Standby switches

Rowby1

I have a 65 DRRI that makes a big thump when I switch it to standby. Is this normal? Should I be concerned?

My other two amps (MJW and Egnater) make no noise at all when I throw the standby switch.

timmysoft

Standby switches are bullshit, that’s most of the issue. 

Modulus_Amps

Depends on where the switch is in the circuit, but......just stop using it, you don't need to.

Rowby1

Modulus_Amps said:

Depends on where the switch is in the circuit, but......just stop using it, you don't need to.

Okay, in that case I will.

RiftAmps

Rowby1 said:

Modulus_Amps said:

Depends on where the switch is in the circuit, but......just stop using it, you don't need to.

Okay, in that case I will.

The ideal situation is to not use it at all, but if you find it useful as a 'mute' switch then solder a 47k 2W resistor across the terminals

MartinB

I'd seen it suggested that they can help with valve life in amps with a cathode follower (which wouldn't apply to the deluxe reverb).  I did put one in my last amp build for this reason, though with a resistor across it as suggested above.  

ICBM

It's not an issue, don't worry about it.

Standby switches aren't necessary, but they are useful and there's no reason to stop using it - the DRRI has the switch in the correct place so it doesn't stress the rectifier valve, unlike many modern amps.

clarkefan

RiftAmps said:

Rowby1 said:

Modulus_Amps said:

Depends on where the switch is in the circuit, but......just stop using it, you don't need to.

Okay, in that case I will.

The ideal situation is to not use it at all, but if you find it useful as a 'mute' switch then solder a 47k 2W resistor across the terminals

Would you recommend that resistor value regardless of amp? I might like to do the same with mine (Marshall JCM2000 DSL 50), thank you.

clarkefan

RiftAmps said:

Rowby1 said:

Modulus_Amps said:

Depends on where the switch is in the circuit, but......just stop using it, you don't need to.

Okay, in that case I will.

The ideal situation is to not use it at all, but if you find it useful as a 'mute' switch then solder a 47k 2W resistor across the terminals

Would you recommend that resistor value regardless of amp? I might like to do the same with mine (Marshall JCM2000 DSL 50), thank you.

ICBM

I wouldn't recommend putting a resistor across the switch, because it removes one of the most useful features of the standby switch, which is the ability to quickly troubleshoot the amp with no HT voltage but without turning the power fully off. With the resistor, the caps will retain some voltage. OK you can always pull the HT fuse if the amp has one, but a switch is easier.

I don't understand the opposition to them. They can be useful, and (unless fitted in the wrong place!) do no harm. Some amp makers go so far as to fit a standby switch which is nothing more than a glorified mute switch - in my opinion this is silly and dangerous. If you fit a switch, have it do the right job and turn off the HT. If you don't want to do that, don't fit a switch at all.

Rowby1

Thanks for the info chaps. Was just concerned that using the standby might be doing some damage as it was making a thump which my other amps don’t. 

ICBM

Rowby1 said:

Thanks for the info chaps. Was just concerned that using the standby might be doing some damage as it was making a thump which my other amps don’t. 

No. If anything it will be just keeping the speaker nicely freed-up .

The reason it will thump is because it's in the correct place for a valve-rectified amp - after the first filter cap. This means that when it's switched on, that cap then supplies a big rush of current to the other caps. This is a good thing, because it means the rectifier valve doesn't have to, so it avoids stressing it - unlike amps which have the standby upstream of the first filter cap.

In amps with a solid-state rectifier it can safely be upstream of the first filter cap, since a solid-state rectifier doesn't mind supplying the current surge.

ecc83

ICBM and I have "agreed to differ" about this for a long time.  Regardless of the harm to valves (if wrongly implemented and really only to those crap things VALVE rectifiers) the "danger to personal" is to me a red fish.

If you are an experienced electronics technician* you will EXPECT everything to be live (all guns are loaded) . The Guitar Amplifier with an HT SBS is an anomaly in the electronics world. NO other equipment has such a switch. Valve hi fi amps never did/do. TVs with 5,000V focus volts ('king HURTS I thell thee!) didn't. Microwave ovens, 3kV, 2 amps+ NO prisoners! are either live or not.

*If you are NOT so experience keep TF out of there or be very careful and stick to simple bias setting with a cold amp and croc clips. And DO stay away from naked mWave ovens!

There is/was a bit of kit with an SB switch. Radio TX sets but these had an expensive TX valve that that pulled a lot of power and the HT was 'blobbed on to talk', also there were portable valve TX sets and obviously conservation of battery power was vital.

Dave.

Modulus_Amps

ICBM said:

I wouldn't recommend putting a resistor across the switch, because it removes one of the most useful features of the standby switch, which is the ability to quickly troubleshoot the amp with no HT voltage but without turning the power fully off. With the resistor, the caps will retain some voltage. OK you can always pull the HT fuse if the amp has one, but a switch is easier.

I don't understand the opposition to them. They can be useful, and (unless fitted in the wrong place!) do no harm. Some amp makers go so far as to fit a standby switch which is nothing more than a glorified mute switch - in my opinion this is silly and dangerous. If you fit a switch, have it do the right job and turn off the HT. If you don't want to do that, don't fit a switch at all.

It is only silly and dangerous when a silly and dangerous tech goes in guns blazing without first checking what the circuit is doing, this is sort of thing is becoming more and more common as the switches used for standby are often not rated for the voltages applied to them. There is one guy on ebay selling standby switch kits for champs and supplying a mini toggle switch, utter madness is what that is.
Anyway we can agree to disagree on this, but I expect you will always check what comes across your bench before assuming how a switch is wired up

ICBM

Modulus_Amps said:

It is only silly and dangerous when a silly and dangerous tech goes in guns blazing without first checking what the circuit is doing, this is sort of thing is becoming more and more common as the switches used for standby are often not rated for the voltages applied to them. There is one guy on ebay selling standby switch kits for champs and supplying a mini toggle switch, utter madness is what that is.

Anyway we can agree to disagree on this, but I expect you will always check what comes across your bench before assuming how a switch is wired up

I do, yes - but the reason I think it's dangerous is that there are a lot of people who only half know what they're doing out there, 'helped' by Youtube videos about how to bias your amp...

I don't have an issue with not fitting standby switches, nor even with switches that are actually marked 'mute' or something, but if a 'standby' switch is fitted then it should turn off the HT. I don't even like the typical Peavey way of using it to turn off the screen supply, since it still leaves high voltages present on the valve sockets.

Yes, it's arguable that if you don't know what you're doing you shouldn't be in the amp at all, but it's a fact that this does not always apply.

Danny1969

I repaired a class D amp the other day which had a switch mode power supply. From the factory the live and neutral wires had been incorrectly spaded on the mains inlet socket so the fuse was inline with the neutral and (being) a switch mode design the live was connected directly to the bridge rect. Now the reason it was on the bench was the switching transistor on the chopper circuit had blown which took out the NTC thermistor and the bridge rect so the fuse had blown but the live was still happily sat on the board where the neutral should be ..... luckily i spotted there was 240v between the neutral and chassis before I did anything else and I corrected it. 
Makes you wonder why Neutrik don't use 2 different sized spade terminals on their powercon sockets to prevent this happening and it also proves a PAT test is a waste of time to a certain extent 

ecc83

IC, you can only go so far in protecting idiots. When have you ever seen a warning inside a car bonnet that said "Don't put hand on fan belt it will rip your arm off"? 

 All mains electrical gear is dangerous to some extent and valve amps more than most. Then almost all amp mnfcrts fit a warning label "Warning High Voltages. No user serviceable Parts inside" I know 'we' certainly do as well as a very plain warning on the amps that need it about the unusual standby arrangements.

Dave.

ICBM

ecc83 said:

IC, you can only go so far in protecting idiots. When have you ever seen a warning inside a car bonnet that said "Don't put hand on fan belt it will rip your arm off"? 

 All mains electrical gear is dangerous to some extent and valve amps more than most. Then almost all amp mnfcrts fit a warning label "Warning High Voltages. No user serviceable Parts inside" I know 'we' certainly do as well as a very plain warning on the amps that need it about the unusual standby arrangements.

[Devil's Advocate]

So why bother sleeving the mains connections?

martinw

ICBM said:

ecc83 said:

IC, you can only go so far in protecting idiots. When have you ever seen a warning inside a car bonnet that said "Don't put hand on fan belt it will rip your arm off"? 

 All mains electrical gear is dangerous to some extent and valve amps more than most. Then almost all amp mnfcrts fit a warning label "Warning High Voltages. No user serviceable Parts inside" I know 'we' certainly do as well as a very plain warning on the amps that need it about the unusual standby arrangements.

[Devil's Advocate]

So why bother sleeving the mains connections?

Yay!

That thought leapt out at me while reading Dave's post, but I resisted.

ecc83 said:

If you are an experienced electronics technician* you will EXPECT everything to be live (all guns are loaded)........

*If you are NOT so experience keep TF out of there or be very careful and stick to simple bias setting with a cold amp and croc clips......

Dave.

Modulus_Amps

ICBM said:

 I don't have an issue with not fitting standby switches, nor even with switches that are actually marked 'mute' or something, but if a 'standby' switch is fitted then it should turn off the HT

That comes down to your definition of what a standby switch is, or more so the standby function. from a users point of view the standby function is a "mute" function, or even a "warm up" function is the way it is mostly sold. Point being that the user  function can be achieved in a multitude of ways and the user does not really care what it is doing internally, it is on that basis that manufacturers change the technology behind the switch.
A bit like when you use you phone to make a phone call, you does not matter if it is analog/digital with a cable/satellite/wifi, you are still making a phone call regardless of technology.

Your point about servicing is valid, however I build loads of amps without standby switches and don't really have an issue pulling HT fuses if I have to.

ICBM said:

ecc83 said:

IC, you can only go so far in protecting idiots. When have you ever seen a warning inside a car bonnet that said "Don't put hand on fan belt it will rip your arm off"? 

[Devil's Advocate]

So why bother sleeving the mains connections?

I have obviously missed a lively discussion somewhere, I assume we all know why some manufactures really fit sleeving on mains connections...

ecc83

ICBM said:

ecc83 said:

IC, you can only go so far in protecting idiots. When have you ever seen a warning inside a car bonnet that said "Don't put hand on fan belt it will rip your arm off"? 

 All mains electrical gear is dangerous to some extent and valve amps more than most. Then almost all amp mnfcrts fit a warning label "Warning High Voltages. No user serviceable Parts inside" I know 'we' certainly do as well as a very plain warning on the amps that need it about the unusual standby arrangements.

[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!

There IS a lot in a valve amp chassis we CAN'T make foolproof but surely we should DO what we CAN do? Naturally 'fools' should not be in there and we attempt to tell them that!

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?

Oh! And just to be fair, there is ONE class of amp that had an SBS. Some  V old PA amps and this was because they could often be used in a field on a rotary converter fed from a lorry battery so the heaters were kept on but a bit of juice saved by shutting of HT.  But these were pretty rare beast even then !

Dave.