Question about using just #1 and #4 tubes in RM100KH...

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Balou

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So I know you can just take out the fuses in the 100KH (either 1 and 4 or 2 and 3)and it makes it a 50 watt head but I seem to remember reading that I need to change the Impedance too? I'm going into a 412 8ohm cab usually?

Also what would be the proper impedance if I have a 412 @ 8ohm and a 212 at 8 ohm to make a 3/4 stack, thats a 4ohm on my head right?
 
You gotta take the tubes in those places out too ;)

And I recommend running the middle pair, as I know when you mix tubes you get more tone from the middle ones, and I think it's the same way when you're running them at 50w too.

When running the amp at 50w, you need to take the impedance down a notch, so it's at 4 ohms. If you're running two cabs though, you would have to take it down to 2, but alas there is no 2 ohm selector on the amp :( You could rewire the cab if you'd like, though.

I'd personally just run one cab or the other :p:
 
Balou said:
So I know you can just take out the fuses in the 100KH (either 1 and 4 or 2 and 3)and it makes it a 50 watt head but I seem to remember reading that I need to change the Impedance too? I'm going into a 412 8ohm cab usually?

Also what would be the proper impedance if I have a 412 @ 8ohm and a 212 at 8 ohm to make a 3/4 stack, thats a 4ohm on my head right?

That second question is for when Im using all 4 tubes.
 
The Randall Demo videos says you can just take out the fuses and leave in the tubes, they do still glow tho but don't get hot. I tried using the 1 and 4 so I'll try using the middle 2 next time. Now I know what to do with the impedance. Thank you.
 
If you take the fuse out, you are disconnecting the cathode from ground.
That disconnects the HV path to ground. The tube is out of the circuit.
The tube still glows because the heater circuit is still connected. No harm.
 
Running on two power tubes out of four:

16 ohm cabs connect to 8 ohms.
8 ohm cabs connect to 4 ohms.
Do not use a 4 ohm cab.

The question that always comes to mind is, was this ability to run on two tubes like that for short term or long term use?

I thought about it so I could save money on tubes, but a couple amp techs advised against it.

The difference in volume is -3 db. It seems easier just to turn down the MV or channel volume just a little bit.
 
Yeah, thats why I bought a RM50. Since Ive had a chance to mess with the RM100KH I feel I might not need that kind of power. I'm probably gonna have one of these listed in here and ebay sometime next week. I only need one and now Im thinking 2 channels is gonna be just fine for me.
 
I like to go to 50 watts for the lower headroom :D And there's a slight tonal difference that I really find cool. I may switch to a RM4-RT2/50 simply because of that!
 
I am going to try this over the weekend with my RM100KH. I have Ruby 6550-STR's, Tung Sol 6550's, and JJ 6L6's and 34L's. I am going to drive myself crazy trying to figure out which ones I like best.
 
so you CAN safely just remove the fuses for tubes you dont want to run? this would be much easier than pulling tubes for quick tonal comparisons

impedance question: (when using all 4 tubes) you obviously set the ohm switch to whatever the load is on the cabinet. but when you have an additional load on the "extension speaker" output, how do you compensate? for instance on my Vetta, i believe if you plug in left mono 8 ohms, the switch is 8 ohms. if you plug in another 8 ohm load on the other side, it stays 8 ohms. but from the sound of this thread, if you put an 8 ohm load on the main, and an 8 on the extension, you need to switch it to 4

the manual is not clear on this...

Impedance select:
From the factory your head has been preset to the 8 ohm position. When using an external speaker cabinet, you may adjust this switch for
proper ohm load of you external speaker cabinet.
6- Impedance select: Set this switch to the correct ohm rating of your internal and external speaker cabinet.
7.- Main Output: This is the main output, which is currently connected to your internal speakers. This can also be used as the main output
for an extension cabinet.
8- Extension Output: Used to connect to an external speaker cabinet. It is very important that you select the correct impedence when
adding an extension cabinet.
 
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