How badly have I damaged my amp

winter_reverb

I was setting up a new pedal set up with my Egnater tweaker this evening, trying to work out which pedals/power supplies were causing noise. I noticed my amp go quiet and the kind of ticking noise you get when an old fashioned lightbulb goes.

When I investigated I noticed my amp was set to 4ohm when the speaker is 16ohm. I have no idea how long it was like that, it could have happened when I was setting up the pedals this evening, it could have happened when I recently changed the pre amp tubes. I still have the previous pre amp tubes that I know work, swapping them did nothing. I tested both the power tubes in my fender champ, one still worked one did not. When I put the working one back in with the working one from the champ it still didn't work. So I know I have done something that has blown a tube plus done some other damage. What is the best and worst case scenario here?

I love this amp but it is cursed.

Mkjackary

how loud were you playing the amp? Where was the volume knob set? how many watts is the amp?

winter_reverb

I wasn't playing it at the time, it was plugged into my guitar and I was turning on and off various power supplies to try and find which pedal was causing noise. The master volume was maxed but gain was very low (thats how the manual recommends it). It is 15w.

ICBM

Best case and by far the most likely is that you've blown one power valve and the HT fuse, which often blows if a valve does and will shut down the whole amp.

Worst case is that you've also blown the output transformer, but very unlikely if the amp was not turned up loud.

Somewhere in between is that it's possible the blown valve also took out another component, but not the OT - eg a screen resistor or power supply chain resistor.

It is also possible that it's pure coincidence and nothing to do with the impedance mismatch - valves can sometimes fail for no obvious reason.

TheMarlin

Does the amp have valve rectifier? If do, check that.

winter_reverb

ICBM said:

Best case and by far the most likely is that you've blown one power valve and the HT fuse, which often blows if a valve does and will shut down the whole amp.

Worst case is that you've also blown the output transformer, but very unlikely if the amp was not turned up loud.

Somewhere in between is that it's possible the blown valve also took out another component, but not the OT - eg a screen resistor or power supply chain resistor.

It is also possible that it's pure coincidence and nothing to do with the impedance mismatch - valves can sometimes fail for no obvious reason.

thanks, I hadn't thought to check the fuse and it has indeed blown. I will try and replace it and the power tubes and see what happens, then if that doesn't work take it to be repaired. It wasn't turned up loud in terms of actual volume as the gain was so low but the actually master volume was very high, could that put the out put transformer at risk?

ICBM

winter_reverb said:

thanks, I hadn't thought to check the fuse and it has indeed blown. I will try and replace it and the power tubes and see what happens, then if that doesn't work take it to be repaired. It wasn't turned up loud in terms of actual volume as the gain was so low but the actually master volume was very high, could that put the out put transformer at risk?

No, the transformer is only at risk if the amp is producing a fair amount of power. The only possible catch is that if you were investigating a pedal noise problem, it's just possible that the amp *was* producing a lot of power, but out of the audio range where you wouldn't hear it.

First, replace the fuse but don't put the power valves in, and power the amp up. If the fuse now doesn't blow, then put the power valves in and try again. If the amp is now working normally it's almost certainly fine. The reason for the HT fuse is to blow and protect the rest of the amp if something like a valve failure happens, so there's a good chance it did its job.

winter_reverb

I have read online that with these amps they can take any tube without the need for biasing, but when I got it repaired in the past they said that it is necessary

ICBM

winter_reverb said:

I have read online that with these amps they can take any tube without the need for biasing, but when I got it repaired in the past they said that it is necessary

Did they charge you for it?

It doesn't need biasing, it's a cathode (self) biased amp.

http://www.egnateramps.com/FAQ.html#Q21

"Are the Egnater amps cathode or fix biased?

All of the models, with the exception of the Tweaker, are fixed/adjustable bias with easy to use test points. Consult the owner’s manuals or contact support@egnateramps.com for information on how to properly adjust the bias. The Tweaker is cathode biased so there is no adjustment required when replacing tubes."

winter_reverb

it was when I took it to be repaired a couple of years ago (like I say this amp is cursed) and they mentioned when I came to pick it up in reference to what tubes replacements to get in future. they charged me for the repairs but I don't think any additional for that.

ICBM

winter_reverb said:

it was when I took it to be repaired a couple of years ago (like I say this amp is cursed) and they mentioned when I came to pick it up in reference to what tubes replacements to get in future. they charged me for the repairs but I don't think any additional for that.

That's good . I have heard of techs adding on a biasing charge to any repair, including cathode-biased amps.

I haven't actually come across many problems with the Tweaker, although there have been a couple in the shop recently (probably just coincidence) - a 15 with a failed PCB jumper connector, and a 40 that I'll be looking at tomorrow and I don't know the fault with yet other than "not powering up".

winter_reverb

ICBM said:

winter_reverb said:

thanks, I hadn't thought to check the fuse and it has indeed blown. I will try and replace it and the power tubes and see what happens, then if that doesn't work take it to be repaired. It wasn't turned up loud in terms of actual volume as the gain was so low but the actually master volume was very high, could that put the out put transformer at risk?

No, the transformer is only at risk if the amp is producing a fair amount of power. The only possible catch is that if you were investigating a pedal noise problem, it's just possible that the amp *was* producing a lot of power, but out of the audio range where you wouldn't hear it.

First, replace the fuse but don't put the power valves in, and power the amp up. If the fuse now doesn't blow, then put the power valves in and try again. If the amp is now working normally it's almost certainly fine. The reason for the HT fuse is to blow and protect the rest of the amp if something like a valve failure happens, so there's a good chance it did its job.

sorry I missed this post. thanks, I will follow this procedure.

I think I worked out how the Ohm switch got flicked, I had very short leads for the send/return which were pulled quite taught as I moved the pedalboard about, if I moved across it could have clotheslined the switch. 

Jimbro66

This thread underlines just how very lucky we are to have on the Fretboard @ICBM and the other amp specialists who frequently and willingly give detailed advice on all issues to do with amps and electronics. There's so much to be learned from their posts. Thanks guys.

winter_reverb

The amp lives!

57Deluxe

why is it that the really shitty amps never shut up!!

robinbowes

57Deluxe said:

why is it that the really shitty amps never shut up!!

Pah, amateurs.

Pete Traynor used to test his amps by dropping them out of his 2nd-floor window.

R.

Cabicular

I had a Traynor that sounded like thats what happened

FarleyUK

Sorry to hijack.... but I thought it was OK if you had a step down mismatch with the ohms...? For example, I run a JVM410HJS in 50W mode (i.e. only two power valves) from the 8ohm output into a 4x12 with 4 16 ohm Greenbacks - I was advised this is fine, but it seems from teh above, you guys are saying it's not...?

ICBM

FarleyUK said:

Sorry to hijack.... but I thought it was OK if you had a step down mismatch with the ohms...? For example, I run a JVM410HJS in 50W mode (i.e. only two power valves) from the 8ohm output into a 4x12 with 4 16 ohm Greenbacks - I was advised this is fine, but it seems from teh above, you guys are saying it's not...?

It depends.

First, if you're running half the full number of power valves, the *correct* match is with the amp set to half the impedance of the cab - that's because the power valve pairs are in parallel, so using four gives half the impedance of two, hence using two when the amp was designed for four means you need to double the impedance the amp sees... if that makes sense! So you're doing it exactly right - 8 ohms on the amp into a 16-ohm cab.

Second, most amps are not very sensitive to mismatching up or down 'one step' (ie 4 ohms into 8, or vice versa) provided the amp is not cranked into power stage distortion. 'Two steps' (ie 4 into 16 or vice versa) gets more risky, but again is unlikely to do any harm unless the amp is being pushed hard. If the amp is running with the power stage completely clean and well below full power, impedance matching doesn't really matter at all. (Although it will affect the power output and tone.)

Third, contrary to popular belief, most *valve* amps actually prefer a *low* mismatch (ie the amp set to a higher impedance than the cab, eg 8 ohms on the amp into a 4 ohm cab) than the other way round. It's a little harder on the valves usually, but not very dangerous to the amp. A *high* mismatch (eg 8 ohms on the amp into a 16-ohm cab, and especially 4 into 16) is actually more risky and can cause arcing in the OT or at the valve sockets, as well as often increasing the risk of valve screen failure. This doesn't apply when running half the power valves because it's then a correct match.

However *solid-state* amps should not be run below their *minimum* impedance - which is slightly different from the 'matching' impedance with valve amps, because there's no output transformer which is what does the matching. You will get away with it at lower volume, but if the amp is turned up there is a major risk of serious damage. Most solid-state amps are totally happy with any higher impedance than the minimum though.

Does that help?

winter_reverb

seems like I spoke too soon, it blew a fuse again and this time when I replaced it it blew it again immediately. Looks like I am going to have to take it to be repaired for the third time since I got it.

ICBM

Damn, that's not good news .

The 40W one in the shop has a cooked power transformer by the way... although I don't think yours will be that if it's blowing the HT fuse not the mains fuse.