Goodbye Valve... Goodbye Valveking...

[GuitarIv]

Well... just an hour ago something happened to me that probably every guitarist with a tube amp experiences in his lifetime at least once: a Valve in my Amp blew up.

It was less something blowing up than me playing my stuff and suddenly recognizing a drop in gain and tone. It became thin and less and less distorted until I noticed that it couldn't be a faulty cable. 1 of the 4 Valves wasn't glowing anymore, so I turned the amp off and the disconnected it.

Now why I am posting this thread is I have a question: should I get the amp fixed? It's a Peavey Valveking 100, the price is somewhere around 400€ new and I know replacing the tubes costs me at least 100€ for the quartet, not talking about what the amp builder gets for his work. I currently have an Orange Micro Terror and my 4*12 Cab, coupled with my Tubescreamer it certainly has enough tone to do the trick, I'm currently not playing any gigs and just writing stuff together with my bassist in our rehearsal room at the moment.

I've been flirting with the EVH 5150 III 50 Watt for quite a long time by now and it certainly has everything concerning tone I'll ever need. 900€.

Opinions? Is the Valveking worth it to blow 200€ for a repair or should I just live with my Micro Terror until I can afford the EVH?

Cheers

[Keven]

I should mention that the ValveKings are fixed Bias so popping in another matched quartet of 6L6GC should do the trick without an amp tech. assuming the amp suffered no damage in the tube death process.

just a thought.

[gordiji]

I'm going to probably show my ignorance here as my understanding is that 'fixed bias' amps Do need adjusting on replacing tubes (counterintuitive as it sounds) in order to maintain a fixed output voltage.
Cathode bias (class A) are the ones that 'bias ' themselves'

Fixed bias includes peaveys, marshalls fenders ,
Cathode bias  Vox Ac 30, tiny terror range
 
If i where you i'd fix it, go to eurotubes (in us!) order your tubes and a cheap meter and biasrite(tube measuring sockets) follow the instructions on their website to bias it yourself. I did and my amps fine since and i won't be scared next time.If i remember rightly the meter and tubesockets only cost about 30€

[Tellboy]

Occasional valve failure/fatique/replacement unfortunately is par for the course for all valve amps. The same would apply to the 5150 if you get it. Presumably if you decide you want the 5150 you would sell or trade in your Valveking - in which case you would have to get it in working condition by replacing the valves (or knocking the cost of replacement off the trade in price).

[dave_mc]

I'm going to probably show my ignorance here as my understanding is that 'fixed bias' amps Do need adjusting on replacing tubes (counterintuitive as it sounds) in order to maintain a fixed output voltage.
Cathode bias (class A) are the ones that 'bias ' themselves'

yep- as far as i'm aware, anyway.

though you can also get non-adjustable fixed bias, which does muddy the waters somewhat...

[GuitarIv]

Well, I'm actually the 3rd owner of the amp and I'm pretty sure it never has gotten any tube swap or any check whatsoever, so this was predictable. However I've been looking for a new amp for a long time by now, so this may be the excuse to get one :P

About the DIY approach: I'm actually pretty shy when it comes to amps. I know my way around guitars, but never opened an amp before and as I know one may fry himself in the process, right? I think I will take a look at the fuse if it's still ok and then think about my next step, right now I'm still saving up money, so in the meantime I guess doing some reading on the matter of amps shouldn't hurt. Any sites, helpful guides I can look up? This may be the right time to get to know tubeamps better :)

[BigB]

About the DIY approach: I'm actually pretty shy when it comes to amps. I know my way around guitars, but never opened an amp before and as I know one may fry himself in the process, right?

You don't need to open the amp to change tubes.

wrt/ the frying part, yes, the big filtering caps store some potentially lethal DC current for sometimes, so you have to take care if and when you have something to do inside the amp. If you do it frequently then you probably have the (very simple) required tooling to discharge these caps when needed, but there are some simple security rules that are enough to not get fried:
 
1/ wear rubber sole shoes and/or stand on a rubber carpet
2/ _always_ keep one hand in your pocket
3/ make sure the place is free and clean so you won't trip on something

I think I will take a look at the fuse if it's still ok and then think about my next step, right now I'm still saving up money, so in the meantime I guess doing some reading on the matter of amps shouldn't hurt. Any sites, helpful guides I can look up? This may be the right time to get to know tubeamps better :)

You'll find some very good material on the ax84 project (specially in the P1 docs), and on Randall Aikens and Valvewizard's sites:

- http://www.ax84.com/p1.html
- http://www.aikenamps.com/TechInfo.htm
- http://www.valvewizard.co.uk/

[jpfamps]

I think we have reached a fairly dismal situation when people consider revalving an amp as "uneconomic".

[Keven]

iirc the ValveKing i retubed has no bias trimpot whatsoever on the insides. make your research but i'm fairly certain that's what the Peavey tech told me on the phone when a buddy of mine had problems with his VK. we just swapped the tubes with a new pair and the amp ran fine. still does :) maybe fixed bias isn't the correct word though!

[38thBeatle]

I've never thought about changing an amp merely due to a valve failure. It would be like buying a new car because I need a couple of new tyres ( well not quite but you know what I mean).Of course it might be that you have hankered after a new amp for a while and this is just a catalyst. Personally I'd buy a replacement valve if I was sure that one was faulty.

[Telerocker]

I've never thought about changing an amp merely due to a valve failure. It would be like buying a new car because I need a couple of new tyres ( well not quite but you know what I mean).Of course it might be that you have hankered after a new amp for a while and this is just a catalyst. Personally I'd buy a replacement valve if I was sure that one was faulty.

+1

[GuitarIv]

Don't get me wrong here guys, I'm the absolute opposite of the "it's not working anymore, let's throw it away and buy a new one" mentality. Fact is that I am going to get myself an EVH 5150 sooner or later, fact is that my Micro Terror can help me out here and fact is that I don't need to hurry with the repair of the VK. That's why I'm opening up this thread here, I want your opinions and I'd be most happy if I could indeed just get a matched quartet of 6L6GC, pop em in and be ready to go. :)

The thing is until now, I never was really into amps. Maybe because the VK satisfied all my needs until a certain point, maybe because I wasn't chasing the perfect tone until recently, maybe because I never had the budget to get myself a new one. So this might be a good excuse to catch up. I'll read my way through the different guides and sites, mail Peavey directly and see what I can do. Thanks for all the help so far!

[Dmoney]

The amp is non-adjustable fixed bias. Like the 5150 and Dual Rec and probably countless others.

Peavey and Mesa used to sell (or still do sell) their own valves which in Peavey's case would be JJ's. They either set a cold bias the amps to err on the side of caution while increasing ease of maintenance, or they do this and suggest you buy matched branded valves that have been tested to work within a given set of parameters (the plate voltage and the bias voltage etc).

I know people who have run amps with dead power valves without even knowing they had an issue. Specifically a 5150. The orange filament glow has no relation to how well the valve is working. It could be useless but still glowing orange. If it isn't glowing orange at all then that is probably a bad sign too. It is hard however to see the filament glow on some valves.

If the valve died in the amp and there is no glow, I'd suggest getting the whole thing looked at. You could find a cheap quartet of valves to put in, after all, there will be no bias adjustment... however a failing valve can cause other parts of the amp to expire. Screen resistors my burn up and short out or the high voltage can end up on the filament circuit and various things can end up fried. You won't be able to tell if anything like that is wrong without opening the amp and doing a few checks. You could be in a situation that you have a dead socket for example, and you put in new valves, they all glow, but one won't be working at all.

If there isn't anything wrong inside the amp it shouldn't take a tech any real length of time to take a look and put new valves in. If they charge for 1hr's work minimum then that should be more than enough time. Remember a tech should have all the correct tools for the job already. I also don't see any bleed resistor in the HT supply on the valveking schem I have here and poking around the octal sockets will expose you the high voltages in the amp unless you can discharge the caps with a discharge lead.

[GuitarIv]

Thank you Dmoney. I guess I will just take it to the tech... I'm kinda intimidated by the various things that could be wrong/fryed. :/

[darkbluemurder]

I'm going to probably show my ignorance here as my understanding is that 'fixed bias' amps Do need adjusting on replacing tubes (counterintuitive as it sounds) in order to maintain a fixed output voltage.
Cathode bias (class A) are the ones that 'bias ' themselves'

You are absolutely correct - no sign of ignorance anywhere.

One prerequisite for a power tube to work is that the cathode must be at a higher voltage than the control grid (the one carrying the guitar signal). In a cathode biased amp the cathode is at approx. 10V to 30V positive whereas the grid is at 0V. The tube finds its operating point itself - that's why cathode bias is also referred to as "self bias". All preamp tubes are biased this way, too.

In the fixed bias scenario, the cathode is grounded, i.e. at 0V. In order to work we need to apply a negative voltage to the control grid of the tube (usually in the range of approx. -25V to -55V). This voltage is "fixed" in the sense as it does not vary when a signal is superimposed on it. In most amps you can adjust how much negative voltage is applied to the control grid by a pot - that would then be called "adjustable fixed bias" as opposed to say Mesa Engineering and older Hiwatts which do not have such adjustment option - that would be "non-adjustable fixed bias.  

Now why can't/shouldn't you change tubes in a fixed biased amp without checking the bias? The idle current drawn by the new tube could be higher than with the old one and be too high with the negative voltage applied to the control grid. Which means that the tube may suffer an early and untimely death. To avoid that, more negative voltage must be applied to the control grid - that's what the tech does by adjusting the pot in an adjustable fixed biased amp.

Now how do I get by in a non-adjustable fixed biased amp? Either the factory applied so much negative voltage (i.e. bias the amp really cold) that it is unlikely that a tube will ever draw too much idle current (that's what Mesa Engineering does), or you have to change the bias circuitry of the amp by changing a resistor.  

BTW: cathode biased amps can be biased too hot and kill tubes prematurely as well (e.g. Vox and Matchless amps are well known for that). If too many tubes were killed or shortlived in such an amp, the necessary bias adjustment is to make the cathode resistor bigger.

Cheers Stephan