HELP my ampeg!!!!

[The Dude]

If indeed the amp is still blowing fuses, my next check would be the flyback diodes. They will look something like this:

[Amp Kat]

If indeed the amp is still blowing fuses, my next check would be the flyback diodes. They will look something like this:

[ATTACH=CONFIG]23266[/ATTACH]

At this point if you want to continue you are probably going to need a multimeter and know how to use it. You need to check some components and see if they are good or bad. Do you have one and feel comfortable with it.

[Orgazmo]

MAIN FUSE IS BLOWN. after ENZO said to check it after pulling the tubes and firing it up, it did indeed blow that fuse. havnt checked the internal yet. it smoked that 15 AMP fuse [i didnt put it there, got this amp for nuthin' a few weeks back]!!

AMP KAT: YES, i have a dmm and know how to use it.

so, i take it all of you who replied feel its the FLYBACK DIODES? sounds like its time to pull the chasis and heat up the solder station. where are these located? i have a schematic but i didnt see them. i saw a couple spots that had the diode symbol but it didnt specify if it was a flyback. but, i take it "flyback" is just a term for what it does and not for a particular kind of diode, correct?

[km6xz]

Hope that it is the diodes but the symptoms and the fact you got it for nothing, or close to it, suggests that something more serious than $0.10 diodes. I would not be surprised if there is a transformer short. Was the loud hum coming from the speaker or acoustically from the chassis? If the chassis, the power transformer is suspect.
If the external fuse blew at 13 amps, it means either the internal fuse is even larger or has been replaced by a solid conductor. Turning it on repeatedly could (probably)damage the amp more.

Take the chassis out of the case and visually inspect it to see if anything obviously is burned or over heated. Note the condition or presence of the internal fuse. See if it has been bypassed or fuse replaced with a very heavy fuse or solid wire.
Report back or take a photo of the power supply are under the chassis and post it. You will get additional suggestions after we see what the condition of the internal fuse and wiring is in.
Good luck

[Orgazmo]

KM6XZ:

THE HUM was coming from the speakers.

the guy i got it from was going through a NASTY divorce and HAD to liquidate his house in 4 days. the guy basically gave me about 6 grand in gear. he told me straight up it had a hum. everything else from him works fine. when i went to his house, i saw the amp sitting in a corner. i asked if he was getting rid of it and he told me about the hum, he hadnt used it and was just sitting. i asked if he would sell it and he said YOU CAN HAVE IT IF YOU WANT IT!! uuuummmm, OK!!

anyhow, i will pull the chasis this weekend and get back with pics. thanks so much for you INFORMATIVE post. this is an awsome board, soem real great people here.

[Orgazmo]

THE DUDE:

the pic of the flyback diode didnt appear in your post.

at least not on my pc.

[The Dude]

Not sure why the pic is gone. It was there up until today. Must have been removed for some reason or against forum rules for some reason. Anyway, rather than post it again only to have it removed, just do a Google image search for "Ampeg flyback diodes" and you'll find some pics. Or, better yet, there aren't that many diodes in the amp. Just check them all.

[Enzo]

Do it this way. Find pin 3 of your power tube sockets. You should have wires from the output transformer wired to pins 3. Probably a blue wire and a brown wire. Now look for anything else wired to pins 3, specifically diodes. Those will be your flyback diodes. You can just disconnect them and see if it changes things.


A bulb limiter will not heal a blown fuse, but it should prevent any more fuses from blowing.

That output transaformer blue and brown wires probably have a red wire friend, that is wired to B+. You can disconnect that red wire and remove all power from th output transformer. That would tell you if the output transforme4r itself, the flybacks, or arcing tube sockets is the issue.

[km6xz]

To clarify the hum, it hums as soon as you plug it in and turn on the power switch. Is that before the standby switch is turned on? Or does it require the standby switch to be on to have the loud hum?

[Orgazmo]

KM6XZ:

this happened on standby mode.

[Orgazmo]

OK!! LETS START THIS PARTY!!!!!

first off, as soon as i pulled the chasis out and opened it up, on the top 2 corners on each side of the reverb unit [not on the unit, on the plate its mounted on] had BIG BLACK blast marks. like someone set off an m80 on each corner next to the reverb. thick, black soot that stuck to my fingers. the OUTPUT wire from the acutronics reverb unit took some of the blast and about an inch of the bare wire was exposed.







as i said, the amp looks great from the outside, but i did notice a hole sloppily drilled in the back. i dont know if someone tried to put a master volume in or whatever [saw a guy who had a drink holder hanging from the back of his amp one time] so, before i popped it all open, i figured someone had been in the amp. there is another underneath drilled between the output trans and the 12ax7 tubes [see pi] and, there was obviously someone poking around. 98.9% of the solder joints were the ones from the factory in 1970, all with the red marking on them. there is a sticker on the back from a place called AMPLIFIER HOSPITAL from 1981 that said POWER SUPPLY DIODES replaced. but, as you can see, there was a real amature poking around at some point. check out the holes and the awful solder joints.............





some blast also made it out of one of the tube holes. funny thing is, outside of the 2 big blasts on the reverb mounting plate, the the black output wire from the reverb and the blast residue out of the tube hole, there is NO sign of anything else that took a hit on the circuit boards or chasis. no blast residue on the tubes.and most of them are OLD tubes. whatever happened, it was a pretty big blast and one would think there would be more residue in more places.



THE FUSE, as i mentioned had WAY to large fuse, 15 amp. i looked inside to see if there was any internal fuses but i didnt see any.






i'll put some over all pics of the chasis in another post below to look over.

[Orgazmo]

here are some various pics of the amp.

hopfully some of you mat spot a thing or two thats not right or out of place. i personally have not done ONE THING to this amp other than pull the chasis and take the pics. there are few NASTY solder joints.

[Orgazmo]

SCHEMATIC, 1970





AND NOW, for you entertainment............................

[g1]

Just a reminder, these things store VERY high voltages, you must drain the caps before doing anything, don't even look in it's direction .
You can see the flyback diodes in your pic sany0251.
It looks like the internal back-up fuse has been removed, they are usually a pig-tail fuse connected directly to the fuseholder inside the chassis (that's why that label is there on the inside).
Many of these amps had master volumes added, usually a hole was drilled in the back, I would guess that is why that hole is there, it was probably removed at some point.
You can see a small ding in the reverb tank where something touched it and did a little arc welding. Whatever it was must have been replaced, possibly the 3.3k 10W power resistor.

[Orgazmo]

G-ONE:

i was wondering if that was the flybacks in the sany0251 pic.

as you can see, that whole string looks AWFUL, those "solder joints" look like someones first attempt at soldering, in fact, that whole string looks like someones first attempt at ANYTHING electronics.

any recommendations on what flybacks to put in? manufacturer? size? etc.....

AS FAR AS THE INTERNAL FUSE, why would someone take that out? what size internal fuse should i put back in? is it the same rated fuse as the main external one, 6 amp/120v?

as far as the MASTER VOLUME is concerned, i think this was added by one of the prev owners. if you look at that hole in person, its ragged, like someone had a chitty drill bit and sloppily hand drilled it leaving an ugly hole that wasnt debured or the slop reamed out. and, i may be wrong but i dont think the factory offered these in 1970, i believe that wasnt an option until 74 or 75.

I KNOW all about the big voltages left over in those caps. i need to drain them. this amp will more than likely go to a REAL amp tech at some point in the near future, but, i want to do as much as i can and my abilities will allow me. i have GREAT solder skills and know how to use a dmm. i have installed and taken out components from both circuit boards and point to point. i can get through most schematics, i know what all the symbols mean and the markings and numbers on the boards. but, i am NO tech in any way shape or form and i want this amp as close to being back to original as possible. not interested in providing any more damage to it by my hand!!

thanks so much for your help. i know us novices can be a real pain for you "in the know" guys.