#1
I'm sure I'll have to take it to the shop to be fixed, but I just can't stop wondering what exactly is wrong with my amp. So I come to the experts here at UG to ease my curiosity...and my worry for my wallet.

It's a Peavey VB-2 bass amp. 2 12ax7 tubes 1 12au7 tube, and 6 EL34 tubes. Recently replaced with E34L tubes. All JJ tubes.

HISTORY: Back when my amp had the original tubes I blew a couple fuses. Always the same one, the one on the circuit board inside the amp instead of the main one on the back of the amp. Once it blew 2 of my preamp tubes. V2 and the driver tube...i guess that'd be V3?(i don't get into this much) I took it in to have those replaced and see if he could figure out what was causing this. The tech said there was nothing wrong with my amp(of course) and was actually nice enough to install a little thing on the circuit board to make it easier to switch out fuses, since i kept having to solder them to the board. yup...soldered it to the board, good thinking peavey >.>

Recent: It worked for a good bit, but i was very careful with it. I always kept the gain at 4 or below. I plugged into the low gain input. I finally got bored with my tone one day and decided to play around. had the gain at about 7 but turned my bass(instrument, not eq) down to compensate. try to get more of the tube preamp's sound than my bass. It blew that same fuse. Replaced the fuse and started fiddling again. Fuse blew taking out at least 1 preamp tube as it wasn't glowing anymore before i turned the amp all the way off.

I can crank the power section to 10 and it gets all raunchy from the power tubes being highly overdriven but it doesn't hurt the amp. Only if i turn up the preamp.

TL;DR and conclusion: what could possible be wrong with a tube amp that keeps blowing a fuse that is apparently saving my power section(even when i replaced the power tubes it was from old age, i've never had a power tube go out) but still taking out my preamp tubes when i try to turn the gain above 5-6?
dean edge one 5 string
Schecter studio-4
Samick fairlane-6
Ibanez sb900
Ibanez btb775
Fender p bass special deluxe

Dean Del Sol
Ibanez prestige rg2610

Peavey TKO 65
Peavey vb-2
Quote by the_perdestrian
listen to revelation, for he is wise in the way of bass-fu
#3
First did you check the biasing when you replaced the power valves?
However, it sounds to me like a dead preamp valve. Try replacing them.
Do them one at a time and test each time so you know which one was actually faulty. That way you can keep the others as spares.
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
Last edited by Cathbard at Jul 30, 2010,
#4
I've replaced all the preamp tubes before. it's done it many times. it did it with the old power amp tubes and i've replaced them and had it biased and it still does it.

All tubes are a healthy orange,except,of course, the one that blew this last time it blew the fuse.

you guys think i've been unlucky enough to blow 3 preamp valves in less than 2 years(or is it 3 years...can't remember exactly when i bought the amp) but have no problems with my power tubes?

I do not overdrive my amp on a regular basis at all. When my band cover's Rush's "Tom Sawyer" I do use my treble knob as a boost but it's just for a bit then it goes back to normal. I can't imagine how this would cause me to go through preamp tubes so fast when guitarists can overdrive their tubes all day for a lot longer than my amp is managing.
dean edge one 5 string
Schecter studio-4
Samick fairlane-6
Ibanez sb900
Ibanez btb775
Fender p bass special deluxe

Dean Del Sol
Ibanez prestige rg2610

Peavey TKO 65
Peavey vb-2
Quote by the_perdestrian
listen to revelation, for he is wise in the way of bass-fu
Last edited by Revelation at Jul 30, 2010,
#6
At this point I'd be checking voltages throughout the amp. I aint going to try to walk you through that but it's about the only thing you can do => take it to another tech.
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
#7
called the only other store other than guitar center within 100 miles. they send it out instead of doing it in the store but it'll have to do. Hope it's nothing expensive
dean edge one 5 string
Schecter studio-4
Samick fairlane-6
Ibanez sb900
Ibanez btb775
Fender p bass special deluxe

Dean Del Sol
Ibanez prestige rg2610

Peavey TKO 65
Peavey vb-2
Quote by the_perdestrian
listen to revelation, for he is wise in the way of bass-fu
#12
Quote by forsaknazrael
You were asking Guitar Center for tech help, before hand?

Put an ad on Craigslist, maybe there's a closer tech.


GOD NO! I'm avoiding them. if this doesn't work...i dunno. i'll prolly end up selling it as a broken amp
dean edge one 5 string
Schecter studio-4
Samick fairlane-6
Ibanez sb900
Ibanez btb775
Fender p bass special deluxe

Dean Del Sol
Ibanez prestige rg2610

Peavey TKO 65
Peavey vb-2
Quote by the_perdestrian
listen to revelation, for he is wise in the way of bass-fu
#13
^I'd try craigslist. There may be a guy who is a good tech, or knows his way around amps, just doesn't run a shop.

Quote by ethan_hanus
I've seen people buy whole new preamps and power amps for their amps before, one guy did it with a elgnator or whatever they are called.

Some Egnators have preamp modules....that's why he was able to.....
#14
Quote by forsaknazrael
^I'd try craigslist. There may be a guy who is a good tech, or knows his way around amps, just doesn't run a shop.


Some Egnators have preamp modules....that's why he was able to.....


The question is, do i really want to pay to have an amp "fixed" a third time...or should i just ditch it like a crappy car.
dean edge one 5 string
Schecter studio-4
Samick fairlane-6
Ibanez sb900
Ibanez btb775
Fender p bass special deluxe

Dean Del Sol
Ibanez prestige rg2610

Peavey TKO 65
Peavey vb-2
Quote by the_perdestrian
listen to revelation, for he is wise in the way of bass-fu
#16
^that does sound cool actually...

Quote by forsaknazrael
^I'd try craigslist. There may be a guy who is a good tech, or knows his way around amps, just doesn't run a shop.


Some Egnators have preamp modules....that's why he was able to.....



Big Fat + 1

look on Clist under services or start your own post in Services and Musical Instruments.

Egnator rocks

Also, if you feel like you've been duped and they keep ****ing Up then call and demand satisfaction and ask if you can take it to their service place yourself on an expedite and have them pay for it all.

Otherwise, ditch 'em like a crappy car and move on

My limited knowledge tells me the amp is biased wrong as mentioned.
#17
I can only hope it's incorrectly biased, because then I can call the guy who put the tubes in and biased it and really rip him one...i played my bass through a seventy something plexi at the last show...you know how hard it is to get a bass tone I like out of a guitar head? even if it is an AWESOME old guitar head. all original tubes etc btw I'm amazed they still work really, I'd love to hear it with fresh tubes. it just sits in the corner at practice.
dean edge one 5 string
Schecter studio-4
Samick fairlane-6
Ibanez sb900
Ibanez btb775
Fender p bass special deluxe

Dean Del Sol
Ibanez prestige rg2610

Peavey TKO 65
Peavey vb-2
Quote by the_perdestrian
listen to revelation, for he is wise in the way of bass-fu
#19
I have a multimeter around actually. any idea where i stick the end probes to get that plate voltage reading?
dean edge one 5 string
Schecter studio-4
Samick fairlane-6
Ibanez sb900
Ibanez btb775
Fender p bass special deluxe

Dean Del Sol
Ibanez prestige rg2610

Peavey TKO 65
Peavey vb-2
Quote by the_perdestrian
listen to revelation, for he is wise in the way of bass-fu
#21
http://www.peavey.com/assets/literature/manuals/03595970_4.pdf

page 15 is a block diagram and a bit down from there is a layout of the tube sockets, as seen from above.
dean edge one 5 string
Schecter studio-4
Samick fairlane-6
Ibanez sb900
Ibanez btb775
Fender p bass special deluxe

Dean Del Sol
Ibanez prestige rg2610

Peavey TKO 65
Peavey vb-2
Quote by the_perdestrian
listen to revelation, for he is wise in the way of bass-fu
#22
Quote by Revelation
I have a multimeter around actually. any idea where i stick the end probes to get that plate voltage reading?

Pin 3
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
#24
Quote by Cathbard
Pin 3


Feel like elaborating?
dean edge one 5 string
Schecter studio-4
Samick fairlane-6
Ibanez sb900
Ibanez btb775
Fender p bass special deluxe

Dean Del Sol
Ibanez prestige rg2610

Peavey TKO 65
Peavey vb-2
Quote by the_perdestrian
listen to revelation, for he is wise in the way of bass-fu
#25
Looks like a short circuit in your power supply, pre amp or power amp. Take it to another tech.

BTW are you sure you're replacing the fuses with correct current value? If you're using fuses take less current, it could explain why it always burns.

If you're equipped with a varactor and other equipments I could help you, but I doubt you do. Taking measures before the fuse blows could damage the rest of your tubes, etc.

If you're gonna try to diagnose it, look if the rectifier in power supply is ok. You could always look at the bias section.
Quote by MH400
a girl on the interwebz?

You have 2 options.

1. Tits.
2. GTFO.

Last edited by Spike6sic6 at Jul 31, 2010,
#26
Pin 3 of an EL34 is the plate. Not sure what you want to elaborate on?
Go to 311's profile and read his blog about biasing. I have a blog about how to fabricate a simple bias probe if you need it too. Just remember, you will be dealing with about 400V, so be very careful and keep one hand in your pocket. If unsure, don't go near it.

It actually sounds like you need to take the amp to somebody that knows what they are doing tbh.
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
Last edited by Cathbard at Jul 31, 2010,
#28
Is the fuse near the 120v(wall outlet) in the amp? Or is it at the output?
Quote by MH400
a girl on the interwebz?

You have 2 options.

1. Tits.
2. GTFO.