Power transformer hum- comes through the speakers too

[pbman1953]

Ok, I'm back again with my Traynor YBA- 3A Custom, Not the super


Thanks to the forum,very recently  I've converted to 6550's and slightly modified my tone circuit. The amp sounds real good, but.


In standby mode you hear a slight 60 cycle hum from the power transformer.  When turned on it comes through the speakers and your hear the transformer, itself, hum louder.


The hum increases as you turn up the Master Volume. From all the tone controls, the bass expander is the only one that increases the lower frequencies of the hum. Turning up the other tones do not add any hum.


I have to add that in the last 5-7 years the I went to discrete  caps


2- 50 + 50uf @ 500 volt  caps-AI Electrolytic


2- 100 uf @ 450 volt-- F&T


1-  16 @475 volt- Sprague Atom


Also, with no tubes it's silent. With only pre-amp power tubes it's silent. With power power tubes, hum.   I have 4 Tung Sol 6650's and I re-checked the bias using my Bias Rite. All tubes are at around 65%-70% dissipation.  27-28 watts. I turned down the bias to see if the hum would decrease. It did some but the tubes would be super cold in the 20 watt range


Other tests-




Leaving in all power tubes-
 
1)      No pre’s =  no hum
2)      V1 & V3 plugged= hum
3)      V2 & V3 and no V1= hum
4)      V1 & V2 plugged , V3 out = no hum






http://www.freeinfosociety.com/electronics/schematics/audio/traynor_customspecial_yba3c.pdf








Any ideas how the hum gets through? Am I talking about either just a noisy Tranny or a problem.


Sound wise it's the best it's ever sounded. Oodles of power


Thanks

[Ed_Chambley]

Is the vibration from the transformer causing a rattle in a V1 microphonic tube.  Change preamp tubes with known good ones first, then report back.  Always check your tubes first. 

Consider changing your topic to something like looking for hum because the only way I know of for a PT to cause its hum to transfer through the amp is shaking a bad tube.  You may get more of the guys to look at you post.

If that does not change anything, post your voltages from your tubes including checking your heater voltage by reading AC voltage across the heater wires and not one wire to ground.

For instance, one probe on pin 4/5 and the other on 9 of the 12Ax7 tube.

Get some readings and Sluckey, Tubenit, Willabe, PRR or HBP will chime in soon.  No worries.

[pbman1953]

The power trans is at the opposite and and really doesn't vibrate at all


I did swap the tubes with my stash, no change


I checked the following- on V1


#1-  240 volts dc


#'s 4/5 and #9-  5.25 volts on a 20 volt AC setting


#6-  154 volts dc

[Ed_Chambley]

I see your voltage is higher on V1 than the schematic probably due to higher wall voltage.  5.25 on the heaters concerns me and heaters will cause hum.  If you can get you hands on a 6 volt lantern battery, disconnect your heater string from the PT and connect it to the battery unless your have a filament tranny.

Of if you have one of those things that hold 4 D batteries that replaces a lantern battery.

This will run your heaters on DC only and eliminate the possibility of heater hum.  If it does we can go from there.

or

Wait until one of the more knowledgeable folks stops by.

[jjasilli]

Are you 100% sure it's 60 cycle hum?  60 indicates a heater issue.  120 indicates a HT Power Supply issue.  Anyway checkout:  http://geofex.com/  > -Tube Amp Debug Page >  Hum

Because turning up the vol increases hum, the hum probably originates before the vol pot.

Remember also to check the bias supply -- caps & grounding.

[pbman1953]

I found this you tube page that demonstrated the 60 and 120 hz hum




https://www.youtube.com/watch?v=GrVtX0QGNls






Mine is clearly the 60

[shooter]

+1

6 volt lantern battery

[pbman1953]

Not too sure what to do with it

[shooter]

you disconnect the twisted pair filament wires somewhere near the PT before they connect to a socket.  Take the battery and hook one filament wire from the tube socket to, say +, then take the other filament wire from the socket and connect to -......Tape of the PT filament wires.. 

I believe the battery will go fast, probably a good idea to gator clip a meter to battery + and -.

If your problem is fil hum, changing the filaments to DC, should confirm, it's the filaments hummin

[Willabe]

Not too sure what to do with it.

To add a little bit;

Vacuum tube heaters/filaments can be powered by ACV or DCV, they don't care, all they need is to get hot enough to excite the cathode to give up it's electrons so current will flow through the tube. ACV heater wiring can sometimes induce hum into adjacent wiring (because of the current flowing through the wires, inducing a radiating static field) , causing hum. Because it's ACV, a sine wave, then it has a frequency and that frequency is a note/pitch and that's the hum. 

DCV has no alternating frequency, well, if pure DCV. A battery IS pure DCV, regulated DCV has some ACV riding on it. But it's still gonna be more 'pure' than a regulated ACV.

So, that's why the guys are saying to eliminate a possible 'hum' source by hooking up the heaters with a DCV source.

The battery won't last long supplying the heaters because of their current draw but you don't need to leave it running very long (~30 to 60 seconds or so, should be enough?) just to hear if it kills off the hum.

When radio 1st came in, - all - the tubes in them were battery powered and that's where we get the B+ and other power supply names from, to this day.

[pbman1953]

Do you want the battery to run the trio of preamp tubes?


I think that's possible because the feeding twisted pair starts from the first power tube

[Ed_Chambley]

It does not matter where you connect the DC voltage, just make sure your transformer filament/heater wires are disconnected.  I will usually disconnect the heater string at the first solder point leading from the transformer.  This removes all the heater supply.

The I just use alligator clip wires, 2 of them and connect them.  Normally I connect them at V1 because V1 usually is the most accessible.  If you are unsure clip the positive of the battery to pin 4/5 of v1 and the negative to pin 9 of v1.  It really doesn't matter which way, I am simply giving a method to help you understand.

Just make sure you have no voltage on your heater string provided by the transformer.  When you connect the battery the filaments/heaters make sure all of your tubes have the filaments glowing.  Then flip on the toggles and the amp should start.

Then let us know if your hum is gone or not.

[Ed_Chambley]

If still unsure, post a photo of the inside of the chassis.

[pbman1953]

I sent a picture showing all 3- pre's. You can see the twisted green wires


The second picture is of the first power tube, closest to V3.  Two twisted pairs come into this tube. One coming from it's power tube neighbor and the other is the first twist to go to V3, which jumps from V3-2 -1 


Looks like I can take off the pairs that come from that power tube and connect to the battery

[Ed_Chambley]

I sent a picture showing all 3- pre's. You can see the twisted green wires


The second picture is of the first power tube, closest to V3.  Two twisted pairs come into this tube. One coming from it's power tube neighbor and the other is the first twist to go to V3, which jumps from V3-2 -1 


Looks like I can take off the pairs that come from that power tube and connect to the battery

You can do that, but you will still need the transformer for the power tubes filaments.  Here is where I lack knowledge.  I always run all the tubes off DC, even the power tubes because I don't know for sure if the power tube heaters can induce hum.

Since I am uncertain, disconnecting all the tubes from the transformer insures I am not getting any potential AC hum.

I am writing this to be corrected as I would like to know.  I have heard the power tubes heaters by themselves will not hum, but I have had to replace a power tube because of hum.

[pbman1953]

Fwiw,


I had the amp off and connected the battery to the green twists that feed the pre's and they all lite up. Then took off


That's all I did because I was waiting for more responses

[jjasilli]

In order of importance power tubes are last to check for hum, because:  i) the least amount of amplification of hum occurs there -- i.e., hum occurring earlier may get louder & louder due to re-amplification by gain stages; and  ii) a PP power amp is humbucking by design. 

In this case:  per the 1st Post, the absence of V3, the PI, kills hum.  This proves that the hum does not originate in the power tube section.  It must originate at V3 or earlier. 



Because turning up the vol increases hum, this suggests that hum originates before the vol pot.  The vol pot is right after V1a, the 1st gain stage.  Therefore, the likely culprits are:  V1a including all of its power, heater and signal circuitry; or the Input Jack and its circuitry.


Anyway, once you have the preamp & PI tube filaments lit with a battery, turn on the amp and listen for hum. 

[pbman1953]

Ok , just did it with the battery, still hums, with the volume going up

[dude]

Then something in the input.....? 

Just following this tread to learn.

al

[jjasilli]

There are definitive steps to debug specific issues with amps.  E.g., go to the Geofex site in Reply #4 above.  Also there are flow charts to follow; e.g., in the book "How to Service Your Own Tube Amp", by Tom Mitchel.  Step-by-step testing procedures are set forth in the old tube amp books.

A shortcut which sometimes works is to apply plain old common sense to the clues provided by the amp. 

Here, hum gets louder by turning up the vol pot.  This suggests that the hum has originated And gotten mixed with signal Before the vol pot.  If hum originated later, then we would expect the hum to remain at a constant vol as the vol pot was turned up.  Looking at the schematic, in this amp the only things before the vol pot are V1a & Input.  Hence the hum most likely originates those spots.

Narrowing this further, we have 60 cycle hum which suggests a problem with the tube itself or its filament supply (including possible bad grounding) at V1a.  Therefore, I would look at V1a first; then the Input circuit. 

This down & dirty common sense approach might quickly locate the problem.  If not, then more elaborate step by step testing is needed to Rule Out possible problems until the Actual problem is isolated and identified.

[pbman1953]

On the advice above , I went back to re-fresh some grounds. I took off both input jacks, because they are V1 ground, and cleaned the metal surface with emery cloth.


The hum is still there , maybe less slightly.  I decided to play plug and play with the pre-amp tubes again.  i noticed that leaving out V2 but  V1 &  V3 in= no hum.


Before with V1 & V3 in I had hum

[pbman1953]

From jjasilli


"Here, hum gets louder by turning up the vol pot.  This suggests that the hum has originated And gotten mixed with signal Before the vol pot.  If hum originated later, then we would expect the hum to remain at a constant vol as the vol pot was turned up.  Looking at the schematic, in this amp the only things before the vol pot are V1a & Input.  Hence the hum most likely originates those spots."


Not sure if you knew, this amp originally came out with one volume, then it cameout with a volume and a Master volume. Mine has the Master. The volume does nothing to the the issue, only the Master does

Thanks  for the help

[shooter]

For giggles and fun, disconnect c19, either end, then gator-clip in a new ecap bigger than say 10uF across R15

[pbman1953]

The largest I have is marked-


405k


100 CEC


yellow bodied, possibly a film cap


The only others IO have are polarized and much larger values


What would this do?

[shooter]

polarized and much larger values

C19 is a an electrolytic cap(Ecap), 250uF according to the schematic, my thought is this might be tired or leaky.  you could just add a new one in place of C19, I was just adding it to the same tube at a different location.  So any Ecap rated 25V and up, with a decent value capacitance >10uF, for experimenting I would use anything up to 250uF   *******make sure you connect the NEG to ground******  This will affect tone, but right now we're trying to kill 60hz hum, then tone will come next.

[jjasilli]

Sorry, misremembered your first post which does refer to the Master Vol pot.  I believe that comes just before the PI.

[pbman1953]

polarized and much larger values

C19 is a an electrolytic cap(Ecap), 250uF according to the schematic, my thought is this might be tired or leaky.  you could just add a new one in place of C19, I was just adding it to the same tube at a different location.  So any Ecap rated 25V and up, with a decent value capacitance >10uF, for experimenting I would use anything up to 250uF   *******make sure you connect the NEG to ground******  This will affect tone, but right now we're trying to kill 60hz hum, then tone will come next.

On my schematic, C19 is a  non-polar- .1 UF @ 600v. 


The only electrolytic caps in that are are near the input are  C1 ( that goes with R4) & C9  ( that goes with R39) , did you mean C9 and not C19?

[Ed_Chambley]

polarized and much larger values

C19 is a an electrolytic cap(Ecap), 250uF according to the schematic, my thought is this might be tired or leaky.  you could just add a new one in place of C19, I was just adding it to the same tube at a different location.  So any Ecap rated 25V and up, with a decent value capacitance >10uF, for experimenting I would use anything up to 250uF   *******make sure you connect the NEG to ground******  This will affect tone, but right now we're trying to kill 60hz hum, then tone will come next.

On my schematic, C19 is a  non-polar- .1 UF @ 600v. 


The only electrolytic caps in that are are near the input are  C1 ( that goes with R4) & C9  ( that goes with R39) , did you mean C9 and not C19?

I would guess Shooter did mean C9 since you are writing about V2 and he mentions a tone change along with anything 25v or higher.  You are getting close to the problem it seems.

[pbman1953]

Ed
Just to be sure-


Lift off one end  of c9 to disconnect


Soft wire in the cap to ground across R15.




 My question is why R15 and not the R39 ?

[Ed_Chambley]

Ed
Just to be sure-


Lift off one end  of c9 to disconnect


Soft wire in the cap to ground across R15.




 My question is why R15 and not the R39 ?

Not sure why he suggested bypassing V2b instead of V2a other than it would reduce gain earlier and add gain to v2b.  Better ask him, I did not notice that.

I know you cannot lift C19 as it is a coupling cap.  If you simply lift C9 you will reduce gain which will not hurt anything to test.  It will get quiet.  Also, there is no reason you cannot test a new bypass cap in R15.

My best guess which doesn't mean much is Shooter was looking to change the gain structure by lowering gain before the tone stack and adding it back after.  It may just be his method of chasing hum.  By changing where the amp adds gain it will narrow down the problem.

Try lifting C9 and fire the amp up and see if the hum is gone.  If so, you can always try a new cap there.

[pbman1953]

While waiting for Shooter to write back, I lifted the positive end of the C9, 


No hum change

[shooter]

C9

sorry, I misread c9/19 .   You can add the test cap either place for testing - in parallel with either cathode resistor for v2.  the whole reason for the exercise, my last build had 60hz and none of the usual suspects fixed it, I added a bypass cap and it killed it, didn't eliminate it from the scope but knocked it into the dirt.

other suggestions on that same tube V2, put a NON polarized cap, something from maybe 500pF to .01uF-600vdc across the plate resistor - in parallel with it.  If no change on v2A's plate, try v2B's plate

[pbman1953]

Lets' recap- On a volume control running from 0-10. The hum starts at 3 on the dial. I did go and tack grounds and checked some connections and the the hum when from 3 to 5 on the dial.




As per Shooter's advice I tried on and off cap tests on c9 and then adding  to r15-  no hum change, still there




Shooter's last test was for me to add a .1 cap across r16. The hum went from 5 to 7 on the dial. From 7 on,  the hum stays the same volume




Shooter was concerned about sound quality (high Freq's) with adding the .1 cap. I used the amp Thursday night and it sounded great. All my tones are around 12:00




So i'm posting the results to see if anyone suggests anything else


Thanks

[shooter]

You said all the caps n R's have been modernized.  I been looking at the schematic, guessing it's now a 3 prong amp.  Do you know if the fan is still working and if the ground lift? is still there? If so, does flipping the switch do anything different?

[pbman1953]

Yes to the 3 prong wiring


The fans does work and the  funny this is, in the beginning of this hum issue  , I thought it must be the fan .  But lifting didn't help


As far as the switch , do you mean the ground switch? If yes, the switch is still mounted but not connected.


Should I reinsert back to the system?

[shooter]

Should I reinsert back to the system

no, I was just looing for *low hanging fruit*

I'll keep thinking!

[pbman1953]

Well after all I've done I think I solved the mystery by replacing the tube sockets for V1 & V2




Can't say it's whisper quite but it's very acceptable and I may even leave in Shooter's cap just to keep the memory alive


You guys are the best !!


Thanks for the help!!

[shooter]

Glad you're happy, sockets are a pain to swap, but they do fail.   Btw, it's not my  cap   If it weren't for those that told me "try......." .   If it doesn't mess with tone, leave it, there will be some amp guy in the future scratchin his head

[pbman1953]

As far as a swap it wasn't terrible . The tricky past was the twisted pair. 2 wires through the small holes.


I know it wasn't " your cap", I wanted to give some cred.