Topic: Newbie and Not-so Noob Thread: Questions (FAQ) on anything Tubes

[gaol]

you have to understand that tubes have cathodes, and as such suffers from emission depletion with time, this is unavoidable no matter how youse your amp. this is more so with power tubes! small signal tubes normally will last  you a life-time and will outlast most electrolytics in your amp. it is the power tube that is prone to exhaustion!

the better sequence would be, turn heaters on, then say 12 seconds later turn on the B+, when powering off, reverse the sequence.

Thanks 2ny, I understand that I will have to replace the tubes (KT88s in my case) probably 1-2 years from now, and the small tubes twice that. I was just wondering what I could to to minimize shortening their life needlessly, given my listening habits.

Actually, my question could be summarized into: which is better, to leave a tube amp on, or to switch it on and off, if my listening sessions are not continuous but spread hours apart during the day?

I confess I don't really understand what you mean in the second paragraph. In my case, the prologue 2 amp has only the power switch.

[eXg]

my 2 cents...

not sure if there's going to be big difference between your two options with respect to the life of the tubes and if ever there is, it'll be easy to tell with certainty.

i would turn it off during non-use. it saves power for sure (approx 10hrs a day!). 

the B+ referred to by 2ny will only apply in your case with a mod (extra switch).  btw, checked this and the soft-start feature somehow achieves same effect.

http://www.audiovenue.co.uk/products_info.asp?id=626&cat=1&sub=1

[ATJr.]

i would turn if off when not using.

[gaol]

Ah yes, I see. The PL2's soft start circuit actually addresses my concern. Autoadaptive bias, then this one, user-friendly pala talaga ang PL2, as it claims to be.

I'll do as you guys recommend, turn it off, that is. Tipid pa sa kuryente. Thanks!

[eXg]

you have to understand that tubes have cathodes, and as such suffers from emission depletion with time, this is unavoidable no matter how youse your amp.

hi 2ny, are there early signs of this "depletion syndrome"? or does the tube just "drop" dead?

[ATJr.]

i'm not sure! but  what you can do is test the emission of the tube when first acquired, then a year later test it again and see what has changed.

[elvenears]

mga sir na experinced sa tubes !!!!is it good buy ba for starters like me to buy tube amps na medyo luma na ,lets say circa 70's and 80's ....totoo ba na ang tubes ay para lang sa mga medyo technically inclined?.....kung sakaling masira san pwede ipagawa to? (yung bang tipong member na with a good reputation when it comes to modifying and repairing) may mga tech support pa yung mga manufacturers nito?ano ang maganda for starter price wise and factors cant be noticed by a newbie like me? 

[bruno]

Got a question.

Tube amps usually use capacitors which are like two caps in one package (eg. 47uF+47uF/500V).  How are these constructed (internally)?  If I use one 47uF for the left channel, then the other 47uF for the right will there be any disadvantage?

Thanks

[ATJr.]

Got a question.

Tube amps usually use capacitors which are like two caps in one package (eg. 47uF+47uF/500V).  How are these constructed (internally)?  If I use one 47uF for the left channel, then the other 47uF for the right will there be any disadvantage?

Thanks

they are parallel to each other, individualy distinct, and can be used any which way you like as long as you observe correct polarity and that you do not exceed voltage ratings.

[bruno]

Thanks for that 2ny.

I had the notion that they are only to be used for C-L-C filtering.

[bruno]

Like this one:

[markmlists]

to those who can share some info...


most of the ss amps I va had, heard or seen have a power on delay-most likely for protection (or maybe for charging the caps?) during power-on. usually a red colored light flashes upon turn on for a few seconds before it produces sound. Now, my amx tube amp do not have this feature.

My question is can this be, or more importantly, should this be implemented for a tube amp? the power on delay-relay i mean?

Salamat

m

[JojoD818]

m,

most ss amps use the delay-relay for the speakers to be protected against those turn-on thumps. most well designed ss amps also has those soft-start circuits to protect the tranny and diodes when the filter caps are all empty, this way they can charge up a little before the full input voltage is applied.

for most tube amps, this has not been implemented since tubes has some soft start of their own especially when tube rectified. however, even tube rectified or ss rectified tube amps can also benefit from such a circuit for tube protection since most tube disasters occur during turn-on. this and several other reasons has prompted me to modify my tube amps to include such circuits to help prolong the tubes life.

cheers

[markmlists]

Thanks for your response.
Tama pala hinala kong beneficial sya.

Follow up questions sir:

Would that be a relatively hard and expensive modification to implement? relay lang kaya?
Would the mod be sonically transparent?
Would an external voltage regulator with power on delay serve the purpose?

Thanks again for sharing your knowledge on the subject.

[JojoD818]

Thanks for your response.
Tama pala hinala kong beneficial sya.

Follow up questions sir:

Would that be a relatively hard and expensive modification to implement? relay lang kaya?
Would the mod be sonically transparent?
Would an external voltage regulator with power on delay serve the purpose?

Thanks again for sharing your knowledge on the subject.

Not too hard if you know what you're doing, not that expensive too. Syempre hindi lang relay yun. 

It should be sonically transparent since the relay shorts out the resistive element.

No it will not serve the same purpose, those outboard delays are only good for sudden power outages.

JojoD

[markmlists]

Thanks.

This hobby makes me want to enrol in an electronics class. but i might be too old to start now. but then...

[JojoD818]

Thanks.

This hobby makes me want to enrol in an electronics class. but i might be too old to start now. but then...

It's never too late, knowledge doesn't care wether your 19 or 90, it's all up to you.

[ATJr.]

My question is can this be, or more importantly, should this be implemented for a tube amp? the power on delay-relay i mean?

yes why not, but in case of tubes, the output side can be shorted for a moment till the whole amp stabilizes. as oposed to ss amps wherein the output is open circuit for a few secs.

i have experienced output transformer burnouts due to operating the amp without a speaker.

[bruno]

Here is a Power Supply Delay Action Board from Sophia Electric:



This board would permit to warm up vacuum tube filament first, and then switch to high plate voltage in about 20 - 30 seconds later. To protect your expensive output vacuum tubes such as 300B/2A3/845, KT88/El34.

- Green wires with LED are for pilot display.
- Braid green wires are for 6.3V AC (from tube filament supply).
- Red/Black wires (2 pairs) are being used to switch up to two (2) sets of power supply.

Instruction: When turn on main power switch, let the tube filament on first, 30 seconds later this delay action board is going to switch on (control two sets of plate voltage supplies).

http://www.sophiaelectric.com/pages/parts/delay_action_board.htm

[JojoD818]

That's a neat circuit, looks like a 555 timer? Nonetheless, this will surely protect your priced tubes.

Tony has posted (in another forum) a very simple circuit which you can use, it's as simple as it gets.

[eXg]

why are SET's OPTs bigger than PP?  At least that's what I notice and hope that's true, generally speaking.   

[ATJr.]

why are SET's OPTs bigger than PP?  At least that's what I notice and hope that's true, generally speaking.   

that is true, SET ouput transformers are much biggger than pp ouputs because of:

1. there is a unidirectional polarasing current that is always present in a SET ouput traffo.
2. we are dealing with two circuits here, one is dc, the other ac. that is why the set ouput traffo is always gapped, that it to prevent core saturation at low frequencies.

[JojoD818]

why are SET's OPTs bigger than PP?  At least that's what I notice and hope that's true, generally speaking.   

I remember this question... transformers, star grounding and chilli! 

 

[elvenears]

mga sir san po pwede mgapagawa ng transformer with specific values...kasi when i was looking at specific diagrams iba-iba nag transformer na gamit nila ..................can you post reading materials po....yung may mga madaling diagrams

[Jakob]

sirs,

tube matching - how critical? will i wreck an amp in using unmatched different branded tubes  . if there would be audible sound difference vs. matched tubes, will an ordinary joe like me hear a difference? will that difference be measureable?

thanks for your patience  

[bruno]

Some AMX amps have a standby switch.  What's it for?

[JojoD818]

mga sir san po pwede mgapagawa ng transformer with specific values...kasi when i was looking at specific diagrams iba-iba nag transformer na gamit nila ..................can you post reading materials po....yung may mga madaling diagrams

depends on what transformer you want, can be a power tranny or an output tranny.

sirs,

tube matching - how critical? will i wreck an amp in using unmatched different branded tubes  . if there would be audible sound difference vs. matched tubes, will an ordinary joe like me hear a difference? will that difference be measureable?

thanks for your patience 

you won't wreck the amp, I've tried it intentionally. yes you can use unmatched and different brand tubes, it will work. yes you can hear the difference, it's somewhat distorted but the more unmatched tube s you have the more difference. you can measure the difference at the cathodes, the higher transconductance the tube has the more current.

Some AMX amps have a standby switch. What's it for?

The stand-by switch employed by earlier AMX tube amps were implemented by removing the center tap of the HT supply. This way you can warm-up your tubes before the application of the high voltage supply. However, some earlier tube rectified versions show some blue glows when switching from standby-to-on position.

[RU9]

The stand-by switch employed by earlier AMX tube amps were implemented by removing the center tap of the HT supply. This way you can warm-up your tubes before the application of the high voltage supply. However, some earlier tube rectified versions show some blue glows when switching from standby-to-on position.

The blue glow, is this bad? I noticed the rectifier emitting a blue glow seconds after power up.  The blue glow disappears after some time. 

I did change the  tube rectifier. The new one doest not emit the blue glow. Is the old rectifier defective?

Regards.

Louie

[JojoD818]

The blue glow, is this bad? I noticed the rectifier emitting a blue glow seconds after power up.  The blue glow disappears after some time. 

I did change the  tube rectifier. The new one doest not emit the blue glow. Is the old rectifier defective?

Regards.

Louie

It has occured that the sudden flash of blue glow is caused either by the sudden demand of current and a fairly large input capacitor. Several of my specimens confirms that the input capacitor used was much too big (100uf) for the rectifier used (which should be about 40uf only), hence the blue glow. I believe this problem has been addressed already in their recent models.

To answer the question; your old tube rectifier may not necessarily be defective, it's just that the tube is exposed to repeated stress while the new rectifier is more stronger, it can handle the sudden load.

One solution I gave these users of those amps is to "manually bypass" this switch. What I mean is if your stand-by switch is part of a selector switch which is also used for the power-on, then instead of stopping at the stand-by position, immediately switch to power-on position. However, this may not be a solution if your input cap is off spec.

With a large, off specification input cap, your tube rectifier is bound to die sooner than is expected.

Best Regards,
JojoD

[ricky]

Hi mga tube gurus, ask ko lang po sana kasi lately yung ts audio ni misis hindi na ganon kaganda tumunog,medyo garalgal na.I suspect yung tube nya medyo mahina na pero up to now tumutunog pa naman,so ang question ko when will i know when to replace the tube and what tube to replace?