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did i just damaged my brand new tube amp? need help. :((


classicrox

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So after weeks of deciding on what tube amp to buy, i finally decided to go for the Blackstar HT-40 over the Marshall DSL40c, as i find the blackstar to be more versatile than the marshall ( though i friggin dig the marshall tone ) but unfortunately, only the blackstar is the only amp available here in my place.

 

After i got the blackstar, i immediately ordered a new speaker ( Vintage 30 ) to replace the stock which is the celestion 70/80. when the vintage 30 arrived, i immediately swapped the stock speaker. the speaker output was plugged in 1x16 to match the impedance of the celesiton 70/80 ( 16 ohms ), not knowing the Vintage 30 that i ordered was in 8 ohms ( so stupid of me that i forgot to specify the ohm), soon as i connected the v30 to the amp ( plugged in 1x16), i played the hell out of it for like 15 to 20 mins, i put the gain on 3 o'clock and almost cranked the volume.

 

Being new to tube amps, i was STUPID enough to SWITCH the speaker output to 1x8 WHILE THE AMP IS STILL ON and not on standby. i was not aware that what i did was very dangerous to the amp.

 

about a while ago, i was searching about the tonal difference about 8 ohms vs 16 ohms, and i stumbled upon a thread in other forums that you should run the speaker output lower than the speaker's ohms. like for example,

 

8 ohm amp to a 16 ohm speaker = safe

16 ohm amp to 8 ohm speaker = flyback, damaging transformers, tube, etc.

 

i am not an electrician nor i am expert on electricity, current, volts. as i only know very basic stuffs.

 

i am afraid that i just damaged my tube amp from the inside or burned something, or damaged the tubes, or what. i feel like i am being paranoid.

 

the amp sounds fine, i haven't notice any malfunctions with the knobs and switches. though i cannot say whether there is a change in tone because i might damaged some tubes or what.. please excuse me if i really sound like a stupid ***t. it's my first tube amp. and i still don't know many things about it. what i only know is that tube amps are the best.

 

are the modern tube amps built to withstand these kind of stuff or im screwed?

 

please help.

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If you haven't smelled smoke, blown fuses or hear bad sound quality, you're probably OK. Tubes and output transformers are forgiving up to a point and one jump from 16 to 8 or 8 to 4 ohms shouldn't cause too much problems short term. If tubes are damaged the entire elements are likely to glow cherry red and the sound quality goes out and the amp shuts down.

 

 

Long term impedance imbalance can damage the tubes prematurely and with some amps it can damage the output transformer depending on how finicky the amp is. This can take weeks to months in some amps. Marshall amps on the other hand don't like seeing an incorrect load and blow fuses very quickly. They have fuses in line with the output transformer to protect them. Other amps like my old Blackface Bassman took a beating for a few years when I was a kid running the 4 ohm head at 16 ohms and the tubes kept blowing out, but the transformer is still fine.

 

 

As far as switching impedance with the amp on, you should have powered it down, but if its still running OK and the sound wasn't affected, you're OK. Just don't pull that trick again.

 

If something did blow, you'd definitely know it. You'll likely smell the fresh aroma of cooked components billowing out of the head, distorted/no sound or at least the fuses blow on you. That didn't happen so I suspect you are fine.

 

Tube amps are pretty durable if treated right and you should get a couple of years out of the tubes depending on how many hours you use them. Combos are shorter life due to the vibrations the tubes see in tight confines with the speaker. Don't get yourself paranoid reading about what could happen. Just be sure to power down when connecting speaker cables and always set the right impedance to match the speakers. Take care moving them because tubes are made of glass. If the amp brand is good you should have minimal issues beyond that. between 5~10 years have the power caps checked and have them changed at maybe 10~20 years. Power caps are cheap and besides providing smooth DC they are what protect the head against line spikes.

 

I'm an old tube guy myself. I got my degree in that technology and have worked on tube amps most of my life both pro and hobby. Modern tubes today are just as good as vintage if not better. Some brands are much tougher then others.

 

Most vintage tubes today are either are worn out junk that came out of used gear and have to many hours on them or they are pirated. Beware of snake oil. Vintage tubes haven't been made for a good 40 years and since most electronic store went out of business long ago its highly unlikely anyone has a stash of NOS around, especially the popular ones that would have been sold off first.

 

There's a bunch of guys out there trying to cash in on ignorant individuals who think old tubes are the cats meow. Nearly all old tubes being sold are completely worn out and should be thrown away like you would old batteries.

 

I'd match a set of set of JJ's and others to just about any other tube out there for both durability and quality. EH makes some great tubes too as do others. There's a few brands that have poor output or can become microphonic quickly but that's really no different then tubes made in the past. Some of the new brands actually last longer and are even more durable then many vintage tubes, and they are getting better.

 

Tubes are computer tested, computer designed and the alloys are many times better then mass produced components of the past so I'd just do my research and choose tubes best for your amp and so long as you buy matched sets and have them properly biased just enjoy how they sound. Life is too short to be worried about things that may never happen.

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8 ohm amp to a 16 ohm speaker = safe

16 ohm amp to 8 ohm speaker = flyback, damaging transformers, tube, etc...

 

granting that amp & speaker impedances should always be matched:

aren't tube amps hurt more by speaker(s) of too high an impedance while

solid state amps hurt more by a too low speaker impedance?

or do i have it backwards?

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If you haven't smelled smoke' date=' blown fuses or hear bad sound quality, you're probably OK. .[/quote']

 

thank you for the reply :)

 

negative. haven't smelled any smoke. is there any indicator if the fuses will blow or blown? the amp won't turn on if the fuses are damaged right?

 

as far as the sound quality, i am not sure. but i did some video recording the other day, that was after i did some stupid things with my amp. so if there's a bad sound quality due to what i did a week ago, it will appear on the recording. but i myself can't tell, as i am new to tubes and still not that knowledgeable about how the tubes sound if they are being damaged or what..

 

i am hoping you could check if there is something wrong with the sound.

 

here's the video i did, i hope you could tell if the sound quality is being damaged.

 

used an iphone for the recording.

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My concern with changing the impedance switch while the amp is running would be the inductance of the output transformer.

 

Inductors resist change in current flow. If current is flowing through the output transformer (sound coming out of the speaker) and the load (speaker) is removed from the circuit, the voltage at the output of the amplifier will spike very high and very fast. 100 watts into 4 ohms will require 5 Amps of current which is a lot considering 1 Amp can kill you. 5 Amps across a high impedance can generate some very high voltages which could cause arcing and physical damage to the amplifier.

 

One way to avoid the voltage spike in this situation would be to use a make-before-break switch for the impedance so the output transformer never sees an open circuit. If I was designing an amplifier, I would use such a switch.

 

In the case of the OP however, if there was no sound coming out of the speaker at the time of the switching then there was no current flowing through the secondary coil of the output transformer and therefore no voltage spike.

 

To make a long story short, I do not believe that you inflicted any damage on your brand new tube amp.

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Tube amps can usually be run at a lower impedance without damage. No load is bad for them.

Transistors are the opposite. Many can be run with no load and lower impedances can overheat the output transistors. When you think of it from a heat aspect its easy to remember. Transistors blow when overheated so you want to avoid feeding that current back into them with a short. Tubes are designed to run hot so low impedance isn't an issue.

 

The key is, in the magnetic effect of the output transformer. The current to the primary coil magnetizes the core and that magnetism is transferred to the secondary coil and generates a secondary current.

 

If you remove the load, and have an open circuit in the secondary coil, it no longer converts the magnetic field into current so the magnetic field from the primary coil is no longer siphoned off by the secondary.

 

That field has to go some place when it collapses and instead of feeding into the secondary coil that provides a reactance and counter force to the primary, it all feeds back into the primary coil generating extremely high current in the power tube circuitry.

 

This can cause a chain reaction to occur damaging the tubes and support circuits which run on low current high voltage. The Grid Resistors are usually the first thing to blow because they are now seeing double the current and the tubes often short out quickly afterwards. Other DC supply components can follow as the current backs up and overloads the power transformer. If you're lucky it takes out the power fuses before the power transformer overheats and opens up, making for an extremely expensive repair.

 

If you need a simple analogy use this. An automobile has an engine and an automatic transmission.

 

The transmission is your output transformer. High RPM's of the engine spin the transmission which converts high speed rotation to low speed rotation of the wheels. and because of the gear ratios high speed low torque rotation gets converted to low speed rotation with high torque.

 

If you add additional load to the vehicle by adding a trailer, (adding more speakers in parallel to lower the resistance) the transmission works harder. You may eventually blow the transmission or engine but that usually will takes some time because they are supposed to see a load.

 

If you put your foot on the brake (short the speaker output) and put it in drive the engine will still run so long as you don't rev it up too high.

 

If you disconnect the transmission (remove the speaker and open the secondary) and run the engine with no load, the engine will rev up beyond its ability to stay in one piece and explode.

 

That's oversimplified of course but it explains how power conversion works. Engine horsepower = High RPM - low torque in the engine (high voltage - low current in the power tube circuit) is converted to High Torque - Low RPM by the transmission (high current - low voltage in the secondary to drive the speakers)

 

Its about proper balance and counter balance.

 

Using the same analogy for transistor amps can be used too. The difference is there's no transmission.

 

The engine drives the wheels directly and provides high torque low - RPMs without the need of power conversion.

 

If you lift the wheels off the ground (remove the speaker load) you can rev the engine up to max and it wont fall apart or overheat. It will simply top out and continue to run without the car moving. If you overload the vehicle (too many speakers in parallel) the engine overheats and blows.

 

If you chain it up so the vehicle cant move (short the speakers) and rev the engine, you'll smoke the tires till they come off the rims and blow the engine if it cant move forward. (When some transistor amps blow, transistors overheat, short out, pass 120VAC through the speakers taking them out as well)

 

Again, this may be over simplified but the chain of events here in mechanics follow the same laws of physics in electronics and having some mental picture of what is actually occurring helps to demystify what actually going on.

 

 

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. . ..

 

 

 

This can cause a chain reaction to occur damaging the tubes and support circuits which run on low current high voltage. The Grid Resistors are usually the first thing to blow because they are now seeing double the current and the tubes often short out quickly afterwards. Other DC supply components can follow as the current backs up and overloads the power transformer. If you're lucky it takes out the power fuses before the power transformer overheats and opens up, making for an extremely expensive repair.

 

. . .

 

 

 

 

I think you meant to say Screen Resistors since tubes are voltage controlled devices and there is no grid 'current'.

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awhile ago while i was changing my tube amp's speaker, i checked the tubes, transformers, etc. i see no physical damage. i hope i just dodged a bullet right there. did some more sound test, amp sounds good. i have not noticed anything out of the ordinary. but i am still worried.

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I think you meant to say Screen Resistors since tubes are voltage controlled devices and there is no grid 'current'.

 

No I meant grid resistors. Voltage doesn't blow components, current and heat does.

 

You can have Screen, Grid, Cathode or Plate resistors depending on the amp type. In this diagram you'll see the 1W grid resistors on the back of the power tube sockets that typically blow in 6L6 tube amps.

http://www.recycledsound.net/5_Inside_a_typical_Fender_amp.pdf

 

I'm familiar with the cause of failure with these resistors in particular because I blew them out enough times on my own amps to know for sure. Later when I did repairs for a living I'd find many other power amp melt involving many other causes, but this one was pretty reliable relating to high impedance loads. I could spot it them blown and confirm it when asking customers about the speakers they were running and advise them to make corrections.

 

In this diagram you'll see ceramic screen and carbon grid resistors. The grid resistors would still be more likely to blow over the screen.

 

http://thenormster.com/DumbleLite/BuildersGuide/D-Lite%20Assembly%20Guide_files/image025.jpg

 

Not all amps use grid or screen resistors. 6V6s or 6L6s that use no choke and with a much larger dropping resistor from the plate filter cap to the screen filter cap, don't seem to need to have screen resistors if the voltage to the screens is low enough in comparison to the plate voltage. It depends on the tube type too. If the tube can take it, then using the smallest value can provide better sound quality.

 

El84s and EL34s are very different animals. You often find 1K 5w screen resistors on EL34s, and even 2w screen resistors on each EL84 tubes with values as high as 2700 ohms!!

 

Different tubes, Different circuit designs, Different biasing, and Different results. I've scratched my head many times trying to figure out the leading cause of melt downs as a tech so I could advise customers on how to avoid the same failures it in the future. Many defy reasoning so you just have to blame it on the quality of the components and give customers the normal Do's and Don'ts when operating a tube amp.

 

You may replace all the bad parts, do a good burn in testing them, and you never see that amp again. You're not sure if the customer took your advise or not. Others may come back and haunt you. Sometimes when you double down you may find additional parts that are still working properly but you change them because they "might" be a cause of failure. I've even see new components cause failures in amps that had been running components with values that have drifted way out of specs.

 

 

The ones that kill you are when you know the cause, and then advise the customer of what they need to do to correct it. Instead of taking your advice, they ignore you and connect it right back up the same way as they had been. Their reason is they went a year running it improperly like that before it blew. Second time it may have only taken a few days and blew out again They bring it back blaming the failure on a poor quality repair. People don't like being told "I told you so"

 

If they were honest and admitted they made the same mistake twice I'd likely cut them a break and do the repair for the cost of parts. This seems to be a rarity these days. People have grown to be so immoral. They lie right to your face and try to pass the blame on anything but themselves. They do that and I have no problems sleeping at night when I have to charge them for the second repair. I guess that's the main reason I got out of doing that for a living. I love the challenge of fixing circuits but I can do without that part of the business.

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No I meant grid resistors. Voltage doesn't blow components, current and heat does.

 

You can have Screen, Grid, Cathode or Plate resistors depending on the amp type. In this diagram you'll see the 1W grid resistors on the back of the power tube sockets that typically blow in 6L6 tube amps.

 

I'm familiar with the cause of failure with these resistors in particular because I blew them out enough times on my own amps to know for sure. Later when I did repairs for a living I'd find many other power amp melt involving many other causes, but this one was pretty reliable relating to high impedance loads. I could spot it them blown and confirm it when asking customers about the speakers they were running and advise them to make corrections.

 

In this diagram you'll see ceramic screen and carbon grid resistors. The grid resistors would still be more likely to blow over the screen.

 

. . .

 

Interesting.

 

I'm not disputing what you say but I've never seen a cooked grid resistor in a 6L6 tube amp however I have seen a lot of screen resistors that have blown to bits or toasted. In fact, I used to carry them in my gig bag.

 

One night an output tube shorted out on my Twin Reverb and took out the fuse. I slid the chassis out of the box, identified the bad tube by what was left of the screen resistor, removed it and one of the tubes from the other side of the push pull, replaced the fuse and finished the show.

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Your amp sounds fine. I would not be too worried about it. I think you are obsessing over nothing. But my good lord, your guitar is either horribly out of tune or you are fretting way too hard and throwing the tuning off. More apparent on the clean clips.

 

But actually while I am listening to your clips, I hear a faint rattle. It may be mic clipping from your iPhone, but is something rattling on or near your amp?

 

To everyone else trying to help this kid, I think your explanations may be over his head / too detailed. They are certainly over mine.

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Your amp sounds fine. I would not be too worried about it. I think you are obsessing over nothing. But my good lord, your guitar is either horribly out of tune or you are fretting way too hard and throwing the tuning off. More apparent on the clean clips.

 

But actually while I am listening to your clips, I hear a faint rattle. It may be mic clipping from your iPhone, but is something rattling on or near your amp?

 

To everyone else trying to help this kid, I think your explanations may be over his head / too detailed. They are certainly over mine.

 

Glad to hear my amp is ok! thanks a lot!

 

yeah, i should've tuned the guitar before i made the vid. my bad :) it is really out of tune, it's a floyd rose! haha.

 

and for the rattle sound, it's the vibration through my drum snare. my room isn't properly sound-proofed. That is my next project, so i can crank the amp without worrying about my neighbors.

 

most of the replies i get are kinda too technical, but it's good coz it makes my brain work! they've been super helpful :)

 

 

 

 

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So after weeks of deciding on what tube amp to buy, i finally decided to go for the Blackstar HT-40 over the Marshall DSL40c, as i find the blackstar to be more versatile than the marshall ( though i friggin dig the marshall tone ) but unfortunately, only the blackstar is the only amp available here in my place.

 

After i got the blackstar, i immediately ordered a new speaker ( Vintage 30 ) to replace the stock which is the celestion 70/80. when the vintage 30 arrived, i immediately swapped the stock speaker. the speaker output was plugged in 1x16 to match the impedance of the celesiton 70/80 ( 16 ohms ), not knowing the Vintage 30 that i ordered was in 8 ohms ( so stupid of me that i forgot to specify the ohm), soon as i connected the v30 to the amp ( plugged in 1x16), i played the hell out of it for like 15 to 20 mins, i put the gain on 3 o'clock and almost cranked the volume.

 

Being new to tube amps, i was STUPID enough to SWITCH the speaker output to 1x8 WHILE THE AMP IS STILL ON and not on standby. i was not aware that what i did was very dangerous to the amp.

 

about a while ago, i was searching about the tonal difference about 8 ohms vs 16 ohms, and i stumbled upon a thread in other forums that you should run the speaker output lower than the speaker's ohms. like for example,

 

8 ohm amp to a 16 ohm speaker = safe

16 ohm amp to 8 ohm speaker = flyback, damaging transformers, tube, etc.

 

i am not an electrician nor i am expert on electricity, current, volts. as i only know very basic stuffs.

 

i am afraid that i just damaged my tube amp from the inside or burned something, or damaged the tubes, or what. i feel like i am being paranoid.

 

the amp sounds fine, i haven't notice any malfunctions with the knobs and switches. though i cannot say whether there is a change in tone because i might damaged some tubes or what.. please excuse me if i really sound like a stupid ***t. it's my first tube amp. and i still don't know many things about it. what i only know is that tube amps are the best.

 

are the modern tube amps built to withstand these kind of stuff or im screwed?

 

please help.

 

I have an Blackstar HT5R and love it. If the HT40 is like mine, 8ohms is the lowest you can go. Don't hook up anymore speakers. Enjoy your new amp. I hope you love your new Blackstar as much as I love mine.

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