Standby switches

MartinB

I have an old Dynacord I use for bass which has a bizarre arrangement for the standby switch. The amp has separate screen and plate rails, and the standby is a multi-pole job that disconnects the screen supply, sets the bias supply to its coldest,  grounds the input to the power supply board and puts a resistor in line with the PT primary.  Seems far more complex than necessary!

Modulus_Amps

MartinB said:

I have an old Dynacord I use for bass which has a bizarre arrangement for the standby switch. The amp has separate screen and plate rails, and the standby is a multi-pole job that disconnects the screen supply, sets the bias supply to its coldest,  grounds the input to the power supply board and puts a resistor in line with the PT primary.  Seems far more complex than necessary!

Wow, wonder is that was to reduce power dissipated during standby to keep the bills down

MartinB

I presumed it was just a bit of Germanic engineering overkill!  It also has a mechanical interlock so that the standby can't be engaged without the power switch.  

p90fool

MartinB said:

I presumed it was just a bit of Germanic engineering overkill!  It also has a mechanical interlock so that the standby can't be engaged without the power switch.  

I have a Dynacord 60w valve head, it certainly is well engineered!

It's worth remembering, as @Modulus_Amps pointed out, that punters don't care how standby switches are implemented, they just want to be able to warm the amp up on mute while they're plugging everything else in. 

When I'm repairing or modding my own amps I tend to treat everything as deadly, regardless of standby switches. 

Voxman

Only two of my amps have a standby switch...2003 Marshall DSL401 and Laney VC30-210. I tend to use these when switching on and off and if I want to leave the valves warm during a rest period, but have no idea re wiring and if these switches give any benefit or not.  

ICBM

ecc83 said:

I think it is a bit of a cheap shot when NOBODY has come up with a reason why Quad lls , Radford 25s and the lovely little Rogers 10x10 amp I had stolen had no standby switches?

Because those amps do not operate the valves at over their ratings, hence it doesn't do them any harm to leave them running continuously.

Guitar amps often (usually!) do, so it's good to be able to extend the valve life a bit by not leaving them cooking away except when the amp is actually going to be played - and better not to turn if off completely because that introduces another heating/cooling cycle.

It is true that leaving leaving valves on standby with no HT applied for a long time also causes 'cathode poisoning', but that doesn't seem to be a serious problem in guitar amps given the relatively short lifespan anyway.

To put the question the other way, why *not* fit a standby switch? (Other than cost.) It does no harm and is often useful.

Some makers seem to get very sniffy about it, even to the extent of deliberately fitting a 'standby' switch that is not actually one - to me this is childish and silly, even if you don't think it's potentially dangerous. If you're going to accept that the 'market' wants a switch, then make it do the job it's supposed to and which most people assume it does. If you really don't want a switch, then don't fit one.

Voxman said:

Only two of my amps have a standby switch...2003 Marshall DSL401 and Laney VC30-210. I tend to use these when switching on and off and if I want to leave the valves warm during a rest period, but have no idea re wiring and if these switches give any benefit or not.  

Yes they do. Both these amps run the valves rather hot, and the DSL is well known to suffer from general overheating problems as well. Putting it on standby will help that not become a problem.

ecc83

Sorry, that won't wash either.  "Our" fixed biased amps run the valves at about 12W and I think most makes only run 25W valves at 15W Pa tops?

It is a poor show that cathode biased amps are run 'OTT' and thus need a special switch to 'save the valves'. In any case, the EL84 and 6V6 WERE run at close to 'book' ratings of 12W in radios and hi fi amps and lasted bloody decades!  The average radio was operated for far longer than any guitar amp, went on when you got up and went off when you pitted!  AND they ran bloody hot as well, the early PCBs went brown and crispy very quickly.

There IS no logic to the stand by switch save possibly as a muting device in the big bands. IMHO.

Dave.

ICBM

ecc83 said:

Sorry, that won't wash either.  "Our" fixed biased amps run the valves at about 12W and I think most makes only run 25W valves at 15W Pa tops?

A bit higher with some, although I would agree that they're not over 100% at idle. Most cathode-biased amps are though.

ecc83 said:

There IS no logic to the stand by switch save possibly as a muting device in the big bands. IMHO.

Well, I find them very useful both while playing and working on amps. There is still no good reason I can see *not* to fit one. (Assuming it's not in the wrong place in the circuit.) But if you don't want to, then don't... it baffles me why there is so much moaning about it from some amp makers, and worse, why some of them will fit the switch but intentionally defeat the purpose of it to prove some kind of point.

martinw

ICBM said:

Well, I find them very useful both while playing and working on amps. There is still no good reason I can see *not* to fit one. (Assuming it's not in the wrong place in the circuit.) But if you don't want to, then don't... it baffles me why there is so much moaning about it from some amp makers, and worse, why some of them will fit the switch but intentionally defeat the purpose of it to prove some kind of point.

+1.

The debate is only really of issue to contrarians and dogmatists (is that a word?)
The rest of us just get on and fit/use them. They've been on guitar amps for 50-60 years with no real issues. 

ecc83

I do agree that properly implemented they "do no harm" especially with Silicon rectifiers.

BTW. I found the Quad ll runs the KT66s at about 22W but at of course at the mercy of the mains supply!

Pretty sure they were reliable (except the cathode resistor which was underated at 3W!)

Dave.

Modulus_Amps

ICBM said:

 There is still no good reason I can see *not* to fit one.

Find a small toggle switch that is, on paper, rated for switching high DC voltage in appliances.... also so that someone  doesn't start a thread on a guitar forum complaining that your amps pops loudly and others don't.

Lots of reasons to not fit them - switch Cost, soldering time, cable routing time, removing a possible point of failure, but most importantly with the current popularity of small amps - real estate.

martinw said:

ICBM said:

Well, I find them very useful both while playing and working on amps. There is still no good reason I can see *not* to fit one. (Assuming it's not in the wrong place in the circuit.) But if you don't want to, then don't... it baffles me why there is so much moaning about it from some amp makers, and worse, why some of them will fit the switch but intentionally defeat the purpose of it to prove some kind of point.

+1.

The debate is only really of issue to contrarians and dogmatists (is that a word?)
The rest of us just get on and fit/use them. They've been on guitar amps for 50-60 years with no real issues. 

I don't think there is a debate really is there? it is generally agreed that they are not needed. So it is the designers choice and the designers choice on its "purpose" (how it is  implemented) and as long as it does not cause failure issues or make the amp dangerous to the user - everything else is just opinion.

ecc83

"everything else is just opinion."

And THAT ^ surely is why we have internet forums? If you don't want to discuss (nicely) don't come!

Dave.

Modulus_Amps

ecc83 said:

ICBM said:[Devil's Advocate]

So why bother sleeving the mains connections?

Because it looks neater, shows somebody 'cares' and also, certain magazine reviewers (not of guitar amps) expect such attention to detail and make a point to mention it when it is not done!

It is also one way to comply with the design codes on creep and clearance that is also signed off by third party's.

Another important reason for doing it is quality control, mains connections have specific guidelines and manufactures have to ensure they are met on every product, now you can hook/crimp the wire in and solder it, but when you are building 150 + amps a week or subcontracting the building to a manufacturing house who may have Jenny Lee, John Woo or Lucy Chang soldering those connections on any day, then it makes ensuring those connections comply with code much easier through design and easy visually inspection.