How do I change tubes in a Vox AC30cc2 amp?

Doogle69

I need to change the tubes in my Vox AC30cc2 amp. however, I have absolutely no idea how to do this. I cant even find the tubes. i cant find anything on the internet, about from getting the idea that I would have to take the amp apart, remove the speakers, then solder them back on and put the amp back together again. Obviously I'm not prepared to do this. Any advice on what to do, or who could do this for me?

Seziertisch

Doogle69 wrote: »

I need to change the tubes in my Vox AC30cc2 amp. however, I have absolutely no idea how to do this. I cant even find the tubes. i cant find anything on the internet, about from getting the idea that I would have to take the amp apart, remove the speakers, then solder them back on and put the amp back together again. Obviously I'm not prepared to do this. Any advice on what to do, or who could do this for me?

There is no soldering required. If it is just the preamp and rectifier tubes you can just swap them in and out. If the power amps tubes (in this case EL84s) are to be changed the amp will need to be rebiased.

I would suggest based on your lack of knowledge you should go somewhere to get it done. It is not a terribly complicated job and relatively quick if someone knows what they are doing. Tube amps can store potentially fatal levels of current so even when unplugged it is possible to do yourself an injury if you don't know what you are doing.

Doogle69

Thanks for that. Is there anyone you'd recommend to do this? Just out of interest, how do I access the tubes just to see if they need replacing?

ball ox

You dont need to bias the CC2, you can do it all yourself.
Just be carefull.

Unscrew the back panel and remove it. Disconnect the speaker leads from the amp.The amp & tubes all sit on a shelf in the top part of the amp. Unscrew the screws under the shelf that are holding it in place and slide it out. Some people leave these screws out, and even grease the shelf, when they re-assemble the amp for easy access. Pull out the old tubes and pop in the new ones. Just make sure they go in all the way and dont be oo rough with them. Be very carefull not to touch anything inside the chasis, only handle the frame. Even unplugged there is enough current in there to f%ck you up. Put it back together and voila.

Paolo_M

boll ox is right, no bias adjustment needed or even possible with the AC30CC2.
Just follow the disassembly instructions he's given.
Changing out the valves is as easy as changing light bulbs, just be careful to follow the keying. The 12AX7 and EL84 valves have nine pins but have space for 10. The 10 spot is left vacant. The corresponding slot of the socket is also vacant, preventing you from putting it in the wrong way. Just keep an eye out for this as the pins will bend, damaging the valve, if you attempt to "shove" it in the wrong way. The GZ34 is keyed in a similar fashion but has only 5 pins.

Generally you'll hear that the valves need changing before you can see any visable indication. Loss of gain/volume, squeeling noises, crackling, excessive hum, intermittant noises, one channel working well but the other not working etc.etc are sings of valve failure.

Doogle69

How about biasing them? I dont know how to do this, I'd need someone who does to do it.

ball ox

The CC2 is self biasing, you do not need to have it biased. You just stick the valves in and it's good to go.

Doogle69

Great! Thank's for that! I feel a bit more confident about this now! Now I have to figure out how not to fry myself! I'm guessing that I still stand that risk? How do I avoid this?

Paolo_M

Doogle69 wrote: »

Great! Thank's for that! I feel a bit more confident about this now! Now I have to figure out how not to fry myself! I'm guessing that I still stand that risk? How do I avoid this?

It's not as big a task as you might believe!!
Frying yourself is not a big risk either, despite what people would have you believe.
The CC2s chassis is firmly earthed, it's fitted with bleeder resistors to drain charge after the amp is turned off, no charged componant is finger touchable outside the chassis.
Despite these safety measures you should still observe the usual safety precautions:
1. Let someone else know what you're doing
2. Wear rubber sole shows
3. Do not put your hand inside the chassis, it's not necessary to change valves
4. Don't drink a six pack beforehand for dutch courage
5. Once you've the back off, put one hand firmly in your pocket, only one hand is required to change the valves
6. Be alert, check that the amp is definitley unplugged a couple of times, make sure your dog isn't likely to come jumping at you all of a sudden, the usual common sense stuff

Doogle69

Thanks, I feel a lot more confident about this now. I felt that it was basically the same as changing a light bulb but I had a few questions that I needed to be answered first. Thanks to everyone for their advice.

artvandulet

Some great info here.
Can I chime in and ask how to tell the difference between needing to replace the preamp valves or the poweramp valves? And is a JCM2000 self biasing? cheers.

Paolo_M

artvandulet wrote: »

Some great info here.
Can I chime in and ask how to tell the difference between needing to replace the preamp valves or the poweramp valves? And is a JCM2000 self biasing? cheers.

Generally speaking preamp valves cause squeeling noises, gain loss, on channel not working properly. They tend only to get damaged by getting knocked about a bit, usually getting lugged in and out of bars. If your stayed in one, cool, dry spot the preamp valves would probably last forever.
Power valves usually cause fuses to blow and dramatic stuff like that. They need to be changed reasonably often, 12-18 months for typical bedroom play, one rehearsal, one gig a week type play.

JCM2000 is not self biasing. It is adjustable fixed bias, with bias adjustments per side to allow for DC balance in the OT, in theory reducing hum.
It's a bit of a balls TBH. The inside of the amp looks more like a Dell than a Marshall!!

artvandulet

Cheers for the info!