STOP USING THE STANDBY SWITCH ON YOUR GUITAR AMP! 

Love these repair videos. Also dig, how you correct yourself and take responsibility for any verbal mistakes you make. Very humble of you....and I really appreaciate being given the best info you have on hand. I have learned a bunch from you and Uncle Doug. Maybe one of these days....I will actually try some small mods on my own units. Thanks again for all the information you have passed on to the public with your efforts. Big love for the Guitologist from Austin Texas!!!

Hi brad please don't stop making repair videos they are very informative i love the older tube amp repair videos i have always wondered about standby switches and now i know

Brad ...I am blown by ALL THE KNOWLEDGE ABOUT VALVE AMPS AND THEIR REDESIGN YOU HAVE !!! It continuous to AMAZED ME ! YOU ROCK MISTER !!!

All of us who miss the amplifier videos are rewarded with this video..This amp keeps having problems. And the guitoligist to the rescue.

Been using tube amps for 50 years and the only time I blew a fuse is when I switched the power on when the standby was in "play". Only happened once, I guess I don't rock hard enough but I still use the standby because the chassis runs cooler when in idle. I have a Marshall DSL that will give a little pop in the speaker if you shut it off with just the power switch so I find the the standby switch useful. Old habits.

Awesome video! Very informative! I'm glad to see you in my RU-vid feed again. I wasn't getting any notifications of new videos you've posted.

Thanks 'for the video Brad. I've heard about the record flooding in Kentucky I hope all is well where you live. Stay safe

Yeah, the whole misunderstanding with using the standby switch came from high voltage / high current use. I was an engineer for a X-ray mfr and we would recommend warmup for our tubes, but they saw voltages of 120,000 volts and the inrush current was carefully limited by circuit design (for dose control as much as equipment protection). The relative low voltage of guitar amps makes this switch not only useless but actual detrimental to the amp's longevity.

I'm so glad you're putting out slightly more content now! I hope RU-vid Keeps the tap on. Maybe they'll turn that tap on for me one day too (not likely). Anyhow thanks for the great video. This is great info. I've always wondered about this.

I was raised as a tag-along kid in my dad's TV repair shop back when folks did that sort of thing and ended up getting a EE degree. I think the power supply filter cap changes, thermistors and biasing mode you've made are very good to improve safety as well as long term reliability of this amp.

This is one of your best videos. I’m going to build an ab763 Deluxe Reverb, single tremolo channel only. I’m using a Princeton reverb chassis. I’ll install a reducer in the first octal tube socket to accommodate the extra 9 pin tube needed. The remaining octal socket openings will receive the 6v6’s. I’ll use solid state rectification WITH the thermistor you pointed out in this video. No standby switch as well. Perfect.

I have a Seymour Duncan convertible that I'd like to keep around for a while. Good advice. Here's to many more years of warm tube sound!

Great info Brad!!! I've been gigging for years now, I never use standby switches! I just turn my amp off after the first set. All my amps have thermistors as well.

Couldn't agree more, Brad. Any modern build, even a clone of an old 'classic', should have a built-in thyristor inrush limiter (and to my mind, internal fusing where appropriate) and a thermistor to prevent voltage spikes from damaging your PT; if the design incorporates a master volume (a la Trainwreck or Dumble), then turning down said control is essentially the same as the function of a 'mute' switch, which is where Leo and others of that time period were headed anyway. None of these additions will do anything to diminish the magical 'tone', but they will add years of usable life to the amp. Don't get too down about not remembering every detail of a particular tube's specs; I can remember when I was a kid, watching the TV repairman come over with his box of goodies (which did not include a digital multimeter or calculator; loved that miniature oscilloscope of yours, BTW) and sort out why the picture was so wavy in short order. In retrospect, don't you think most of those cats were near-geniuses on some level?

This standby debate has always confused me... All my old Marshall, Hiwatt, and Fender amps have a standby switch which I've used for decades. I haven't noticed any diminished tube life and never had any electrolytic cap failures. Some of my amps still have the original caps and tubes going on 60 years of use!

Good video, Brad. I agree about the Standby switch. The Thermistor needs to cool down a bit before you re-apply power. When the Thermistor is hot its resistance is low, so it is not offering you much in current limiting. It was an excellent demonstration of what happens when power is applied to a hot Thermistor.

Great solution Brad, I am with you and I too wonder what that power transformer’s spec at.

So, based on the schematic for my 2204 clone, the standby switch only has the potential to harm the rectifier and transformer because the filter caps will charge as quickly as they can, resulting in a current spike upon closing the switch. All subsequent power stages are current-limited by resistors. It seems to me like a current limiting circuit would be the best course of action. A simple constant current circuit set at 1A should suffice. If the amp is drawing less, it's wide-open; if the amp tries to draw more, it cuts off. Though the BJT version that I know of probably isn't feasible at 120-240VAC. Your thermistor solution may be the best solution without over-modifying an existing power section.

You could also consider a resistor to limit the higher current that FB pot on the back causes. it wouldn't probably take very much away from the amp. I was surprised how much the current draw changed when you varied that pot! I assume more neg FB (lower pot resistance) *decreased* the current?

I always wondered what those thermistors do .. thanks for sharing

what Merlin Blencowe suggested was also put 2w/5w resistors across the standby switch to create a low current flow that partially fills the filter caps caps, which is then shorted when flipping the switch.

PLEASE READ: This video was meant to discourage amp designers from designing in Standby Switches. It applies more to tube rectified amps than solid state rectified amps as the tube rectifier takes time to warm up, and needs to charge the reservoir capacitor from cold to prevent arching due to excessive inrush current brought about by flipping a Standby Switch with a fully heated rectifier tube. But even amps with a solid state rectifier don't need a Standby Switch! The only reason to use Standby would be to prevent overloading a power capacitor or blowing fuses. As long as the power caps have been properly spec'd with voltage ratings exceeding the maximum voltage of which the power transformer is capable (something the amp designer should have considered already) and fuses are slo-blo and properly spec'd, this should be no problem. The best preventative measure for ensuring the life of components is for amp designers to design in ROBUSTNESS in capacitor specifications and use thermistors to help ease inrush currents. I had been meaning to do a video touching on this subject for some time, and this amp finally reminded me. For a detailed discussion on this topic, see this article from the great Merlin Blencowe: www.valvewizard.co.uk/standby.html Note that in his article, Merlin points out that if a Standby Switch is used in a design, the reservoir capacitor should be wired BEFORE the switch, not after. Also, someone asked about choosing a thermistor. For this I went with a CL-70 Amphenol. Most Fenders use CL-60. These thermistors have cold ohms ratings and current rating in amps. Both are important considerations. Here is a datasheet for comparing thermistors: www.mouser.com/datasheet/2/18/AAS-920-325D-Thermometrics-NTC-Inrush-031814-web-1315885.pdf

Great video. Super informative...thanks for your hard word.

Hi Brad, Glad to see you back on the channel. But your comment did raise a question with me. See I have been hard wired to believe that with a tube amp the stand by switch acts as a Power tube cool down after playing I have always switched the play mode to stand by to cool down the power tubes And to eliminate any crackle pops if accidental chord disconnects. And you are saying that the stand by switch is no longer needed. Thanks brother

I have seen other videos explaining about how standby makes little difference in spikes for solid state rectification and it makes some difference for tube rectification but is not really necessary as well as that cathode poisoning/stripping is not really a concern for guitar amplifiers because they don't use massive voltages and such compared to some other tube devices. Lower wattage tube amps often don't have a standby switch at all because they have an automatic standby function or just let the tubes warm up as normal.

I have started using a variac in all of my amps to 115 volts instead of 120volts. I rebiased my amps and everything seems to run much better and even sound better at that voltage. Johnny Hyland country guitarist on RU-vid talked about using the brown box variac. It really does sound and play better.

Are you going to demo the amp? I was looking forward to hearing you play through it

Been playund for decades, never use the standby... Just unplug or zero volume... Thank you for this video...

Awesome I always wondered about standby and why solidstate usually doesn't have one, but does this all still apply to more modern tube amp designs like a dual recto, 6505, newer marshalls?

Great video!! Very informative, thanks!

I just watched the DLab video about the standby switch. On a scope the Marshall spiked the same if you used the standby switch after the tubes warmed up, or just left the standby on and just turned the amp on. My whole life, I’ve been told I was going to ruin my tubes from not using the standby switch.

Hey Brad hope all is well with you and the family. Crazy times.

I have been using Ampeg svt's for years. I've always used standby on the vintage amps as they were hardwired with a standby tube and the new vr has an automatic 20 second standby.

I couldn’t agree more. Just plug into the wall outlet. So much tone!!!!!

Good to see you Brad

Brad, I have a F.R.E.D. rectifier in my Bassman 100. It must be heard and played to be appreciated.

Doesn't the use of the "inductor filter" directly after the rectifier mean that the voltage and current will be quite a bit higher on power up than the more common "capacitor filter" designs? That is what I have found when testing power supply designs. Thank you for the idea of adding thermistors. I will update the design I'll currently working on.

standby switches have the advantage of reducing thermal shock to the valves. the heaters come on first and you can hear the 'tinkling' noise as the internals expand. then the H.T is applied and the anodes begin to heat as electrons crash into them. upon switch off its more severe because the anodes are usually quite hot. you can hear them cool. i usually give it a few minutes then switch off the heaters and you can hear that too as they cool. it's surely better to cool more gradually to reduce stress on the internal welds and parts. on the subject of cathode stripping : it seems to apply to very hight h.t voltages only. several thousand volts. i had an amateur radio transmitter with 700 volts on the anodes and when it was switched to receive only, the heaters were turned off and the anode voltage remained. this never caused any issues

ohh that's the amp that had all the caps painted up... I remember that one now, you got it sorted, sweet

My main amp is a professionally made Blackface Deluxe clone and my understanding is that the rectifier tube releases voltage slowly to the power tubes so I would never use the standby switch because there is no need. This question plaqued me for decades before I learned this.

Haven’t seen the whole vid, but thumbs up! Reason, ppl always told me you should put a tube amp on standby. I know I’ll hear the real best thing to do with my amp. Trust a tech that works on actual amps more, than that other guitar guy that also has a tube amp. Also love your vids! I keep coming back to learn. Wish I had your knowledge, I always wanted to build something, meaning one of those build your own amp things. But I get so scared, I have a brother that knows more how to put things together but far apart. I try and try to learn electronics and…..my mind goes kinda mush… lol. 😂😂 not that smart for that, but hope one day I can put those “build your own kits” together by myself. But man. I’d hate to mess it up and not the tools to find what went wrong. Sorry just a lil story. Much mahalos 🤙

Brad - Love your tube diagnostic and repair vids. Learn a shit-ton every time. Damn, need to send you my original Silver Jube (50W) for a "tune up." It's making too many damn noises.

I have not used my standby switch at all since i got my jmp 2204 ... just power up, and tune the guitar and quick warmup of fingers, and then switch of the tunerpedal and go ... no problems for 6 years

Hi Brad, Great idea to add the thermistor, but a question for you. Rather than add in two, why don't you just add one after the standby?

Hello, sorry for asking but I am a newbie. I just purchased a tubes Bugera V55 and it has the stanbie switch. Is all that has been discussed here to ne applied to my ampli? Thanks in advance.

The advantage of the GZ34 tube over a 5u4 is the the go is an indirectly heated tube-the warm up time for them is longer that the 5u4 which has a directly heated cathode-it’s warm up is faster. With tubed rectifiers a standby switch isn’t needed at all.the slow arm up of tubed rectifiers makes them safer for tubes than a solid state rectifier which’s applies power instantly-long before the circuit tubes have warmed. And the sis can be harder of filter caps-a standby switch or in the case of transmitter s I deal with a time delay relay in the primary circuits of the hv rect transformer. Seen the gz34 in hi-fi amps.

Hey Brad thanks for the heads up.

Hey Man, I have a Brown Eye 100 deluxe i mostly turn the master volume down and go on standby before i go off is this good or not?

Hey Guitologist, I have a hand wired amp 1987 Plexi replica. On the back of the amp there's a b+ switch. It's a 3 way toggle switch. Please tell what it does. Thank you sir

I don't have the tech qualifications, just a hobbyist. In any of the valve amps I've made, I have never used a standby switch. For higher draw amps, I've tended to use gz34, 5ar4, gz37, 5v4, with separate cathodes to the heater. I would even tweak the power supply to optimize for them. I find that there's a slower ramp up on the B+ as compared to 5u4g. With the 5y3, I've used on choke input. Another thing I've done, given as advise by other hobbyist 20yrs ago was to put a resistor before the cap input to make an RC filter which slows the inverse rush to the rectifier as we tended to use tx to hand and over spec'd for versality in future projects. Any of these unadvisable?

Hey what size thermistor would I need to use in a 100 watt 1959 Marshall solid state rectifier

What kind of voltage is coming from the standby switch? Did you use a second CL-70 on it as well?

Wouldn't using a scope to check the inrush current show a more realistic peak current value by holding the value ?

I don't have a stand by switch on my amps ,but I was wondering if using a RX brown box would help with the situation you are describing here. I usually drop the voltage down by 4 volts on the brown box , unless I use it to keep the voltage coming in to 120 volts from the wall socket .

I had a Vox AC30 and soon learnt that leaving the standby button on saved the rectifier valve.

Some makers use the standby switch to bleed the big filter caps prior to switch off. My VHT Special 6 for instance..

To make sure I understand, I should turn both switches to “on” when I start my amps? RedBear MK60 (2204 clone-ish), 5153 EL34, Mesa 50/50 But once the amps have been running for a while and I go to take a break, THEN it’s okay to turn it on standby?

Thank you, Brad, and Root Mean Square at al. Until the next time: To You and Yours. Rab 👋

Had to watch this as I now have a Lee Jackson designed amp that lacks a standby switch. Even my amps with standby I never use then because I'll forget and leave them on when I walk away. Good shit to know.

I wonder about my “modern “ tube amp. Line6 DT25. I’ve been using my standby switch since I bought it 12 years ago. It eliminates the loud click during power down and keeps the Soundman from pulling out his hair.

Brad, I always turn all the knobs to zero before I switch from standby into power, then I turn them up after waiting for a few minutes. Is this still causing the voltage to spike? TY this is news to me, I thought the SB was to protect the amp. ??

Hey Brad I heard you mention about using an attenuator on this particular amp I have a 1972 Marshall 50 watt the original output Transformer has been replaced with a replica and it has been recaped with j.js, currently running tongue soul el34 original power cord replaced with a ground and I'm pretty sure my guy bypass the polarity switch my question is, is it okay to run this amp with a Bugera PS1?

Haven’t used a standby switch in years going back to the early 80’s with Marshall‘s and I’ve had zero issues in that time. I turn my amp on at gigs and if I need to mute it for breaks or anything else I’ll use my tuner. Amp is ready to go at anytime.

is the standby switch the warm-up switch? my victory amp asks me to warm up for 30 secs before full switch on

Your setup's even sweeter now ^^

Is this why they put a standby switch on the Valco built Harmony 430, a near dead ringer for the Gretsch 6162 with the exception of a 5Y3(?) -can’t remember if that’s different on.schematic vs. reality. The 430 Schematic shows a 5Y3 but actually has a 5U4. The power transformer in mine actually took a bath and they installed a much smaller Hammond PT. I’ve also read that the standby switch in these valco’s are a source of noise. Im spinning plates trying to decide whether to ditch it or not. I never use it as such except when powering on. I need to install a 3 prong and eliminate the the polarity switch. I wasn’t told what fried the PT but this discussion might shed some light on it. I’ve got RCA black plates and my wallet gets a bit jumpy when I play for these very reasons. Cheers’

Great post as usual. However let’s talk about Groove Tubes for a moment? Don’t forget to mention: Groove Tubes doesn’t make tubes. They’re just a distributor with a matching system. They use Sovtek/Electro Harmonix, Chinese and JJ tubes. Looks like you have either a JJ or Chinese rectifier

100% instructive. Thanks a million Brad

What about a vtm120? This is kind of blowing my mind. Have no issues with amp but this intrigues me a lot.

What's the difference in turning the power on without using the standby, or turning the standby switch off,and getting a rush of power doing it that way? Seems the same thing to me! In the Marshall booklet, they tell you to use the standby when the guitar;s not in use.

Yeah ! thermistors are great for overcoming inrush current ptoblems. You ended up setting the bias so it is pretty cold when overdriven.... That amount of crossover distortion is pretty audible when You see that degree of X-over distortion, and thin brittle sounding. I think the main problem is the power transformer, is overpowered, and the filaments represent close to zero ohms when they are cold thus all the inrush current. It would be better to put 44 uf's at the 1st filter cap. The bouncing waveform when overdriven is intermodulation distortion with 120 HZ ripple in the supply, caused by less than optimum filter capacity. Also that lovely red paint was probably lacquer with drying agents in it, which are nitrogen compounds, which can act like an electrolyte, and can cause leakage at high voltage. It is a really bad idea to paint a circuit board or rusty transformer with lacquer spray paint. By the by, I have also run into too many bad 5AR-4's lately, that arc.

I'm now wondering if I should stop using the standby on my Marshall JCM 900 4100 from the mid 90's...

The Vox AC30 CC2 suffers _really_ badly from this exact problem. Have blown three rectifiers because of this issue. I changed the valve rectifier out for a solid-state plug-in replacement.

My Orange TH30 head blows HT fuses a lot! I'm gonna try not using the standby switch man! Hope it solves that

So the advice is power up by flipping standby before power to mitigate tube harm. I'm guessing that doesn't apply powering down? Powering down w standby first to avoid gross speaker thump should not cause issues right? Apologies if this was addressed in the video and I just didn't catch it.

I had my Mesa rectoverb connected to a THD hot plate with the volume all the way up. I turned the standby switch off because I needed to disconnect my guitar for a second. I connected with my guitar back up after reconfiguring a few pedals. I then flipped the standby switch back on and then it was a huge pop and smoke😢

Well, being none of my amplifiers ever had Stand By switches (including a cool, rather heavy, loud all tube/valve 1979 50 Watt Garnett), how could I?

I might stop using my standby till I can get some thermistors soldered in or some way to prevent spikage think I do have a SS rectifier so good idea I guess, had no idea it spiked that high...

Thak you so much for another brilliant video

Cold tube filaments tend to draw a lot of inrush current. Placing an appropriate ntc thermistor is good practice. In P.A. power amps even with a timed ntc bridging power relay. It makes your stuff more relaiable and keeps the power mains fuses from failing....so your studio isn't in the dark...

I thought in the previous video the fuse blew because 1) 2 not 3 amp 2) not slow blow fuse 3) you eent straight off to on bypassing standby- I though you said THAT could cause the current spike too?

EveAnna Manley(Manley Laboratories) told me that the way they implement stand by in their tube amps is to have a tapped power transformer so you can go to half voltage on the AC side, before it hits the circuit. There is enough voltage to keep everything warm but stop any electron migration in the power tubes(another problem with stand by switches). I guess it also quells the inrush current too. I hope I'm remembering this correctly.

My understanding has been that tube amps with solid state rectifiers should be allowed to warm up in standby to prevent a sudden inrush of current that could potentially damage the amplifier. This would not apply to amps with rectifier tubes, as those tubes, like the preamp and power tubes, would also warm up gradually. Is this not the case?

I had the same problem with a super lead that I bought used. I took it back and got my money back. dude didn't tell me it was blowing fuses and it only did it when after it was warm and played for about 30 minutes or so. He said he was unaware but he was a musician and back then it was not a cheap amp by any means and I bought it because it was not expensive because he he said he would help me out. I ran into him on the back street music store in what once was a thriving city at the time of about 70,000 citizens with 4 music stores and at least 6 pawn shops.

Hey Brad, where can I get some multi meter leads like you have? The clip on. I'm digging the cigar box current limiter!

I've always wondered the purpose of a standby switch and if it's even necessary to use every time the amp's powered. My amp is an '84 Carvin X-60 and I've often mistakened the standby switch for the on/off switch both located in the upper right corner of the control panel and never had any similar issues since i bought it as a Valentine's Day present to myself 23yrs ago!

Hey Brad thanks for the video. Was really nice to hear another one of your videos especially on amps. And I learned a little something which is always priceless at least that's how I was brought up anyway hope things are well with you buddy and your family your girls your wife and everyone else that's important to you LOL just wondering though I have a cheap too bad really cheap one it's a stage right 15 watt and it seems like when I cut my EQ down off you know base mid and treble sounds like the almost all the volume is gone and I heard somewhere a term called boy I don't even know if it's the right term it's just what pops up in my head or a negative EQ I don't know if that's the right term to be honest I don't even know if that's a thing lol. But if so could that be why it's just kind of Acts differently than other ramps I've experienced two but otherwise or maybe this is something just indicative to this amp I don't know but you know the only stupid question is the one I asked right buddy I do like the amp and I don't have a huge experience with two bands in relation to guitars I did buy in the early eighties at a yard sale I think it was a 1950s Epiphone electoral zephyr amplifier which needed work but I was able to use it anyway and that's my only experience I mean it was so old it had electromagnetic speaker really cool grill though but yeah so I you know this whole foray into electric electric tube world is very new to me and again I like it it's really basic and simple you know and for me that's like really important by the time I could strum a note of course and get to the right knob on an amp any amp at this point sometimes the sustain is gone before I get to the knob which becomes really frustrating trying to set a tone that you want so yeah the less knobs the easier it is the same does have a tone knob I guess that's probably like a bright knob or something like that from what I've tried to find out anyway just glad to have listened to another one of your videos and you don't pop up into my feed all that often as you used to but I'm assuming that now that I clicked on this one I'll start getting more of you in my feed you know the saying how to sight out of mind out of ears out of mind all right buddy hope you keeping cool on top of all this oh yeah there was nothing you said you won your first the court case as a lawyer really cool to hear congratulations I did catch that video I guess and yeah pretty exciting I guess no I would think so pretty exciting and something to be proud of so congrats sincerely Bob the blind bedroom guitars

Marshall explicitly says to operate my amp using the standby switch. I don’t understand how this is harmful when the manufacturer designs it that way?

Its been a kind of moving target for you brad, great job tho and fingers xst nil desperundum!😊👍

I have mostly heard not to use standby switches. On dr z'channel he says only use standby if you have a solid state rectifier. Other than that i had an amp that said put it on standby for 2min. Mostly though techs say don't bother. Now standby or not my my current amp "fades in" at about the same rate

I enjoyed this - some good info. Sort of agreeing with what you were saying - I am not saying for certain, but I had recently a bad batch of JJ GZ34s - they worked for a while but promptly failed after very limited use. Unfortunately, I bought several at a time and by the time I use them and they fail I have had them too long to get my money back on them. I hate eating the cost of crap tubes. I quit buying JJ rectifiers for a little while and was buying Sovtek. But I have also heard they (Sovtek) had bad batches too (from other folks) and they are harder to get/more expensive due to the current war going on. I never liked Chinese rectifiers, but I may have to consider them. Interested in who made the GT you decided to use. Use american or english if you can find one! But GZ34s are crazy expensive for NOS. I have used a .01 or .02 mfd 630v polyprop cap (like those little brown ones you like to use) across the standby to eliminate pop and prolong the switch life - and it does a good job for that. Curious if it affects the inrush current as I've never taken time to measure it. I expect it may because that is likely what causes the POP sound to begin with. I have never tried the varistors in the standby I certainly have replaced a good number of them in power section in newer amps. I also am a proponent of putting vintage correct values of capacitance in tweed era designs. Messing with the vintage values (adding more mfd) will mess up the tone and breakup in the amp. After all, the lower filtering is part of the design that affects the tone of the amp. Now if you are building an amp to be cleaner or to provide more thump - filter away. Also, get a chop stick/spudger and point things out - please don't use your finger. I know you know better but makes me a nervous wreck. One accidental brush against something nearby where you are working and it will light you up.

Wow so oscilloscopes are a thing of the past? That is cool. It looks like the screen I have on my EuroModular kit build osc.

The only amp where I'm a stickler about the standby switch is my 70s SVT. Because I'm pretty sure it'll eventually start a fire burning some old crud in that power switch.

I have a Carvin V3 from like 2000 something.. the manual suggest to power on then switch on standby and do the opposite to power off.

Great video Brad.

Very informative as always. I have a late-60's/early 70's Vibrolux--should I also not use the standby?

Good video Brad. I gotta say, it sure seems like the wrong transformer is being used. Just a hunch.

Hi, A Little Bit Of Historically Correct Standby Switch information, Originally At Radio Transmitting Stations and TV Stations Using Water Cooled Power Valves/Tubes With Out Side Water Reservoirs, The Size Of Swimming Pools to Cool The Transmitter Power Valves and Driver Stages, There Was A Power Up Sequence, Early Valves/Tubes Were Directly Heated, Later Valves/Tubes Indirectly Heated, Irrespective Of Either With 10KWatts Of Radiated Power Or Considerably More Than That In Various Instances, If HT,(Several Thousands Of Volts Or More), Is Switched On Without A Power Up Sequence, And The Heater/Filament Voltages/Currents Monitored, For Steady State And Correct Operational Area, Then When Certain They Were Correct The HT, Was Applied and Monitored As It Was Ramped Up, Also Being Monitored for Voltage/Current. So If A Duff Expensive Valve Tube, as Big as A Six foot Man, Or Smaller, Three/Four Foot Tall, Water Cooled Had A Problem, It could Be Seen On The Monitoring Meters, During The Power Up Sequence And Shut Down Before It Destroyed The Power Source Or Caused Other Major Destruction To The RF Transmitter Circuits. I Have The First JTM 45, I ever Repaired, At Sixteen Years Old, Originally It was a Bass Model, It Has A Standby Switch, Single Pole Single Throw, Fed Off Of A GZ34 Cathode Pin, Valve/Tube Base Tag , A.05uF 600Volt Polystyrene Capacitor Connected, On Cathode, Then To Earth/Ground, Then To The Input Side Of The Standby Switch. The Output Side Of The Standby Switch Has The First, A, Section Of A Dual Under Chassis Mounted Dual Section, 32uf-32uF 500 Volts/ 525 or 550 Surge Volts, UK Style Can Electrolytic Capacitor Connected Direct To Output Side Of The Standby Switch, The Output HT 450 Volts From That Standby Switch Also Feeds The Choke Input , The B Section 32uF Capacitor,(Dual Section UK Can Electrolytic Capacitor), On The Choke Output, The Centre Tap Of The Output Transformer, A 1 K Ohm 5 Watt Wire wound Ceramic Resistor, Then Off This Resistor Feed The Two Screen Grid Resistors, Each 470 Ohms 1 Watt, Wire Wound Ceramic, ( Though I Have Seen On Others Of This 1965 Production Year Model JTM45, Use 1 or 2 Watt Carbon Resistors Used Instead Of Wire Wound 1 Watt) Original R.S. Components Makes Carbon, Or More Correctly Badged, From Morganite UK Name, Manufacturer/Allen Bradley USA Parent Company., Then Phase Splitter Drop Resistor And It's Capacitor 16 uF Then Tone And Preamp/Front End And It's Drop Resistor And 16uF Capacitor. The HT Fuse Anti Surge/Slo Blo 500mA Is Fed From The Transformer Centre Tap To Chassis Earth/Ground, Transformer Mains Input Fuse Is 2A Anti Surge/Slo Blo. To A 240/250 volt Primary Transformer Tap Winding, With Tapped Other Voltages Available The Only Time I Ever Saw A GZ34 Flash Over Is After This Amp Took Out The Original Power Transformer, Due To Some Damn Fools Modification Of A Crude Bias Control That Shorted That Valve Rectifier Out, I Had replaced The Power Transformer And Had To visit My Best Friend's School Friends Who I Repaired For, The Brothers It Belonged To, They Having Sourced A Later Marshall Power Transformer Through A Canterbury Kent UK Music Shop In 1979, I Fitted It And Got The Amp Working Again, Not Sure What This Extra nob/Pot Inside on top Of The Back Chassis was There For at The Time and I'd Got From Marshall Via Rose Morris, UK distributor At That Time Still Till 1980/81 An Original Circuit Diagram/Schematic, No Such Control On There, So it was Not giving Good Sound, With A Guitar, So I Turned This Knob Thinking It was a Master Volume, Added around The Phase Splitter Valve/Tube, Wrong, I spotted in Time A Brief Mini Lightening Storm In The GZ34, I Quickly Backed It To Near Were It Had Been, But To The Right Place Where The Amp Stopped The Lightening Storm In The GZ34 And Sounded Good, The Amp Got Sold To A Friend In Their Band, I swapped It With Him For My Rose Morris Resurrected, (Pre Korg) Take Over Vox Sound Ltd AC30, Had To Do A Lot Of Work On That Too After Purchasing/Buying New For £210.00 Pounds In 1982, It's Filter Capacitors Ended Being A Rubbish Make And Got Replaced With R.S. 32uf-32uf Dual Section Cans And The HT With The By Now IN4007 Silicon Bridge rectifier Diodes was Way Over Dick Denney's Original GZ34 Valve/Tube Rectified HT Rail Voltage of 320 Volts, With The Silicon Bridge Rectifiers, It Was Way Over At 345 Volts, So a Poer Resistor Was Added To Drop The H Rail To 320 Volts, So Increasing The Life Of The Four EL84/6BQ5 Valves/Tubes And Allowing Them To Tun Cooler And Not Edge On Red Plating, The Amp Also Gained An Improvement In The Quality Of It's Nice Clean Sound. No HT Fuse On A Fender Bassman , Output Transformer Centre Tap Is Placed Before The Choke On Input Side Of The Choke as are The Two 20uF Capacitors Each At 600Volts In Parallel, Screen Grid Fed From Output Side Of The Choke And No 1 K Ohm Resistor Either To Feed Screen Grid Resistors, 470 1 Watt Each. Standby Switch Single Pole Single Throw, In Same Position As JTM45 From Marshall, Also with A .05uF To Earth/Ground From Cathode Valve/Tube Base Tag, Then Input To standby Switch., No Varistor/Thermistor In Either Amp. Bassman Mains Input To Transformer Fuse Is 3A To A 117 Volt Primary, No Tapped Primary transformer Winding.

the input capacitance reduction was a good move .. but i am sitting here wondering now; if old amps ever have lacquered wire problems that develop, in the filter chokes? .. leaky shorts that could reduce the inductance ? ... i think stand by switches are a good thing, on class-a amps at the very least.... of course if i had an amp that was blowing fuses, i would stop using the standby switch ... because that's the least expensive way to solve the problem ...and it would give me time to think about it.

You can also slow down inrush current with a ... mosfet ? 😇