#1
So I'm going to check out an amp in a few days, it's a Marshall JCM900 50W halfstack. . To be honest, I've never had a tube amp before. I decided that I'd rather wait and go all the way with my purchase than get something that is just a small improvement, so I've been saving for the past year or so.

But I need to know: what are some things that I should check to verify the quality of said amp, and make sure it's not a ripoff or a piece of ****?

Also, since it's a halfstack, how can I make sure that the cab is genuinely a JCM900 (or does it not even work like that?).

I'm woefully ignorant of everything amp-related, so I want to know everything that I should check.

Humbly,
Commodity

Also, I've read the Ultimate Gear Sticky and searchbar'ed aaaand googled.

Thanks
Creator of the Llamastack


#2
I don't know much about the amp, but I saw one at my local pawn shop yesterday for $500.

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My rig is simple
Haha. UG's Chuck just said chuck. haha
You're not truly playing guitar unless you know theory.
#3
Just plug in, and test it out. Mess with all the nobs, look out for scratchy or broken pots. If you find them they're a pretty easy fix, but you should be able to knock some off the price if they are there.

The cab, if it is a Marshall cab should have a plate in one of the corners showing what model it is. It may not be a Marshall cab though, it doesn't matter. They don't need to be the same brand.

Ask some questions like, how old is it? where did the previous owner buy it? have they had trouble with it before? has it been retubed or biased lately? etc...

If you can take someone else who knows their guitar equipment with you, that would be helpful too.

Good luck, and I hope you enjoy the amp!

Edit: don't pay too much for it, I wouldn't pay much more than $700-$850 for the whole halfstack. It's totally up to you, but that's about the typical price of a JCM 900 plus cab.
Tele - EP Booster - DLS - Big Muff - Ekko 616 - Rocker 30/AC15
Last edited by Hesh_09 at Jul 13, 2009,
#4
as far as the cab goes, it doesn't matter whether it is Marshall or not. You can use whatever cab you want. be creative.
"If A is a success in life, then A equals x + y + z. Work = x; y = play; and z = keeping your mouth shut."
--Einstein

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--Einstein
#5
First off, whether the cab is a 900 or not is irrelevant, unless you really care what it says on it. As long as you enjoy the appearance and it sounds good with the head, I'd go with it.

After the amp warms up, I like to play a single chord like G and fiddle with every knob to make sure there are no dirty pots. If there are, try to talk down the price. Also, make sure both inputs give you a signal, if the particular model you're testing has two inputs.

It's usually good to borrow a pedal from the seller to test the loop.

As far as the hardware goes, open up the back and check the transformers and chassis for signs of rust. Some people like storing their gear in damp basements and it can wreak havoc on the innards. Try to talk down the price a tad if present.

While the back is open, make sure the power tubes are working properly (no red-plating) and tap the preamp tubes with a pencil eraser to check for microphonics. Ask when the last time the tubes and filter capacitors were changed. If the answer is "I don't know" or over 10 years, try to talk the price down a touch because you'll probably need a cap change soon.

Finally, when I test a tube amp, I like to ask the seller's permission to crank it to at least 6 so I can really push the speakers and see what the amp can do. Testing it at like 2 Master isn't going to give you a good idea of what kind of tonal capability it possesses.

Good luck!
Everyone is entitled to an opinion.

Feel free to express yours so I can make an informed judgement about how stupid you are.
#6
Quote by bubb_tubbs
First off, whether the cab is a 900 or not is irrelevant, unless you really care what it says on it. As long as you enjoy the appearance and it sounds good with the head, I'd go with it.


I'm not a brand *****, I was just curious

After the amp warms up, I like to play a single chord like G and fiddle with every knob to make sure there are no dirty pots. If there are, try to talk down the price. Also, make sure both inputs give you a signal, if the particular model you're testing has two inputs.


How would I detect a dirty pot? Would it just be a significant tonal change, or lack thereof?

It's usually good to borrow a pedal from the seller to test the loop.


*feeling noob* What does that mean and how would I do it? ( I don't own a pedal, I predominantly play unplugged )


tap the preamp tubes with a pencil eraser to check for microphonics.


What exactly would happen if there were?

Good luck!

Thanks
Creator of the Llamastack


#7
Quote by Commodity
I'm not a brand *****, I was just curious


How would I detect a dirty pot? Would it just be a significant tonal change, or lack thereof?

You'll hear scratching when you turn it


*feeling noob* What does that mean and how would I do it? ( I don't own a pedal, I predominantly play unplugged )

Google it. If you don't know what an FX loop is you probably gonna wanna bring a friend who is knowledgeable if you have one.


What exactly would happen if there were?

You'll hear the tapping through the amp. This isn't terrible, but it does mean that tube is bad. Talk some money off for this


Thanks


I don't give a shit if you listen to me or not
#8
Quote by Commodity
I'm not a brand *****, I was just curious


Quote by Commodity
How would I detect a dirty pot? Would it just be a significant tonal change, or lack thereof?

Horrible scratchy sounds emanating from the speakers as you turn the knobs. It means there's a bad connection in areas because of oxidation or crud in the pot (for want of a better term).

Quote by Commodity
*feeling noob* What does that mean and how would I do it? ( I don't own a pedal, I predominantly play unplugged )

Borrow a pedal from the seller if he owns one - preferably a delay or reverb because they're easy to track the effects - and see if the loop is functioning properly (i.e. no tone loss with stuff plugged in vs no pedals in the loop).

Quote by Commodity
What exactly would happen if there were?

Rattling/humming sounds emanating from the speakers after you tap it.

http://www.tubedepot.com/microphonics.html if you want a video on it.

Quote by Commodity
Thanks
Don't mention it. Good luck testing.
Everyone is entitled to an opinion.

Feel free to express yours so I can make an informed judgement about how stupid you are.
#9
Quote by Hesh_09
If you can take someone else who knows their guitar equipment with you, that would be helpful too.


bingo. for a complete amp noob (no offense) this is your best defense.
#10
Quote by GrisKy
bingo. for a complete amp noob (no offense) this is your best defense.



Yes, I wish I'd had some help when I made my first purchase. First time I went to GC looking for an electric guitar I ended up with a Squier Affinity strat and a fender FM10
I don't give a shit if you listen to me or not
#11
JCM 900 is a great amp, I would just check out everything, play it at low levels and loud levels and make sure that you like the tone, if you try it and don't like it than don't buy it.

Nice choice.
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right Metallica is a given. Personally I like to pretend the bus exploded and killed them all in '86.

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