Help, My H.H. Scott tube amp died

No warning or anything. Working fine last night, and stone cold dead this morning. The fuse doesn't look cloudy, so I doubt it blew. I've got a tube tester, but, for some perverse reason, it has no setting to test a 5AR4 rectifier tube. Given the symptoms, if it is a tube, I'd guess that would be the primary culprit.

Also, if a tube rattles like a dead light bulb, does that mean it's dead?

 

PM me if you'd like to get your 5AR4 tested - my B&K 747B has settings to check them. Is your 5AR4 new production, or is it a NOS one from Mullard/Amperex? Those Philips factory made rectifier tubes are 40,000 hour rated tubes; new production are nowhere nearly as robust. I had a Chinese 5AR4 run a couple hundred hours before it died.

Are there any fuses under the chassis? Which model amp do you have? Folks here might be able to help narrow things down to possible culprits.

 

I would think you would see something loose if it rattles....and that would be bad.

 

Are the tube heaters coming on? Not that familiar with Scotts, but they're usually on a separate winding that doesn't go through the rectifier. I'd check that fuse (or the outlet) again.

 

General question—have a Scott 299b, needs the rectifier replaced and needs new tubes. Who does this sort of work? I'm in the Central Valley, CA if that's any help.

 

No, I have a few working ones, NOS Mullard and new SOVTEK and some of them do rattle.

 

Nothing is coming on. The fuse looks fine. I could see the thread of copper still whole when I looked closely under a strong light.

 

The amp is an H. H. Scott 208.

My rectifier tube is a Chinese Cherry. The guy who sold it to me said he didn't like their power tubes, but their rectifier tubes were ok. I don't remember what happened to the original, I think it may have fried when my capacitors went bad and had to be replaced many moons ago.

 

Even if the Fuse looks fine it might have disconnected from one of the end caps. Replace the fuse and see. If that is not the culprit it will only have cost you a few pennies.

 

I sent my 299b to this guy and my only negative was that it reeked of cigarette smoke when I got it back, but it performs amazingly now! I had a turnaround of less than a week, FYI!

http://www.nosvalves.com/index.htm

 

Check the fuse. Also, always try another power outlet if you are using a surge suppressor strip. The devices that limit surges can go bad on some of them where each outlet is individually protected.

 

Craig is highly recommended by me. I had him restore a 299b for me which sounded wonderful. I also purchased his stereo amp he manufactures, and his post sale service is second to none.

 

When you go to Rat Shack or whatever to get your new fuse it wouldn't hurt to buy a cheap volt-ohm-meter to have on hand, you'll be glad you did. The schematic for your amp is online and the filaments don't go through the rectifier, so that's not or at least not the whole problem. Without being able to measure any voltages my first guess would be fuse, line cord, no power at outlet or busted solder keeping the voltage off the transformer primary.

 

Third. Craig has restored two Scott 222c for me and they are simply wonderful. He is on Facebook too ;-)

 

It's been too many years for me to remember, but I do recall sending this amp to California for it's original rebuild, as it was a basket case. It would be a coincidence, but not inconceivable that this is the same guy who did my work.

 

Fuses must always be tested for continuity because they can look fine and be open.

If the fuse is good but the rectifier bad you should still have filament voltage

 

You need a multi-meter to check for continuity. $10 at Rat Shack.

 

I know it's quite a distance from you, but this guy is a tube genius and a world-class amp restoration expert.

http://deanzink.com/


Dean has serviced my H.H. Scott 299-B, Cary amps and vintage Fender guitar amps.

Also, does your Scott have a selenium rectifier? Experts tell me those always need to be pro actively replaced.

 

If you can afford tube audio, you can afford a Fluke. Cheap DMMs cause a lot of frustration.

Radio Shack used to sell an analog meter that was just like a Simpson 260 except the case was a much cheaper kind of plastic. Electrically it worked well. They also had some DMMs that were semi-decent but even those usually died in a year or two. While other companies make a usable DMM they aren't all that much cheaper than a Fluke.

 

It's not him, I think. Craig is up there in the vicinity of Chicago/Green Bay - a passionate fisherman!

 

The filaments for the tubes are not tied to the rectifier - eg, if the rectifier is not working the tubes should still light up, provided a working fuse is in place.

Another longshot - the primary on the power transformer went bad/open, meaning no voltage for the filaments and the power supply. Getting a transformer to fit into the same space and have the same voltages and filament taps may be a difficult undertaking. Probably not the case but you never know with vintage tube gear.

 

Alright, so now that video that you posted has me convinced to spend the extra dollars on a FLUKE, but wait ...

Watch the following video, skipping up to the "9:20" mark, before you buy the FLUKE 117 model

http://www.youtube.com/watch?v=3k9nVg03Wi4

 

Dean is the guy who has kept my Fender amps and Scott 299 amp going for over 20 years now. Never ask him to work on anything solid-state, though......

AFAIK, my Scott amp is still running the original rectifier.

 

If it is the fuse, you still want to figure out what caused it to blow. They don't just fail for no reason. I also would suspect the power transformer. Or if you are really "lucky" the power switch -- either a failed solder joint or really dirty contacts.

 

Fuses fail from thermal fatigue. The fuse wire expands and contracts so it can fail after a period of time. Sometimes the wire will pull free from one end inside and you can't see it at all. But, yes, I would still be sure to measure the power draw if you can or at least have a close look for any heat discoloration on wiring, circuit boards and resistors. And..."that smell".