Switching a Marshall 50/100 from high to low power while on

[gui_tarzan]

Someone posted a thread either here or on MEF recently where he switched down to low power while the amp was on and I can't find the thread anywhere. Was it here?

[Reeltarded]

I haven't seen it here. I don't recall there being anything wrong with flipping a 25/50 hot.. that stops the amp from working if it's a backline rental. lol

[sluckey]

Google search for "Switching a Marshall 50/100 from high to low power while on" brings up lots of discussion.

[gui_tarzan]

It's a DSL 100H and apparently the guy said when he did that it made a horrible noise and he shut it off. I haven't looked at it yet, I just wondered.


And this should probably have gone in the Marshall forum.

[Leo_Gnardo]

It's one of those Yogi Berra things, consider his theory/practice quote. In theory no problem. In practice, it's a good idea to have some patience, put the amp in standby & let it settle down for a couple seconds before making triode/pentode switches, then put back into operate mode. This is why I don't put footswitch/relay operated triode/pentode mode switches in amps though it's been requested.

[Littlewyan]

Why would you want to switch from 100 to 50 or 50 to 25 when the amp is on? I can't understand why someone would be so desperate to drop 3dB so quickly.

[Leo_Gnardo]

Why would you want to switch from 100 to 50 or 50 to 25 when the amp is on? I can't understand why someone would be so desperate to drop 3dB so quickly.

Live concert/show playing, you know some of our guitarist friends are button-happy. Why reach for your guitar volume control or pickup selector when you can step on a switch? It's an artistic choice that must not be denied.

Also - besides the tone/level changes as you navigate from intro to verse to chorus to solo etc., some bands have a habit of moving from song to song instantly too, no time between to fiddle faddle with the gear. One of my best ever customers found that out when he went from local guitar hero to national touring band. At home he was the purist, guitar straight to amp, then on the road he had to get some buttons underfoot to accommodate the zero-time between songs his new employer required. Didn't much like it but that's what it takes to keep the paychecks coming

[Littlewyan]

That man needs an Express . No more pushing buttons, just adjust the guitar volume. I played 50s and 80s songs at my last gig with the Express by just adjusting the guitar volume.

[pdf64]

What model #, or how does it achieve the lower power mode?
If it's just a pentode/triode thing, I don't see a problem with switching it whilst it's in operational mode; it may give fairly loud 'click / pop' though, which customers (on and off stage) may not appreciate.

[gui_tarzan]

DSL100H - it has a switch on the back panel that changes it from pentode to triod mode and the manual states NOT to do this unless it's in standby mode.

Honestly, I haven't even looked at it yet so I'm just going by the manual and schematic. It's a little vague because the switching isn't shown, but once I get inside it I'll have a better idea of what's going on.

Just for my own sake (and anyone else reading that hasn't worked on one of these) what exactly can physically happen to the amp by switching when it's not in standby?

[Littlewyan]

It may be because its switching DC and there is a possibility of an arc.

[Leo_Gnardo]

That man needs an Express . No more pushing buttons, just adjust the guitar volume. I played 50s and 80s songs at my last gig with the Express by just adjusting the guitar volume.

Oh I modded a Deluxe Reverb in just about every way & he was happy with that, just saw him play it early May, but pentode/triode remote control switching was out.

Yes switching hi voltage especially with relay contacts or toggles that aren't meant to handle 400 - 500 or more V DC (or even if they are) can raise arcs. OTOH from the output tubes' point of view, a screen grid with no voltage on it just shuts off the current. For that instant when the pole isn't at either connection the tube's off, no harm right? Yeh, except for those pesky arcs. Hence my Yogi Berra remark. Some people manage to get away with it, some switches work better than others, but it's still best practice, while the amp's off or in standby, to select your mode for the session and stick with it.

[gui_tarzan]

I hadn't considered an arc but that makes perfect sense.

[pdf64]

At such a low screen grid current draw (ie static conditions) I can't see that an arc would be likely to form?
And the change in Vdc from pentode to triode would be minimal.
Flipping whilst the amp was screaming would be a rather different matter; perhaps that is what Marshal were trying to ensure didn't happen?

[gui_tarzan]

Finally got to this today. Plugged it in, turned it on and no sound. The 270 ohm power resistor is cracked and one of the fuses in the power circuit is blown. So apparently it did cause a surge somehow. I don't see any other obvious damage so I'll replace those and see what I get.