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Out of interest: What guitar is this?


One day I turned on my newly purchased 64 Blond Bassman amp and there was a great hum then a burnt smell that came from the 2nd power tube socket. Now all I had was hum. I opened it up and could not see anything. To say the least I was disappointed. Other friends with vintage amps told me how when their amp broke they were told by the tech that the power or output transformer had overheated and blown up therefore needed replacing.A friend of mine with a 1956 Fender amp got his output transformer rewired and the sound was totally screwed when he got it back. I rang around and was getting the same sort of thing.”probably your transformer” A couple of friends of mine who are electricians said it was extremely highly unlike the transformer would blow, and if it did, I would know about it with black smoke coming out of the amp. A GDP member who knows these amps extremely well told me “your transformer is fine, they’re almost impossible to break”

I thought, “ok, lets go back to basics” Upon testing the original speaker cable from the head to cab, I discovered a short. It was an intermittent depending on what angle the cable was twisting. I was told a short in the cable could blow things up. To cut a long story short I replaced the cable, put a new tube in and presto! All fixed It seems the tube had taken the brunt of the short.

A broken transformer seems to be commonly used money-spinning trick by dishonest techs and a commonly believed myth guitar amp owners beleive including myself up to now. Don't let anyone tell you your transformers screwed without proving it to you! Cheers.


From what I have heard transformers rarely go bad. Just what I heard.


Welcome to blonde ville! That bass channel is so freakin awesome one you clip out the treble bleed cap (shunts high end to ground essentially). My slab gits love that channel! the normal channel is reserved for holy hollows.


Don't forget solid state rectifiers! They often get fried too and only cost a few dollars. Signs are: some burning indicator lamps but no sound or a completely dead amp. Can be the rectifier and would not be expensive to fix.

Or sometimes simple fuses! People pay hundreds of dollars to have a two cent fuse switched.

Tubes seem to be the most vulnarable part in an amp (or transistors in a solid state).

So, never ever use fiddly wiring to hook up speakers! At least learn how to solder and put some solder on bare wire ends, to prevent fluffy copper tassels that short circuit everything! Ask me, if you don't know how to solder...


The fact is that you could blow an output transformer if you play your guitar without a speaker connected to your amp.

Here are a few things I always do before playing any note on my guitar:

-Always make sure the amp is connected to a speaker, before you switch it on. Also, make sure impedance is correctly set.

-Let the amp a few seconds on stand-by, so the tubes take the time to warm up(they will last longer this way).

-Flick the switch of the stand-by, and BEFORE playing listen; there should be a hum coming from the speaker. If not switch immediately on stand-by(the amp is "safe").

Check your speaker cable and never use instrument cable.


I've blown both power and ouput transformers, it does happen.

And I think it's not neccessarily a scheme by techs to rip people off, I think a lot of people who call themselves "techs" just don't have a clue.


Walter Broes Good point about "people who call themselves "techs" just don't have a clue" Were you given back the broken transformer?

The culprit: Photobucket



I had a blown output transformer in a Hot rod deluxe.

It happens rarely but it does happen.

Smoking amps that smell like French cigarettes = bad.


What were the circumstances when it happened? Were you giging? Did you actualy see the broken transformer?


Luckily, I've never blown a transformer. Have had that smoke thing though. Turned out to be a fried resistor downstream of a failing SS rectifier in an Ampeg Gemini II. A great relief to find it was not the OT.


Failure due to playing the amp without a load/speaker would be different from failure due to insulation issues. Some older transformers can short internally if the insulation on the wires break down. You can usually check for this by using an OHM meter. Mostly this will depend on where the amp was kept…it if was humid or not. We have all seen fabric covered wires loose their insulation. I have seen a few bad Ots, and some PTs. Tim MBL


I would agree with Walter. Assuming it wasn't blown I would suspect ignorance rather than deception. You can't really make a killing installing trannies.


what walter said... paticuarly when buying used british tube heads.there's a 95% chance it's been "hot roded" by a friend of a cousin,always bad news....


The common source of the "burnt smell" from the tube socket area after a power section fault is the screen grid resistor cooking. You should have it checked just so you don't have more problems down the road.

mrock said: What were the circumstances when it happened? Were you giging? Did you actualy see the broken transformer?

I was just noodling around. then sumthin' smelled funny. I turned around and saw smoke coming from the amp. I looked round the back and there were two glowing lava lamps there what used to be power tubes. I shut it down right away. Brought to a tech who replaced the tranny. I got the old one back. It short circuited. He unwrapped the paper coil and showed the burn marks.


Output transformers (or even power supply transformers) can and do blow for a variety of reasons.

A power tube shorting can take them out, along with some other parts.

Especially if corrosion has infiltrated the laminations of steel core.

Anytime you wrap a lot of enameled insulated wire into a pickup, speaker coil, electric motor, or transformer, you are dependant on those windings not heating up above 40 degrees centigrade for long periods and degrading the insulation, or corroding and shorting out between windings which quickly builds up heat to catastrophic failure, etc.

Old Fender amps with rusty laminations on their transformers are liable to suffer this casualty. Used to be the end of the amp if vintage, and quite common, until some manufacturers began making replacement transformers.

Normal enameled wire insulation is good for 20 years service life if kept at 40 degrees centigrade or below. Above that, and the service life shortens accordingly. If corrosion infiltrates to the windings the life is shortened with or without extra heat.

Stopping surface corrosion of the laminated steel with paint or the like can help, but the clock is ticking, especially with guitar pickups wound directly onto the magnets or poles. Plastic spacers are more common now to remove that metal to metal contact in pickups, but there is still a lot of fine wire depending on a friendly environment in motors, speaker coils, and the like.


If your speaker wire were shorting out,you wouldnt get a hum from your speaker,you would get nothing,the hot signal wire would be grounded causing no signal or noise to get to the speaker,essentially taking the speaker out of the circuit.It sounds more like you blew a power tube,which should have,but apparently didnt blow your fuse.I would look into what fried that tube before assuming the amp was "fixed".Playing thru an amp with a shorted speaker wire would normally cook the OT before the tube,the OT is between the shorted wire and the tube,making it more likely to be the "fuse" between the wire and the tube.


If you do have rusty laminates on the OT,as someone mentioned,what could happen is that when your idle current (bias) is set everything is cool.Rusted laminates cause "eddy currents" which simply put is additional current in your transformer,so at idle your tubes and primary winding of the OT see about 35ma,lets say.You start putting a signal thru the amp the current in your tubes/OT primary go up,which is normal,but if you have rusted laminates causing the aforementioned eddy currents,things get hotter and hotter and cause a gradual breakdown of components,the first being the tubes and OT.I aint saying this is definately what is happening in your case,nobody can say without the amp in front of them.Since rusty laminates was mentioned,it is something to consider.If thisa is the case your amp may seem to be working fine for now,but over time the extra heat will take its toll.


That article is total B.S.I cant believe they would actually print it.They state that laminates must be insulated,which is true,but rust causes the insulation to break down and rust does not insulate,it causes the laminates to short,they actually state that rust increases resistance,there should be no resistance to "increase" so if after it rusts they read resistance,the whole theory is blown,insulation has no resistance.Please tell me you dont buy into that B.S.,Billy.I dont know what they are trying to sell there.The rust eats away the insulating paint on the ends of the laminates causing the laminates to short out to each other,the only truth I read there is where they say dont sand off the rust,as that will just cause more contact between the laminates.


Just noticed another problem with their "tests".They state that they left the secondary connections open,so there is no load on the transformer,so any results are useless,of course the transformer ran cool,it isnt running.


The only thing I was taught about rust, is that it never sleeps.


This is from Mercury transformers...a company that many people on this list believe in.
No, I don't agree with it, and I don't care for their transformers either. On the other hand, I also haven't noticed a significant degradation in the performance of transformers with a modest amount of surface rust. Unless it looks like it was stored outdoors, I wouldn't worry.
Generally speaking, you won't blow a transformer as long as you use the correct fuse. There are a few exceptions...the original Ampeg B15's had underrated power transformers that blew frequently, The Fender Bandmaster heads were 50 watt amps with 35 watt output transformers and they blow when pushed, and vintage Voxes had transformers that look like they were wound by hand and they sometimes fall apart. Some of the newer low-priced amps have transformers that are underrated. Even so, a blown transformer is a rarity, and it's almost unheard of in something like a Fender Bassman.


Yes,a modest amount of rust,but rust is definately not your friend.What they are selling here escapes me.If you've ever read Randalls "White Papers",he gives a lot of half truth there,but obviously to sell his "pre-selected" power tubes to go with his amps.The pictures that are shown in that article are also decieving,if a PT has no load it will show no current draw.If the transformer they depict has no paint on it,some use transparent paint,it may show some current as the laminate ends will incur eddy current since they arent insulated.That is what the rust will ultimately do,remove that insulating paint,causing eddy current.So much for the article,I wasnt implying that his OT was blown,just giving a possible cause of his power tube blowing.Rusty laminates were mentioned,nobody addressed it,so I did.Something blew his tube,I stated the reasons I may doubt it was his allegedly shorted speaker wire.You mention the correct fuse.It seems his didnt blow,a shorted power tube should blow it,assuming it is correct value,something is going on here,I dont think it should be left at"the tech tried to rip me off",or as it seems he went to a number of techs who said the same thing,could they all be dishonest?I hope not,but I guess anything is possible.It could very well be a case of just a bad tube,like I said,without having the amp in front of us,we can only offer possibilities,and I offered one that might explain him running into some number of techs saying the same thing.Maybe saying the OT is blown is an overstatement,but in the scenario I gave,it would amount to the same thing,just would take longer to manifest itself.Oh,and add to that list of underrated OT's the Tweed Deluxe that used a 15watt OT.

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