made for those socket

Yes, +1000.

Just slide 1 on anyway, even if you have to hold it down with your hand. You can put a pot holder between your hand and the tube shield to insulate your body's capacitance from it, if need be. It's just temporary, and clip a wire to it to ground, if you can? It's worth a try, worth?        Sorry,     


                 Brad      
  

[Willabe]

If I pull 1 6V6, the other will red-plate pretty quickly, unless I double  the cathode resistor value.

I was wondering if you might find the buzz that way? Might not help, but if you have a second cathode R laying around you could just clip it in for a fast test?


              Brad      

[Willabe]

The input grid R belongs on the tube socket, it's a grid stopper R.

Most OT's do not have primary taps, some have secondary taps for different ohms load for speakers.


              Brad     

[worth]

I misunderstood your post.. of course the OT has different primary taps,, 2.5K, 4k, and so on, as well as the primary to the B+. But lifting the NFB only DOUBLES thebuzz.

I keep forgetting this.    

If you have a FB loop disconnect it and see if the buzz goes away. If it does swap the OT primary B+/plate wires and reconnect the FB loop. And double check the FB R's values.


             Brad      

[stratele52]

There's only one OT primary wire.

Huh? Can't be, has to be a start and a finish to the OT primary wind, so 2 wires. 1 goes to the B+ PSU and the 2'nd goes to the 6V6 plate. You can't run the OT primary and secondary wires together.

What are the 3 wires on top of the chassis in between the OT and choke?

 

 [/quote]


                 Brad      
 

[/quote]

OT with one wire ?????  

Yes what are those 3 (?) wire on the side of output transformer ?

[worth]

Like I said , Ill try anything.. so I'll try it with one 6V6.

If I pull 1 6V6, the other will red-plate pretty quickly, unless I double  the cathode resistor value.

I was wondering if you might find the buzz that way? Might not help, but if you have a second cathode R laying around you could just clip it in for a fast test?


              Brad     

[worth]

Those are a few ot wires that I wanted to route away from the front of the amp.

There's only one OT primary wire.

Huh? Can't be, has to be a start and a finish to the OT primary wind, so 2 wires. 1 goes to the B+ PSU and the 2'nd goes to the 6V6 plate. You can't run the OT primary and secondary wires together.

What are the 3 wires on top of the chassis in between the OT and choke?

 

 

                 Brad     
 

[/quote]

OT with one wire ????? 

Yes what are those 3 (?) wire on the side of output transformer ?
[/quote]

[Willabe]

Those are a few ot wires that I wanted to route away from the front of the amp.

We know that.    

Exactly which OT wires?


             Brad        

[labb]

Have you tried putting a shield around the 12ax7 and between the PT and OT?

[worth]

They are.. the B+ primary, the 2.5K tap, and the 4K tap. I wish my amp hummed, it's easier to figure out than a buzz.

[stratele52]

They are.. the B+ primary, the 2.5K tap, and the 4K tap. I wish my amp hummed, it's easier to figure out than a buzz.

I don't like B+ so close of the secondary wire but this not seem to be a problem if with no 12AX7 there is no more buzz.

[worth]

This is my last 5F1 build in a smaller chassis than the current noisey one... 9"x5"x2". The two are identical, same PT same choke, same everything except the PT in the quiet one isn't a Hammond. See.. the closeness of components doesn't have to be noise issue, if things are arranged correctly, ( grounding, transformer orientation, etc. )... that's why I think I have either a faulty PT or OT.

[Willabe]

The amp pic. you just posted has a copper band around the PT along with bell end shields. Should be a quieter PT.

I'm surprised it's quite with the primary and secondary OT wires going through the same chassis gromit and the 12 _ _ 7 so close to the OT .


                 Brad      

[worth]

See how MUCH closer the 12AX7 is to the OT , in the 1st quiet build , than the current noisey build ? That is not a factor . Don't forget.. this is a buzz, not a Hum. The current builds' Hammond does have end-bells. But .. it May be the PT, Thanks for your many replies.. I'm not seeing any solution , but to live with the noise, and hope other instruments can drown it out.

[Willabe]

The current builds' Hammond does have end-bells.

Yes it does but the other PT has end bells and a copper band.

If the wires are originating from the same side of the OT, It's not going to make any difference if they are together, or not together, further up the line.

But it looks like yours are not coming from the same side. And I respectfully disagree, it can make a difference. The more contact they have the more bad effects can add up. It's also best to always tightly twist all pairs or trios of wires from the same wind to limit any stray EM/ES radiation because of opposite field cansulation. It can't do any harm and might stop an amp from having problems.

If you take an extension cord and run it up close parallel with a guitar or speaker cord for say 20', you will get/have problems than if you were to have them only touch at 1, 90 deg. intersection. You believe in twisting the heater wires right? Why not other PT, choke and OT wires? Same principle whether all the wires come from the same side/hole in the end bell.

It could also be said that the amp would be quieter if you would have put the end bells of the PT facing to the front and back of the chassis and the OT end bells facing left to right, length wise with the chassis.

This way the bulk of the EM/ES radiation from the PT does not go towards the OT and the input stages and input jack.

Now put the OT primary facing towards the input end of the chassis with it's secondary facing towards the PT end.

The smaller a chassis you use (and with higher gain amps) the more this stuff matters. Plus a SE amp losses the noise rejection/cansultation that a PP amp has natural built into it's power stage.

I still think you'll find/fix the problem or one of the other guys will figure it out.


         Brad        

[worth]

I just realized that my new Hammond 270FX is buzzing .. the SAME buzz I've been hearing all along. I can hear it when the amp is in standby... then when the amps' in play mode , the PT buzzing is amplified.