Removing 2 of 4 Power Tubes

[BowerR64]

Man, this is a tough room for sure.



And now I will sacrifice myself and let the flaming begin on me.

What NOGE posted is good advice.

The primary reason you will not hear any (well, that much of) change in volume when pulling two of the four power valves is because the entire amp power supply is now running at a slightly higher voltage. This is why you should check the bias when doing this. The plate voltage is now higher and the bias supply voltage is also slightly higher BUT not high enough to compensate for the higher plate voltage and put the bias/idle setting back to the same setting it was at while the four power valves were in the amp. Also, the heater filament circuit is now slightly higher voltage as well. The preamp B+ will be slightly higher changing the bias of the 12AX7 preamp valves. In some amp designs, the higher preamp B+ voltage will have an influence on the tone and feel of the amp as well.

So why is everything running higher now with 2 tubes taken out? How much higher are we talking about?

Ive set my bias on 50 watt amps before really cold, the plate voltage goes up im thinking because the tube is not running as hard? Then ive set the bias hot and i noticed the plate voltage drops again i figured because its putting more load on the supply.

Does the amp consume more electricity with 2 tubes or 4 or is it the same no matter how many tubes are in it?

 

[RickyLee]

So why is everything running higher now with 2 tubes taken out? How much higher are we talking about?

Ive set my bias on 50 watt amps before really cold, the plate voltage goes up im thinking because the tube is not running as hard? Then ive set the bias hot and i noticed the plate voltage drops again i figured because its putting more load on the supply.

Does the amp consume more electricity with 2 tubes or 4 or is it the same no matter how many tubes are in it?

Yes, you should see a slight increase in voltages in the amp if you physically remove two power tubes. And yes, you are then consuming a bit less electricity.

It is as you said, the load on the supply. And then you have to also realize your wall voltage can fluctuate a bit as well. Just as you will see your air conditioner or any other big appliance in your home pull down your electricity and then bring it back up when you shut those appliances off, removing two power tubes will lessen the load on the amp. EL34's are more noticable than 6L6's because they draw much more heater current. The heaters and then the amp being played or cranked is where the power consumption mostly comes from.

Then to confuse you even more, a hotter bias will also affect the plate voltage by a few volts. That is why you need to keep an eye on the plate voltage when you make adjustments on the bias pot either way.

 

[EdHopper]

Mickey, according to https://www.wingedc.com/.... Well, they say...Rest assured that the Svetlana factory in St. Petersburg, Russia is still producing vacuum tubes and has no plans to stop.

All current production St. Petersburg factory tubes -- and only those tubes -- do bear the

mark, while in the past some did not. In today's world if you want the tubes that you've come to know in the past as "Svetlana", the only way to be sure you're getting that tube is to look for the

mark.

 

[charveldan]

https://www.tubedepot.com/t/brands/sed-winged-c

These are SED =C= [winged C's] not Svetlana's currently made. The SED =C='s are extinct.
SED's had welded plates, Svetlanas are crimped, there are other differences.

 

[mickeydg5]

Mickey, according to https://www.wingedc.com/.... Well, they say...Rest assured that the Svetlana factory in St. Petersburg, Russia is still producing vacuum tubes and has no plans to stop.

All current production St. Petersburg factory tubes -- and only those tubes -- do bear the

mark, while in the past some did not. In today's world if you want the tubes that you've come to know in the past as "Svetlana", the only way to be sure you're getting that tube is to look for the

mark.

http://sedtubes.com/sed_news.html

This is noted on their website:

SED NEWS
Production of SED glass tubes ceased in 2012.
Production of SED glass tubes ceased in 2012 and there is currently no intention to recommence production. The remaining supplies of tubes is limited and are treated as NOS stock and priced accordingly.

Any change from this situation will be announced as soon as practicable.

 

[BowerR64]

Yes, you should see a slight increase in voltages in the amp if you physically remove two power tubes. And yes, you are then consuming a bit less electricity.

It is as you said, the load on the supply. And then you have to also realize your wall voltage can fluctuate a bit as well. Just as you will see your air conditioner or any other big appliance in your home pull down your electricity and then bring it back up when you shut those appliances off, removing two power tubes will lessen the load on the amp. EL34's are more noticable than 6L6's because they draw much more heater current. The heaters and then the amp being played or cranked is where the power consumption mostly comes from.

Then to confuse you even more, a hotter bias will also affect the plate voltage by a few volts. That is why you need to keep an eye on the plate voltage when you make adjustments on the bias pot either way.

See then thats what i dont understand then, if pulling 2 tubes raises everything because there is less load just like running the bias colder why are we even having a debate over all of it? If pulling 2 tubes put more of a load on the transformer and it really lagged it down then i could see there being an issue but so far it seems like less of a strain on the transformer.

 

[RickyLee]

See then thats what i dont understand then, if pulling 2 tubes raises everything because there is less load just like running the bias colder why are we even having a debate over all of it? If pulling 2 tubes put more of a load on the transformer and it really lagged it down then i could see there being an issue but so far it seems like less of a strain on the transformer.

This debate will go on forever LOL. There will always be people on both sides of that fence.

Yes, you can also look at it as taking some stress off of your amp. BUT, just never rule out that the running voltages can now be a bit higher. Its a bit of a contradiction in that regard. If you have an amp that runs at 490V B+ with four power tubes and it has 500V rated filter caps, then you remove two power tubes and your B+ voltage then rises close to an additional 10VDC, where are you now? You are pushing the limits of those caps. But then you can say, "Well, 490V was pushing close to their limits as well." LOL.

I think one reason why many people just do not do it is the practicality and danger of remembering to adjust/compensate the impedance. And I should add in something that never gets brought up: Now you are running about half less current but have a twice as high rated fuses installed. If your amp uses a 1A HT fuse with four tubes, it would be a good idea to put in a 500mA if you are going to be running only two of the power tubes for an extended time or permanently. And adjust the MAINS fuse as well, but only reduce that by about 35% or so if possible.

And I will say it again: The best way to do this is to compensate the front end MAINS/wall voltage. This keeps the running voltages the same and removes the spiked or higher voltage possibility. And always check bias. If you keep the running voltage the same then the bias will be good is both modes.

 

[EdHopper]

The Groove Tube EL34M's are outstanding in DSL100's and TSL100's. And then don't get me started on how they sound in my old '87 Silver Jubilee 2555 . . . .

Is the '87 Silver Jubilee hand wired? Are the tubes mounted on the chassis or the PCBs?

 

[RickyLee]

Is the '87 Silver Jubilee hand wired? Are the tubes mounted on the chassis or the PCBs?

The original Jubilee amp, all models, has a printed circuit board. All tube sockets are mounted to the chassis like the later JCM 800's.

 

[EdHopper]

Ricky, I've heard good things about them....I've got to try one.

 

[RickyLee]

Ricky, I've heard good things about them....I've got to try one.

Beware. A good percentage of people that try one end up wanting one. I do need to get mine out and start playing it more. Actually, I took my '87 Silver 2555 to the very last practice we had with the Sabbath cover band we were just getting rolling. It was the same bass player, drummer and myself from my Trower cover band but with a different singer. The Jubilee was doing a great job on the early Iommi tones at that rehearsal. I was impressed. Then shortly after that we had a falling out with the drummer, just regarding the Sabbath material. But then his feelings were hurt and did not want to play drums in the Trower band after that as well, which is understandable. So the Jubilee got put to the back of the ol amp pile and has not been played since . . . .

 

[timmfun]

loudness-does nothing
tube cost- not that big a deal unless you replace them once a year
what it does do is reduce the headroom and that's why a lot of people do it.

also,you did make sure to pull either the 2 outer or inner tubes right? not 1&3 or 2&4? that will damage the amp.

Actually not true, as most 4 tube amps have their tube pairs connected next to each other symmetrically in halves, so pulling 1&3 or 2&4 is same as pulling either inner 2 or outer 2, as they are all still running as push pull pair halves. Just dont pull 1+2 or 3+4.