# Is my output transformer dead?



## mrmatt1972 (Apr 3, 2008)

I bought a Peavey Windsor studio last march as a birthday present to me. Worst gift I ever got... I finally got it sounding pretty good after tube and speaker swaps and cutting out the attenuator. I eventually put the the original speaker back in because I wanted the Weber for something else. Unfortunately, when I did that the amp stopped working. The tubes still glow, the power light is on, all wires are connected properly, the fuse is OK (I took the chassis out today).

The speaker works, another working cab plugged into the Studio produces no sound. Different tubes produce the same result. Unplugging the reverb has no effect...

To be clear, there is NO SOUND at all. I think it might be the output transformer. Is it possibly a loose connection or some other simple thing I missed? What do techs here think?


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## greco (Jul 15, 2007)

*I'm not a tech*, but this might help.

I had an old amp with 2 big trannies and I offered it to Wild Bill in trade for some electronics goodies.

I told him that I had no idea if the trannies were OK or not, but that they looked new. He said...if they weren't good, you would likely smell them. 

I remember hooking up a small tranny without a load...in a very short time it was smoking and smelling DISGUSTING. The tranny survived the overheating...I'm not sure how....LOL

Just trying toi help

Good Luck with the amp.

Dave


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## JMC Amps (Dec 19, 2009)

mrmatt1972 said:


> I bought a Peavey Windsor studio last march as a birthday present to me. Worst gift I ever got... I finally got it sounding pretty good after tube and speaker swaps and cutting out the attenuator. I eventually put the the original speaker back in because I wanted the Weber for something else. Unfortunately, when I did that the amp stopped working. The tubes still glow, the power light is on, all wires are connected properly, the fuse is OK (I took the chassis out today).
> 
> The speaker works, another working cab plugged into the Studio produces no sound. Different tubes produce the same result. Unplugging the reverb has no effect...
> 
> To be clear, there is NO SOUND at all. I think it might be the output transformer. Is it possibly a loose connection or some other simple thing I missed? What do techs here think?


Re: OT
Did you happen to unplug the Weber while the amp was still on?
Did you unplug the Weber immediately after you switched the amp off (filter caps still charged)
Are you confident enough to test the B+ rail?

-JMc


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## mrmatt1972 (Apr 3, 2008)

JMC Amps said:


> Re: OT
> Did you happen to unplug the Weber while the amp was still on?
> Did you unplug the Weber immediately after you switched the amp off (filter caps still charged)
> Are you confident enough to test the B+ rail?
> ...


NO for all 3. But I'm willing to learn how to test the B+ rail if you'll tell me what that is and how to do it. :smile:


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## GuyB (May 2, 2008)

JMC Amps said:


> Re: OT
> 
> Did you unplug the Weber immediately after you switched the amp off (filter caps still charged)
> 
> -JMc


This might not be directly related to this thread but how long do the filter caps stay charged after switching the amp off ? And does leaving it on standby for a couple of minutes before shuting down makes a difference ?


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## Wild Bill (May 3, 2006)

GuyB said:


> This might not be directly related to this thread but how long do the filter caps stay charged after switching the amp off ? And does leaving it on standby for a couple of minutes before shuting down makes a difference ?


Depends on the circuit, the condition of any bleeder resistors and the age of the filter caps.

It can be anywhere between 6 minutes and 6 months!

That's why a tech will always bleed them off before working on the circuit. Less excitement and sense of anticipation, but also less pain.:smile:

:food-smiley-004:


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## keeperofthegood (Apr 30, 2008)

kqoct If you have a DMM or a continuity tester, and are handy with it, see if the output transformer is open or not. For the complexity (if the schematic bits and pieces online are any indication) of this amp, if you are unsure how to test for the RESISTANCE (thanks Wild Billl) of the OT's windings ... I would respectfully suggest taking it in to a tech.

For testing the output transformer, there is less risk of getting a hot cap, unless while testing it you poke it in the wrong spot, or rest you elbow on the wrong spot while getting at the right spot with your meter kqoct


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## JMC Amps (Dec 19, 2009)

mrmatt1972 said:


> NO for all 3. But I'm willing to learn how to test the B+ rail if you'll tell me what that is and how to do it. :smile:




B+ designates the positive DC high voltage or “B side” of the power transformer. The first node (Va) on the high voltage side powers the output transformer (typically), followed by the screen supply (Vs), splitter (Vd), then preamp supply voltage.

The idea is to check if sufficient B+ (probably around 370 VDC on a 15W amp) is reaching the OT and tube socket(s) before ruling the OT as dead. A likely culprit of having no B+ would be a faulty standby switch or filter cap on the Va (OT) supply. I’ll wager the switch.

Of course, you have an attenuator on that amp don't you? Hmmm...

Happy Holidays:smile:
-JMc


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## JMC Amps (Dec 19, 2009)

GuyB said:


> This might not be directly related to this thread but how long do the filter caps stay charged after switching the amp off ? And does leaving it on standby for a couple of minutes before shuting down makes a difference ?



In my Marshall 100W, sometimes, the first filter cap seems to hold 493 Volts indeffinately.

I treat ALL caps as charged, and check accordingly (drain). Your DMM is your lifeline. Voltage sharing/bleeder resistors can become faulty at any time, leaving no path to ground for the caps to discharge to.

Happy Holidays:smile:
-JMc


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## keeperofthegood (Apr 30, 2008)

>.<

It is a loaded question asking "what is the B+?" because it is and isn't the same deal in each amp.

All tubes have two parts in common. The Anode and the Cathode. The cathode is the end of the deal that gets hot, and can in fact be the filament. The Anode is the destination end of a tube. To attract electrons through a tube, from the Cathode to the Anode, you have to put a chunk of change on that Anode (in 80% of cases, thats a whole nuther story in low voltage tubes).

Because people 100 years ago were both simple minded AND inventive, they gave rise to a lot of interesting and today somewhat obscure words. In a tube set, batteries were the norm and the first end that got power was the filament so that was the A power, the next end that got power was the Cathode so that was the B. Yes, grids came late and they got the C power but I think by then the naming got wonky.

We still use A and AA and AAA cells today. They are 1.5volts typically but 100 years ago the same ones were 1.2, the chemistry improved is all. The modern C and D cells .... no idea @)@ but the A's arose due to tubes.

The Anode that was the B voltages end of the deal that got that fair chunk of change is still called the B supply in anything tube related. Usually B+ to remind you it is a Positive voltage.

So, in a modern tube deal, even though there are no batteries or such, the B+ is the "high voltage deal" from the power supply end of the amp. It goes through resistors to drop it down, and then to the various Anodes (plates) of the various tubes in your amp. Though, the typical is to put it through the Output Transformer. In this example here, there is 210 volts into the OT primary that goes to the Anode of the tube.












Now, if in this example that part marked 470uf 400V shorts out, your tube will still light up, but you will not get any sound from it. If those parts marked BYV96E open, you also will no get sound out. If the winding on the mains transformer open you will not get sound out. Now, this one is simple, the next more complicated arrangement of Power Transformer is to have a Center Tap, this goes to an on/off switch called Stand-By, if that switch stops working you will have no sound out.

So your first task will be to get a schematic and layout of your amp. Then identify the parts. Once there, you will then have a general idea what to expect where. To drain the filter caps, wire to the ground, and to a 10K resistor, place the resistor to the non-ground end of the caps (tape the resistor to a sick, dont hold it with your fingers). This is sorta simple job, the caps will be well marked with at - that tells you the negative end and that is the ground end. The other end is usually not marked +

There are parts you can now test with it off. The continuity of the output side of the OT, if the OT primary is not parallel with anything resistive or with th power caps you can test continuity there too. If it has tube rectifier then you can also test the main transformer continuity too.

The next steps are simple or complicate depending. Clip (use clips) a lead to ground, and a lead to the hot and to your DMM set to the highest voltage range, then turn the amp on. If you have no power reading, turn to the next lower but if on the 500 or 600 volt range you are getting nothing, then you know your problem is in the B+ supply chain (the caps, the chokes, the rectifiers or the HT winding of the main transformer). If you get your 300 to 400 volt reading then the issue is not there, if there are chokes or resistors you have to power down, drain the caps, remove the clips, replace them at the next part of the supply, power up and do again. 


@[email protected] yea, it is a bunch of steps, Im not a professional, Wild Bill can probably spot 10 billion errors in what I have said but I think that is the general gist of what you will have to do to walk through your amp to locate the issue. It is not "hard" but it is a bunch of steps, involves being able to read a schematic, to follow that to the layout, to step through a sequence of investigative steps. And being safe at each step, draining your caps safely and consistently each time. 

If you are comfortable with giving it a go,  do so. But I think you will need that schematic and layout to start off with.


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## parkhead (Aug 14, 2009)

probably not 

more likley something you changed was not reconnected properly 

OT's are not that easy to kill unless you are not telling us something 

p


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