Author Topic: Reasonably priced JCM900-alikes? (Read 9682 times)

Twinfan · « **Reply #15 on:** November 14, 2007, 08:59:51 AM »

Sounds like a dodgy valve base to me. Easy and cheap fix that the shop should do for.

Failing that, take it to Gee Electronics. They're in your neck of the woods and know valve amps.

Mr Ed · « **Reply #16 on:** November 14, 2007, 09:23:31 AM »

Cheers amigos, I'll have a look for Gee Electronics.

Do you reckon if it is a dodgy "valve base" as you chaps seem to think, the valve that's in there at the moment will be buggered, ie, would that just not be powering it at all or could it have blown it too? Sorry, I'm useless with ampage.

I've been eyeing more amps though... even once I get this fixed, the biasing thing is always gonna be a problem for me.

I've gone against myself and been looking at Boogies - F50's, DC-5's and DC-10's. :oops:

Twinfan · « **Reply #17 on:** November 14, 2007, 09:35:27 AM »

Yep, if the valve base has shorted out it'll cause bits of the valve to be connected that shouldn't be connected.

What do you mean when you say V1 "cr@pped out"? If it's black inside and rattles then it's plainly busted and you wouldn't be asking the question!

Mr Ed · « **Reply #18 on:** November 14, 2007, 09:48:37 AM »

It's not getting any power - I popped the back off and had a peek inside, turned all the lights off as it was running. Working on the principle of left ro right:

-- Pre-Amp ------------------ Power Amp

V1 | V2 | V3 -------------- V1 | V2| V3 | V4

The first pre-amp tube had no light so I figured was getting no power to it. With my lack of amp experience, I didn't know whether to point the finger of blame as tube or amp but you guys seem to be fingering the amp. Har har, fingering.

Hell, while I'm going I may as well ask the guy if there's any way he can permanently fix the bias on it.

Mr Ed · « **Reply #19 on:** November 14, 2007, 03:49:33 PM »

Hmmmmm. Like I say, I think I'm gonna speak to this amp dude next week and see if there's any way he can permanently bias the amp - in the Mesa Boogie fashion - without it effecting the tone or anything. If so, I'm sorted.

If not, I got some good news today... I've been given about a thousand pound from my Grandma as a sort of... nest egg, she's still alive like, and I'm tapping into £700 of it in order to pay my car insurance and then paying it back into this account over the next 12 months. Basically, I'm loaning off my own emergency fund.

So. That leaves me with about £300... if I was to sell the 900 (if the guy can't bias-fix it) then I'd have about £600 (post sale) to spend on a new amp... plus the possibility of a little extra if i get this promotion in work.

Come the new year... if things do (and don't) go my way, I could drop a grand on a beast.

FELINEGUITARS · « **Reply #20 on:** November 14, 2007, 04:00:09 PM »

Quote from: Mr Ed

Hmmmmm. Like I say, I think I'm gonna speak to this amp dude next week and see if there's any way he can permanently bias the amp - in the Mesa Boogie fashion - without it effecting the tone or anything. If so, I'm sorted.

If not, I got some good news today... I've been given about a thousand pound from my Grandma as a sort of... nest egg, she's still alive like, and I'm tapping into £700 of it in order to pay my car insurance and then paying it back into this account over the next 12 months. Basically, I'm loaning off my own emergency fund.

So. That leaves me with about £300... if I was to sell the 900 (if the guy can't bias-fix it) then I'd have about £600 (post sale) to spend on a new amp... plus the possibility of a little extra if i get this promotion in work.

Come the new year... if things do (and don't) go my way, I could drop a grand on a beast.

You should have Dakine's Knucklehead - such good amps!

You dont need a fixed bias like the Boogie but rather have the amp biased for a particular geade of tube - like Groove Tubes do and then you can swap outthe valves for similar graded ones with no changes required (in theory)

Mr Ed · « **Reply #21 on:** November 14, 2007, 04:10:14 PM »

Quote from: FELINEGUITARS

You should have Dakine's Knucklehead - such good amps!

You dont need a fixed bias like the Boogie but rather have the amp biased for a particular geade of tube - like Groove Tubes do and then you can swap outthe valves for similar graded ones with no changes required (in theory)

I wish! Knucklehead's make me damp.

So... if I was to have it biased for, say, a full set of 3+4 JJ tubes and I ONLY stuck with them, I'd never need it rebiasing?

Will · « **Reply #22 on:** November 14, 2007, 04:36:42 PM »

Preamp tubes don't need biasing.

and I don't think JJ do that. It would have to be a graded tube, like Groove Tubes do. If your amp is biased to a particular grade, in theory, you could buy that same grade with no need to have it rebiased....in theory (as feline said)

Mr Ed · « **Reply #23 on:** November 14, 2007, 04:41:15 PM »

I think I see what you mean, each brand of tube is graded differently and you only need to bias when moving between different grades.

Right.

Will · « **Reply #24 on:** November 14, 2007, 05:17:04 PM »

I think its only Groove that grade them

FELINEGUITARS · « **Reply #25 on:** November 14, 2007, 05:20:33 PM »

Have a look here for an explanation of the power tube grading

As said before Preamp tubes are not biased but are often graded for tonal characteristics etc

http://www.guitarxs.com/groovetubes/default.asp

Mr Ed · « **Reply #26 on:** November 15, 2007, 12:05:14 AM »

Oohhh I getcha mate.

After some calming down, I think the logical thing to do is get the valveplate looked at and fixed and spend a few hundred quid on a backup amp.

Now taking suggestions on that, hehe.

Twinfan · « **Reply #27 on:** November 15, 2007, 09:11:30 AM »

Backup?

Laney GH50L. No question. £250.

martinw · « **Reply #28 on:** November 15, 2007, 09:17:34 AM »

If you go to Hotrox or Watford Valves and buy a set of output valves, they will come with a number on the box, in mA.

If you bias for these valves, you can then order from HR or WV (others may do this too) a set of valves with the same number on the box, and fit them without biasing, as has been said.

There's nio reason why that amp shouldn't be reliable, given a good tech.

Mr Ed · « **Reply #29 on:** November 15, 2007, 09:53:02 AM »

Quote from: Twinfan

Backup?

Laney GH50L. No question. £250.

I have considered that, a lot... I would prefer a dual channel amp but if it's only gonna be backup, hmmmmm. I'm watching one on ebay, could really do with testing one out at some point to make sure it's gainy enough for a gain slut like me.

Plus, Gilberto uses 'em so that's a bloody good start, heh.

Quote from: martinw

If you go to Hotrox or Watford Valves and buy a set of output valves, they will come with a number on the box, in mA.

If you bias for these valves, you can then order from HR or WV (others may do this too) a set of valves with the same number on the box, and fit them without biasing, as has been said.

There's nio reason why that amp shouldn't be reliable, given a good tech.

AAAHHHH! Right, ok, that's the level of English explanation I need! NUMBERS ON BOXES!!

I'll be visiting a tech next week, christ knows how I'm gonna pay for it though but yeah...