How do fix a Amp when you Do Not Know Whats Wrong

[J M Fahey]

Sorry to hear what happened.
1) what was the original problem, which started all this nightmare?
Please be as clear as possible describing it.
Was that particular problem corrected the first time you got it back?
2) itīs statistically impossible that an amp breaks down in a "catastrophic" way, (audibly weak/power loss/distortion) only after 1 1/2 hours of playing, fresh from a repair job.
Only possible if a *gross* error was made (160V cap receiving 400V DC ; backwards mounted electrolytic; redplating biased power tubes; 1/4 W resistor dissipating 2W; I meant *gross* stuff like that).
What was the diagnosis for this second, new failure?.
3) itīs statistically impossible that a lot of different parts break down all at the same time causing the second failure.
Long parts "laundry lists" , as mentioned above, mean shotgunning and not diagnosing anything.
4) forget "Gurus", go for non-romantic, skilled, Pro service guys. Period.
Incredibly, you have more than a couple of them hanging around this Forum.
Distance is no problem, any freight across the US is reasonable compared to proper servicing and reasonable bills.
Nobody said cheap and thatīs not the point.
5) Iīd PM or Mail a few (your choice); would try to choose the one who shows himself the less Guru type; the most practical, experienced, feet on the ground, no nonsense guy possible.
6) Please be very clear and specific as to what the original problem is and what you want toachieve.
A practical goal is to have the amp perform exactly as original. Itīs a killer amp that way.
7) *If* you are not sure of what you want , are vague explaining that, or have unreasonable expectations about it , you are the perfect guy to be conned by unscrupulous or plain incompetent guys.
As I said, aiming for it to perform as God and Leo wanted in 1964 , is an excellent goal.
Forget about the "Mr XXX hot guy" Mods or whatever, Mojo is undefinable.
Good luck, you have excellent possibilities of having your amp sounding as good as new, and, as was also mentioned above, for the next 30 years, which is a lot.
jm2c

[Chuck H]

Just two notes... Hedging against advice to avoid diagnosing conditions without testing... But...

Two things I might consider after such an ordeal. First would be that the poor amp has been poked and prodded ad nausium. Under these circumstances I've seen those black fiber circuit boards become conductive. That could explain the popping switches. If there was/is such a problem it might also partly explain the recurring failures. The other would be that BF amps can be layout sensitive. The poor amp has had circuits stuck in and pulled out, etc.. If the lead wires have been altered much this could partly explain the new tonal problems.

Both of these things are not what I would consider standard type problems. And a little guru-ish to even mention them. But they can be very real with the BF amps. And devilishly difficult to diagnose and fix.

EDIT: One thing that is notably missing is how the amp is being used. Not to imply anything but it's a fact that it seems to keep breaking after it's sent back to you working. I don't really expect that your misusing the amp but I can't know that either. Do you plug into any different loads or use unusual input signals, etc. For all we know part of your MO when playing could be to whack the cabinet with a bat because you like the way it sounds.

[Jazz P Bass]

Ju
For all we know part of your MO when playing could be to whack the cabinet with a bat because you like the way it sounds.

Or a hockey stick

[km6xz]

Just a little comment(not my usual long winded sort). If a part lasts 36 hours, it is more likely to last 3600 hours than a new part. "Statistically" the greatest odds of a failure is when a part is new or past its design life. Particularly tubes which is why techs burn in the tubes to make sure they pass 3-24 hours of rated operation before trusting an amp to go out the door. After initial set up, then burn in, and mechanical stressing, a final re-biasing and listening test before being packed up for pickup. We used large dry cleaner plastic covers for gear ready to pick....customers always comment when their gear looks cleaner and fresher than when they bought it. It cost $0.05 and no time but leaves a strong impression on customers. Also on the service report is a full spec sheet of measured before and after for noise, clean distortion, power out, current draw, etc...which are collected at the beginning of every repair unit anyway. That was recorded in the database so if it ever came back there is a base line of of data to compare with.

[Enzo]

I don;t bag them, but I do like to clean an amp up before I return it. It is especially easy to clean a panel when the board is out so the pots are not there. Even if the customer doesn;t realize what you did, it just looks better when they come get it.

[dumbassbob]

Bandmaster Amp

With no invoice or records, there is a problem for you but a bigger one for the rip off shop...he can't prove that the transaction took place to your satisfaction. That means he has no credit card authorization. File a charge back request from your credit card issuer and just report that the work requested was never done. It will take a month or so but you will get your money back. He needs your signature on a card authorization to prove the work was done as requested.

The second post, relating to the OC tech finding a bad cap that he put in, probably has resulting in your power tubes being overstressed from lack of bias. A cap if open will put pulsing DC on your grid and at the swings closer to ground potential means full saturation anode current was being pulled. Make sure he checks the power tubes properly and replaces them for free if there is any deviation from spec.

The popping switch will be pretty easy to find, did he know about that when it was on his bench? One way a customer can protect himself from less than complete repairs is being a proactive owner. Make sure the tech has enough information to be able to clearing know what you are requesting and what conditions are needed to reproduce the problem. It is best to use a local tech and demonstrate the problem so you are both speaking the same language. If a tech can reproduce the problem on the bench, it can be repaired without much drama. For example does the popping mostly show up with some specific control settings or note being played? If so tell him or better, show him.
When I had my large shop, with 15 full time techs and 28 fully equipped work benches, the girls at the counter had it their resposibility tyo witness and be able to reproduce the problem. They had a little test bench in the lobby that allowed them to safely test out the reported symptoms while the owner was present. If reproducible, any repair is much easier, and much more likely to not come back as a do-over. That one step of verifying the problem often took care of the problem without accepting the unit, by finding a switch out of place or power supply module problem. Some devices such as a mixing console has so many possible combinations of settings that can occur only when a specific set of conditions and control settings are present that step reduced returns and labor charges greatly for every unit worked on. A customer was not considered serious if they just said "check everything" meaning they know why they brought it in but will not share that with us. A larger console or keyboard is very difficult to test every possible combination of conditions, levels, temperatures, mechanical stress etc that might be required to make the defect appear. When commissioning a large format console in a studio it might take 2 techs 7-10 days to fully test it before signing it off as functioning.
Good luck with keeping your amp going, you have both been through a lot.
One bit of advice, do not follow the common internet "wisdom" of replacing commonly suspect parts in an attempt to repair something. That is pure amateur and likely to confuse the problem and the repair. Repair and diagnosis is very different than restoring an amp. Repair to stock and full function before starting any restoration. Replace only what you can prove to yourself it in need of replacing. If in doubt, get on here and ask. Be wary of any tech or shop who replaces a laundry list of parts in a repair, they did not diagnose the problem and the real problem might exist. The just added cost and confusion by changing parts until the symptom changed or disappeared. When hiring techs, even ones claiming years of experience, I put them through thorough vetting by having them diagnose various units and explain to me what they found, and how that evidence relates to the symptoms. Those thought experiments showed whether they could think through a problem logically or were just throwing parts at something. Most techs work by habit, not by knowing how something really works and what would be expected in any test result. Putting a test probe on any point, should tell a tech what would be expected to be observed. Another exercise that turned into a game was competitive diagnosis where a tech would "bid" on the number of separate test points or conditions that would need to pinpoint the problem and why. One might claim a problem could be diagnosed with 10 measurements and another might think they can do it with 9 and the winner gets some prize, usually one of the promo gifts reps brought or an hour off work early(they were all on salary not hourly so that mean something). That exercise showed the newer techs a new way to think through a problem, to be actively ferreting out the most significant information the most effectively instead of blindly probing around until something did not appear to be right. What failure could account for all the symptoms? Some things, most possible things, are easily ruled out before opening the unit because those possible defects would not fit all the symptoms, just some of them. As a general rule, if a mode of failure and mechanism of fault was not known in 30 minutes of bench time, the tech did not understand the circuit or the symptoms were not reproducible with the information provided by the customer. That is why I am convinced many of the tube gurus are poor techs despite(or because of) the high prices and long repair times.

Most Techs hear in California take your amp and tell you to come back in a month or so,Change a cap or two a few (R) and put New tubes in Even if you give them good tube,just so they can add to the bill....The poping was there from the start when I got it back from the Texas Amp Guru and it blew for the 4th time..Thats why I took it to someone closer,He did replace the power tubes 3 times,Glad I took out the RCA BP I have..The bright switch popping is any time to turn on or off(the bright switch) like something not too ground...The OC tech did try to fix the problem,But he is more a electronic enginier, He Only goes by a scope..I said the amp was sick but his scope said it was OK until he put a DVM meter on the bias cap he had replaced and said I was right.I have been blasting away for 45 yrs,I know when something is not right or Bad Tone.Being left handed I had to learn to build my own guitars,and because of these forums and alot of reading Ihave learned how Not to Kill myself inside a 100w. Marshall or a Fender Amp Thanks

[dumbassbob]

Just two notes... Hedging against advice to avoid diagnosing conditions without testing... But...

Two things I might consider after such an ordeal. First would be that the poor amp has been poked and prodded ad nausium. Under these circumstances I've seen those black fiber circuit boards become conductive. That could explain the popping switches. If there was/is such a problem it might also partly explain the recurring failures. The other would be that BF amps can be layout sensitive. The poor amp has had circuits stuck in and pulled out, etc.. If the lead wires have been altered much this could partly explain the new tonal problems.

Both of these things are not what I would consider standard type problems. And a little guru-ish to even mention them. But they can be very real with the BF amps. And devilishly difficult to diagnose and fix.

EDIT: One thing that is notably missing is how the amp is being used. Not to imply anything but it's a fact that it seems to keep breaking after it's sent back to you working. I don't really expect that your misusing the amp but I can't know that either. Do you plug into any different loads or use unusual input signals, etc. For all we know part of your MO when playing could be to whack the cabinet with a bat because you like the way it sounds.

Good point It has been poked A LOT,and it was stolen from me by a guy in a band I had for over 10 yrs That was the BIG problem But as far as me I have been playing for 45 yrs I take it really easy each time I got it back..I let it warm up for 5-10 min I NEVER turned it past Vol-5 Tone-31/2 Bass-2,into 4 Ohm load 30 watt speakers It sounded great for a week, I played it for 1 hr everyday and then pop,it would start to sound weak, low volume, distortion..The OC tech changed the (R) on the power tubes Grid and pulled the death cap.and the Bias Cap again and a diode on biasboard

[dumbassbob]

Yeh I am Back,It sort of sounded ok for a hour now the high end is harsh When I have a few dollars I will try again

[Gtr_tech]

I don;t bag them, but I do like to clean an amp up before I return it. It is especially easy to clean a panel when the board is out so the pots are not there. Even if the customer doesn;t realize what you did, it just looks better when they come get it.

I do this as well. Sometimes I think i'm just wasting bench time, but I can't stand to look at filthy gear.

As far as guitars go, I do see them come in with a half inch of finger funk on the fretboard. I always clean them up before I even tackle the requested work. Its just disgusting...and I don't wanna hafta touch it. In this case, I'm thinking of tacking on a cleaning fee when they're real nasty. It takes time and materials which I shouldn't have to eat....but have been for while. New years resolution....

[dumbassbob]

Someone's laughing all the way to the bank....

Gerald Weber... I sent it back to him and this time he fixed it in 4 days. He said that he worked on it for 16 hrs.. "chasing a ghost' he said there was a curcut in it that he had never seen before.. paracitic ocsilation my girlfriend is mad at me and Weber he charged me another $425. So thats $465.+$235.+ $425 for a few filter caps 3 resistors and 2 coupling caps.. I am a dumbass!!! Thanks for the replys i got here. I will let you know if it last longer than a week

[Dave Mac Farlane]

Your story is hellish.
First thing I would have done is to see the amp quiesce for an hour, after checking the bias current.
I recently learned that my JCM 900 which I bought with EL34's had actually been modded to take them - and on following Marshall's advice, set up 5881's on voltage.
After popping two expensive 5881's from different matched and new sets, I called up basic theory, went right into the circuit and read the current - what I found made me feel like an ass.
Result - re modded amp with 5881's properly biased- sounds sweet as a bell (euphemism) and stands any punishment.
km6xz, although long winded (his words, not mine), is right - we need techs who know what they are doing, rather than those who think they do - but you have been caught by the worst. I think we all feel that if we stayed near you, we would come and fix it ourselves.
Keen to hear how you get on.
Dave.

[dumbassbob]

I didn't want to start a new thread,but I thought this was strange...The Great Amp Guru called me and said "nothing was wrong" he strumed the high GBE and over the phone I could hear the hard scrathing tonee ..GW started telling me ,that he didn't hear anything,and call one of his guys over...I kept telling hin I could ...and that he should call Eric Johnson up..so he can tell you it sucks...Then he tells me my guitars must be bad..my 1962 strat and my 1956 Tele my 2 copy of both guitars and my fly'nV all suck..then my cords where bad my pedals ,onj and on But when I told him "His" bias cap popped after 8 hrs total of playing it 1 1/2 hrs and day he said Oh... I will look some more...I can't believe he would try to tell me I was nuts...The tech in OC did the same thing to me until he put it on a scope....If none can fix a 50 yr old curcuit I hate to own a 3 channel, fx loop, bells and whistle amp.....I will keep you posted thanks for your time and input... D.B.

[Chuck H]

I'm sure everyone here actually believes that most of the problems with repair techs in these threads are due to gross ignorance, that we are all above it and could easily poke a couple of probes into your amp and send you home grinning in an hour. To be sure, there are some problems that get by even the clever among us now and then. Unfortunately no one is as clever as they see themselves in their minds eye. The real pisser is that a bad tech can actually CAUSE problems, not just fail to fix them. Why in the H E double hockey sticks is that amp back with GW?!? Even a self proclaimed dumbass can work with the advice here to fix their own problem. The best advantage to that is we keep each other in check. This is a pretty effective method for getting better than average information. At least here. Where there is a greater than average number of very good techs that seem willing to police errors. This HAS GOT to be better than continuing with the "tech" you've been using. Who's name I won't mention. But it rhymes with Werald Geber.

[R.G.]

Perhaps it's cursed, or haunted.

I can see one or two baffled or differently-clued techs, but this...

I have a maxim that I remind myself of every now and then - if what is happening doesn't make any sense, it's because you don't understand all the rules or conditions. It is possible that you have the worst luck with amps AND techs in the known universe. It is also possible that there is a mysterious flaw hidden inside the amp that competent (and less competent) techs cannot find. And it is possible that something about your location/setup is causing problems. I think the comment about your guitars being the cause was uncalled for.

But it occurs to me that the techs were not testing the amp with your speaker cab(s) or your AC power line, both of which can cause issues if they have certain conditions. An intermittent open in the speaker wiring can do ugly things to a tube amp. So can an AC power line with a lot of nasty transients, or one which has a high-impedance neutral.

I have no idea which of these is right - if any - but I do think it's important to keep thinking.

[J M Fahey]

Sorry for being crude, raw, you name it .... but maybe the problem lies in dumbassbob himself.
This said with the utmost respect.

Like Sherlock Holmes said,

when you have eliminated the impossible, whatever remains, however improbable, must be the truth

I very much fear that any of us solves this amp's problems ... and dumbassbob will still say: "hey, are you deaf, can't you hear the hard scrathing tonee?"

The very title of this post is pointing that way.

How do fix a Amp when you Do Not Know Whats Wrong

Sorry for being politically incorrect, but somebody has to say this.