It looks like you're new here. If you want to get involved, click one of these buttons!
Subscribe to our Patreon, and get image uploads with no ads on the site!
Base theme by DesignModo & ported to Powered by Vanilla by Chris Ireland, modified by the "theFB" team.
Comments
Standby on and off as necessary in use.
Power off - doesn't matter. Both off together if you like.
That of course assumes that the amp is correctly designed and the standby switch is in the right place when the amp also has a valve rectifier! Many modern ones aren't - Orange and Vox in particular. If your amp has a valve rectifier and you aren't sure if it's one like that, it's probably better to never use the standby at all.
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
The amp is a Fender Blues Deville reissue model.
Re amps with a valve rectifier but with standby in wrong place eg AC30 I believe, why do manufacturers add a standby when this can actually be more damaging to tubes?
Good question - ignorance? It's probably because the designers grew up with solid-state rectifier amps (where it's fine to put the standby upstream of the first filter cap) and failed to realise that this will then exceed the rectifier valve current rating when the standby is switched with the valve hot. Basic lack of thorough knowledge of valve circuits, really - surprising, but it's the only explanation I can think of.
Although if you think that's bad, some of the design mistakes in modern Marshalls are quite shocking for anyone with repair experience. Lack of proper separation between high-voltage-difference traces, unnecessary switching in the speaker circuit, fail-unsafe bias adjustment (unlike vintage Marshalls), it just goes on and on...
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
"why do manufacturers add a standby when this can actually be more damaging to tubes?" ....Promise I won't go on!
No idea where the standby switch came from on guitar amps, virtually no other audio device has or had one. Some say it was a mute function in the dance band era but who knows?
Dave.
I'm not sure if Fender were the first to use them, although they must have been among the first. Given that Leo Fender was a notorious penny-pincher except when something had a reliability benefit, I'm fairly sure there was a good reason.
One thing it's quite useful for is allowing the amp to warm up and dry out any condensation before applying the HT to things where it might arc, like valve bases… Leo probably worked this out from experience with cold amps being taken into humid dancehalls in the winter.
It's unnecessary as a mute when you can always turn the volume down to zero or just pull the cable halfway out of the jack, so it's unlikely to be that.
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
Fender introduced the standby pretty soon after they started using a DC-couple cathode follower to drive the tone stack.
This can arc over if the HT comes up before the valves are conducting, so it could have been introduced to protect the valve in the cathode follower.
It could also have been introduced to protect the filter caps from the unloaded HT.
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
http://tertl.blogspot.com - personal blog
Although he doesn't mention one fairly useful advantage to a standby switch, for techs… it's extremely handy for troubleshooting and valve swapping .
The big problem with quickly troubleshooting an amp with no standby switch is that it's hard to tell where the problem is if it just blows fuses when you turn it on.
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
It wouldn't be a huge job to fix it though, unlike some of the more complex PCB amps, eg the AC30CC.
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
There are a couple of mods you can do to an AC side S/B switch circuit which protect* the GZ but I would still rather do without them! As a valve TV tech in a former life with "live" chassis and later all chassis at 1/2 mains input I got used to shit or bust power.
*The point about protecting a DC coupled stage I had not thought of (Merlin tells of it) Leo F did not of course have silicon diodes back in the day!
Dave.
It also had a noisy fan that was intolerable at low volumes. I suppose I could have asked a tech to install a far better fan, but it annoyed me, so it went.
https://soundcertified.com/speaker-ohms-calculator/
If you wanted to fix it properly you could do one of three things:
Move the first filter cap to upstream of the switch. (Not totally straightforward given the layout.)
Add a resistor across the switch to 'trickle charge' the cap, as suggested in the link above.
Add an extra smaller filter cap on the upstream side of the switch.
If it was me I'd probably do the last - since that requires the minimum of work and disturbance to the amp but retains the advantage of having no HT on the circuitry if you want to change valves or troubleshoot.
For what it's worth I wonder if the bad standby switch location is responsible for the PT failures I've heard about with these amps… as Merlin Blencowe says it can cause a flyback voltage in the PT. (But which having the cap on the right side of the switch also stops.)
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein
But since part of the job was replacing the filter caps, it was obviously best to simply rewire it correctly - with the first filter cap upstream of the switch - at the same time.
Today's other job is a 90s Marshall-built Vox AC15TBX - with the standby in the wrong place - and a blown power transformer. I wonder if that's related... the arc is in the HT winding so it's quite likely.
"Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski
"Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein