mm hey im new..i have a filament problem..
im hooking 2x12ax7 filaments in series with 25.2 volt dc.
i know it may not all warm simultaneously..
im not using resistor to control the current cos i figured i didn't needed to by using it all in series..
is it ok? will it cost a high ware on the filaments?
have a great day David🙂
im hooking 2x12ax7 filaments in series with 25.2 volt dc.
i know it may not all warm simultaneously..
im not using resistor to control the current cos i figured i didn't needed to by using it all in series..
is it ok? will it cost a high ware on the filaments?
have a great day David🙂
Magnetmaz said:
Funny you should say that. It is something that has puzzled me for a while. A lot of musicians also use the standby when having a break from playing (valves @ working temprature)
in most of the amp, ive have looked @ with standby, it is wired so that it cut off the B+ to the anodes. In the valve data manual I have it states "do not run a hot cathode without ht on the plate
as this will cause damage, unless the data for the valve states
that you can do this.
mmmmm another spec in a guitar amp that seems unadvisable
apart from the usual "max charecteristics" being exceeded.
regards stormy
Hi,
David,
That's perfectly fine.
Hi,
Not plate but cathode stripping actually.
Yep....
Thank god we have the guitar amp industry replacing their tubes so often...
Cheers,😉
David,
That's perfectly fine.
Hi,
Not plate but cathode stripping actually.
Yep....
Thank god we have the guitar amp industry replacing their tubes so often...
Cheers,😉
Re: standby switch
So I'm not the only one who's noticed the dilema w/ a standby switch. You get a HT delay on startup to prevent cathode stripping (to what extent that actually happens is unclear to me). But then when you use the standby to keep the amp "warm" while not playing you risk cathode poisoning from extended time w/o cathode current.
Which effect dominates is the question. I tend not to worry about either in a guitar amp. In my experience most tubes can survive hundreds to thousands of powerups without noticeable effects in an amp without a delayed HT. Maybe a hi-fi amp with expensive tubes would be more worthwhile to protect, but many of these have DH cathodes that warm up in a couple seconds anyway. Flicking the stanby off and on every so often should keep the second effect from doing damage.
another solution is to use a 5ar4 rectifier and forget the standby switch.
So I'm not the only one who's noticed the dilema w/ a standby switch. You get a HT delay on startup to prevent cathode stripping (to what extent that actually happens is unclear to me). But then when you use the standby to keep the amp "warm" while not playing you risk cathode poisoning from extended time w/o cathode current.
Which effect dominates is the question. I tend not to worry about either in a guitar amp. In my experience most tubes can survive hundreds to thousands of powerups without noticeable effects in an amp without a delayed HT. Maybe a hi-fi amp with expensive tubes would be more worthwhile to protect, but many of these have DH cathodes that warm up in a couple seconds anyway. Flicking the stanby off and on every so often should keep the second effect from doing damage.
another solution is to use a 5ar4 rectifier and forget the standby switch.
Ah, so if the tube has a 12.6 volt filament you wire one 6.3 to pin nine and the other to pin 4 with a jumper to pin five. As, for example, a 12AX7. And if you have a 6.3 volt heater element there is no center pin. You just connect pins to 2and 7. As in an EL34.
I'm a car mechanic, DC I understand. AC, not so much.
I'm a car mechanic, DC I understand. AC, not so much.
I do seem to recall a discussion about standby-switches on guitar amps a while ago and another reason for them. Running very high voltages with caps with marginal headroom. I use a standby switch on one of my HI-FI amps for the simple reason that i an running around 465 volts b+ and i am using 500v caps. When I just flick both switches together, the 5AR4 always heats faster than the KT88's and produces an extreme over-volt condition for the reservoir cap, which made me a bit uneasy. This is even worse with a 5U4 or other directly-heated rectifier. When I preheat the valves the voltage stays under control and stabilizes faster.
Cathode poisoning takes long periods of time without anode voltage applied. It is a well documented phenomenon.
mctavish has the best (most logical) reason for a standby switch. I have changed caps on a number of guitar amps and they were all under-rated for voltage if you don't have a standby switch. The standby switch allows the heaters to bring the cathodes up to temp before applying B+, so there is no overshoot from applying B+ without the load of warmed up tubes available (a lot of guitar amps have SS rectifiers so no tube rectifier warm up time).
mctavish has the best (most logical) reason for a standby switch. I have changed caps on a number of guitar amps and they were all under-rated for voltage if you don't have a standby switch. The standby switch allows the heaters to bring the cathodes up to temp before applying B+, so there is no overshoot from applying B+ without the load of warmed up tubes available (a lot of guitar amps have SS rectifiers so no tube rectifier warm up time).
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