Running RM100 on 2 power tubes

Just a question: Can you pull 2 power tubes out of the RM100 to bring the power down to 50 watts? If this is possible, which 2?

Thanks!

the outer 2, or inner 2.

Thanks for the info!

Do you have to account for impedance changes on the amp? I've heard something to this effect.

KonkeyDong said:

Do you have to account for impedance changes on the amp? I've heard something to this effect.

Click to expand...

I think you half the ohms on the head unless your already running 4ohms which means you cant.

KonkeyDong said:

Do you have to account for impedance changes on the amp? I've heard something to this effect.

Click to expand...

When pulling tubes:

If your cab is 16Ohms, set the amp to 8Ohms
If your cab is 8Ohms, set the amp to 4Ohms
If your cab is 4Ohms....don't do it

I heard that doing this reduces the output volume by half. Is this true?

Cos I followed all the steps above, but still, the output volume is the same.
I basically wanna run the power tubes hard to force more compression at lower volumes.

What am I doing wrong?

Cheers,
Ashish

ashishk said:

I heard that doing this reduces the output volume by half. Is this true?

Cos I followed all the steps above, but still, the output volume is the same.
I basically wanna run the power tubes hard to force more compression at lower volumes.

What am I doing wrong?

Cheers,
Ashish

Click to expand...

It reduces the output *power* by half but I believe the perceived volume difference is 3dB...i.e. not much at all.

If you want to push the amp harder at lower volumes, look into an attenuator - sits between amp and speaker and soaks power. THD Hotplate is an example. I use one but never usually more than 8dB of reduction, since it affects tone and squishes the signal too much at 12 and 16dB settings.

8dB of reduction is still more than 2x the power tube reduction though....

I deliberately bought a 50W MTS because a) I think they sound better and b) 50W is still too loud

Alternative methods of power reduction are - use THD YellowJackets and run EL84s ... this will be another power halving but even the 22W is still bloody loud and EL84s will change your tone a lot...maybe also look at 6v6 power tubes.

The master volume on these amps is pretty good, there are two ways to run it:

1. MV high and a trickle on the module Level control...produces a thinner, more metallic/agressive tone
2. Module level at 11 to 12 o'clock and a nudge above 1 on MV...produces a thicker, rounder tone.

JKD said:

ashishk said:

I heard that doing this reduces the output volume by half. Is this true?

Cos I followed all the steps above, but still, the output volume is the same.
I basically wanna run the power tubes hard to force more compression at lower volumes.

What am I doing wrong?

Cheers,
Ashish

Click to expand...

It reduces the output *power* by half but I believe the perceived volume difference is 3dB...i.e. not much at all.

If you want to push the amp harder at lower volumes, look into an attenuator - sits between amp and speaker and soaks power. THD Hotplate is an example. I use one but never usually more than 8dB of reduction, since it affects tone and squishes the signal too much at 12 and 16dB settings.

8dB of reduction is still more than 2x the power tube reduction though....

I deliberately bought a 50W MTS because a) I think they sound better and b) 50W is still too loud

Alternative methods of power reduction are - use THD YellowJackets and run EL84s ... this will be another power halving but even the 22W is still bloody loud and EL84s will change your tone a lot...maybe also look at 6v6 power tubes.

The master volume on these amps is pretty good, there are two ways to run it:

1. MV high and a trickle on the module Level control...produces a thinner, more metallic/agressive tone
2. Module level at 11 to 12 o'clock and a nudge above 1 on MV...produces a thicker, rounder tone.

Click to expand...

Thanks heaps for that JKD! I read about the hotplate, and was trying to avoid getting that by pulling out the tubes. But 3dB of reduced perceived volume is really nothing usable.

Would you say this is a better set up, i.e. running 2 tubes instead of 4 in the long run if the amp never gets turned up past 10 o'clock on the Master Volume? Are there any downfalls to doing this?
Lastly, if running on 2 tubes, do they need to be the same kind? e.g. 2XEL34s as opposed to 1XEL34 and 1X6L6.

I usually run my module Levels at about 1.30-2 o'clock cos I like that full, warmer tone that it makes.

Cheers!

ashishk said:

JKD said:

ashishk said:

I heard that doing this reduces the output volume by half. Is this true?

Cos I followed all the steps above, but still, the output volume is the same.
I basically wanna run the power tubes hard to force more compression at lower volumes.

What am I doing wrong?

Cheers,
Ashish

Click to expand...

It reduces the output *power* by half but I believe the perceived volume difference is 3dB...i.e. not much at all.

If you want to push the amp harder at lower volumes, look into an attenuator - sits between amp and speaker and soaks power. THD Hotplate is an example. I use one but never usually more than 8dB of reduction, since it affects tone and squishes the signal too much at 12 and 16dB settings.

8dB of reduction is still more than 2x the power tube reduction though....

I deliberately bought a 50W MTS because a) I think they sound better and b) 50W is still too loud

Alternative methods of power reduction are - use THD YellowJackets and run EL84s ... this will be another power halving but even the 22W is still bloody loud and EL84s will change your tone a lot...maybe also look at 6v6 power tubes.

The master volume on these amps is pretty good, there are two ways to run it:

1. MV high and a trickle on the module Level control...produces a thinner, more metallic/agressive tone
2. Module level at 11 to 12 o'clock and a nudge above 1 on MV...produces a thicker, rounder tone.

Click to expand...

Would you say this is a better set up, i.e. running 2 tubes instead of 4 in the long run if the amp never gets turned up past 10 o'clock on the Master Volume? Are there any downfalls to doing this?

Lastly, if running on 2 tubes, do they need to be the same kind? e.g. 2XEL34s as opposed to 1XEL34 and 1X6L6.

Click to expand...

When I had a 100W head(Mesa DR), I used to pull two tubes and preferred the feel/sound of it. Downfalls are I guess it wears two tubes..but you can switch 'em round and get twice the lifetime

Tubes pairs need to be same...not sure of technical reason other than they'd be mismatched on output.

Sounds good JKD! Thanks again.

Gonna stick to running 2 tubes for the next few gigs and see whats the comments from the punters.

Cheers!

it's all going to be a matter of preference.

i prefer the hotplate approach as you get the additional deep and bright switches to add that much more verisitiliaty. (<--yikes)

JKD said:

When I had a 100W head(Mesa DR), I used to pull two tubes and preferred the feel/sound of it. Downfalls are I guess it wears two tubes..but you can switch 'em round and get twice the lifetime

Tubes pairs need to be same...not sure of technical reason other than they'd be mismatched on output.

Click to expand...

Well, aside from the fact that two different tubes would not amplify symmetrically (remember, in a push-pull amp half the circuit amplifies one half of the signal waveform, the other half of the circuit amplifies the other half of the waveform) there's also the fact that EL34s and 6L6s have different bias points.

I'm not just talking about the bias voltage applied to the grid so it doesn't matter if the amp can adjust each tube individually. I'm talking about the idle current. 6L6s are generally run at a higher current than EL34s, and that would create a DC offset in the output transformer. That can cause the core to saturate, which, at best, really messes up frequency response.

Even if you were to run the 6L6 at a colder bias point to match the EL34, there would still be a slight effective offset due to the asymmetrical signals. It may or may not cause a problem in this case, but I don't know that it would sound good either.




A note about 6V6 tubes and such: When trying to reduce power, try to remember this; you are cutting the power output of the POWER AMP, not the drive capability of the PREAMP. Personally, I don't find the sound of 6V6s in a high power amp to be, "too compressed" or anything, but they can quickly get there if you don't keep the master volume in check. The master volume in most amps is actually a simple variable attenuator between the preamp and the power amp. With tubes capable of less power, you have less headroom. If you don't also turn the volume down, you'll be hitting them just as hard as the higher power tubes and what do you think is going to happen? Yep, squish. Cutting the power down to 20-25ish watts by running a pair of 6V6s in there won't suddenly allow you to crank it to 10. The point is that it'll sound better at like 3-4 than it used to! A lower power in the power amp section allows you to sound better at a lower level, not to crank up the level.

That's my opinion and how I hear it anyway.