#1
I've been playin my original series 5150 for about 4 years and I've always been really happy with the sound. I play a heavy hardcore style and I love the crisp and powerful chugging I get from it.

Prob about 4 or 5 months ago, I began to notice that the sound was becoming less crisp and more muffled. It's less defined.. Like a speaker's out or something. I checked the cab and the speakers are mint. I retubed and it still isn't what it used to be. (I generally use Ruby 6L6s and JJ 12AX7s.) There's no bias on this amp either. I'm at a loss.

My band is recording a new album soon and then we're hittin the road, so I'd really like to get this all squared away ASAP ya know.

Any ideas?????????????????
Thanks!
#2
I'm not sure about this... but have you had a tech checked the state of the filter caps?
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#3
It sounds like you've got a good start. Eliminate your guitar, pedal, cables, and cab as the source of the issue first. Else we're just pissing in the wind with a possible diagnosis.

Try with different guitars, no pedals, different cables, etc. Make sure it's the amp that's causing the issue.

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#4
Have you tried JJ power tubes (or anything else besides Rubys)? The reason I ask is that a few weeks ago, on a whim, I put my Ruby 6L6s back in my 6505+ to hear the difference between them and my JJ 6L6s. With the Rubys, it sounded like I had placed the amp under a pile of blankets and perhaps a mattress or two. To reach the same volume as with the JJs, I had to turn the post-gain up 2 WHOLE numbers on the dial. Needless to say, I switched them back in short order...
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#5
I would take it to a tech. Base on its age the electrolytic in the caps is near end of life...

It's still worth checking the bias, maybe eve having the bias mod done.

Sorry to hear the troubles.
#6
^ +1

Sometimes just having someone with some experience look over an amp is the best thing.
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#7
Rubys are rebranded shit. Chances are the "good" ones you had were rebranded JJs or something, and now the ones you have are something crappy like EHX 6L6s or something else.

I don't know why someone would willingly use Rubys, it's not even something you can say that you use, because it's a grab bag every time you buy them.
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#8
^Yeah, I have gotten more piss-poor ruby tubes than I can remember (most of them have come in amps that I have bought)

Lousy stuff indeed.
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#9
Thanks for all the replies!

I've also had problems with having to keep my post gain up stupidly high in order to reach the necessary volume. I'm gonna switch out the rubys for JJs and see if it that helps.

Aside from that, I think the filter caps are my next move. Should be also careful about which brand I buy when it comes to these?
#10
Quote by dundundundun
Thanks for all the replies!

I've also had problems with having to keep my post gain up stupidly high in order to reach the necessary volume. I'm gonna switch out the rubys for JJs and see if it that helps.

Aside from that, I think the filter caps are my next move. Should be also careful about which brand I buy when it comes to these?


For the caps- Nichicon and Panasonic are OE suppliers for many amps. Your local tech will probably use these.(hopefully, as you really want to avoid cheap Chinese ones)

It really sounds like a tube took a shit...
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#11
if u've used the amp regularly, the caps will be fine. visually inspect them, if they're bubbling out on the tops or sides, then they need replaced.

otherwise, i would suggest other things like output tubes, a failing phase inverter tube, or a failed screen grid resistor on the power tube board. i recently serviced 2 5150 amps that each had 1 or more SGR dead in them. the symptoms of this are: amp isn't loud like it used to be, and usually a louder than usual hum that wont subside.

while power tubes can be hit or miss, generally, they dont have to be perfectly matched quads...5ma between the farthest tubes is fine when biased up to about 60% mpd in this amp. you're not going to notice any difference if they're perfect or off by a few ma.

quality IS however a definite issue from MOST current production tube companies, not just one or the other....the difference is testing down the line during the rebranding process to each specific distributor (ie, GT, mesa, tad, ruby, etc).

i like the ruby 6L6mstr biased to 36 or so (60%) in these amps..or the sovtek 5881wxt+ (biased to 32, also 60% for a 25watt tube <even though sovtek says the wxt is a 30 watter, i run it cool>.

i would check those things, and report back....or you can email me, i might be able to help you. I wouldn't just go blindly stabbing around, or guessing as to what the problem would or could be without following a diagnosis chart...

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Last edited by George I. at Apr 3, 2013,