Impedance change when pulling two power tubes?

[Kapo_Polenton]

There seems to be conflicting info on this... from You will blow your transformer! To, Not a good idea, to, it doesn't matter. So two pulled power tubes ( 2 inner or two outer), I currently do this and had left the amp in 8 ohm into 8 ohm cab and it seemed just fine. I just picked up a Torpedo Cab 8 ohm for cheap and i wanted to use it to load down the amp and slave into another power amp or just leave it on that amp ( Randall Lynch Box) for when i want to go straight into my DAW and not mic. Kevin O'Connor from what I have seen on the youtoobz has said it doesn't matter. Others say you HAVE to half the impedence on the amp. I don't want to blow this Torpedo captor up and take my amp with it so what's the skinny on this from your experiences?

 

[SoooRad]

I feel like it probably has a few factors. I recall in the manual for the Metaltronix M1000 I used to have I believe it talked about pulling two tubes and the impedance adjustment. (Something like running the amp at 8 ohms with two tubes was equivalent to running with 4 at 16)

I was also listening to Jim Gaustad on some talks lately about some additional stuff he hadn't touched on in previous (ToneTalk, etc) interviews about not pulling in/out pairs, but rather side-by-side, or even running a Plexi on One power tube. Fun stuff to experiment with for that type of amp, assuming you are willing to risk the damage.

if I had a Plexi in the house, I'd be willing to risk the damage just because its fun screwing around with shit.


EDIT. I found the manual online, and it reads...

If you want to turn your M-1000 100 watt into a 50-watt you need only follow these instructions. Firstunplug the amplifier from the A.C. outlet and allow 15 minutes for it to cool if it has been played recently.Next remove the 2 center output tubes (the big ones) – this cuts your output power in half. Because youhave removed the tubes, your output impedance changes also, you have to change the impedance selectoraccordingly. THIS IS VERY IMPORTANT! On the impedance selector 16ohms becomes 8ohms, 8ohmsbecomes 4ohms, and 4ohms becomes 2ohms. WARNING: WE DO NOT RECOMMEND RUNNINGTHE AMPLIFIER AT 2ohms!

This is not a "one size fits all" thing, so please don't take it as such.

 

[harddriver]

When I pull two power tubes either the inner pair or outer pair in a 100 watt Marshall amp I always reduce the impedance by half. If driving a 16 ohm load then set the amp to 8ohms. If driving an 8 ohm load set the amp to 4 ohms. I have always done this and never had an issue.

Kevin O'Connor knows his shit but I will err on the side of caution and what has been established protocol when you pull two tubes in a 100 watt amp.

It has also be stated that reducing the amp impedance by half when loading down an amp into a load box for slaving will lessen the stress on the output transformer when being ran at high volumes into the resistive/reactive load. This applies even if you don't pull two power tubes, On a plexi it will tighten the woofy low end response as well. I did this with my 68 plexi even when running all four power tubes and never had an issue with the output transformer.

 

[Kapo_Polenton]

So if i am running a 100 watter and pull 2 power tubes, I should technically set the amp to 4Ohm if i want to go into an 8 Ohm Captor or an 8 Ohm 4x12 cab.

 

[harddriver]

So if i am running a 100 watter and pull 2 power tubes, I should technically set the amp to 4Ohm if i want to go into an 8 Ohm Captor or an 8 Ohm 4x12 cab.

Yes, you are 100% correct.

If you pull two power tubes and the 8 ohm Captor is used for the load or an 8 ohm 4x12 cabinet then set your amp to 4 ohms.

 

[blackba]

If the captor is designed right, it should handle a 100Watt amp no problem, in which case you don't need to pull two power tubes.

I would check it both ways with 4 power tubes and with 2 power tubes into the captor and see what you prefer

I am getting a captor X in a trade in a few weeks. I hope its as good for slaving as the suhr Reactive Load and the attenuator switch is useful.

 

[Kapo_Polenton]

Yes, you are 100% correct.

If you pull two power tubes and the 8 ohm Captor is used for the load or an 8 ohm 4x12 cabinet then set your amp to 4 ohms

My use case is a bit different in that I do want to use it to slave my 100 watter with Jose style gain mods into a 50 watt JCM800 ( through metro loop) into my 4 x 12 to get volume down.

Second use and the reason for pulling two tubes is that tubes are expensive now and my RM100/Lynchbox allows me to run 34's, 6L6, 6550 etc and two at a time, I like the idea of matching the preamp. So Marshall style preamp EL34, Peavy 6L6, my Salvation Ampeg preamp ( not many of these were made), run with two NOS 6550. As cool as the synergy stuff is ( especially the newer designs) I think Randall had it right and closer to my ear. Better and bigger sounding power amp and less shit jammed in each module.

So this thing will give me options.. they say the load affects the tone and they may be right but if you use a Suhr iso box between the amp and load, I still think that tone hit is significantly lessened than if you take the DI out of the Captor.

So a few things to play with. But i got this thing half price like new in box and I already have the Reload that i use for attenuation. It was just too cheap not to try for the slaving thing. I like it's size too.

 

[skoora]

I like pulling two tubes on my 50 watter. Soundmen seem to like it.

 

[The~Kid]

Honestly I just wouldn't do it in general matched ohms or safe mismatch or whatever..... or whatever anyone on the internet says or whoever in real life.


When your pulling tubes and this and that to affect wattage our output the amp wasn't necessarily designed for your just asking for trouble in general........


I'd just get a Boss Waza Tube Amp Expander Core, Fryette PS2 or Tone King Ironman ll. It's just not best to mess with your amp like that IMO.

 

[311boogieman]

Honestly I just wouldn't do it in general matched ohms or safe mismatch or whatever..... or whatever anyone on the internet says or whoever in real life.


When your pulling tubes and this and that to affect wattage our output the amp wasn't necessarily designed for your just asking for trouble in general........


I'd just get a Boss Waza Tube Amp Expander Core, Fryette PS2 or Tone King Ironman ll. It's just not best to mess with your amp like that IMO.

da fuk?

 

[The~Kid]

da fuk?

I just wouldn't pull tubes from an amp for whatever reason......


Matched, safe mismatched ohms or not...... the amp wasn't intended to operate like that and well your just asking for trouble especially on a top dollar piece of kit.


You don't want to Mickey Mouse shit like that......


If your doing it to bring down wattage or for tone purposes or whatever it's just not advisable and a Waza Tube Amp Expander, Fryette PS2 or Tone King Ironman ll is the more sensible thing to do.


Risk it at your own leisure......

 

[harddriver]

So this thing will give me options.. they say the load affects the tone and they may be right but if you use a Suhr iso box between the amp and load, I still think that tone hit is significantly lessened than if you take the DI out of the Captor.

You don't have to run the Suhr Iso line out box between the amp and the load. You can plug the Suhr Iso line out box directly into your other unused speaker jack with a second speaker cable. That way your amp is connected to the captor load box with just one speaker cable.

I prefer to do it this way, I installed an extra speaker jack in parallel on my 68 for this very purpose.

Let us know how things sound when you try it out!

 

[MadAsAHatter]

Honestly I just wouldn't do it in general matched ohms or safe mismatch or whatever..... or whatever anyone on the internet says or whoever in real life.


When your pulling tubes and this and that to affect wattage our output the amp wasn't necessarily designed for your just asking for trouble in general........


I'd just get a Boss Waza Tube Amp Expander Core, Fryette PS2 or Tone King Ironman ll. It's just not best to mess with your amp like that IMO.

How do you explain half power switches that disconnect tubes from the power stage?

Edit: Even Jason Tong; who is one of our amp guru's said it's fine to pull 2 tubes from his Alta; just make sure you correct for ohms.

 

[The~Kid]

How do you explain half power switches that disconnect tubes from the power stage?

Edit: Even Jason Tong; who is one of our amp guru's said it's fine to pull 2 tubes from his Alta; just make sure you correct for ohms.

Yeah a couple amps can do this but it isn't Mickey Moused or rig jigged..... thats how the amps were designed and intended to operate if you ran em that way......

Im no expert but IMO I just wouldn't do it and avoid the risk but that is me

It would be better and safer in general to run a pedal as a Faux amp at low volumes and just do that short of getting a Waza, Fryette or Tone King but that's just me.

 

[LP Freak]

Why not just half the Ohms be safe? Can’t hurt anything right? But by not doing you may.

 

[VonBonfire]

You don't want to Mickey Mouse shit like that......

If it means being able to limp my amp through the rest of a show and be able to feed my kids the next day gimme the Mickey Mouse shit, lol.

 

[ZEN Amps]

There seems to be conflicting info on this... from You will blow your transformer! To, Not a good idea, to, it doesn't matter. So two pulled power tubes ( 2 inner or two outer), I currently do this and had left the amp in 8 ohm into 8 ohm cab and it seemed just fine. I just picked up a Torpedo Cab 8 ohm for cheap and i wanted to use it to load down the amp and slave into another power amp or just leave it on that amp ( Randall Lynch Box) for when i want to go straight into my DAW and not mic. Kevin O'Connor from what I have seen on the youtoobz has said it doesn't matter. Others say you HAVE to half the impedence on the amp. I don't want to blow this Torpedo captor up and take my amp with it so what's the skinny on this from your experiences?

I run most of my 100W Marshalls like this on the 8Ω output into a 16Ω cab. Never been an issue over the last 20 years or so. There's not much real world risk involved, although it's worth rebiasing the amp due to the potential rise in B+.

You may be safe with a mismatch but there's no way I'd risk it with a basic device like the Captor - its LF load characteristics are very different to a real cab (or good reactive load).

 

[Kapo_Polenton]

You don't have to run the Suhr Iso line out box between the amp and the load. You can plug the Suhr Iso line out box directly into your other unused speaker jack with a second speaker cable. That way your amp is connected to the captor load box with just one speaker cable.

I prefer to do it this way, I installed an extra speaker jack in parallel on my 68 for this very purpose.

Let us know how things sound when you try it out!

Ahhh smart! Never thought of that.. the second speaker jack on my 800 is unfortunately used for a resonance pot but I will keep that in mind for my Lynch Box because it has multiple speaker outs. In fact, my plan for the silent recording thing is using my old Torpedo Cab + pedal so I don't even need the Suhr in this case, I can just put it in one side of the thru on the Cab M. Not sure why I never thought of that. Doesn't mess with the impedence or anything either correct? Technically with just one load ( be it a load box or a cab) I can technically take the other speaker out and do what I please with it. The suhr controls the level but I am thinking the Cab pedal also has input value choices depending on the signal and it is made for exactly that, to sit between amp and cab anyway.

 

[Kapo_Polenton]

Why not just half the Ohms be safe? Can’t hurt anything right? But by not doing you may.

I've done that on the Randall just for precaution yes. Down to 4 Ohm which allows me to use the 8 Ohm captor and swap 2 inner or outer power tubes in / out as I please depending what I am doing.

 

[Kapo_Polenton]

Well I can say that the DI out of the Captor sounds good but it does totally impart that characteristic you always hear on load shoot outs.. hyped highs and lows with a bit of a scoop. Using the other speaker jack direct into the Cab pedal is definitely better and more realistic to the sound of the amp and speakers I feel. That's def the way to go. I was really enjoying playing through some old IR's I made.. almost kind of defeats the purpose of the cab closet I set up. These captors are so cheap and totally the way go for home studios. No power cord needed either.. much more convenient than my Torpedo Reload. (The Reload def has a better sounding load though.)