And, Merry Christmas to all! 
If you're asking about dropping the B+ from 320 volts to 300 volts, then I think it will still work OK. The plate-to-cathode voltage will drop to about 100 volts, but the plate curves still look fairly linear at that point assuming line-stage voltage swing levels (2 volts rms or so). You could back down on plate current a bit by putting a larger resistor in the LM317 circuit (say, a 47 ohm value) and use the freed-up voltage to split between a larger plate load resistor and/or a larger plate voltage operating point. How much all this is audible is debatable. The point is that, within limits, this circuit is not THAT critical.
fdegrove said:Hi,
A 300VDC PSU you said?
Here you go:
Cheers,
Quite fun it was actually this PSU I wanted to try at some time as I also would like to try your 12bh7a circuit with it. Though I wanted to be able to try the 12b4a aswell as I am not sure if I can live without the gain, but only a test will show me that.
Martin
hi guys----happy new year first of all -
i would like that somebody here explains nice and easy what will happen if i accidently pull out the 12b4 while preamp and amplifier are working......
also - another thing.....
i have made my 12b4 preamp with 26mA and 130V on the anode of the tube... i have 4k7 resistor in the plate.... this is not quite the line stage from our Brian but it is working nice... also i have got no strange treble i was having problems with (before i have paraleled the cathode capacitor with the smaller one MCap-Mundorf 1uF/400V).... - - - - BUT - - - , i have perceived big humming when the preamplifier is turning on... this humming is gone after arround 20 seconds..... what is happening.... probably the tubes but i am not sure and this is not comfortable to listen to when i turn the preamplifier on....
best regards and have fun during new years evening......
sunny
i would like that somebody here explains nice and easy what will happen if i accidently pull out the 12b4 while preamp and amplifier are working......
also - another thing.....
i have made my 12b4 preamp with 26mA and 130V on the anode of the tube... i have 4k7 resistor in the plate.... this is not quite the line stage from our Brian but it is working nice... also i have got no strange treble i was having problems with (before i have paraleled the cathode capacitor with the smaller one MCap-Mundorf 1uF/400V).... - - - - BUT - - - , i have perceived big humming when the preamplifier is turning on... this humming is gone after arround 20 seconds..... what is happening.... probably the tubes but i am not sure and this is not comfortable to listen to when i turn the preamplifier on....
best regards and have fun during new years evening......
sunny
Hi,
Nice and easy, he?
I don't think I'd call "accidentally" pulling a tube with the gear up and running errrrr........An accident.
Apart from some noise nothing much will happen but I'd advise seeing some kind of doctor if you have habits like that.............
Mute switch ring a bell?
Maybe you heard about tubes needing a little time to warm up? Like about twenty seconds perhaps?
Sunrise, maybe you should put that Tequila bottle back where you found it........
Ciao,
Nice and easy, he?
I don't think I'd call "accidentally" pulling a tube with the gear up and running errrrr........An accident.
Apart from some noise nothing much will happen but I'd advise seeing some kind of doctor if you have habits like that.............
Mute switch ring a bell?
Maybe you heard about tubes needing a little time to warm up? Like about twenty seconds perhaps?
Sunrise, maybe you should put that Tequila bottle back where you found it........
Ciao,
oh yees, fdegrove.... that was good
no - in reality.... i was asking myself what will happen if one of my tubes loose conection inside of the tube socket..... o.k. now i am more peacefull
well, this humming was not that loud when the anode voltage was lower (i have had the anode voltage arround 65V and the current was 26mA) - now the current is the same but the anode voltage higher and the humming at the power on is giving me creeps
but i have faith in your opinion - if you say this is o.k. and that i should put an mute circuit - no problem - as long as my preamp is o.k.
i don't like tequila but wine and beer yeees.... still it is new year almost....
no - in reality.... i was asking myself what will happen if one of my tubes loose conection inside of the tube socket..... o.k. now i am more peacefull
well, this humming was not that loud when the anode voltage was lower (i have had the anode voltage arround 65V and the current was 26mA) - now the current is the same but the anode voltage higher and the humming at the power on is giving me creeps
but i have faith in your opinion - if you say this is o.k. and that i should put an mute circuit - no problem - as long as my preamp is o.k.
i don't like tequila but wine and beer yeees.... still it is new year almost.... I think Fedgrove was a little too brief in his explanation of what might happen....
If you have a DC coupled solid state amp pulling an "alive" tube out can mean the end of the line for your speaker(s), especially the more efficient type speakers. It can create a huge DC offset momentarily while the line stage's coupling capacitor's charge normalizes. A really bad thing to do...
! He is absolutely correct in his statement though that if you enjoy doing this sort of thing you should go see a doctor . Aside from possibly blowing or damaging your speakers it also might destroy any plate side solid state regulators or current source you have in there. It probably wouldn't hurt an LM317 in the cathode though.Just my thoughts and warnings....
Everyone have a very Happy New Year!
Mark
nothing will happen if somebody is so stupid to pul da tube from socket
when both amp and preamp are in working condition....
ha -just joking,in moment when your tube loose connection in bad socket,all can happend is that inner side of output cap (plate end ) start wandering around....,but-just because every smart tuboholic didn't forget to solder one tiny 100k-1M pull-down resistor right after cap,and in front of even DC coupled amp,nothing major can't happend.
only when severe multiple and fast erratic contact problems are in case, they can evolve oscilations in amp and further damage in loudspks......
same as with gas tubes-during ignition time (if you are as I sometime stupid to power up power amp before preamp) only soft pop sound can be heared... but -if mains voltage is so decreased to lowest useable shunt current,tube can fall in repetitive off-on cycles and than pop is not just one gentle pop, instead that you can hear short sawtooth or simillar louder sound........
hehe-I tried that with variac ,and some cheap amps and spks....still without burnin' anything
when both amp and preamp are in working condition....
ha -just joking,in moment when your tube loose connection in bad socket,all can happend is that inner side of output cap (plate end ) start wandering around....,but-just because every smart tuboholic didn't forget to solder one tiny 100k-1M pull-down resistor right after cap,and in front of even DC coupled amp,nothing major can't happend.
only when severe multiple and fast erratic contact problems are in case, they can evolve oscilations in amp and further damage in loudspks......
same as with gas tubes-during ignition time (if you are as I sometime stupid to power up power amp before preamp) only soft pop sound can be heared... but -if mains voltage is so decreased to lowest useable shunt current,tube can fall in repetitive off-on cycles and than pop is not just one gentle pop, instead that you can hear short sawtooth or simillar louder sound........
hehe-I tried that with variac ,and some cheap amps and spks....still without burnin' anything
Pulling the 12B4 with everything powered up can cause bad things to happen. The voltage normally seen at the plate will rise to the B+ value rather abruptly because there is no plate current flowing. With the large value coupling capacitor present in this design, a large positive going voltage spike WILL be present at the preamp output. A resistor to ground will only change the duration of the spike, not eliminate it. If you are feeding a typical tube amplifier the result will probably be a loud thump. A solid state amp with good low frequency response might push the cone right out of your speakers. A solid state or digital amplifier may go unstable and self destruct with a 10 volt or higher transient at its input.
Hi,
Maybe I should have kept it even briefer:
DO NOT PULL TUBES UNLESS YOU HAVE POWERED THE SYSTEM DOWN.
There's little point in guessing what can or could possibly happen when you know for sure that something bad can happen by doing it.
When you decide to pull a tube make sure also that it has had sufficient time to cool down.
You may be in for a nasty burn if you don't and tubes do not appreciate being mechanically stressed whilst still hot.
Metals expand under heat so you risk damaging a grid or have a heater stuck to a cathode sleeve. Whatever........
There should be a sticky thread on the top of this "Tubes" section containing all the dos and don'ts so I won't rehash the lot here.
Cheers,
Maybe I should have kept it even briefer:
DO NOT PULL TUBES UNLESS YOU HAVE POWERED THE SYSTEM DOWN.
There's little point in guessing what can or could possibly happen when you know for sure that something bad can happen by doing it.
When you decide to pull a tube make sure also that it has had sufficient time to cool down.
You may be in for a nasty burn if you don't and tubes do not appreciate being mechanically stressed whilst still hot.
Metals expand under heat so you risk damaging a grid or have a heater stuck to a cathode sleeve. Whatever........
There should be a sticky thread on the top of this "Tubes" section containing all the dos and don'ts so I won't rehash the lot here.
Cheers,
hi,
thnx for the replies.... i will not pull the tube out of the socket - i am not that stupid .... but i was wondering what might happen if one or two of the pins of the tube, inside the tube socket, loose contact....
power amp is not dc coupled
i have my power amplifier turned on while powering the preamplifier because i want to hear if everything is o.k. during the power on process and i perceived those things i was telling you about.... o.k. now i know that everything is o.k. and i will use mute circuit... that seems to be the best solution......
thnx for the replies.... i will not pull the tube out of the socket - i am not that stupid
.... but i was wondering what might happen if one or two of the pins of the tube, inside the tube socket, loose contact.... power amp is not dc coupled
i have my power amplifier turned on while powering the preamplifier because i want to hear if everything is o.k. during the power on process and i perceived those things i was telling you about.... o.k. now i know that everything is o.k. and i will use mute circuit... that seems to be the best solution......
fdegrove said:Hi,
A 300VDC PSU you said?
Here you go:
Cheers,
Happy newyear to you tubefreaks
Thanks all for this wonderfull tread, I followed it every day.
Hobe to start the building soon
Dificult to collect what to use here in Denmark, but found
som good places in Germany.
Fdegrove,
Can that suply be rised to b+ 320V, to follow the
schematic from Brian 100%
You dont use at tube rectifier?
I don`t know a lot of powersuply´s. But some
have been mention in this tread.
Is this the one to build, low riple and impedance?
Cheers Jan
Hi Blaaberg,
Its hard to reccomend which supply is the "best type" as there really is not a "best type" of supply for any particuluar purpose. Some prefer shunt regulated, some prefer the pass type regulator, some will only use tube type, and then others use only lots of iron....., and then there the folks that only use lab grade power supplies. In the end let your ears make the decision which is best for you. You'll want to do like I am doing.... slowly build them all over a long period of time and listen to each one. Thats the real beauty of this hobby!!
Mark
Its hard to reccomend which supply is the "best type" as there really is not a "best type" of supply for any particuluar purpose. Some prefer shunt regulated, some prefer the pass type regulator, some will only use tube type, and then others use only lots of iron....., and then there the folks that only use lab grade power supplies. In the end let your ears make the decision which is best for you. You'll want to do like I am doing.... slowly build them all over a long period of time and listen to each one. Thats the real beauty of this hobby!!
Mark
Mark A. Gulbrandsen said:
It`s my first real project, so I just want a "good" one
I understand that Brian Becks solution with 140V on the plate, and CSS on the cathode is fine, so I`ll go for that.
Building the supply look, for me, to be the most complicated.
So could I find one, that easy could be ajusted at the 320V,
it would suit me fine.
Otherwise I found some supplys here:
http://www.supertube.de/
-that could be easy to get in duty, but I`ll rather building something myself
Cheers Jan
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