I recently obtained some 12AU7s for my preamp. Some Mullards from Blackburn and Funkwerks. The funny part is the FunkWerks tubes when the preamp is switched on - they flare up like a lit match for a second at two points on the base, before settling down.
Is something wrong with these tubes? Like slight leak in vacuum or something?
They sound superb though! Very musical with great top-end!!
Thanks for any advice.
Is something wrong with these tubes? Like slight leak in vacuum or something?
They sound superb though! Very musical with great top-end!!
Thanks for any advice.
These are the heaters. There is often a flare as their cold resistance is lower than when at running temperature so they will draw more current. This will reduce as they heat up. Nothing to worry about.
Sadly I have had a couple of NOS Mullards (12AX7A/12AU7A) burn out in a relatively short time frame due to uncontrolled cold inrush current, this is a particular problem if the filament supply has a very low source impedance. Based on my experience I would recommend an NTC thermistor to limit the initial inrush current to a safe value.
You scare me! 😱
My Mullards, or BEL or Shugangs or JJ/Teslas dont flare up, only the funkwerks do.
For a few seconds actually. When I switch off and switch on immediately, it doesnt happen... So I am thinking (or want to believe) like Bone said, "nothing to worry about" .
However perusing your line of thought, NTC thermistor - part number (edit: ok google was easy, but are there different parts/ratings for different circuits ) ? where in the circuit do I place them? I am only a solder specialist and a dud at electronics. Can I copy the circuit schematic so you can tell me where?
Anything that might potentially increase the life of my precious toobs 🙂
Cheers
Thanks.
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You scare me! 😱
My Mullards, or BEL or Shugangs or JJ/Teslas dont flare up, only the funkwerks do.
So I am thinking (or want to believe) like Bone said, "nothing to worry about" .
However perusing your line of thought, NTC thermistor - part number (edit: ok google was easy, but are there different parts/ratings for different circuits ) ? where in the circuit do I place them? I am only a solder specialist and a dud at electronics. Can I copy the circuit schematic so you can tell me where?
Anything that might potentially increase the life of my precious toobs 🙂
Cheers
Thanks.
How many tubes in the string, and what is the filament voltage ? Something on the order of 5 ohms cold and <0.5 ohm hot at an amp would do well for this directly in the filament circuit if it is a 6.3V filament circuit... (Particularly if the filament voltage is just a bit on the high side.)
Need a little more information, my preference is for DC heating with a CCS or current limited voltage regulator. (Limit current to about 10% greater than the required current.)
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Hello All,
I use GE sensing CL-90’s from Digikey. These are used in series with the primary winding of the transformer.
IIRC this device has 120 ohms cold and 9 ohms when warmed up.
DT
All Just For Fun!
I use GE sensing CL-90’s from Digikey. These are used in series with the primary winding of the transformer.
IIRC this device has 120 ohms cold and 9 ohms when warmed up.
DT
All Just For Fun!
Is Funkwerks a manufacturer? I'm not familiar with that name. If they are not a manufacturer it is possible that the flashers are the ones that are "supposed to" flash, no?
I have a Zenith branded Blackburn Mullard 12ax7 that flashes, and it does so with pride.😉
I have a Zenith branded Blackburn Mullard 12ax7 that flashes, and it does so with pride.😉
I had always been told, and because of witnessing it myself, that 12xx7A's will flash up on start-up. The 12xx7's do not, only the 12xx7A's. I can't remember why but I bet you can google it
3 12AU7s. One for L and R each and one common. Voltage supplied is 12.6. The circuit takes anything between 12 to 15V as a recommended range.
Thanks
I googled CCs, it looks over the top for a novice for me. I am looking at at component that can be soldered in ot provide the magic solution. 🙂
Not something this complicated: http://www.diyaudio.com/forums/tubes-valves/163680-help-needed-grounded-grid-ccs-upgrade.html 🙁
Thanks for the tip though. I am definitely going to study this as part of my electronics brain upgrade over the next few years. 🙂
-Gobble
Yes http://www.jacmusic.com/html/club/tube-brands1.pdf. No these are not Funky lights !! 😀 It distinctly looks like somebody just lit a match for a smoke. Thankfully no smoke yet ... 🙂
Cheers
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Barring the rectifier and smoothing (which is needed for any kind of DC operation, with or without CCS) a CCS can be as simple as one integrated linear voltage regulator (such as LM317) and one current setting resistor.
Hi,
The A suffix in the tube's nomenclature indicates it's build with a controlled heater warm-up.
E.g. 12AX7A indicates controlled heater warm-up whereas a 12AX7 may show a flash at start up.
Technically both work fine, the A version is only there because you guys should stop worrying.....
Cheers, 😉
The A suffix in the tube's nomenclature indicates it's build with a controlled heater warm-up.
E.g. 12AX7A indicates controlled heater warm-up whereas a 12AX7 may show a flash at start up.
Technically both work fine, the A version is only there because you guys should stop worrying.....
Cheers, 😉
Hi,
As far as the 12AX7A goes, while disguising the filament flash some manufacturers (RCA for starters) also improved this particular type of valve's sensitivity to microphony.
After all, a wise move which such a high gain type.
This later on culminated into the development of the low noise 7025. 7000 series often being pro audio types.
Cheers, 😉
As far as the 12AX7A goes, while disguising the filament flash some manufacturers (RCA for starters) also improved this particular type of valve's sensitivity to microphony.
After all, a wise move which such a high gain type.
This later on culminated into the development of the low noise 7025. 7000 series often being pro audio types.
Cheers, 😉
Hmm Attaching the diagram of the existing circuit. Could you draw over it and show what exactly? 😕
Much appreciated if you can. Thanks.
-Gobble
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