# 2 tubes glowing Red, Other 2 normal, loss of volume.



## EchoWD40 (Mar 16, 2007)

Well the problem is in my thread title. if i play for a bit at higher volumes,the tubes start to go whack, i lose almost all volume, and 2 tubes glow bright red. 
this is a 6l6 12ax7 tube setup, the 6l6's being the ones glowing like crazy.
what can be the issues here? it's never only one, always both, and always the same tubes. yes i have tried moving them around, to no avail.


----------



## keeperofthegood (Apr 30, 2008)

Tech time.

Short list

bad tubes

longer list

bad caps/resistors/coupling/grounding

loner list yet

.... you don't want to wait to get here.


----------



## WCGill (Mar 27, 2009)

Those puppies are over-dissipating and they're under-biased, for whatever reason. It could be bad screen resistors, bad input caps, bad grid resistors, gassy tubes, bad cathode resistor if your amp is cathode-biased, or not enough bias voltage if fixed bias. It needs to go to a tech. I'll bet it sounds great though.


----------



## EchoWD40 (Mar 16, 2007)

WCGill said:


> Those puppies are over-dissipating and they're under-biased, for whatever reason. It could be bad screen resistors, bad input caps, bad grid resistors, gassy tubes, bad cathode resistor if your amp is cathode-biased, or not enough bias voltage if fixed bias. It needs to go to a tech. I'll bet it sounds great though.


problem is, its at this point where i don't think its worth it... 
It has no chassis as the original one was destroyed in car accident, so i am left with the bare electronics. 
i am strongly considering at this point getting a new amp.


----------



## keeperofthegood (Apr 30, 2008)

:thisforumneedsauslesswithoutpicsemote:

kqoct that is hard to envision, really, a chassis being a hard metal enclosure and tubes being hot and all. But, it is that far gone, there is no value then to keep it going, would be more economical to start with a new amp!


----------



## EchoWD40 (Mar 16, 2007)

keeperofthegood said:


> :thisforumneedsauslesswithoutpicsemote:
> 
> kqoct that is hard to envision, really, a chassis being a hard metal enclosure and tubes being hot and all. But, it is that far gone, there is no value then to keep it going, would be more economical to start with a new amp!


 Yeah, gonna need to finance this one through L&M probably. Insurance shafted me big. 
Any ideas on a good head, or even a combo that will give me anywhere from angus young up to dual rec territorry, and fairly cheap? 
I would like 50+ watts, but less can potentially do. 
i wonder if i can part this head for anything...

I was thinking of going with a Hybrid amp... any reviews on the line 6/bogner spidervalve head? 
Or even this one has me particularly intrigued... http://guitars.musiciansfriend.com/product/Vox-AC30VR-Valve-Reactor-2x12-Guitar-Combo-Amp?sku=584528


----------



## GuitarG. (Apr 1, 2010)

TDeneka said:


> Yeah, gonna need to finance this one through L&M probably. Insurance shafted me big.
> Any ideas on a good head, or even a combo that will give me anywhere from angus young up to dual rec territorry, and fairly cheap?
> I would like 50+ watts, but less can potentially do.
> i wonder if i can part this head for anything...
> ...


Looks like you're looking for a heavy metal type amp? And for cheap? Yeah that Vox might do the trick. I haven't tried that one out. If cheap is what you are going for i would probably go all tube something along the lines of a Randall or Peavey mabe? I've never really been a big fan of Line 6 stuff personally, but the last time i tried anything in their line they were still fairly new company.
If you can save a few more dollars I would personally look for a used Marshall JCM 800. They can still be had for under a thousand. They won't do dual recto stuff but put a pedal in front and mabe have some tweaks done to the amp and they will get you what your looking for likely. Afterall it was the most common hard rock metal amp of the 80's. Just my 2 cents.


----------



## Wild Bill (May 3, 2006)

TDeneka said:


> Well the problem is in my thread title. if i play for a bit at higher volumes,the tubes start to go whack, i lose almost all volume, and 2 tubes glow bright red.
> this is a 6l6 12ax7 tube setup, the 6l6's being the ones glowing like crazy.
> what can be the issues here? it's never only one, always both, and always the same tubes. yes i have tried moving them around, to no avail.


You didn't mention the model of amp but from what little you told us of WHAT WE ACTUALLY NEED TO KNOW it sounds like you're describing 4 4L6's, of which 2 on one side are redplating.

I'll bet you 2 beer that the problem is either severely mismatched tubes or a loss of bias control voltage to the red tubes. The usual culprit is a shorted coupling cap, the one coming from the last 12AX7 to the pair of 6L6's that are redplating. A cap will cost you only a dollar or two, if you understand how to change it.

I think you must be describing a busted cabinet, not chassis. The chassis is the actual metal box/frame that all the transformers, resistors, tubes and stuff is mounted on. The cabinet is the wooden box that contains it. If the box also has a speaker(s) it's called a combo.

A chassis is always worth a few bucks, depending on the amp. Somebody willing to do a bit of sawdust work can make another cabinet. It might not always look as good as the original but it would be functional. A chassis electronics problem can always be fixed. If the trouble is really bad you can always use the parts, like the transformers, for a homebrew amp. For that reason even a "blowed-up" chassis is worth $20-$50 or even more, depending on what type of amp it is and how much it will cost to fix it.


----------



## EchoWD40 (Mar 16, 2007)

Wild Bill said:


> You didn't mention the model of amp but from what little you told us of WHAT WE ACTUALLY NEED TO KNOW it sounds like you're describing 4 4L6's, of which 2 on one side are redplating.
> 
> I'll bet you 2 beer that the problem is either severely mismatched tubes or a loss of bias control voltage to the red tubes. The usual culprit is a shorted coupling cap, the one coming from the last 12AX7 to the pair of 6L6's that are redplating. A cap will cost you only a dollar or two, if you understand how to change it.
> 
> ...


Yeah it's the cabinet, my mistake.
It was a kustom 72 coupe. And i wish i knew people who could make the cabinet for me for a few bucks.


----------



## Greg Ellis (Oct 1, 2007)

I pulled this off the web:

Technically speaking, the '72 Coupe runs on four 6L6 power tubes with a 12AX7 preamp. Furthermore, it uses a self-biased power amp design in tandem with a secondary, partially fixed-bias technique. This produces an amplifier with the best of both worlds: self-biased reliability and the increased power and dynamics of a fixed bias design.

COUPE TECH

Probably doesn't help, really. You'd need a schematic to really understand what this marketing copy means.


----------



## mrmatt1972 (Apr 3, 2008)

TDeneka said:


> Yeah it's the cabinet, my mistake.
> It was a kustom 72 coupe. And i wish i knew people who could make the cabinet for me for a few bucks.


After you send it to Wild Bill to get fixed, ANY woodshop can make you a cabinet. Mississauga is Ontario's woodworking mecca, so you should have no shortage of people to call. The trick is finding one small enough that they're willing to make a one-off cab fo you.


----------



## EchoWD40 (Mar 16, 2007)

mrmatt1972 said:


> After you send it to Wild Bill to get fixed, ANY woodshop can make you a cabinet. Mississauga is Ontario's woodworking mecca, so you should have no shortage of people to call. The trick is finding one small enough that they're willing to make a one-off cab fo you.


At this point, it is almost not worth it though. I can find the same amp for about 400 bucks used, and probably without this problem after the accident.


----------



## keeperofthegood (Apr 30, 2008)

TDeneka said:


> At this point, it is almost not worth it though. I can find the same amp for about 400 bucks used, and probably without this problem after the accident.


Well... I think any amp is worth something to someone, even 'free for shipping' at the dirt cheapest. If you were to take a photo and show someone who knows prices (I think Wild Bill does) and see what kind of value there may be in selling it or dumping it, then put it up as a parts chassis FS:


----------



## Wild Bill (May 3, 2006)

keeperofthegood said:


> Well... I think any amp is worth something to someone, even 'free for shipping' at the dirt cheapest. If you were to take a photo and show someone who knows prices (I think Wild Bill does) and see what kind of value there may be in selling it or dumping it, then put it up as a parts chassis FS:


No, I'm not that good on prices. Remember, I'm a build and service shop, not a used amp store. So I don't get much experience with prices.

Anyhow, "when I was a lad..."....don't younger folks DO anything anymore?

I don't mean to be an old curmudgeon but when I was a teenager I would have thought nothing about buying or scrounging some pieces of wood and whacking together some kind of cabinet! It may not have been that pretty but it would have done the job.

Times have really changed, I guess. A friend and I have talked about how you can tell by looking at a variety store magazine rack. Up until the 1980's you would see all kinds of magazines with "do it yourself" articles about whittling your own furniture or building your own stereo speaker system. All sorts of people worked on their own cars or did their own home repairs.

Today that magazine rack has really shrunk! Most of the old names are no longer published. Obviously, not enough people still bought them!

There are a lot of reasons for this trend, I guess. People don't have the same amount of free time. Cars have become more complicated and less easy to work on, although you can still do your own brakes, air filters, plugs and some stuff. It's cheaper to buy a new stereo than build one, although you can build a tube stereo power amp and save a bundle! After all, the ones in the stores cost upwards of $5000!

The attitude from the schools amazes me! It's assumed that to know how to even wipe your own butt you need at least a 3 month course and a certificate. If you don't have a certificate then of course you can't be expected to know how to wipe yourself! Back before the last Ice Age when I went to high school my buds and I did all kinds of things ourselves, just for the fun of it and/or to save some money. Usually schools didn't teach a lot of interesting stuff. Electronics courses tended to be particularly poor. You were lucky to get even some electrical house wiring teaching. So we just did it ourselves and thought nothing of it!

I cry when I remember how my next door neighbour used to work on his own muscle cars! He often loaned them to me and those were the cars on which I learned to drive. Spoiled me for life. A couple of years later I was old enough to buy my own car but the OPEC thing had happened and the price of gas had soared sky high. People scrapped all those wonderful, gas guzzling muscle cars. All there was left for guys like me were gutless little sh*tboxes. Today's vehicles just don't do it for me. All I care about is air conditioning and the sound system. The horsepower just isn't impressive.

Anyhow, some guys still make sawdust and would likely give you a few bucks for your amp! It won't cost them hundreds of dollars to build a cabinet, 'cuz they only have to pay for the wood. Their labour is free when it's for themselves.

Some months ago I listed a Peavey 4-12 cabinet in the buy/sell. I was selling it for $125, which I thought was a good deal. The cab was in good physical shape but the speakers needed some cone repair and I wasn't sure about the voice coils in a couple of them.

Despite the low price, I only had two offers! I was really surprised. A couple of months later, one of my customers was picking up his amp and noticed the Peavey cab. I told him what had happened and mentioned I'd really like it out of my shop as I could use the room. He spoke for it on the spot!

I got an email from him a few days later. He had patched the cones, checked the wiring and the cab was working great! ALL the speakers were just fine! 

For doing a bit of work himself he got a 4-12 cab good for a couple of hundred watts, for $125.

It warmed my heart to see what he had done! It also warms my heart to see the learn/build amp project Greco, Keeps and others are doing.

The flame still burns!:rockon2:


----------



## EchoWD40 (Mar 16, 2007)

Wild Bill said:


> No, I'm not that good on prices. Remember, I'm a build and service shop, not a used amp store. So I don't get much experience with prices.
> 
> Anyhow, "when I was a lad..."....don't younger folks DO anything anymore?
> 
> ...


no, by all means, you're right. I would do this kind of project but it's more so being tired of the constant problems it has. 
like for one, i would love to mount it like a fender tube amp 
http://waynereno.net/images/back_of_amp.jpg
but i do not know how it would sit on top of the cabinet without falling down. kqoct
Funny thing, i bought some unloaded GBX cabinet off this site for like 50 bucks. Unloaded. So i decided just to do my research on the wiring, got 4 speakers and now i have a 412 heh. 
It's more of the fact that i don't know really where do begin. I know woodworking, i just don't know how to mount the damn thing.


----------



## Greg Ellis (Oct 1, 2007)

TDeneka said:


> no, by all means, you're right. I would do this kind of project but it's more so being tired of the constant problems it has.
> like for one, i would love to mount it like a fender tube amp
> http://waynereno.net/images/back_of_amp.jpg
> but i do not know how it would sit on top of the cabinet without falling down..


Screws (bolts, actually) go through the top of the combo cab into the chassis (the metal part). Those bolts keep the chassis from falling down.

Same applies to a head cabinet, except the bolts come up from the bottom of the head cab, and keep the chassis from falling up 

PS - the bolts need to go in specific places, where the chassis has a threaded hole. You don't want to screw into a chassis at a random location. Won't turn out well.


----------

