Do Not Use Standby on an AC30

[Lyle Caldwell]

According to the previous post, anything with a GZ34 rectifier tube. So if you AC15 has one, then yes... if it's solid state - then no.

Notice the AC15CC has a SS rectifier but no standby. Cathode stripping really isn't an issue at these voltages.

[Lyle Caldwell]

Wow....So I guess all of those R&D folks at Korg/'Vox'/Marshall are just a bunch of idiots? This is quite revealing...

I think that's unfair.

The early 90s Korg designs, including the AC30TB series and Marshalls, had a host of serious problems.

Steve and Mitch addressed all the TB series' existing problems with the CC design, but the standby was IMO a mistake.

However, standby is traditionally a sign of a "high end" amp, so many players associate standby with quality. I can see why they might have felt a need to include it, though I do not think this was a great implementation of a standby circuit.

So a mistake? IMO yes. A sign of idiocy? No, and I strongly think that's a poor choice of words given that Steve and Mitch read this group and have been so helpful to so many members.

No one in this industry bats a thousand.

[Digam11]

Wow....So I guess all of those R&D folks at Korg/'Vox'/Marshall are just a bunch of idiots? This is quite revealing...

I think that's unfair.

The early 90s Korg designs, including the AC30TB series and Marshalls, had a host of serious problems.

Steve and Mitch all the TB series' existing problems with the CC design, but the standby was IMO a mistake.

However, standby is traditionally a sign of a "high end" amp, so many players associate standby with quality. I can see why they might have felt a need to include it, though I do not think this was a great implementation of a standby circuit.

So a mistake? IMO yes. A sign of idiocy? No, and I strongly think that's a poor choice of words given that Steve and Mitch read this group and have been so helpful to so many members.

No one in this industry bats a thousand.

+ 1

[Mayhawk]

Ditto.

[R.G.]

Wow....So I guess all of those R&D folks at Korg/'Vox'/Marshall are just a bunch of idiots? This is quite revealing...

I think that's unfair.
...
So a mistake? IMO yes. A sign of idiocy? No, and I strongly think that's a poor choice of words ...

I think I'd take that even further. There are things that you simply must put in an amp to sell it. It's a *social* and *emotional* rather than technical expectation. I believe that the standby fell into that range. The reasoning probably went:
"... and let's get rid of that silly tube rectifier."
"No, we can't. The customers have this thing going on the internet where they think that they can hear differences between tube and solid state rectifiers."
"That's silly. They can't"
"Well, they think they can. And they'll think we cheaped out if we only offer SS."
"OK, but then we'll probably have to put in a standby switch too."
"That's all right. They think that you have to have a standby, even if it's not needed."
"Ok, Ok. Put it in."

I do have some mental reservations about how many of "all those R&D guys at Korg/Vox/Marshall" are. It could be as small as two. 99% of the work in an amp design is mechanical engineering, not electronics.

[Grog]

I think a lot of guitarist like the stand by as a mute in between sets etc with out really understanding what it's doing.

In his book The tube Amplifier Handbook Dave Hunter basically states that they are not required with valve rectifiers only with SS, which I suspect is where they made their first appearance

The original AC30 didn't have one, but I guess we got used to using them as a mute and so thats why its there now

[AC50]

I strongly think that's a poor choice of words given that Steve and Mitch read this group and have been so helpful to so many members.

I totally agree, even if they didn't read these discussions. That's just wrong.

[drewl]

It's amazing how many of the standby circuits in alot of different makes are wrong, actually causing more harm than good!

[Pagey]

Lots of interesting information on this thread. But just to recap, as an AC30CC2 owner: If you're using the GZ34 rectifier tube in your amp, you should NOT use the standby switch. If you're using a Weber Copper Cap, you CAN use the standby, but it's still not necessary -- am I correct here?
Also a question - when firing up the amp without using the standby switch, should you have your amp's master volume turned all the way down to zero?

[Lyle Caldwell]

Pagey,

Your recap is correct, and you don't have to worry about the Master Volume when powering on, though you might want to turn it down before powering off, just to eliminate any pop through the speakers.

[Lyle Caldwell]

As RG says, so much is about player expectation rather than "design".

That that Fender 59 Bassman RI. Yes, they implemented standby better, though it is not necessary with the Bassman either. But they left the stupid "death cap" AC polarity switch, even though the amp has a three wire power cord with chassis/safety ground.

[riscado]

with all this into discussion I can't help but ask for an example (circuit wise) of what a well designed standby switch/circuit ought to be...

I'd like to make sure I implemented the right one on my home built amps, even though most of them use directly heated rectifiers, therefore making the standby a welcome addition (or at least I'd like to think so), but then again they're lower voltage amps, so maybe the standby ends up being pretty much redundant

[Lyle Caldwell]

A varistor across the mains power switch, to eliminate a voltage spike there.

Series diodes between the secondary of the PT and the rectifier. 1N4007s should suffice.

Standby implemented on the B+ output of the rectifier.

Voltage should go from the rectifier to the switch, with a 100K or so 10 W resistor across the switch, and then the switch should feed a thermistor and then a 10ohm 10W resistor before going to the first filter cap. This first cap should have a 1W resistor in parallel across it, with a value in the 220K-330K range. This will bleed off the cap when the amp is powered off but won't affect the DC filtering when the amp is powered on.

[R.G.]

I dug out some circuits I did for Workhorse prototypes. I had a MOSFET current clamp and standby switch on it that turned off DC power on it. I'll see if I can upload that to GEO for some examples.

[rogera]

After having been used to using AC30s and other Vox amps since the 60s the way that I've always dealt with muting the amp is to pull the input jack out about halfway.

It takes no longer than using a standby switch.