Need Some Guidance For Testing Process On Vacuum Tube Amp

[Planobilly]

Actually I guess the only thing that can cause a tube to over heat in current flow, what ever the cause of the current flow. Correct??

 

[Planobilly]

What actually happens for example when the load/speaker is disconnected from a amp while it is running? I assume the current is still flowing to the plate and overheats the plate until it melts and then could short out to other parts of the tube. That condition could send the current to other circuits in the amp and cause a cascade effect taking out other components.

Am I on track here with my thinking?

 

[Planobilly]

FIXED! Loud enough that my wife yelled at me when I plugged in my guitar and played super loud rock and roll...lol

Installed new output transformer which fixed the issue.

Learned a few new things in the process and a million thanks to Reallllly OLD Jim for all the kind help...I say he is old because he is one year older than me..!...lol

I have a spare bed room with a new bed so come on down to Florida Jim. The boat is tuggin at the dock lines..lolThanks to all the guys that helped.

Cheers,

Billy

 

[jim hardy]

Actually I guess the only thing that can cause a tube to over heat in current flow, what ever the cause of the current flow. Correct??

yep

 

[jim hardy]

What actually happens for example when the load/speaker is disconnected from a amp while it is running?

When that happens voltage in the transformer can run amuck and pierce the insulation
it happens often when the speaker wire falls off (or a thermally protected speaker disconnects itself wrecking a hundred dollar transformer to save a twenty dollar speaker)

you might solder a 50 or 100 ohm ten watt resistor across transformer secondary's highest tap to absorb voltage run amuck

Glad to hear you feel more confident now. Troubleshooting is a process of drawing a circle around the trouble and tightening it up.
Your intuition was right in the first place,
you're a natural !

I hope you'll measure K for a good transformer
that is a test you could do without disconnecting it.

and see my post 48 i made a mistake in it, fixed now

old jim

 

[Planobilly]

Thanks Jim...you have been a super nice teacher. Electronics is big fun for me but it is even more so when I have someone to talk to.

Lookin at post 48 in a few. I also read the Leo Fender post/link, cool stuff. I am going to dig up a link for you about transformers that twisted my head up good and proper if I can find it.

Billy

Looked at 48...think I will print it out an post it on the wall. I have CRS...lol...I will be nice and say that means "Can't Remember Stuff" lol

 

[Planobilly]

Number Next...lol

 

[Planobilly]

This was a pretty cool link on transformers http://education.lenardaudio.com/en/14_valve_amps_5.html

And here is everything you never wanted to know about the subject...lol http://www.dissident-audio.com/Transfos/Papers/Wolpert_Audio_Xfmr_Design_Manual.pdf

Time for Friday night TV wit the wife!

 

[jim hardy]

i REALLY like that Leonard article

Valve amps were part of the vinyl era where deep bass caused the needle to jump off the record. Most HiFi valve amps had a rumble filter to reduce sub-bass. The majority of speakers were approx 6dB to 10dB more efficient and larger than most speakers boxes today. A few Watts was very loud.

In those days speakers were likely vented because you get that 6db more sound per watt, and with tube amps watts were scarce.
Now a vented enclosure doesn't oppose low frequency over-excursion like a sealed one does
and I've watched the speaker try to follow the warp in a vinyl record . Switching in the rumble filter stops that.

Extreme high Voltages are generated across the primary winding if the speaker is disconnected while music is playing. Flashover between windings was a major problem with valve guitar amps.

Think about that - when the speaker wire falls off, the considerable Inductance of the transformer sees an immediate current drop , that is it experiences a large di/dt. e=Ldi/dt, so a huge voltage is produced. A snubber resistor in parallel with the speaker jack will help.

 

[jim hardy]

i re-read post 48 again

for the guy who made that chart, K is the knee.

I was thinking along the lines
volts = K X amps, K being the slope of that curve's straight part.
100 volts at 10 ma , K would be 10,000 and measuring from high side it might be that good

A good inductor opposes AC current stoutly, ie lots of volts to push amps through = large K
l
one with shorted turns is not stout , ie doesn't resist amps nearly so well, smaller K

that's why i hope you measure a good transformer so you'll know a real number

 

[Planobilly]

Hi Jim,

I am sure I will need to study this whole transformer issue in much more detail. I am also sure I will have some questions for you.

In general, I am trying to get a handle on some basic concepts and reduce things to the most basic factors. That was the reason I ask the question about what causes things to over heat. i.e the current question. I am well aware that electronic circuits can get pretty complex in their inter relationships but there is not an unlimited amount of cause and effect relationships. Also when something is not working there are faults that are much more likely than others to be the cause. I am trying to come to a method of step by step troubleshooting combined with a good "guess" style of troubleshooting.

I assume everyone at times thinks "this is the answer" without any apparent way of knowing why they think that. I don't know how that works and I guess it is not really important how it works. It just does, and when it does it is a super fast way to get to the solution. Because just guessing does not work very often, a method that always works need to be devised.

Your advice and direction put me on the path of a much better understanding of of this amp. It took me many hours ( perhaps 30 hours) to get to the final solution. It was time well spent.

Yesterday I started on the second one I own which had several issues and was displaying the same sort of symptoms. The troubleshooting time to resolution went from 30 hours to 30 minutes!
I have one more that I will work on this afternoon. It will be instructive to see if this reduced troubleshooting time line continues!

In any event, thank you ever so much for the kind help and putting up with my questions.

All the best,

Billy

 

[jim hardy]

Your advice and direction put me on the path of a much better understanding of of this amp. It took me many hours ( perhaps 30 hours) to get to the final solution. It was time well spent.

time well spent indeed.
"Junk" has enriched my life too.
When i was 13 i bought, for $6 from a Miami junk shop, and carried home on my bicycle handlebars a bushel of outboard motor parts.
With advice from a kindly couple who ran a boat shop i was able to assemble a Johnson QD11 ten hp outboard. Wow, did i learn a lot !
Used that motor all through my teen years.

If your other amps have blown output transformers too,
i would add that 'snubber' resistor across secondary. Fifty or a hundred ohms won't waste enough power to notice. Ear being logarithmic, 2X the power is barely noticeable..

Also feel your transformers. Same plate current that heats the tubes heats the transformer, so your early on attention to the output tubes is prudent.

Salvador has started a thread on vacuum tube amp, maybe you can help him along..
https://www.physicsforums.com/threads/vacuum-tube-x-ray-question.859427/

 

[Planobilly]

Thanks Jim...be glad to take a look at Salvador's post.

I had to finish a small machining job for a friend this morning. Built a transport part for a CD juke box from Europe which we could not buy. Crazy I know...lol

Like my grand father use to tell me..."with 300 dollars worth of tools you can build a 3 dollar ironing board' !...lol

I hear my wife calling me for lunch...I have learned the correct to all her questions. "Yes dear"

BIlly

 

[jim hardy]

I get a lot of mileage from
"That's a big ten-Yes,dear !"