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Broken HRDx

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(@gjbrake)
Reputable Member
Joined: 21 years ago
Posts: 235
Topic starter  

Hey!

So, my HRDx is screwed. Hoping you guys would be able to help me diagnose the problem before I go running off to the guitar store and cost myself a lot of money I don't have.

Here's the story:
I turn the amp onto standby and set everything up. Ready to go, so I flick the switch, but have hardly any volume, where I should have loads. So I check everything is dialed in correctly and go to check my attenuator connections when I notice two things:
One, one of the power tubes is a bright, bright orange all the way through.
Two, it smells like a mini barbeque in there.

I turned it off for 10 mins and tried again, but I got about 30 seconds of an OK sound, but quieter, and then that tube started to light up like a cigarette and I got a horrible distorted noise along with the guitar sound.

Now, my diagnosis from those things would be a knacked tube, but as I have an extremely limited knowledge of and virtually no experience with tube amps, I thought I'd see if anyone else knows better.

Gonna have another play tonight and see what's going on. Then probably try replacing the power amp tubes. Otherwise I'll take into the shop.

Any comments/help very much appreciated!!
G

Listen Louder Than You Play


   
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(@ignar-hillstrom)
Illustrious Member
Joined: 21 years ago
Posts: 5349
 

Fear you might have to drag the amp to your local repair centre. That tube definitely ain't behaving the way it should. I myself would really wait till replacing a single poweramp tube until Joe spots this topic though...


   
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(@dagwood)
Noble Member
Joined: 20 years ago
Posts: 1024
 

GJ,

I do believe its just the tube(s). No worries. However you didn't say which tube(s) were glowing, V1, V2, V3 or your P1 or P2 Tubes.

Of what I've read here: http://studentweb.eku.edu/justin_holton/
and other places:

Tubes are just like light bulbs. You know how when a light bulb goes off there is a quick flash before hand? Well put an amp Tube in slow motion, if you will, compared with a light bulb.

The reason, of what I can surmise, is that the tubes aren't maxed out on power like a like bulb, they don't get a full load/current to make them glow super bright like a light, thats not their purpose.

Yet just like a light bulb they will sometime "pop" or "explode" the filaments etc that are responsible for being the conduit of all that current, it just happens really slowly sometimes.

If its one of your Pre-Amp "V" slotted Tubes, its not a big deal, you should be able to replace just the one or two. I doubt you'd need to replace all three of them.

If its the Power Tubes, the larger ones, then I'd replace both with a "Matched" pair and you should have them rebiased. "I'd have that checked anyway".

There are a lot of folks here that know a lot about Tube Amps, just ask questions they're more than happy to help out. Also check out Justins page, the link above. Lots of good stuff there and his other links.

Cheers.

Research is what I'm doing when I don't know what I'm doing. - Wernher Von Braun (1912-1977)


   
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(@forrok_star)
Noble Member
Joined: 21 years ago
Posts: 2337
 

Being I can't do a hands on trouble shooting about all I can do give you ideas to start from. A healthy power tube will light up and give off a medium-intensity orange glow. Try another power tube of the correct value in the socket. If the new tube still glows bright red, there is probably a failed component in the circuitry to that tube, you should take your amp to a professional and have it fixed. If you are comfortable working on it and safety smart you can do the work yourself.

How long have the tubes been in the amp? I would start with that, if they haven't been changed in awhile. Being you said your using an attenuator you'll need to consider the tubes life will be cut in half. Tubes wear out in direct proportion to how hard they are worked and how often and loud you play your amp. Swap the offending with another tube or move the tubes around inside the amp. If condition appears in the same socket with a different tube indicates either a bad or wrong connection to that socket or a bad socket. If condition follows the tube, this indicates a probable defective tube or possibly bad solder joint inside the tube pins.

Amps are not maintenance-free, as they get older and how hard they are run, they undergo changes. The tubes are subjected to wear and tear, some of the electronic parts lose their initial properties. Bad tubes can cause premature failure of other parts, such as the output transformer and other vital components.

Here is a list of possible causes:

Improperly biased output tube
Failing/shorted output tube
Failing bias supply on fixed bias amplifiers
Failing cathode resistor bypass capacitor on cathode biased amps.
Failing/shorted rectifier tube
Failing power filter capacitor
Failing power transformer
Failing output transformer

Best Advice: If you don't feel comfortable working on it take it in to a professional and have it fixed. I don't mean to sound like scratched record, I ruined and been bite by caps more times than I can count. I'm harder than most with equipment. There's times my equipment is on for days without being turned off, along with being run hard they get real hot. Not to long back one of my external cooling fans stopped and the tubes got to the point they exploded. Having this happen is very rare. Still love them tube amps.

Joe


   
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(@wes-inman)
Illustrious Member
Joined: 20 years ago
Posts: 5582
 

Yeah, you've been pushing them tubes hard. Probably just need to replace them.

Eurotubes is a great place to get replacements. Very good tubes for a great price. Very quick shipment too. Bob the owner is very helpful as well. Drop him an e-mail. He has re-tubed hundreds of HRDs, so he can probably give you a good idea of what's wrong.

Eurotubes

Here's the order page for replacement tubes specifically for the HRD.

Hot Rod Deluxe/Deville Replacement Tubes

Let us know what you find out.

If you know something better than Rock and Roll, I'd like to hear it - Jerry Lee Lewis


   
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(@gjbrake)
Reputable Member
Joined: 21 years ago
Posts: 235
Topic starter  

Hey!

Well, the plot thickens.

I turned the amp on last night to see if the same things would happen as before.
Well, the tube didn't light up bright like it had before, and it didn't start to smell like a barbeque - they both just ticked over like they are supposed to.
However, the horrible grating noise that comes and goes inexplicably was still there.

Looking at that website, I found this bit:An issue that commonly pops up in Hot Rods is the Plate Load Problem. These amps sometimes develop a loud intermitten crackle/static that's mainly caused by the 82K plate load resistor of the phase inverter (R57). Sometimes this resistor will come completely "open," or, in other words, it will internally break into two. This results in a dramatic loss of volume, as only one power tube is amplifying, and a terrible sounding break up even when the amp is supposed to be clean (i.e. severe crossover distortion).Maybe this could be my problem?

Either way, the tube is certainly not behaving how it was before, but the amp is still unusable in this state. Gonna take it in to the store I got it from tomorrow and get them to fix it - even if it is just a tube refit. I have every intention of getting some of Bob's tubes and refitting/biasing myself at some point, because I'm not going to take it to the store everytime it needs new tubes in future. However, I have neither the time or the inclination at the moment, and after last night, I'm not even sure that it's the power tube causing problems!

Muchly confused! Although I've managed to borrow an amp for Saturday and then I've got until the 19th to get mine back in working condition, so I'm not as bothered as I was when I last posted!

Thanks for your time on this one so far guys!!
G

Listen Louder Than You Play


   
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(@ricochet)
Illustrious Member
Joined: 21 years ago
Posts: 7833
 

A power tube "glowing orange all the way through" and smelling like a BBQ sounds like a badly overheated tube. There's a big gray piece of metal called the "plate" inside the tube that should NEVER glow. Only the small cathode inside the plate should glow, visible at the ends. If the plate glows, TURN THE AMP OFF and get it checked. Something is causing far too much current to flow in that tube. You risk damaging the amp playing it that way.

"A cheerful heart is good medicine."


   
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