Repairing an old Crate VC-3112W

[Pitsi]

Hello,

I was given an old Crate VC-3112W as a gift to my son who plays the guitar.

My Amp has one of the four EL84 tubes broken and also the only 10,000uf/16V capacitor is swollen. Those are the "visible" problems.

I would like to ask if anyone knows whether the two pairs of the EL84 tubes are matching pairs and where the best place that I can order a full set of new tubes the SOVTEK EL84 & the SOVTEK 12AX7W or 12AX7LPS for better sound

I have the schematics found on the internet.

If I manage to have this Amp up & running by Christmas I would make a big surprise for my 15year old son !

Many Many thanks in advance to anyone who can help.

[Amp Kat]

Several Tube Distributors around the net like Mojo,Eurotubes,Tubesandmore ect.... and you can either get current production tubes or NOS. The NOS will be much more expensive but will also sound ,last and have the amp closer to how it was at original. Current production Sovteks may develope rattling which is common in current production butI like the JJ EL-84's and do note that a 6BQ5 is the same tube.
Same with the 12AX7 and the LPS is a nice tube for AC operation but not so good for DC because of the spiral filaments. You may also look into replacing as many Electrolytics or all if they are really old but 10,000uf doesn't sound like an old amp but the more ecaps you replace the better off in the future you may be. Just to get it ready for December you may just change what's bad but hope he enjoys when it's done.

[Gtr_tech]

Its best to replace all the pwr tubes at once with a matched set. THe JJ EL84 is the best sounding variation out there IMO. YYMV with preamp tubes. Generally the Sovtek 12AX7 WA/WB tubes are pretty bland sounding. Anything is better than those. Preamp tubes last quite a long time, I wouldn't be in a hurry to replace them unless they are those crappy Sovteks.

CAn you post a pic of this cap? It may be just fine despite the appearance.

[52 Bill]

And I don't know where you are located, but those tubes are so common, you could buy them at your local guitar store as well.

You never mentioned what was wrong with the amp. Does it power up? Does it pass a signal?

[Pitsi]

Repairing an old Crate VC-3112W

Sir,

First of all many thanks to your reply.
I must let you know that although I'm an electronic engineer I was never involved (other than listening to - which I very much enjoy) to any of the guitar stuff so I know only the basics.
Also I'm based in Athens Greece & I'm thinking to try to get the tubes from a web shop on e-bay as those components are very expensive here and the local representative of most of the US amp brands is one spesific shop. (monopoly )

So please first of all let me know what NOS means.
Secondly I understand that you do not suggest to get the SOVTEK EL84s
(although I read somewhere that they sound quite well) so I will check for the JJ for them or for the 6BQ5.
For the 12AX7s I also read that what matters more is the one closer to the input (the one who has the DC fillament voltage) so what do you suggest there ?
Sould I leave the two first (DC powered) the same W version? and replace the third & buffer (fourth) with the LPS or you propose another setup with different types altogether?
Finally the Amp was designed by Crate in 93-94 so mine should be a later model and the guy who owned it said that it stayed idle for 6 years so the components & caopacitors as well as board look very nice without any sign of problem apart from that big cap used in the DC fillament voltage generation.
I attach the schematics for your ref.

Many thanks again for offering to help.

Several Tube Distributors around the net like Mojo,Eurotubes,Tubesandmore ect.... and you can either get current production tubes or NOS. The NOS will be much more expensive but will also sound ,last and have the amp closer to how it was at original. Current production Sovteks may develope rattling which is common in current production butI like the JJ EL-84's and do note that a 6BQ5 is the same tube.
Same with the 12AX7 and the LPS is a nice tube for AC operation but not so good for DC because of the spiral filaments. You may also look into replacing as many Electrolytics or all if they are really old but 10,000uf doesn't sound like an old amp but the more ecaps you replace the better off in the future you may be. Just to get it ready for December you may just change what's bad but hope he enjoys when it's done.

[Pitsi]

Sir,

thanks for yor below reply/suggestion.

Yes I intend to replace all 8 of them.
I'll check for the JJ on the EL84s
The Preamp ones are the SOVTEKs so what brand do you suggest should I look for? JJs as well ?

OK I will send you a picture of the cap durring the WE.

Thanks again.

Its best to replace all the pwr tubes at once with a matched set. THe JJ EL84 is the best sounding variation out there IMO. YYMV with preamp tubes. Generally the Sovtek 12AX7 WA/WB tubes are pretty bland sounding. Anything is better than those. Preamp tubes last quite a long time, I wouldn't be in a hurry to replace them unless they are those crappy Sovteks.

CAn you post a pic of this cap? It may be just fine despite the appearance.

[Pitsi]

Repairing an old Crate VC-3112W

Hi,

I'm based in Athens Greece so it is rather difficult to get good stuff here at reasonable prices.

The Amp was not powered on (by me at least) with one EL84 broken.
During the WE I'll get one old EL84 (I have) installed and power it up to see if there are more problems. What concerns me is that swollen top high capacity cap in the DC fillament network.

Thanks & B.Rgrds.

And I don't know where you are located, but those tubes are so common, you could buy them at your local guitar store as well.

You never mentioned what was wrong with the amp. Does it power up? Does it pass a signal?

[Pitsi]

Repairing an old Crate VC-3112W

Sorry one last question:

Regarding the EL84s in the output diagram which ones are matched pairs ?

V5 with V6 parallel and V7 with V8 parallel two matched pairs or the whole quad is matched due to the push-pull setup?

Thanks again.

Several Tube Distributors around the net like Mojo,Eurotubes,Tubesandmore ect.... and you can either get current production tubes or NOS. The NOS will be much more expensive but will also sound ,last and have the amp closer to how it was at original. Current production Sovteks may develope rattling which is common in current production butI like the JJ EL-84's and do note that a 6BQ5 is the same tube.
Same with the 12AX7 and the LPS is a nice tube for AC operation but not so good for DC because of the spiral filaments. You may also look into replacing as many Electrolytics or all if they are really old but 10,000uf doesn't sound like an old amp but the more ecaps you replace the better off in the future you may be. Just to get it ready for December you may just change what's bad but hope he enjoys when it's done.

[Gtr_tech]

I really can't speak from experience. I do have that same amp, but its not stock (the gain channel I redesigned/rebuilt, and the clean side is independant of the dirty now). The preamp tube in the clean channel is a NOS GE and the rest are JJs. The gain channel can be kinda bright and the JJs knock that down a little.

[rockon1]

Hi,

I'm based in Athens Greece so it is rather difficult to get good stuff here at reasonable prices.

The Amp was not powered on (by me at least) with one EL84 broken.
During the WE I'll get one old EL84 (I have) installed and power it up to see if there are more problems. What concerns me is that swollen top high capacity cap in the DC fillament network.

Thanks & B.Rgrds.

If the top of the cap is "swollen" up like a bubble its probably nothing at all. They all bubble up from heat-but only the plactic cover -not the actual cap itself. Heres a picture of mine in my VC50 which is perfectly fine. The cap cover on this one was the worst and very swollen looking. Its cosmetic most likely like this one. You can pop it off and check it if you like. Bob

[Enzo]

Hi
Your whole quad is matched, not pairs. However, be aware the tubes the factory installed new were never matched sets. Matching is something many of us prefer for very subtle improvements in sound and possible hum reduction. The amp will work perfectly fine with random EL84s.

Many of us have preamp tube preferences, but not everyone agrees on what is "better." Not everyone likes the same tones. ANy 12AX7 you use, the amp will always sound like a VC3112. The selection of preamp tubes is for more subtle differences.

And be aware that ANY brand and model of tube can be a bad tube. No brand is immune from getting a noisy or microphonic tube.

NOS means "new old stock." It refers to tubes that are unused and so are "new" but they were made long ago so the stock is old. New Old Stock. COmpared to new stock tubes, which means current production of tubes, like JJ and Sovtek.

You are an engineer, so imagine you bought parts for a project 20 years ago and forgot them in a drawer. If you find them now, they are still new, but old.

[Pitsi]

rockon1

Great ! and many thanks for the picture.

Yes mine looks exactly like this, so it is good to hear that it may be OK.
I'll take my chance not to replace it and power it up tomorrow. (after replacing the bloken EL84 that is).

Enzo

Thanks for the info on the tubes. I agree that the sound is entirely pesonal so I'll let my son judge this who palys the guitar... I'll try to power it up tomorrow with a spare Ultron EL84 tube I have and let you know how it went.
As for the matched quad, yes seen some prices on the internet & today I found a JJ quad at 80 Euro locally (have not bought then yet) so it sounds reasonable and it's worth the expence I guess to have a new final. The Preamp section is 4x12AX7W by Sovtek so will let them be at the beginning.
Thanks also for the jargon term NOS

Two quick questions.

The tubes orientation on the amp when the board is fixed in place is on the side. Is there a problem with this (guess not) for the life of the tube?

The guy whom I talked this morning locally for the 80Euro JJs (builds his own amps) said that I should make an adjustment after replacing the EL84 tubes to the anode current.
In the diagram I do not see any means of adjustment in the final stage! How could that be?

Many thanks again.

B.Rgrds.

[rockon1]

The VC3112 is cathode biased. There is no need to really worry about the bias as its basically "self biasing". There is no problem with the orientation of the tubes either. Bob

[Pitsi]

Thanks a million !

[Pitsi]

Repairing an old Crate VC-3112W

Bob,

I powered up the amp today after cleaning it up & replacing the broken EL84 tube with a spare I had.

I did not have much time to start measuring the voltage levels at the test points but will do this next week for sure.

It powered up well and I could plug in a bare cable just to see if it worked.
As I said before the amp is a surprise present to me son so I could not get his guitar to test it.
So it went quite well and the amp was very loud at least with this okward input....
I have taken the picture of the cap that I did not replaced so far. (attached - what do you think?)
Next step is to plug a Guitar and see how it goes.
In the mean time I will order the EL84 JJ matched quad. And maybe a NOS GE black plate I found to replace the first 12AX7...?

So will let you know how it goes but mant thanks for all the help so far.

B.Rgrds.

If the top of the cap is "swollen" up like a bubble its probably nothing at all. They all bubble up from heat-but only the plactic cover -not the actual cap itself. Heres a picture of mine in my VC50 which is perfectly fine. The cap cover on this one was the worst and very swollen looking. Its cosmetic most likely like this one. You can pop it off and check it if you like. Bob