A good motivation for going wireless. I can change instruments between songs without a noise, without muting anything.Gene Pink said:
Tube gear standby switch.
- Thread starter Zander
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From the longevity of the tubes perspective Id rather have a rectifier tube ramp up the ht nice n easy anyday ,but sometimes the rectifier sound isnt what you'd want other times limited mains transformer selection prevents even it being an option ,Id always fit a standby to a silicon ht rectifier,the way the standby is wired and used is another matter ,and wrong useage or poor implementation may well be worse than no standby at all . The heat the standby can save an amp on stage I think shouldnt be underestimated either ,as was said previously its only takes a few seconds for an amp switched from standby to sounding near its best ,where a tube amp turned on from cold is going to take probably half an hour to stabilise properly .In the first thirty minutes from turn on in virtually all tubes theres all kinds of funny tinkling noises coming from grid wires and other parts of the tube structure as it reaches temperature ,switching from standby this noise is much reduced and typically the tinkleing of grid wires only lasts a few seconds until the full temperature inside the tube is reached .A properly implemented standby, virtually silent in opperation especially the power on cycle is just nice to have ,if its elegantly done ,no click is heard when you go to on ,the ht ramps up slowly ,its like a fast fade up from zero if you have sound going through .As far as changing instruments in the live setting and muting ,isnt it just as easy to simply pull the input jack on the amp halfway out ,closing the contact from the grid to ground before unhooking the output jack from the instrument. I guess if people want to come down from the trusses like something from spinal tap wireless is all the rage and it does prevent the roadie having to tunnel his way out on stage a lot ,in a studio situation Id strongly discourage any kind of wireless transmission at least on the input signal path ,for monitoring I dont see any issue with it .
Indeed, but changing instruments in the studio is not an issue, is it?Tubetec said:
No changing instruments in the studio isnt an issue of course,
Ive seen a few wireless systems in for repair ,naturally enough you end up reading product blurb when your trying to find and fix problems in such things. Some do say better than cable in sound terms ,theres no doubt wireless has come a long way .I guess if your plugging in a bug transmitter to the guitar jack ,theres a lot less capacitance on the line than say a ten foot guitar lead ,before you hit a buffer stage ,so maybe there is some truth to the claim in terms of frequency response.In noise terms, with the bug your ungrounded from the rest of the system ,also the large area rf loop formed by the input lead isnt an issue ,so probably better immunity from hashes and buzzes too. I guess all the pluses above are more or less equally valid for studio ,but still why digitise,transmit ,recieve and convert back to analog if you dont have to .
I have used the rotary three position four way switch as combo mains/standby ,the extra poles on the switch can be used for a limiting/inrush/bleed resistor too , as pointed out by JR . Its a nice neat one dial solution.I think back in the very early days mercury vapour rectifiers were common ,as far as I know these can be damaged if they are not given a period of time to preheat,might explain the tube rectifier and standby on very early gear.
I have the peavey nano valve ,I wired the mains on permanently and rewired the mains switch as standby/on ,course I have to remember to remove the plug after use .Ht normally in this amp in around the 275 volts mark ,this is already high for a single EL84 and at switch on with cold heaters 350 volts is probably more like it ,even using hard as nails Russian millitary EL84's this amp chewed them up and spat them, the usual 'bag of bones' electrode rattle and intermittant 'farting' was becoming audible in only a month or two of use ,since Ive changed the switching arrangements , never had to change a tube in it since . Ive also seen people with bad mains/standby usage ,mainly the kind who simply flip both switches on without allowing the warm-up phase ,again Im certain this has a negative impact on tube life,theres also the needless high voltage spike delivered to the caps at switch on to think of . I usually apply a standby on the ac output terminals of the transformer secondary with a dual pole switch,I found this to be generally very quiet in opperation ,the arrangement of smoothing lcr and location of the switch can make the difference between virtually silent and on with a 'thump'.
Hot switching the ac(ht ) on a tube rectifier I think is best avoided too ,in the old days most tube rectified stuff had no standby ,if you do want it ,its best to put the standby down the line from the rectifier ,lifting the centre tap of the Ht winding from ground is another way of doing it .
Ive seen a few wireless systems in for repair ,naturally enough you end up reading product blurb when your trying to find and fix problems in such things. Some do say better than cable in sound terms ,theres no doubt wireless has come a long way .I guess if your plugging in a bug transmitter to the guitar jack ,theres a lot less capacitance on the line than say a ten foot guitar lead ,before you hit a buffer stage ,so maybe there is some truth to the claim in terms of frequency response.In noise terms, with the bug your ungrounded from the rest of the system ,also the large area rf loop formed by the input lead isnt an issue ,so probably better immunity from hashes and buzzes too. I guess all the pluses above are more or less equally valid for studio ,but still why digitise,transmit ,recieve and convert back to analog if you dont have to .
I have used the rotary three position four way switch as combo mains/standby ,the extra poles on the switch can be used for a limiting/inrush/bleed resistor too , as pointed out by JR . Its a nice neat one dial solution.I think back in the very early days mercury vapour rectifiers were common ,as far as I know these can be damaged if they are not given a period of time to preheat,might explain the tube rectifier and standby on very early gear.
I have the peavey nano valve ,I wired the mains on permanently and rewired the mains switch as standby/on ,course I have to remember to remove the plug after use .Ht normally in this amp in around the 275 volts mark ,this is already high for a single EL84 and at switch on with cold heaters 350 volts is probably more like it ,even using hard as nails Russian millitary EL84's this amp chewed them up and spat them, the usual 'bag of bones' electrode rattle and intermittant 'farting' was becoming audible in only a month or two of use ,since Ive changed the switching arrangements , never had to change a tube in it since . Ive also seen people with bad mains/standby usage ,mainly the kind who simply flip both switches on without allowing the warm-up phase ,again Im certain this has a negative impact on tube life,theres also the needless high voltage spike delivered to the caps at switch on to think of . I usually apply a standby on the ac output terminals of the transformer secondary with a dual pole switch,I found this to be generally very quiet in opperation ,the arrangement of smoothing lcr and location of the switch can make the difference between virtually silent and on with a 'thump'.
Hot switching the ac(ht ) on a tube rectifier I think is best avoided too ,in the old days most tube rectified stuff had no standby ,if you do want it ,its best to put the standby down the line from the rectifier ,lifting the centre tap of the Ht winding from ground is another way of doing it .
I don't worry about it anymore; I've modified most of my amps with an NTP in series with the primary.Tubetec said:
I can see the logic of the NTP in the primary from the point of view heater inrush at switch on ,but does it also hold back HT and if so what sort of ramp up times do they allow ?
I can see how a correctly chosen component could give extra overall protection to a tube amp that develops a fault ,but I do wonder if it might effect the dynamics to some degree under hard rock output drive conditions .
I can see how a correctly chosen component could give extra overall protection to a tube amp that develops a fault ,but I do wonder if it might effect the dynamics to some degree under hard rock output drive conditions .
abbey road d enfer said:
I have read through the topic and it is interesting reading. But this quote about an NTP i series with the primary is something new to me.
May I ask if we could see a schematic of this input stage of yours?
Best regards
/John
Just the fraction of second it takes to damp the inrush caused by the magnetizing current of the magnetic core and capacitor charging. Definitely not the kind of slow ramping some are advocating.Tubetec said:
When properly dimensioned, the voltage drop caused by the NTC's resistance will be about 1V at full load. Not significant.
gyraf said:
Standby switch is really not a bad concept as long as the user is aware of its purpose. Surge voltage on the HT rail has always been an issue with tube power amplifiers in particular... the typical silicon diode or 5U4 type rectifier supply applies HT immediately to all the amplifier tubes with possible cathode stripping effects down line. The power supply filter capacitors often carried an operating and surge voltage rating (i.e. 40 uF 450 v 525 v surge). Usually, filter capacitor problems occur at turn on. Not nice when an electrolytic capacitor explodes and the chassis is coated with goo. It's hard to beat up a 6L6GC but the EL34 and 7027A types are more sensitive.
The HT surge voltage is typically higher than the operating voltage for a few seconds until the tube cathodes are up to temperature and stabilized. The HT supplies using the 5V4, 5AR4, etc. have a delayed warm up and the surge effects aren't as noticeable. It's possible the cathode of the 5V4 or 5AR4 types may undergo some cathode stripping for a few seconds while heating.
Some amplifiers (typically commercial) may use mercury vapor rectifier tubes such as the 83, 816, 866, 3B28 (gas), etc. The 83 uses a filament, but the higher power MV rectifiers have heat shielded cathodes with a required warm up time before application of any HT. For best results preheat tubes in any equipment using a mercury vapor or gas rectifier. Having worked on tube type RF transmitters up to and including the 50 kw range, it's essential to follow the start up procedure where it is specified. (HT voltage in the 9 kv to 16 kV range for a 50 kW transmitter is nothing to be careless with!)
Amperite built a thermionic time delay tube (like the 6NO31) which had a 6 volt heater, normally open contact, and 30 second delay to contact closure. I've seen these used in commercial equipment, and some of these have been wired into other amplifiers to minimize HT surge problems and get around manual switching.
It goes without saying BE CAREFUL when working on tube gear due to the HT involved.... make sure the unit is OFF before making any changes, discharge the capacitors to ground. I prefer to use clip on test leads for measuring voltages; clip on the leads, check for shorts, turn on the power, read, and turn off. Much safer than probing around on a "hot" chassis where a slip of the test probe or fingers across HT will result in damage or injury....
Many Fender amps e.g. this onejohnheath said:
https://fr.scribd.com/doc/123978870/Fender-Blues-Deluxe-Service-Manual
The thermistor is rated at 10 ohms; that's the nominal resistance at ambient temperature. As soon as current goes through, the thermistor heats up and its resistance decreases drastically, to a fraction of ohm.
saint gillis
Well-known member
abbey road d enfer said:
Only "problem" is if the amp is switched off and immediately on again, then the thermistor is still hot and does not act.. right?
But there will not be a current surge to charge already charged capacitors, etc.saint gillis said:
JR
It all depends on the sequence of events; as JR mentioned, if the caps have not yet discharged, there is only the magnetizing current surge. The time constant of the commonly used NTC's is a few dozen of seconds. Clearly there is a possibility that switching back on appears before the NTC has gone back to nominal (ambient) resistance. Such a simple implement cannot be 100% foolproof.saint gillis said:
I've done standby switches on some larger tube amps and even a couple of preamps ... not had a problem either way.
I always thought the larger units could benefit from switching plate voltages well after the main (heater) switch is thrown.
..
Another place where 'standby' switching can be useful is in tube limiters .. I've done a couple of the classic types, and for my next big one, I'm going to have an 'idle' switch for the gain cell.
In the vari-gm gain cell application, the tubes are hit pretty hard at the get go and thence after at the 'silent' passages ..
SO, I typically switch on a tube limiter and it sits 'idle' for periods of time ... I'm adding an 'idle' switch to increase the negative bias to the gain cell to a low value of current.
So it can 'idle' without bluto-ing the gain cell .. when I get distracted ... like a 'mute' switch more or less.
I always thought the larger units could benefit from switching plate voltages well after the main (heater) switch is thrown.
..
Another place where 'standby' switching can be useful is in tube limiters .. I've done a couple of the classic types, and for my next big one, I'm going to have an 'idle' switch for the gain cell.
In the vari-gm gain cell application, the tubes are hit pretty hard at the get go and thence after at the 'silent' passages ..
SO, I typically switch on a tube limiter and it sits 'idle' for periods of time ... I'm adding an 'idle' switch to increase the negative bias to the gain cell to a low value of current.
So it can 'idle' without bluto-ing the gain cell .. when I get distracted ... like a 'mute' switch more or less.
Newmarket
Well-known member
abbey road d enfer said:
+1
Yes it depends on the details of the system: Cap Values ; Voltage ; Bleed Load value etc... I use these in my (non audio) designs eg PFC function implemented by means of a boost converter. There is indeed a possibility that the timing of switch off / on results in excess surge current. You sort of have to assume that the user isn't going to be furiously operating the power switch for some reason ;D Not had a problem with them once after choosing a suitable device from IIRC Raychem.
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