#1
So, I've pretty much settled on a Jet City JCA20H for my next amp sometime this summer, once I get the cash for it. However, I've got a couple questions.

First, for tube amps in general: how bad would it be to have an amp played without a cabinet hooked up for a few seconds or so? The JCA I tried at a Guitar Center originally didnt have a cable connecting the two, and while I stole one from the HT-5 right next to it, I have no idea how many people tried to play it without noticing. I've read on here that it could damage the amp, but is that over an extended period? Or would four or five people flipping the switches, trying to play a chord, and then turning the amp off cause some permanent problems?

And second, related to that: would most Guitar Centers have more, unused amps in the back? I'm aware tubes wear out, and coupled with the potential problems above, I plan on asking to see if they could bring another JCA20H and 12S cabinet out. Is that something they're likely to have? I've played the display amp a few times, and I don't think it's a different one, since it hasn't moved and there's another head on top of the half stack. But could I get a fresh one in-store, or would I just be better off ordering from Musicians Friend or Amazon or a similar site?

Finally, tube-related: I have no idea what a tube amp requires in terms of upkeep. I know to let it warm up for 30sec before flipping it off of standby so I can play, but in terms of tube replacement (and other stuff I don't even know about) I'm pretty much clueless. It's got 12AX7s and EL84s in it stock; a bit of research has shown that a bunch of companies make replacements. If a tube goes bad (or whatever happens to them), do I just order from anywhere and pop the replacement in, or should I take it to a tech to get that done?

Thanks in advance for helping out a tube noob.
#2
1. Firstly, yeah it's a really bad thing to play a tube amp without a speaker load connected. For a few seconds or so, though, it shouldn't do much damage. However, if you crank the amp wide open and start hammering away on your guitar, you'll blow the output transformer quite easily.

2. Yeah they should have some more in stock out the back. And if they don't, you can get a discount off the floor stock. Plus you'll have full warranty, and if something's screwed up with the amp, you can take it back and have it replaced.

3. It all depends on how often you play your amp. Generally, if you're playing every day for a couple of hours, poweramp tubes can last for 6 months to a year, and preamp tubes can last for 4 years +. And www.eurotubes.com is a great place to get tubes from. They have tube sets for particular amps too.

And swapping tubes is pretty easy. Just make sure you don't touch the glass with your bare hands, as oil from your hands will get on the glass and there's a risk of the oil burning and cracking the glass as the tube heats up. And you'll have to learn how to bias your tubes as well - there are heaps of tutorials on the internet, and the equipment needed is quite cheap.
Last edited by NakedInTheRain at May 16, 2011,
#3
I dont trust stuff from in the store sold as new, i order from sweetwater personally. They gave me free candy + free NICE guitar picks with my ht-5 head. They have the best customer service IMO they ship ultra fast and free. Even if something costs a bit more from there (which it doesnt) id still buy from there. Great company IMO And yes a floor model tube head at gcenter, people probably dont even use the standbye and such on tube amps.
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#4
Retro: didn't even think about that, actually, in terms of how people (ab)use those amps. Buying from Musician's Friend instead is starting to look a bit better. What's the shipping like, though? I doubt they'll just overnight a 40lbs, 2-foot-tall package to my front door...

Naked: thanks. Now, some follow-ups if you don't mind. Is there any real way for me to tell if the transformer's shot? It played just fine while I was putting it through its paces, but should I take it into the loud room and really crank it, or does that mean it's probably okay? And regarding biasing, will that have to be done every time, or are there certain tubes I could literally just drop in? The amp supposedly has a fixed bias, but I'm not sure how that affects things.
#5
The only real way to tell is to A/B it with another perfectly functioning model, or to have it tested. But if it still sounds great and gets up to high volumes without sputtering or anything like that, I'd say you're fine. But ask for a new model from out the back anyway, or have them order one in if you don't mind waiting. Better to be on the safe side.

And the Jet City has a bias trimpot. This means you can set the bias. The reason it's called fixed bias is that it's a 'set and forget' bias which is 'fixed' by you (until you change power tubes, in which case you check the bias and adjust if needed). There is also non-adjustable fixed bias (which is probably what you're thinking of) but we won't get into that. And cathode bias is essentially when the power tubes bias themselves. See this thread for more details if you're interested in learning about the different types of bias.
#6
Yeah, I'll probably just end up asking for a fresh one. And thanks for clearing up the bias thing, I was wondering if "fixed" had a new meaning once I started seeing people changing their biases in the JCA thread. I'll look at the thread you gave me over breakfast, I'm sure it'll be more than helpful.
#7
Quote by horser4dish
Yeah, I'll probably just end up asking for a fresh one. And thanks for clearing up the bias thing, I was wondering if "fixed" had a new meaning once I started seeing people changing their biases in the JCA thread. I'll look at the thread you gave me over breakfast, I'm sure it'll be more than helpful.


Just as an FYI - In most cases, if you ask the GC salesperson, they'll send you home with the floor model while the new one is shipped in (if they dont have one on-hand).
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#8
Quote by NakedInTheRain
1. Firstly, yeah it's a really bad thing to play a tube amp without a speaker load connected. For a few seconds or so, though, it shouldn't do much damage. However, if you crank the amp wide open and start hammering away on your guitar, you'll blow the output transformer quite easily.

2. Yeah they should have some more in stock out the back. And if they don't, you can get a discount off the floor stock. Plus you'll have full warranty, and if something's screwed up with the amp, you can take it back and have it replaced.

3. It all depends on how often you play your amp. Generally, if you're playing every day for a couple of hours, poweramp tubes can last for 6 months to a year, and preamp tubes can last for 4 years +. And www.eurotubes.com is a great place to get tubes from. They have tube sets for particular amps too.

And swapping tubes is pretty easy. Just make sure you don't touch the glass with your bare hands, as oil from your hands will get on the glass and there's a risk of the oil burning and cracking the glass as the tube heats up. And you'll have to learn how to bias your tubes as well - there are heaps of tutorials on the internet, and the equipment needed is quite cheap.


bolded text completely untrue. don't spread heresay.

to the OP, there really isn't much that goes into maintence, just warm it up for 30 secs to 1 min, and play.

when you do replace tubes, i strongly recommend picking up some deoxit, its a contact cleaner type thing, and you spray it on the tube, and work it in and out a little bit and then set the tube in, that helps everything stay happy and healthy. it costs $11 at radioshack and will last you quite a long time, and can also be used on jacks, switches, and pots too if you ever were to develop a problem with one of those on that amp or something else.
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#9
LEPIV: Thanks for the heads-up. That was the one thing I didn't like about ordering one: the wait. But if GC will (possibly) loan me the floor model until mine comes in, well, that's sort of the best of both worlds there. Instant gratification and I get a brand new one.

trashed: So it's perfectly safe to handle the glass, or that's not the specific problem? I hadn't intended on, like, groping them or anything prior to installing the tubes, but what you're saying is I don't need to treat them like sacred relics, as long as I'm not careless? And I'll be sure to pick up some DeOxit when I get the amp, I could definitely see how it would at least be a good safeguard against problems.

Naked: That thread was helpful, I have at least a basic idea of what you're talking about. But you still didn't totally answer my question: are there any tubes I can just drop in, no biasing required? Or will I have to make some adjustments no matter what I replace them with?
Last edited by horser4dish at May 17, 2011,
#10
Quote by horser4dish
LEPIV: Thanks for the heads-up. That was the one thing I didn't like about ordering one: the wait. But if GC will (possibly) loan me the floor model until mine comes in, well, that's sort of the best of both worlds there. Instant gratification and I get a brand new one.

trashed: So it's perfectly safe to handle the glass, or that's not the specific problem? I hadn't intended on, like, groping them or anything prior to installing the tubes, but what you're saying is I don't need to treat them like sacred relics, as long as I'm not careless? And I'll be sure to pick up some DeOxit when I get the amp, I could definitely see how it would at least be a good safeguard against problems.
Naked: That thread was helpful, I have at least a basic idea of what you're talking about. But you still didn't totally answer my question: are there any tubes I can just drop in, no biasing required? Or will I have to make some adjustments no matter what I replace them with?


you could molest them all you want, you are not going to shorten the life of the tube at all. obviously i wouldn't toss a tube to your buddy from accross the room, or leave them lying around on the floor to get stepped on, but oil on the glass of the tube WILL NOT do anything. it will simply burn off within a minute or so of use.
WTLT 2014 GG&A

Quote by andersondb7
alright "king of the guitar forum"


Quote by trashedlostfdup
nope i am "GOD of the guitar forum" i think that fits me better.


Quote by andersondb7
youre just being a jerk man.



****** NEW NEW NEW!
2017-07-07 2017-07-07 Update and a Chat On Noise Constraints *** NEW FRIDAY 7/7
2017-04-13 RUN AWAY from COMPUTERS!!! TCE? RANT ALERT!!!
2017-03-02 - Guitar Philosophy 1001- Be Prepared For the Situation (Thursday 2017-03-02)
2017-02-21 How to Hot-Rod the Hell of your Stratocaster for $50! (Tuesday 2017-2-21)
Resentments and Rambling from a Guitar Junkie
---> http://trashedengineering.blogspot.com/