TRRI blew up - no power - please help

[los]

last night my amp blew up. the power went out in my studio briefly and when it came on again, i saw sparks coming from the back of the amp, it turned off, and smelled like something burned. now the amp won't power on at all and one of my tubes is a little melted on the plastic base where the pins connect. the fuse looked ok so i'm not sure why it won't turn on but something bad must have happened. this is really frustrating as i've been dealing with so many small issues over the years that i've had this amp but now, this seems like a big problem. any guesses as to what happened? i need to get this fixed as soon as possible as i have a gig next tuesday and then a really big show on halloween. i've had problems with every tech i've had do work on my musical gear in the area (new paltz, ny) but i may have just found someone new to try out. if anyone knows a tech in my area, please let me know. thanks in advance for all your ideas.

[MWJB]

Sounds like a tube fried, amp drew more current, tripped a fuse in the studio. When power came back on, the amp was still malfunctioning, took another dose of current & died.

First question...what is the rating on the fuse? Usually when a PT secondary supply gets an unreasonable demand the fuse blows saving the amp's transformers. If your fuse is intact, for some reason, it does not appear to have done its job? Check continuity of the fuse with an ohmmeter.

Pull out all the power tubes, replace the fuse with correct type & rating (it's written on the amp back panel by the fuseholder)...does the amp come on/stay on without blowing a fuse? If so, your PT may have survived...you still need to see a tech to ensure that nothing else in the amp is blown (rectifier diodes, screen grid resistors, heater virtual centre tap, etc.) and to install & bias up the new tubes.

If the amp still doesn't come on, you probably need a new PT, maybe a new OT too? Either way, you need a tech.

[52 Bill]

And if there is damage at the tube base of the power tubes, the sockets need to be checked for carbon arcing.

And when you take it to the tech, bring in the old fuse for him or her to check.

[los]

Thanks for the replies. I picked up some fuses last night and got the amp to power on so hopefully the damage is minor. Coincidentally I just found a new tech in my area (new paltz, ny) and brought the amp to him last night. I'll have to wait for him to check it out to learn more. I have a backup rig to use in the meantime but am frustrated with the twin after putting so much love and money into it over the years for fixes and tubes (i just retubed so if they're fried, they didn't last too long).

[MWJB]

In a fixed bias amp like a Twin, you need to check/adjust bias EVERY time you install new tubes. Just slinging a different pair in without checking can kill the tubes and eventually damage other components.

[los]

follow up

I took the amp to a new tech I found in the area (50 minute drive) on Thursday, 10/9. After emailing back and forth and saying he'd have a quote for me...and after we agreed he would talk to me before doing any work....and almost 2 weeks after i dropped the amp off....the tech tells me it was just a couple resistors and a capacitor that he needed to replace. i'm not even sure if these were related to the blow up. now he's asking for a good amount of money for the work. i questioned him about the work - he ran the amp at 85 volts, passed sine waves through it, and determined the problems and fixed them without plugging in a guitar! he said the tubes were ok even though one of the bases was melted slightly. please give me some feedback on what you think about this, what kind of money you would expect to pay for this, and any other advice. this guy was nice and sounded like he would know what he was doing, but i have my doubts as he didn't really read the info i sent him (some of it was specific technical info) and has somehow fixed a guitar amp without plugging in a guitar. thanks for your replies.

[MWJB]

Many techs use a signal generator & scope to confirm an amp is putting out the correct wattage (I'm assuming he said, "85 Watts", not volts) to spare their hearing, their neighbours and families, there's nothing suspicious about that in itself. It's the industry standard for establishing power output & it's how it would have been verified at the factory...no one would have played guitar through it there either! Some techs don't even play guitar...or any instrument at all (like Leo Fender).

I wouldn't be happy about using a tube that had developed enough heat to melt anything (though I can't recall ever seeing that, even in amps that have blown both transformers). A new set of power tubes would seem logical. What is actually melted, the plastic base of the tube or the tube socket? Be aware that tubes are sometimes a bit wonky in the base & came from the factory like that?

He can't quote you for the job until he has established what's wrong, to establish what's wrong he has to remove the amp from the cab & set it up with his signal generator, scope & dummy load, observe waves, measure voltages...this is "work", it takes up his time which you obviously have to pay for. If you didn't want him to fix the amp why leave it with him?

What info did you send him, did he say why he didn't read it?

If he is charging you hundreds of dollars then something is wrong, I'd expect a bench fee, parts & a little labour for fitting the parts...or a couple of hours labour plus parts.

I'm not suggesting that you have no reason to be suspicious, but I think we need more specifics. You say you don't think the parts that were changed were related to the failure...what parts were changed? To a degree you seem to be playing it both ways...

"Don't work on my amp until you can quote" - determining what's wrong IS chargable work. By the time he has come up with a price he may as well carry out a simple repair. If you didn't want to approve he repair then he has to stick the non-working amp back together & still charge for time spent, which sounds like more than the parts. If you seem concerned with cost he may not feel that you would be grateful if he threw in $60-$80 worth of tubes (it wouldn't bother me, I'm the & tech I decide what your amp needs, that's what you pay me for).

"I don't know if the parts that were changed were related to the blow up" if you knew what WAS the cause of the blow up why drive 50 minutes to ask someone else? A 50minute drive isn't really a big deal when talking about a several hundred dollar amp.

As I said, I can't say for sure whether you are justified in being suspicious...if you can tie up some of the open ended issues it would help?

[los]

thanks for responding!

he did run it at 85 volts because "It means that instead of plugging the amp into 120 volts AC wall voltage I run it up tp 75% of AC voltage & check it. Like running a nuclear reactor at 75% of rated output & monitoring it."

the plastic base of one of the tubes shows signs of melting...and i just replaced the tubes 2 months ago so i'm sure it wasn't like that before the blow up.

i understand that it takes time/money to diagnose amp issues. i'm not trying to be cheap about getting it fixed. it's just that upon questioning him about the job and his efforts, it didn't seem to justify the costs. he is pulling out an arbitrary number without even looking into some of the issues i talked to him about. he didn't read the info i sent because he says he looked at it and didn't really read through it all...typical lazy email reader...the info i sent him related to certain resistors related to the bias current which i think may have had to do with some issues i've been having with the amp. i also asked him to do the reverb on normal channel mod which is simply connecting a wire from a capacitor to a resistor and clipping those leads from the board. he didn't read my info which details exactly what to do (i just don't feel totally confident to do the work) and said it would be a lot more money.

i left him with all new tubes...even some extras.

i brought him the amp because i am no tech but have a good understanding of electronics and could eventually work on stuff like this myself with some more practice. but really i just want to play and hoped to find someone who could do the physical work quickly and hopefully have more knowledge than me about the amp.

he says he only replaced a couple of resistors and a capacitor...these may or may not have been damaged in the blow up.

i'm still not sure how you can ultimately test a guitar amp without plugging in a guitar...after all the testing you do, that is the best way to determine if it sounds good.

[MWJB]

OK running the amp at 85VAC from the wall seems odd for a final check, if the amp has ONLY been run at 85VAC then the job is not finished & the amp is not ready for collection.

I'm familiar with the reverb on both channels mod, never tried it on the RI.

If you left him with new tubes, then I'd expect him to fit them.

It's possible to ensure that voltages, currents & clean power are within tolerance without playing an instrument through an amp...you can only evaluate tone though by doing just that & listening.

Some techs are familiar with tube technology and very good at their job but have little idea about what a player wants regarding tone...others are players and often prefer a client to check he amp's performance before taking it away (though I don't expect customers to play half set at full volume to achieve this). A lot fall in between the two, and there are good & bad accross the board...like anything in life. As long as the amp is functioning correctly with tubes that you like the sound of, it's likely that the amp will sound ball park for a TRRI. Actual method for determining performance will differ from tech to tech depending on their background/facilities/disposition of those in close proximity that will have to listen to/tolerate it.

[Enzo]

And sometimes the customer has so little technical knowledge the communication breaks down. You say you presented him with a lot of technical incormation but suspect he didn;t read it. Well, I often get items in for repair and the customer wants to tell me everything he can think of short of the phase of the moon when it failed.

The technician needs to know what is wrong - why is the amp there in the first place. I know you want to help, everyone wants to help, but as a tech, I don;t want to know all your voltage readings and stuff. I want to know the complaint, and I would like to know if someone did anything to the amp in an attempt to repair it. And the only reason I want a report on someone's repair attempt is so I can look over what they did in case it was wrong. Other than that, most techs don't need further information.

Most good techs do not want to hear what some other tech's diagnosis might be. if the other guy couldn;t fix it, why should I trust his diagnosis? And as experienced as I am, I don't expect another tech to take my diagnoses as gospel. A tech has his own systematic approach to repairs, he wants to know scertain things at certain points in the process. I will take my own voltage readings for example, because I know what conditions they were taken under.

And what might be a cosmic blowup to the customer might be to the tech the 1,493rd time he has seen a bad tube take out a couple grid resistors. And i can easily imagine an amp coming through with a leaky coupling cap, killed the bias to a tube, caused it to melt, shorting out and taking out a screen resistor or maybe the two 100 ohm hum balance resistors on the heaters. Zero challenge for me to repair, even though the smoke was pretty dramatic for the amp owner.

Your guy might not have the best bedside manner, but repairs often are not complex and the explanations won't be very exciting.

The only way you can tell if the amp sounds good for guitar is to play a guitar through it, yes. But i usually do most of the service to am amp without the guitar. I have a music signal coming from my bench stereo, and I can do most repairs with that signal. the guitar gets in the way and ties up my hands. That serves to tell me the thing amplifies, that it is not distorting hugely, that all the controls work, that the amp is not going to run away and overheat or redplate its tubes, and so on.

It is usually only when I feel the amp is working that I grab the guitar for a real checkout. The guy really should have a guitar, or at least have someone play through it to verify its function - even if it is the customer. But not everyone plays guitar. I sure would be hard pressed to check out the wireless mic on someone's saxophone, I can tell you, if they expected me to play it.

But from your description, it sounds like your guy was pretty thorough. I have to say I don;t often bother to cycle the mains down to 85 volts for a look-see.

[Steve A.]

... the plastic base of one of the tubes shows signs of melting...and i just replaced the tubes 2 months ago so i'm sure it wasn't like that before the blow up...

As MWJB said earlier if you don't rebias new output tubes in your Twin Reverb Reissue it could cause problems. If the tubes were running too hot because of improper biasing it could cause the plastic base to melt a bit- especially since the tubes are upside down in the classic Fender BF/SF design.

I dealt with a lot of electrical problems as an HVAC service tech and the electrical problems you describe might crack a plastic base, but not melt it, because that usually takes a lot more time.

If the amp was biased improperly it could have weakened other components inside the amp, and the surge when the power came back on might have been enough to push them into an early grave.

Steve Ahola

P.S. I would have thought that the amp tech would have put in your new output tubes and set the bias- especially if the repair bill was a bit high. (He could maybe justify $30 of the bill for rebiasing amp for tubes supplied by customer- at least it sounds good on paper.)

The fact that he did not call you with an estimate for the repairs is pretty flaky as well. I'm not sure if you signed any papers when you dropped off your amp (as you might do if it was your car being repaired). But you are often only authorizing a maximum charge for the diagnosis, and you need to approve any additional work or charges.

As for whether the parts he replaced were in fact the problem, time would be the best judge of that. And be sure to bring along a backup amp to your gigs coming up...

[Steve A.]

And sometimes the customer has so little technical knowledge the communication breaks down. You say you presented him with a lot of technical information but suspect he didn't read it. Well, I often get items in for repair and the customer wants to tell me everything he can think of short of the phase of the moon when it failed...

In HVAC work I would usually listen to whatever observations the customer might have made, even if they sounded pretty screwy. And they would often insist on jumping to very wild conclusions with no basis in science...

But every now and then, something that the customer had noticed would help solve a problem that had baffled other service techs. And the customers always liked having someone listen to them- besides I was working by the hour so what the heck- it was easier to listen to customers than change out compressors on the hot rooftops!

I bet that you have heard some pretty interesting electronic theories from the musicians who have brought in amps!

Steve Ahola

P.S. I hated it more when the customer did not pay attention to any details- "I dunno- I turned it on and it didn't work. You're the expert, you tell me what's wrong!" (In HVAC work maybe 1/3 of the problems were caused by the customers not knowing how to operate the equipment properly. Like leaving the AC set to 60 degrees overnight when the weather changes can often cause the whole system to ice up and fail to work at all the next day.)

[Enzo]

Oh imagine a blower motor that won't start, and the customer wants to show you chartsd of the temperature settings on his programmed thermostat, and the charts of temperatures the house dropped down to overnight because of it, and the fact that he filled his propane tank twice last month instead of just once, and the fact he turned the programming off to over-ride twice during the week because he took a day off, and that he noted the flame on the #3 flue was a quarter inch taller than the other two, and the humidity was low all week, and and and...



Yep, needs a new starter cap.

[Steve A.]

And sometimes the customer has so little technical knowledge the communication breaks down. You say you presented him with a lot of technical information but suspect he didn't read it. Well, I often get items in for repair and the customer wants to tell me everything he can think of short of the phase of the moon when it failed...

In HVAC work I would usually listen to whatever observations the customer might have made, even if they sounded pretty screwy. And they would often insist on jumping to very wild conclusions with no basis in science...

But every now and then, something that the customer had noticed would help solve a problem that had baffled other service techs. And the customers always liked having someone listen to them- besides I was working by the hour so what the heck- it was easier to listen to customers than change out compressors on the hot rooftops!

I bet that you have heard some pretty interesting electronic theories from the musicians who have brought in amps!

Steve Ahola

P.S. I hated it more when the customer did not pay attention to any details- "I dunno- I turned it on and it didn't work. You're the expert, you tell me what's wrong!" (In HVAC work maybe 1/3 of the problems were caused by the customers not knowing how to operate the equipment properly. Like leaving the AC set to 60 degrees overnight when the weather changes can often cause the whole system to ice up and fail to work at all the next day.)