Amp Low End Gone


Drew77
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Drew77
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12/24/2007 6:12 am
Hey guys. I just did some maintenance on my amp (re-soldered input and changed the tubes) and when I plugged everything back in and started playing it sounded like crap. The high end seems alright but the lows sound all farty and weak. I am really hoping that I haven't blown my speaker considering it isn't that old (I have had it for a year) and I don't play it loudly hardly ever.

I am thinking it has to be my the new tubes I put in since that is really the only thing that changed but I don't know why that would be happening. Maybe I didn't line the pins up right? there were more holes than there were pins and the old tubes pins were numbered but the new ones weren't. I aligned them the same as the old ones were though.

They are supposedly matched JJs, 6l6 tubes. I have a vk112 (peavey), and I put in a Eminence Wizard speaker. I tried playing with someone today and it blew hardcore seeing as the idea was to play aggressive music and I have no low end. But anyway.

I was wondering if anyone had any idea whats up since I don't know. Tomorrow I'll try switching my tubes back to the stock ones since they were working all right (getting worn and unreliable at high volumes but still working).

Like I said the low end is just farty and broke. very depressing sounding.
# 1
Kevin Taylor
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Kevin Taylor
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12/24/2007 6:26 am
If you had two speakers I might guess that you had them wired out of phase. (the + and - plugged in backwards on one of them)

As far as being blown, you can check most speakers by just pushing in on them. If it feels scratchy or has resistance then there's a good possibility it's been blown. And contrary to popular belief, most speakers are blown from being underpowered and driven with too much distortion as opposed to turning them up too loud with a powerful amp. For instance, you can blow a speaker with a 20 watt amp turned way up because all it's doing is putting out distortion which quickly heats up the coils. A more powerful amp can rarely blow a speaker but rather than burning the coils it's usually literally blowing the cone out of the speaker casing.

Other than that, I'm at a loss. Most of my experience comes from stereo systems so I'm not too familiar with amp problems.
# 2
Drew77
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Drew77
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12/24/2007 3:24 pm
Alright thanks. I am going to try and do a proper diagnosis today, but if anybody thinks they might know please tell me.
# 3
Lordathestrings
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Lordathestrings
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12/24/2007 7:48 pm
When you replace the power tubes, the bias should always be checked. Some circuits have a design (called Cathode bias, or self-bias) that adjusts for differences in tube characteristics, but I doubt very much that your amp has this feature. More likely, it has Grid bias, which does not compensate for different tubes.

Try re-installing the original 6L6 tubes, and see what it sounds like. If the amp sounds normal with the old tubes, then the new ones have different bias requirements, and the amp will have to be adjusted by a tech to work with them. Or, you can continue using the old tubes.
Lordathestrings
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# 4
Drew77
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Drew77
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12/24/2007 8:41 pm
alright. Well supposedly the Valve King has a fixed bias or something (like the 5150) and any 6l6 is supposed to work. But I am going to try the old tubes again. I do not really know how much of this works so I suppose it could still be a problem with the bias. I just hope this doesn't end up costing me a bunh of money.

could it be that I hooked the speaker up wrong when I put the leads back on it?

I couldn't remember how I put them on originally and I'm not sure it matters.
# 5
Lordathestrings
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Lordathestrings
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12/25/2007 12:28 am
Fixed bias is the kind that has to be adjusted to suit the tubes. It applies a 'fixed' voltage (one that does not change) to the power tube Grid connections.

If you have only one speaker, and you disconnected the wires at the speaker end of the cable, it doesn't matter which way they go. There are only two terminals on the speaker, and only two wires, right? Polarity does not matter for a single speaker.

Things get 'interesting' with multiple speaker cabs, or if you messed with the wiring on the output transformer itself, but I don't think you did that.

Did you? :eek:
Lordathestrings
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# 6
Drew77
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Drew77
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12/25/2007 4:38 am
no definitely not.

I will check the tubes as that seems to be the prime suspect at the moment.

How involved is getting the bias adjusted for the tubes? I don't expect to do it myself.
# 7
Lordathestrings
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Lordathestrings
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12/25/2007 7:27 am
Biasing the power stage might be as simple as adjusting a trimpot, or as tricky as swapping out some resistors. Either way, the voltages present on a tube circuit (even after the amp is turned off and unplugged!) can be deadly. Leave that to someone with the right equipment, and the necessary skills.

If the amp still sounds bagged with the the old tubes back in, that means that something else has changed.

Let us know how it goes.
Lordathestrings
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# 8
Drew77
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Drew77
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12/28/2007 1:37 am
ALright this isn't cool. I went to put the old tubes back in right and I was having a really hard time getting them to fit for some reason. They came out super easy the first time and I didn't have a problem getting the new ones in after that. So trying to get these thing in the plastic colum on the center of the bottom of them that I guess is there for stability broke off into the hole. So I went and got some pliers to get a grip on it and get it out of there since it wasn't all the way in and to get the tube in I'd have to push it in to the point where getting it out would be impossible. The damn thing is as brittle as **** and breaks apart everytime I put any pressure on it. So now it is stuck in there any way... oh well may fiish putting the old tube in at least. I do it, it fits maybe it will work. Turn on my amp and I get nothing.

So now I'm screwed. I'm not sure if all the pressure I had to put on the first tube to get it in damaged the board or broke of the stupid plastic thing on that one as well.

So my amp is out of commission and I don't feel like breaking it anymore I guess I am taking it in to a repair place. I'll have to borrow my friends acoustic for a while... could actually be beneficial in the end but still, annoying and expensive.

I can't believe that the hard part of this (fixing the input and soldering the board) went perfectly well and I managed to **** it up with putting new tubes in it. That's a bitch.
# 9
strat-man
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strat-man
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12/28/2007 12:52 pm
Maybe if you had followed >This < advice?
Strat totin
Six string slingin
Son of a gun

I met my maker, i made him cry, and on my shoulder he asked me why, his people won't fly thru the storm, i said, listen here man they don't even know your born.

strat-man rocks with vox
# 10
Drew77
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Drew77
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12/30/2007 4:58 am
I'm not gonna fight with you over your snotty "told ya so" comment.

But I will point out that the part you told me not to do worked fine and I didn't die or even become injured as per the reason you told me not to do it and now that is fixed.

In fact it went perfectly, the tubes were what screwed it up (an unrelated operation that shouldn't have been a problem but was because the stock tubes are cheap pieces of crap).

So pretty much your just a prick.
# 11
earthman buck
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earthman buck
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12/30/2007 8:11 am
Originally Posted by: Drew77I'm not gonna fight with you over your snotty "told ya so" comment.

But I will point out that the part you told me not to do worked fine and I didn't die or even become injured as per the reason you told me not to do it and now that is fixed.

In fact it went perfectly, the tubes were what screwed it up (an unrelated operation that shouldn't have been a problem but was because the stock tubes are cheap pieces of crap).

So pretty much your just a prick.

You're.....
# 12
strat-man
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strat-man
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12/30/2007 3:24 pm
Originally Posted by: Drew77I'm not gonna fight with you over your snotty "told ya so" comment.


Your attitude says otherwise

But I will point out that the part you told me not to do worked fine and I didn't die or even become injured as per the reason you told me not to do it and now that is fixed.


Nobody can tell you to do anything! you were advised you chose not to follow the advise given.

In fact it went perfectly,


That is good.

the tubes were what screwed it up (an unrelated operation that shouldn't have been a problem but was because the stock tubes are cheap pieces of crap).


Because tubes, especially cheap ones always break of their own accord.

So pretty much your just a prick


Clearly i am, for trying to help you in the first place.

Have a nice day
Strat totin
Six string slingin
Son of a gun

I met my maker, i made him cry, and on my shoulder he asked me why, his people won't fly thru the storm, i said, listen here man they don't even know your born.

strat-man rocks with vox
# 13
Drew77
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Drew77
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12/30/2007 9:17 pm
Well I fixed it again. I'm still getting static on the low end and I will be taking it into someone who knows what they are doing because I wouldn't even know where to start with that.

Stratman, I am sorry for being a bit of a dick, but I was still pretty pissed I couldn't play my guitar right and your comment was very prickish.

I did not mean to imply that the tubes broke on their own, they broke because when putting them back in I put to much pressure on them. However they are cheap pieces of crap because they couldn't withstand the pressure required to get them into the amp a second or third time. They may still work without that plastic piece and the sockets are no longer clogged. Hell I'm pretty suer I wasn't but it is possible I was putting them in wrong.

I still stand by my statement that the thing "everyone" advised me not to do went fine and the thing that, had I asked about it, everyone would have told me was simple enough to do on my own. Which it is, I screwed it up some how or just have bad luck.

I don't mind people being dick's as long as their ok with me being a dick back, so lets not delude ourselves you were not trying to help even in the other thread.

whatever this honestly isn't worth continuing, I am at the same place I was when I got the advise I was looking for with this thread. Thanks to everyone who helped and thanks to Earthman for being kind enough to correct my grammar.
# 14

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