too much light on heathers when turn on

[12afael]

I´m finishing a guitar preamp. I use the G9 style power supply for the heathers. (12vAC, bridge, 1000uF, 7812 , 47uF)
the preamp have 2 12ax7.

when I turn on the preamp the heathers glow too much, then go to normal . I fear to burn the tube.

I don´t have a oscilloscope to see if is the voltage the problem, a overshoot I think .
ideas are welcome

12afael

 

[nacho459]

It's common for some tubes to flash bright when they first turn on. EI's and Mullards do that. If it glows bright for more than a second you probably have a problem.

 

[mcs]

Check that the voltage is actually 12V. If it is, then there's no problem.

Best regards,

Mikkel C. Simonsen

 

[12afael]

I will try with diferent tubes to check .
my 1987 plexi amp don´t glow on that way. so I think it could be a problem .

thanx

12afael

 

[nacho459]

I just noticed that you said you hooked the heaters up to 12VAC, I'm pretty sure that 12AX7's are supposed to be hooked up either to 12VDC or 6VAC.

 

[mcs]

[quote author="12afael"]my 1987 plexi amp don´t glow on that way. so I think it could be a problem . [/quote]
With the same tubes? If the same tubes behave differently in different amps, then there probably is a problem. Otherwise there isn't.

Some tube (like Philips/Mullard ECC8x) light up like light bulbs at poweron - bot that's normal. Other tubes don't do this at all.

Best regards,

Mikkel C. Simonsen

 

[gyraf]

[quote author="nacho459"]I just noticed that you said you hooked the heaters up to 12VAC, I'm pretty sure that 12AX7's are supposed to be hooked up either to 12VDC or 6VAC.[/quote]

AC is fine. You can use it on either 6V or 12V, depending on how you wire the centre-tapped heater.

 

[CJ]

Try a tube change if you have any extras. I had a tube that did that all the time. Not enough time to damage anything really. Is it a white glowing flash that slowly diminishes? That's what mine did. That tube lasted forever.
Looks cool. Plus, it scares people away who might want to plug in for a jam. Tell them "the last guy who plugged into my amp got his 59 PAF chrombuckers cooked by that weird heater. :grin:

Check the tube socket.

cj

 

[12afael]

well I try some tubes a amperex (Holland) was the only one with the problem , the funny think is that I have other amperex and it don´t have that glow . the tube work well . it appear to be normal for that crazy tube :wink: .

I try some RCA, heath (by mullard) , Hewlett packard, telefunken.

I just noticed that you said you hooked the heaters up to 12VAC, I'm pretty sure that 12AX7's are supposed to be hooked up either to 12VDC or 6VAC.

I put the circuit description 12v AC then rectified, filtered and reguled.
I use 12 volts DC on 4 and 5 pins .

Is it a white glowing flash that slowly diminishes? That's what mine did. That tube lasted forever.

is exactly what I have.

Looks cool. Plus, it scares people away who might want to plug in for a jam. Tell them "the last guy who plugged into my amp got his 59 PAF chrombuckers cooked by that weird heater.

I will do that!! :grin:

provably the heather material don´t have a soft change on resistance from cold to hot , so a big current flow throught the filament. but it don´t produce problems while the tube is on.
I would like to be able to measure the current on that moment. maybe could be a problem if we have a lot of that tubes.

thanx to all

12afael

 

[Butterylicious]

All of my Amperex tubes flast upon heat. They're supposed to. Just 1 more thang that makes them the coolest tubes, IMO.

 

[mcs]

[quote author="12afael"]well I try some tubes a amperex (Holland) was the only one with the problem , the funny think is that I have other amperex and it don´t have that glow.[/quote]
Amperex (Holland) is a Philips tube, and they have the "problem"/feature. Other Amperex tubes (made in the US), are most likely Sylvania tubes and they are very different.

Best regards,

Mikkel C. Simonsen

 

[CJ]

There are some weird country codes on those Phillips/Amperex tubes. Here is a chart with some of them. I have other code info- if you can provide the whole code, I might be able to decipher the date, etc. Look on the base also. Not positive on all of these: