Tech Tip : Does This Amp Need Standby? Episode 1 : Solid State Rectification in a '67 Fender Bassman

A lot of myths and misconceptions about Standby on the internet. I'll be doing a series of case-by-case examples of when Standby IS needed, when it's not, and when using it can actually damage your amp.
For more info, Subscribe to this channel, join us at PsionicAudio, or email us at [e-mail].

[@martinreid1740]

Best article I read on this is Power and Standby Switches - The Valve Wizard.

[@mattjohnson6916]

Great video, Lyle! I love how you explain theoretical stuff some of us might have once read about by demonstrating it in a straightforward manner. I hope your gallstone issues have been resolved and that you continue to be on the mend!

[@voxpathfinder15r]

Thanks Lyle for this video! Was looking forward to seeing it since you told me about it. Will check my Carvin Belair now and let you know my results.

[@GregoryHillSr]

Thank you for this video, very informative!

[@Satchmoeddie]

Vox used something called a "Brimistor" on the rail in their EL34 powered 50 & 100 watt amps. It's just a thermistor that used to be made by Brimar Valve. I think they were 3000-4000 ohms @ 20 degrees C, and dropped off as they heated up. Technically they limit current inrush more so than they limit voltage. DC voltages perpetuate arcs a whole lot better than AC voltages do because the AC voltage is alternating from + to - and therefor it's crossing zero 50-60 or 100-120 x a second. That crossing zero kills the arc sooner. With DC it's either + or - from common, and it stays in that state.

[@jaycee30865]

Awesome.

[@bigmac4948]

Thanks Lyle. Very informative. Always wondered about those switches ability to handle such high DC voltage. How would one wire 47k 2W resistors to 'soften' affect, as you briefly alluded to at the end of the video? (ie, an amp using ss rectification such as a Fender Twin.)

[@PsionicAudio]

Thanks! You just solder the resistor across the switch. There will always be some voltage this way, and a low volume output, but it drastically cuts things and eliminates most popping at the switch. There are other considerations such as flyback diodes across the choke, etc, but that gets into theoretical esoterica more than things you actually need to worry about.

[@peterstephen1562]

What Lyle says here is dead on true. But don't forget what he mentioned briefly about cathode follower stages. I have a Holden wasp amp from 1971 that is still working with the original tubes except the cathode follower before the tone stack and a cathode follower tube after the phsse splitter to drive the KT 88's. If the tubes are not warmed first by using the standby , which in this amp simply removes the voltage from the output tube screens, those cathode follower stages arc over with annoying regularity.

[@peterstephen1562]

The preamp and phase splitter HT is down stream from the output screen supply.

[@elwrongo]

Very useful video that clears up a lot of questions. "you meet interesting people when they're about to gash you" or was it gas?

[@PsionicAudio]

They did both. Fortunately I got the gassing before the gashing....

[@DanielBobke]

In general, I think most people recognize that a standby switch is rarely a needed item - specifically on newer amps. As I understand it, Leo Fender included it in the tweed amps because he was trying to protect the small capacitors that he used in the amps and the switch was cheaper than the capacitors at the time. I don't think that is true any longer and most amps have capacitors that can take the voltage prior to the tubes warming up. I have also heard it said that from a tech's perspective, they are a useful, but I don't really understand why. Is there any reason to have standby switches in modern amps, either from a user perspective or a tech's perspective? So many people think it is a "go get a beer" switch or a mute - neither of which I think is true.

[@jimcastillo8950]

Hello, why on Fender blackface or silver face amps when the amp is ON along with the standby ON then when you turn off the standby switch with the power switch ON you hear a pop through the speakers? I know your supposed to power on first, let the amp warm up then turn on the standby switch on. This is the correct way right? thank you for your videos.

[@devinmastersislame]

I have an svt cl from the 90’s, an ampeg b15s, and a 93’ 410 deville. I should probably stick to using the standby on these, right? 😂

[@MartinMCade]

Is it accurate to say, as a general rule, that a standby switch is needed if an amp has a solid state rectifier? And if an amp has a tube rectifier you don't need to use standby? Or does it depend on the specific amp and the details of how it's built? (I have multiple tube amps - Trace Elliott, Fender DRRI, Marshall, Goodsell, Carvin, and one or two others. Some have a standby switch and some don't.)

[@jaycee30865]

5r4, 5u4, 5y3 do need if not mistaken due to near-immediate b+.

[@PsionicAudio]

It's not a matter of when the B+ flows but whether that B+ exceeds the rating of the filter caps when the circuit is not drawing normal amounts of current. This Bassman has immediate high DC but the 500V caps are rated for it. If the amp had 400V or 450V caps, no bueno.

[@jaycee30865]

OK sounds like I could damn well be mistaken.

[@jaycee30865]

@@PsionicAudio ha ha. I was making comments as I was watching and I think you can see. It’s so good to hear you and that you are doing well. You are absolutely my new favorite channel partner. Funnily was taking a walk through the neighborhood looking at some under-construction houses and observing some sagging window frames and some cracked glass beneath them. Within the unfinished wall somebody had drawn an arrow and written “no Bueno.” I thought if in 20 years somebody removes the sheet rock and sees that... the applicable statute of limitations is doubtless going to be tolled. As if the construction company were still going to exist in 20 years...

[@PsionicAudio]

@@jaycee30865 admitting mistakes makes us better people. See the '66 Super Reverb video I'm about to post showing one of my own goofs.

[@jaycee30865]

@@PsionicAudio re no bueno: as you might say, “I digress.“ New vid: looking forward as always. The most applicable scenario I have for this topic right now is an AC 30 cc and an AD 30. I prefer 5r4 in the AD. Calms it down quite a bit. The AC 30 is basically just right right now. And thanks to you I now know to not use the standby switch in either one (I think). Just due to the risk of power transformer failure due to rec tube failure/shorts. Fwiw I have discovered that 5Y3 made by sovtek (freq branded by Fender) are completely out of spec. Much higher B+ voltage than in vintage spec. A real freak of nature kind of tube. Strongly advise against - particularly in a deluxe.

[@artysanmobile]

Standby merely defeats the ideal natural behavior of power tubes warming up, with a current draw that gracefully ramps up, saving many components from unnecessary trauma. I keep my vintage JMP standby in an always on position. Power tubes will last longer, transformers forever.

[@PsionicAudio]

That is really really bad advice for an amp with SS rectification and a cathode follower stage.

[@michaelnewell3823]

Hi , I have a 1965 Blackface Fender Bandmaster amp. Do I need to use the standby switch with the amp being 40 watts and solid state rectifier? I never use my standby switch on my Vox AC30. I have a Ceriatone HMR Dumble clone, do I need to use the standby switch on this amp to turn it on? The amp is solid state rectification. I also have a 1994 Mesa Boogie Tremoverb 100 watt amp that pops everytime you flip the standby switch into the play mode or when turning it off. It doesn't sound good. Don't know if I am doing damage to the amp or not. Thanks from Michael Newell in Niagara Falls, Canada

[@PsionicAudio]

A tech would need to perform the same measurements I show here to know which of your amps other than the AC30 might need standby. It depends on the filter capacitors' voltage rating and the unloaded DC voltage present in the amp is. And that can vary. I cannot say without measuring your actual amps. Until then, follow the manufacturers' recommendations.

[@PsionicAudio]

But no, that standby won't hurt your Mesa. But have a tech take a look - it shouldn't do that.

[@mikejamieson419]

I decided to not use the standby on my jtm 60 combo after watching this this and now I powered it on and there is no sound :/

[@PsionicAudio]

Does your JTM60 say Bassman on it?

[@_-_Michael_-_]

My AC30 does not have standby switch. Nor it needs one...

[@PsionicAudio]

Um, this video is about this Bassman with solid state rectification. Most Voxes use tube rectifiers and don't need standby - even the models that have one. I'll cover those in a different video.

[@_-_Michael_-_]

Oh sorry, mine is 1978 Rose Morris version that has a SS rectifier so I thought it’s related...

[@PsionicAudio]

Gotcha. If you haven't had any issues, you should be good. The point of this series will be more for amps that DO have standby. Sometimes it's needed, sometimes it's not, and sometimes it can do damage (looking at you, Vox AC30C2X, among others). But I'll get to those later in this series.