Can I take out 2 tubes from my 2466?

[LedZeppelinGuns]

Hey everyone,

I blew a tube in my amp the other day, and the store I got the amp from is gonna be closed for the next like three days. I was wondering if I could take out two of the tubes in the amp and run it as a 50W? Is it easy? Do I have to do anything special to the tubes to put them back in? Any help on this topic would be GREATLY appreciated.

Thanks!

[slowpokerhino]

NO! DO NOT DO THIS! This subject was discussed quite awhile ago (may want to try the "search" function) and Steve said that by doing this you are at serious risk of damaging your amp.

I'm afraid you're just going to have to wait it out. I'd suggest replacing them with a matched quad (all four tubes) and then getting it biased. You then will have a couple spares as to not be in this situation again.

[LedZeppelinGuns]

Ok thanks. Someone told me that if you remove the two outer tubes or the two inner tubes you'll be fine. Ill check out the older posts though. Again, thanks a lot!

[surfnorthwest]

Someone told me that if you remove the two outer tubes or the two inner tubes you'll be fine.

That can be the case on some amps but NOT this bad boy. Like slow said, best to just get a matched quad and rebias them. If you are in the US there are many online tube sellers that will overnight them to you.

[LedZeppelinGuns]

Ok thanks for the help guys. I'll bring the amp in as soon as possible. This is my first real amp and I don't want to mess it up. Thanks again!

[SteveD]

You may well get away with it but I could never recommend it because it increases the HT on the plates of the remaining two valves thereby pushing them further from the KT66s comfort zone.

Like the guys said, if you can stretch to a new matched set and keep the others as spares, that's always a good idea.

[LedZeppelinGuns]

All right guys, thanks for all of the help! Turns out that it was just the fuse...I popped a spare fuse out of the back and stuck it in and now I finally have my Vintage Modern back!

[MKB]

You may well get away with it but I could never recommend it because it increases the HT on the plates of the remaining two valves thereby pushing them further from the KT66s comfort zone.

Like the guys said, if you can stretch to a new matched set and keep the others as spares, that's always a good idea.

Just curious Steve, is the dangerous voltage rise using two tubes the actual plate voltage, or the screen voltage on the power tubes?

[SteveD]

Both the screens and the plates will rise due to less loading on the HT. It's not actually a dangerous voltage rise as such, but the original mains input tolerance range the amp was designed for was +6% to -10% of a territory's nominal domestic mains voltage. The amps were officially safety approved as per their stock configuration when shipped from the factory. Hence, I can not recommend anyone to effect changes that vary from that in the position I am in.

If anybody wants to pull output valves then it is at their own risk.

[ClubAndCountry]

Might this have anything to do with the dropping of the valve failure fuses between JCM900 and JCM2000? Since it was possible to deliberately pull one of the fuseholders on the 100s to run the amp on two valves...

[MKB]

Both the screens and the plates will rise due to less loading on the HT. It's not actually a dangerous voltage rise as such, but the original mains input tolerance range the amp was designed for was +6% to -10% of a territory's nominal domestic mains voltage. The amps were officially safety approved as per their stock configuration when shipped from the factory. Hence, I can not recommend anyone to effect changes that vary from that in the position I am in.

If anybody wants to pull output valves then it is at their own risk.

Understood, thanks for the info.

[SteveD]

Might this have anything to do with the dropping of the valve failure fuses between JCM900 and JCM2000? Since it was possible to deliberately pull one of the fuseholders on the 100s to run the amp on two valves...

Good point, I wouldn't be at all surprised. I'm not really sure why Steve Grindrod couldn't carry that over to the 2000 range. Maybe a test house issue.

[frank9310]

I heard that if you're going to pull 2 tubes then you need to change your cabinet impedance to half of what it was. For example, if you have a 16 Ohm cabinet, then you need to change the impedance switch to 8 Ohms for it to be compatible. Otherwise, you risk damaging the amp.

The problem I see with the VM is my 2x12 cab uses 2 Marshall Celestion G12 V30s which are 16 Ohms each. So running those together in parallel, I get and 8 Ohm cabinet. So to pull 2 tubes, I would also need to set the selector switch to 4 Ohms.

You can't run the 2 x 16 Ohms speakers in series or you wind up with 32 Ohms. Since these are rated at 70 watts each and the 2466 is really supposed to be around 68 watts RMS or 110 watts peak, the 2 speakers should be adequate I would think.

The problem though is that the VM only has a 8/16 Ohm selector. Why was 4 Ohms eliminated or can the 16 Ohm selection be used? Reason I ask is on some Marshalls I've seen it where it says 16 Ohms and in parenthesis (4 Ohms). Does this mean you can use either one there?

[Bailz]

I heard that if you're going to pull 2 tubes then you need to change your cabinet impedance to half of what it was. For example, if you have a 16 Ohm cabinet, then you need to change the impedance switch to 8 Ohms for it to be compatible. Otherwise, you risk damaging the amp.

The problem I see with the VM is my 2x12 cab uses 2 Marshall Celestion G12 V30s which are 16 Ohms each. So running those together in parallel, I get and 8 Ohm cabinet. So to pull 2 tubes, I would also need to set the selector switch to 4 Ohms.

You can't run the 2 x 16 Ohms speakers in series or you wind up with 32 Ohms. Since these are rated at 70 watts each and the 2466 is really supposed to be around 68 watts RMS or 110 watts peak, the 2 speakers should be adequate I would think.

The problem though is that the VM only has a 8/16 Ohm selector. Why was 4 Ohms eliminated or can the 16 Ohm selection be used? Reason I ask is on some Marshalls I've seen it where it says 16 Ohms and in parenthesis (4 Ohms). Does this mean you can use either one there?

Can't comment on having to change the impedance and can honestly say I've never heard of that - doesn't mean to say it's not true mind. However, the VM transformer has the option of running at 4 ohms; you just need to open her up and swap either the 8 or 16 ohm plug over onto the 4 ohm option on the tranny.

[frank9310]

ah yes thanks, I did mention that in the post but maybe not explained it fully. You just unplug it from the 16 and move it to the 4 Ohm tap.