Need P2P Tube easy project
Apr 4, 2006 at 7:16 PM Post #16 of 31
Quote:

Originally Posted by sbelyo
I'll just stick with the spec'd values for now.


Even Rick will tell you to not bother with the parallel output cap. It will likely do more harm than good.


Quote:

Originally Posted by sbelyo
If something failed, what is the maximum voltage the power supply caps would see? Same goes for the output caps in the amplifier section.


1.414 * the unloaded V of the transformer. Allow for at least 230V here.


Quote:

Originally Posted by sbelyo
2. Or are any of these capacitor values over spec'd?


The output cap is under spec'd. I am not going to say it again, and I am going to quit this thread. If the tube shorts (because you tapped it, because the cat jumped on the table and bumped it, because the phone rang and you turned your head too fast, because of a power surge, or because it just went bad), the output cap (and possibly your head) will see B+. Generally, a blown cap will not short, but, and this is the important point, it can. Even a short moment of 150V on your head will be unpleasant.

-d
 
Apr 4, 2006 at 7:20 PM Post #17 of 31
Quote:

I think you misunderstood me. My comment had nothing to do with sonics or value, or even reliability.


Is that not EXACTLY what we discuss in the DIY forum ?


Quote:

Anyway, this isn't a new vs old concern, it is a high voltage strapped to my head concern. Others should do as they choose, but for me, I can look in a tube and see that there is not much more than a tripped over cord seperating parts at high voltage from my head, so I'd err on the side of caution.


Not sure I understand that.Headphones are not electrodes and if they were even your opamp based amp would fry your brains in short time and since 40V @ 200ma is deadly any discrete transistor amp would kill you

Quote:

I wouldn't trust my life to a new tube either. There just aren't any new manufacture 6080's (though there are new 6as7g's) and my experience has been that many of the ones available are in less than good condition.


NOS means New Old Stock so are BRAND NEW tubes in the box never used.Unless damaged there is zero that can go wrong since the very word "vacuum tube" means the element is in a "vacuum" and not effected in any way by the environment.Six months or 50 years makes no difference.
BTW-New tubes are being made and more numbers added yearly

Quote:

When a tube amp is on the other side of the room, the worst case scenario is that it blows up some speakers and maybe starts a fire. But, when one is strapped to it, there is an added danger that one is on close enough proximity to touch it. Further, tubes become more fragile when they are hot, so a powered tube that is fragile strapped to ones head equals extra caution for me.


Exactly what are you getting at here ? Under what scenario is ANY amp blowing up a good thing and why is it worse if that amp uses triodes ??????
confused.gif


If it is a relaibility thing,triodes win hands down and even amps made in the twenties and treated very badly still work fine,a scenario you would be hard pressed to match in solid state gear.Fragile is DEFINATELY not a word having any connection to tube gear but IS descriptive of solid state equipment and why when it was introduced there was another thing introduced soon after-protection circuits to protect the FRAGILE solid state circuitry.
 
Apr 4, 2006 at 7:32 PM Post #18 of 31
Quote:

Even Rick will tell you to not bother with the parallel output cap. It will likely do more harm than good.


Yup.A bypass cap may add "sparkle" but that is not an accurate representaion of what went in in myopinion but a treble control but more time butcher than any "true" tone control
wink.gif


Quote:

1.414 * the unloaded V of the transformer. Allow for at least 230V here.


tube gear is not dangerous during the assembly stages but is pure deadly once you apply power so you need to pay attention and use the proper TOOLS to probe around inside,not curious fingers.Discharge EVERY SINGLE HV CAP before going back inside and making changes or if you touch one sonics will be off your list of important and funeral arrangements will be.No Joke on this one-dangerous stuff here

Quote:

The output cap is under spec'd. I am not going to say it again, and I am going to quit this thread. If the tube shorts (because you tapped it, because the cat jumped on the table and bumped it, because the phone rang and you turned your head too fast, because of a power surge, or because it just went bad), the output cap (and possibly your head) will see B+. Generally, a blown cap will not short, but, and this is the important point, it can. Even a short moment of 150V on your head will be unpleasant.


The best sounding caps have the highest voltage rating so go with 600V up rated caps .If it goes "ping" for whatever reason you are safe because it will be an open circuit,if it is still intact no matter WHAT the amp does it will block DC voltage because that is ehat a cap does.

It is the DC output amps that have the potential to be a shock hazard but only because there is no cap or transformer on the output to block the HVDC is something gets squirrely
 
Apr 4, 2006 at 7:49 PM Post #19 of 31
Quote:

Originally Posted by dsavitsk
The output cap is under spec'd. I am not going to say it again, and I am going to quit this thread.


Take it easy.... I'm taking your advice. I was just trying to understand how the circuit was designed and why the values were chosen. I didn't change the schematic, it's the original Van Waarde one from headwize.

I now understand that for safety's sake 100V is under spec'd
 
Apr 4, 2006 at 8:14 PM Post #20 of 31
Quote:

Originally Posted by sbelyo
Take it easy.... I'm taking your advice.


smily_headphones1.gif
Well, at least I got your attention. I have built a couple of tube projects, and they still scare the pants off of me.

The good news is that there are a number of good choice for high voltage high uF caps. Percy has some 470uF/450V nichicons that are reasonably cheap. There are also some blackgates. Motor run caps (ASC's from allied or ebay or percy or pxn) are reasonably priced and of good quality and there are the afore mentioned Solens. Also, Jensen and JJ make electrolytics in this range. You may need to parallel a few, or accept a higher 3dB point, but this isn't so bad.
 
Apr 4, 2006 at 8:22 PM Post #21 of 31
Quote:

Originally Posted by dsavitsk
smily_headphones1.gif
Well, at least I got your attention. I have built a couple of tube projects, and they still scare the pants off of me.

The good news is that there are a number of good choice for high voltage high uF caps. Percy has some 470uF/450V nichicons that are reasonably cheap. There are also some blackgates. Motor run caps (ASC's from allied or ebay or percy or pxn) are reasonably priced and of good quality and there are the afore mentioned Solens. Also, Jensen and JJ make electrolytics in this range. You may need to parallel a few, or accept a higher 3dB point, but this isn't so bad.



May I ask why you are so scared of them? I woudl say that I am careful when working on them, and I have a healthy fear of them (just to keep the ego in check
smily_headphones1.gif
) but I'm not so scared as to avoid them all together.

Rick does make a good point, a sloppy SS amp can do a heck of a lot of damage, as many of the opamps used provide enough current to be lethal in very unlikey circumstances.
 
Apr 4, 2006 at 8:24 PM Post #22 of 31
Quote:

Well, at least I got your attention. I have built a couple of tube projects, and they still scare the pants off of me.


when you stop being afraid you will get "sloppy' and at that time i don't expect you to be posting anymore
wink.gif


A healthy dose of fear is essential foy high voltage work and any old TV guy who lived to be an old TV guy will tell you "keep one hand in your pocket there buckshot or I will be dragging your dead carcass out the back door and will swear I never heard of you when asked about it "
very_evil_smiley.gif
 
Apr 4, 2006 at 9:04 PM Post #23 of 31
Handmade has some decent prices on the solens.... It looks as if I'll use electrolytic first and then try the solens
 
Apr 4, 2006 at 9:24 PM Post #25 of 31
Quote:

Originally Posted by rickcr42
when you stop being afraid you will get "sloppy' and at that time i don't expect you to be posting anymore
wink.gif



That's why. I use the tubelab.com method of first powering things up, which is to connect about 6 meters to the amp to check as many different voltages as possible, put on some safety goggles, and stand across the room to power it on. Probably unnecessary at 150V, but maybe not at 550v. Also, unless it is absolutly necessary (and so far it has not been) I don't probe around a live circuit. Harbor Freight sells meters for $5, and bought a bunch.
 
Apr 4, 2006 at 9:28 PM Post #26 of 31
Quote:

Originally Posted by dsavitsk
That's why. I use the tubelab.com method of first powering things up, which is to connect about 6 meters to the amp to check as many different voltages as possible, put on some safety goggles, and stand across the room to power it on. Probably unnecessary at 150V, but maybe not at 550v. Also, unless it is absolutly necessary (and so far it has not been) I don't probe around a live circuit. Harbor Freight sells meters for $5, and bought a bunch.



I use the "light bulb box" trick and a healthy does of double checking everything before hitting "ON"
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Apr 4, 2006 at 9:30 PM Post #27 of 31
I forgot about that place....

Now I understand that bypass caps on the output may be a waist of time, but how about in the power supply?
 
Apr 4, 2006 at 9:41 PM Post #28 of 31
Quote:

Now I understand that bypass caps on the output may be a waist of time, but how about in the power supply?


totally different functions.

A signal "coupling" cap is in series with the audio signal so everything must pass through it on its way to the next thing

A power supply "bypass" cap is a parallel connection (in parallel with the voltage) and is used to shunt certain frequencies to ground rather than block as in the series connection and is used to get rid of stray RFI that could if it passes through the power supply contaminate the audio signal
 
Apr 4, 2006 at 9:47 PM Post #29 of 31
Ahhh Haaa I understand now...

And I'm building one of those lightbulb boxes. I figure it can't hurt along with my discharge stick and a pair of latex gloves.
 
Apr 4, 2006 at 9:57 PM Post #30 of 31
Quote:

Originally Posted by sbelyo
Ahhh Haaa I understand now...

And I'm building one of those lightbulb boxes. I figure it can't hurt along with my discharge stick and a pair of latex gloves.



The "box" and discharge stick yes,the gloves i doubt will handle the voltage as will not every wire covering so you need to be aware a high voltage can actually "jump" from wire to wire if the insulation is lacking
eek.gif


some tid bits you may find useful

http://www.geofex.com/Article_Folders/SPO_Test.htm

http://www.geofex.com/tubeampfaq/TUBEFAQ.htm#safety

http://www.geofex.com/tubeampfaq/TUBEFAQ.htm#basics

http://www.geofex.com/Article_Folder..._tube_amps.htm

http://www.repairfaq.org/REPAIR/F_captest.html

http://www.geofex.com/Article_Folder...nd/stargnd.htm

http://www.geofex.com/ampdbug/ampdebug.htm


http://www.geofex.com/Article_Folders/boxtemplate.htm
 

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