Tube amp help needed

[RR_1525]

I found a nice tube head that I got for a song cause it was supposedly blown. I did some small repairs and low and behold it works. Only problem is one tube is bad I think. It gets hotter than the rest when I run it on full power, when on half power they all stay the same. It also has a blue looking spark in it on full power. Does this meen the tube is bad and if so, should I replace all the tubes including the 12ax7's? Can I just replace all 4 6L6's? Im sorry for the stupid questions, but I got this amp for a hundred bucks and its a Peavey Ultra+.

Thanks for any help you can offer.
Don

[Shotgun]

Re: Tube amp help needed

Not sure what you mean by full and half power, or how you know that the one tube is getting hotter than the others, but a blue tube could be either no big deal (dark blue?) or a bad / soon to be bad tube (light blue).

If the amp is otherwise operating, and doesn't have a problem that is causing power tube(s) to go bad, then yes, you can just change the power tubes if all the preamp tubes are good. Unless the amp is autobias, or fixed, you'll need to rebias.

You'll probably find R.G. Keen and his www.geofex.com Tube Amp FAQ to be a better resource on the subject than the good folks of the JCF. Maybe an Ultra+ owner with chime in?

Keith

[slayer]

Re: Tube amp help needed

Did you get that one form Ebay? I was going to try for that, but my electronics knowledge is nill [img]images/icons/grin.gif[/img] Congrats, I hope you get her working well. I have a Peavey Ultra 2x12 and they sound great!! Jack.

[taxistationary]

Re: Tube amp help needed

I always thought that if a tube was glowing any color blue, that it was a healthy sign for the tube and amp. The reason is, I bought a what seems to be untouched Peavey butcher from the 80's with the original tubes that all glow blue, so now I'm wondering about their state. Could someone explain? Thanks!

[nandrewjackson]

Re: Tube amp help needed

I'd have the powersection retubed.
It should only cost 60 bucks for the tubes, and possibly a 30 or 40 dollar charge for the bench fee/ biasing fee.

It would be worth it.
The oddly glowing tube could indicate that the tubes aren't matched correctly, or that the bias is screwy.

If you have it tubed and biased, and over a short time 10 or more hours of playing, another tube starts looking different, , then you probably have a bit more in depth problem with the amp, but if it is working at all, It can't be that bad.
(not to mention you got the amp for 100 bucks!!)

nandrew

[Matt]

Re: Tube amp help needed

Originally posted by john:
I always thought that if a tube was glowing any color blue, that it was a healthy sign for the tube and amp. The reason is, I bought a what seems to be untouched Peavey butcher from the 80's with the original tubes that all glow blue, so now I'm wondering about their state. Could someone explain? Thanks!

<font size="2" face="Verdana, Helvetica, sans-serif">It depends. Most often a blue glow is fine. A couple of my amps have a light blue glow to them and there is nothing wrong with them. I dont think you want to entire tube to glow blue but a nice blue glow between the plates is fine.

[Cleveland Metal]

Re: Tube amp help needed

Blue is generally cool, it's the cobalt metals in the tubes flourescing a bit under effect of the electrons bouncing off the parts inside. Different tubes show more blue than others. Purplish, is not cool, could be impending failure looming in the distance or a gassy tube.

If it sounds funny, or is noticeably different in coloration than the others, I'd probably contemplate retubing and biasing as mentioned earlier.

[Twisteramps]

Re: Tube amp help needed

When you're running it at 1/2 power, it's only using one pair of the tubes... so when you go full power, it's using all four.

Swap the 'bad' tube with another one. See if the problem stays in the socket (amp problem) or follows the tube (tube problem).

If it's a tube problem, get a new set. If it's an amp problem, go see a tech. Please don't email me for a guide to getting into the guts, because the last choad who did cursed me out when I didn't give him a lengthy discourse/free tube amp seminar.

Pete

[RR_1525]

Re: Tube amp help needed

OK, let me try to eplain more now that Ive looked at it better. On the fromt of the amp it has a selector swith to run it at 60 watts or 120 watts output. If I leave it set at 60 watts output all 4 power tubes light up dull orange and look the same. When I switch it to 120 watts out, one tube gets white hot and shows light blue plasmaspark(dont know the term for it).

Anyway, the same tube does it in all 4 sockets and none of the other do it anywhere.

As far as getting this one off the bay, A friend of mine locally bought this one new and left it in the back of his jeep till it quit qorking and then decided he didnt really want it so I picked it up for 100 bucks. I took everything out and fixed it and the only problem is that one tube.

[Shotgun]

Re: Tube amp help needed

Since Don already said "the same tube does it in all 4 sockets and none of the other do it anywhere" the it is safe to say that it is the tube. So if a re-tube and bias doesn't straighten it all out, you won't find a more competent, friendlier guru (via computer) than Mr. Keen @ geofex.com.

Keith

[ February 02, 2004, 02:06 PM: Message edited by: Ralph E. ]

[Twisteramps]

Re: Tube amp help needed

I replied when I read the first message - it was late, just threw in my 2 cents. FYI, 'autobias' is really cathode biasing. THD tries to make one believe they reinvented the wheel, but it's just cathode biasing which is cheaper and much simpler than fixed.

Also, 'fixed' bias is the same as 'adjustable' bias - adjustable just means they put a potentiometer in the circuit to fine tune the amount of voltage. It's entirely possible in a 'fixed' bias non-adjustable amp to get tubes that will run way too hot ot cold. that's when you need to solder in a resistor or a bias pot... I had to do this to a '68 princeton because the original resistor had aged off spec.

By all means, he should consult anyone who would know the answer with his question... but it's 99% likely the tube. I'd just warn him of saying stuff like "fuck you" to someone when they don't like their answers.

Pete

[ February 02, 2004, 02:07 PM: Message edited by: Ralph E. ]

[Ralph E.]

Re: Tube amp help needed

Err.. [img]graemlins/scratchhead.gif[/img] this was a thread about tube amp help, right?

R

[Shawn Lutz]

Re: Tube amp help needed

now, now boys...play nice or you'll get a time out! [img]images/icons/grin.gif[/img]

[Boxcar Willie 84]

Re: Tube amp help needed

Jesus H Christ!! Live and let die fellas!! It's over with!