valve amps must be connected to speaker cab b4 powering up?

[skidder652003]

Hi folks
theres a bit of a debate going on another website about this. Does anyone know if it's true that you should always ensure valve heads are connected to the speaker cab before you switch on?
Slightly paranoid about destroying expensive amp!

Edited July 20, 2014 by skidder652003

[discreet]

Yes, yes, and yes again. I always connect my valve amp to its cab(s) before even plugging it in just to be on the safe side. You can run SS amps with no cab attached, but not valve amps.

At least this is the wisdom I have always received. My view is that I don't see any possible advantage to running a valve amp without cabs anyway, so why take the risk if it can very easily be avoided?

Edited July 20, 2014 by discreet

[Billy Apple]

A valve amp must be connected to a load or you risk damage to the power section of the amp. The load is usually the speaker, but you can get dummy loads for DI'ing in a studio or to work on the amp. Always remember to have to right selection of ohmage on the head for the speaker

Edited July 20, 2014 by Billy Apple

[spaners]

[b]Never[/b] ever fire up a valve amp without a cab connected. you will blow the output transformer or damage the power valves due to the impedance mismatch. For amp testing we use what is known as a dummy load (an amp tech will normally make there own)
[b]No cab connected = many £ spent![/b]

[0175westwood29]

as far as i know if you want to put it on standby then thats fine but if you want to use the head then as above always plug it into a cab, or if you wanted to use the di out say for silent recording, you can get dummy loads to make the amp think its plugged into a 4 or 8 ohm load.

andy

[mart3442]

My mates mesa boogie 400+ was left on standby for 15 mins with no speaker connected. The amp is now f****d.....

[ahpook]

Just to add another 'not a good idea to run a valve amp with no load' post.

It can be a good way of destroying an expensive output transformer

[JTUK]

[quote name='discreet' timestamp='1405852249' post='2505719']
Yes, yes, and yes again. I always connect my valve amp to its cab(s) before even plugging it in just to be on the safe side. You can run SS amps with no cab attached, but not valve amps.

At least this is the wisdom I have always received. My view is that I don't see any possible advantage to running a valve amp without cabs anyway, so why take the risk if it can very easily be avoided?
[/quote]

Old valve amps always needed a load. ALWAYS.
Never really understood why but so hard to repair back then...
so utmost care was taken with loads and impedances.

[KiOgon]

[quote name='JTUK' timestamp='1405858372' post='2505826']

Old valve amps always needed a load. ALWAYS.
Never really understood why but so hard to repair back then...
so utmost care was taken with loads and impedances.
[/quote]Aah! Those old valve amps always have a cab plugged in & usually a pie in a foil tray & chips wrapped in newspaper on top, over the vents to keep nice & hot for after the gig. Never stand your beer on top though - can't stand warm beer although it's always handy to have a pint or 2 closeby in case the newspaper catches light

Usual disclaimers apply, please don't try this at home, your home may be at risk etc.etc.

[discreet]

And remember that the value of your pie and chips can go down as well as up.

[JTUK]

I recall an old Selmer TnB which had a cooked transformer... as did quite a few valve amps back then, probably thru not running
a load when powered up... (we said switched on back then ) and you couldn't get them repaired.
Maybe this was because the schematics weren't readiliy available or it was too much work for the money
but it meant if an amp got cooked...it pretty much stayed cooked for years.

So, then, thank god for H/H... and if you know H/H and Carlbro, you'll get how much of a pain valve amps were
to put up with that pile of poo...
You soon learnt to look after them if you wanted to keep them running..

[KiOgon]

[quote name='discreet' timestamp='1405859185' post='2505841']
And remember that the [b][i][u]calorific value[/u][/i][/b] of your pie and chips can go down as well as up.
[/quote]Fixed

[icastle]

I haven't used valve amps for 20 years, but I still connect my speaker(s) before powering my amp up.

Just get into the habit of always doing it and you'll never have a problem.

[Bill Fitzmaurice]

It depends on the amp. Many, most notably Fender, employ a closed circuit switched output jack that shorts the output transformer when no speaker is plugged in. That would be death for a SS amp, but prevents damage to a tube amp with no load. Not having a load won't bother a tube amp at idle, only when it's being played through.
[quote]My mates mesa boogie 400+ was left on standby for 15 mins with no speaker connected. The amp is now f****d.[/quote]When on standby only the heater voltage is active, the B+ voltage is not, so even if being played through no damage is possible. I haven't seen Mesa schematics but being basically upgraded Fenders I very much doubt that they don't use switched output jacks.

[barkin]

[quote name='icastle' timestamp='1405864428' post='2505931']
I haven't used valve amps for 20 years, but I still connect my speaker(s) before powering my amp up.

Just get into the habit of always doing it and you'll never have a problem.
[/quote]

This. I just wouldn't dream of plugging stuff in/out when it's powered up - be it valve, SS or steam driven.

[Dad3353]

It's similar to [s]traficators[/s] indicators for cars; one uses them, whether or not there's anyone around. It becomes a very useful reflex. Us old'uns will probably cancel them, too, as it wasn't done to leave 'em on after the manoeuvre. Much the same for speaker cables, and indeed, the sequence for turning on and switching off (Last thing on is the volume knob, which is the first to turn down at the end...). It's true that some amps have built-in protections. They won't help if the jack is in the amp, but not in the cab, for instance. Do it right, every time, whether one needs to or not. It costs nothing.

[yorks5stringer]

I never drive anywhere without sending the Missus a few paces out in front with a red flag......

[Grissle]

If the amp only has valves in the preamp however you can generally treat it like any other SS amp. Anyway I'm not aware of any amps with non-valve power sections that require a speaker load?

[bassmachine2112]

Get in the Good habit of plugging in cab/s before plugging in power cable just in case the power,on/off standby switch is on.

[Dad3353]

[quote name='bassmachine2112' timestamp='1405962628' post='2507000']
Get in the Good habit of plugging in cab/s before plugging in power cable just in case the power,on/off standby switch is on.
[/quote]

Good advice, but shouldn't matter too much as long as there's no signal (volume down, or no instrument plugged in...). Best to get the habits right, though, so I would agree.

[brensabre79]

I like to keep it simple. Regardless of some amps are OK some are not. No harm has ever come to an amp by connecting the speakers before powering up so I ALWAYS set up amps in the same way.

1. connect speaker
2. connect mains
3. turn on / power up

[bassmachine2112]

As above-1,2,3

[Merton]

Ditto

[discreet]

You can't argue with that.

[mart3442]

[quote name='Bill Fitzmaurice' timestamp='1405866648' post='2505949']
When on standby only the heater voltage is active, the B+ voltage is not, so even if being played through no damage is possible. I haven't seen Mesa schematics but being basically upgraded Fenders I very much doubt that they don't use switched output jacks.
[/quote]

I'll tell that to my friend with the fried amp......