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 Post subject: Re: GU-50 Single Ended Amplifier Design
PostPosted: Tue Mar 15, 2011 1:17 pm 
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Шаман, типа...

Joined: Tue Feb 10, 2004 12:30 pm
Posts: 7312
Location: Pleasant Hill, California
quikie22 wrote:
the circuit is a simple one that is posted all over the web. http://fhs-consulting.com/ind/HV_REG_cropped.png


It can blow up because of oscillations. I would add 100 Ohm - 1K gate stopper.

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 Post subject: Re: GU-50 Single Ended Amplifier Design
PostPosted: Wed Mar 16, 2011 1:41 am 
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Posts: 238
wavebourn wrote:
quikie22 wrote:
the circuit is a simple one that is posted all over the web. http://fhs-consulting.com/ind/HV_REG_cropped.png


It can blow up because of oscillations. I would add 100 Ohm - 1K gate stopper.


Actually, I do have a gate-stopper ~ 270 ohms. As I said before, the circuit I used is a very common circuit, and built with most of the safety features expected in a regulator of this type.

Initially, my friend made it with NO safety features... to save cost.... it lasted about 2 years without a problem then one day just blew up. All efforts to replace the semiconductors ( zeners, mosfet, transistor) all just blew up.

So another friend (an SS engineer) redesigned the circuit with "triple" protection and stability features. The circuit is now doing duty in a FU-13 high voltage amp as a screen grid voltage regulator for the driver stage. This one also blew up a couple of times, reason was still unknown. Currently it has been stable for a couple of months without any hiccups Pray We suspect fluctuating lines voltage was playing havoc with Peak voltages encountered by the IRF840. My friend is contemplating a power line conditioner/regulator to minimise the mains fluctuations.

Another circuit was made to supply power for my Aikido line stage and another one for my RH84 tube amp. The RH84 power supply is running at a higher dissipation than the circuit mentioned above for the FU-13. So far, these two have remained very stable with no issues whatsoever. Very Happy

The last iteration of the circuit with the same values was made to supply power for another aikido line stage. This one blew all the zeners used and burnt through a couple of IRF840. I gave up on the circuit and decided to go for a tube rectifier and CLC smoothing in the end. Evil or Very Mad

All I can say is, 2 circuits rock solid, two circuits randomly blowing. 50% success rate?

BTW, I did not have time to post schematic earlier as I was travelling. Subsequently my daughter was admitted to hospital for a viral fever, and I did not have any time to answer/post anything. I slept in my car overnight while my daughter was in hospital. I did not expect anyone to be mind readers but I really did not have the time nor energy to do anything this past one week.


 
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 Post subject: Re: GU-50 Single Ended Amplifier Design
PostPosted: Wed Mar 16, 2011 9:18 am 
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Шаман, типа...

Joined: Tue Feb 10, 2004 12:30 pm
Posts: 7312
Location: Pleasant Hill, California
I would suspect IRF840, as Frank suggested, to be not completely good... Or, may be even fake...

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 Post subject: Re: GU-50 Single Ended Amplifier Design
PostPosted: Thu Mar 17, 2011 7:10 am 
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Joined: Mon Mar 22, 2010 1:10 am
Posts: 238
wavebourn wrote:
I would suspect IRF840, as Frank suggested, to be not completely good... Or, may be even fake...


A big possibility of it being fake. Relabelling cheap transistors as higher spec parts is common in my region. Due to to difficulty getting the high spec parts, prices are at a premium for even these useless fakes.


 
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 Post subject: Re: GU-50 Single Ended Amplifier Design
PostPosted: Thu Mar 17, 2011 8:28 am 
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Joined: Wed Oct 01, 2008 9:14 am
Posts: 41
Location: Denmark
Sorry to hear about your daughter, Quikie, hope she is getting better.

One thing I always try to remember is that - for me at least - posting here is a hobby activity. That means I just put this and other similar sites on hold if time is short.

When I asked for a detailed schematic, then I was not trying to be troublesome, nor was there any specific deadline. It really isn't possible to guess what might be wrong in something another person has built, unless you have *exact* schematics, including accurate component values actually used. Sometimes the physical layout can provide clues as well, which is why you frequently see people asking for under-chassis photos of people's contraptions. Saying that you have built a copy of a schematic, which is all over the 'net, unfortunately isn't good enough. I had already figured you were building source follower voltage regulators, yet if I was to try and simulate what you have built, and in general understand the schematic, then I need to see the whole thing. This does in particular include the load, your amps in this case. Otherwise you are forcing me to make guesses with my hands tied behind my back.

Also note that we have sort of an unofficial saying here in Denmark, I suspect you may have heard something similar before: "1 trillion flies cannot be wrong. Eat sh!t!" Meaning in this context that just because a schematic is popular doesn't mean it actually works as described! From what I have seen, then a *lot* of people are making mistakes when they mix tubes and semiconductors. Even being an EE doesn't seem to protect from this, because many people are unaware of some of the funny failure modes that tubes have and semiconductors doesn't. Unfortunately it is usually the semiconductors, which ends up biting the dust, even though the core problem is a tube issue. A problem, which would probably have gone completely unnoticed in a more classic schematic only involving vacuum state electronics.

In other news, then I am contemplating ordering the electronics for this project within the next week or so, once I have the order confirmation on the transformers and have created a detailed BOM. I'm thinking about mailing you some free MOSFETs, just so I can rule out fakes the next time you encounter a problem, and thus be able to force you to post a detailed schematic. Laughing

More comments to follow, still have some loose ends in this thread.

- Frank.


 
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 Post subject: Re: GU-50 Single Ended Amplifier Design
PostPosted: Thu Mar 17, 2011 1:01 pm 
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Joined: Wed Oct 01, 2008 9:14 am
Posts: 41
Location: Denmark
wavebourn wrote:
No, I feel I may let you know my personal preferences so you one day may try and check for yourself if you like it or not. Screen grid current is non-linear and depends on signal level. Looking from another side, screen grid is one more control grid, and anode current depends on voltage on it. R-C network integrating current consumption peaks varies regime of the tube, depending on signal level. On higher loudness idle anode current will go down, anode voltage will go up. And vice verse. If you like it, or don't care, it is fine, of course.

Well, I am aware of the technical aspect of the problem, and has been so for a while. Running a very stable screen grid voltage in pentode mode is a big deal for amateur radio power amps expected to be linear. Unfortunately I also seem to be thinking too much along those line, and not enough about audio...

When I examined the circuit, it seemed to me that the screen grid current variations in the driver had to be fairly small. The simulation results confirmed that, though one has to be just slightly suspicious of those, of course. In my setup the screen grid current is amazingly stable at very close to 1mA for Vin = 1.0Vrms (full power). Even with the simple RC filtering, the voltage didn't budge more than 0.1%, or 0.15Vpp. I assumed that was stable enough at least for a start. Using a voltage reference and a source follower ought to do better, of course.

Think the dynamic impedance of a VR tube is about 50 ohm. Hmm...?

Have now paid for the transformers, so now all I have to do is wait. And wait... Whistle


 
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 Post subject: Re: GU-50 Single Ended Amplifier Design
PostPosted: Thu Mar 17, 2011 1:33 pm 
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Шаман, типа...

Joined: Tue Feb 10, 2004 12:30 pm
Posts: 7312
Location: Pleasant Hill, California
I try to minimize all dynamic distortions as well as possible, however without sacrificing of legs and teeth. Wink

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 Post subject: Re: GU-50 Single Ended Amplifier Design
PostPosted: Sat Mar 19, 2011 8:17 pm 
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Joined: Wed Oct 01, 2008 9:14 am
Posts: 41
Location: Denmark
Well, that was my mistake. I didn't really consider that the total distortion of the amp will be down around 1% or less. At this point removing, say, 0.05% due to screen grid sag would be worthwhile. Throwing another MOSFET and a voltage reference in there isn't too much to ask.

Have order confirmation now for the four transformers, so time to draw detailed schematics and buy some discrete components. BOM next.


 
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 Post subject: Re: GU-50 Single Ended Amplifier Design
PostPosted: Sat Mar 19, 2011 9:23 pm 
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Шаман, типа...

Joined: Tue Feb 10, 2004 12:30 pm
Posts: 7312
Location: Pleasant Hill, California
Good lock with your project!

By the way, speaking of dynamic distortions I did not mean THD numbers. You can get low THD level on stable sinusoidal signal, but when signal level changes s**t happens that can't be caught up by standard THD measurements. But it adds a dirt to clean music that is well audible as a dirt.

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А женщина даже в мужской рубашке выглядит гораздо приличнее, чем мужчина в женских колготках! Be-be-be!


 
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 Post subject: Re: GU-50 Single Ended Amplifier Design
PostPosted: Thu Mar 24, 2011 12:12 pm 
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Joined: Wed Oct 01, 2008 9:14 am
Posts: 41
Location: Denmark
Got both a bunch of GU-50s and sockets now, plus all the other tubes (5U4G, 6J5P, SV83...). Just battling the problem that I seem not to be able to push the GU-50s into the sockets. Both sockets and tubes certainly are the right ones, just wondering if the tolerances on the parts I used for testing are working against me... Think

Don't want to break any tubes, so will try again tomorrow when rested.


 
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 Post subject: Re: GU-50 Single Ended Amplifier Design
PostPosted: Thu Mar 24, 2011 12:36 pm 
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Шаман, типа...

Joined: Tue Feb 10, 2004 12:30 pm
Posts: 7312
Location: Pleasant Hill, California
What kind of sockets do you have: stamped from sheet aluminium, or die-cast with a lid?

Here are 2 different examples pictured:

Image


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 Post subject: Re: GU-50 Single Ended Amplifier Design
PostPosted: Thu Mar 24, 2011 12:53 pm 
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Joined: Wed Oct 01, 2008 9:14 am
Posts: 41
Location: Denmark
Stamped Aluminum, ceramic bottoms, made in '88 with diamond mil spec seal, grindstone marks and all. Brand new ones all from the same batch by the looks of it. Seems identical to the ones in your last photo.

I can photograph them tomorrow if needed. Just wondering if I am doing something stupid here, so stopped while the going was good before I broke anything.


 
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 Post subject: Re: GU-50 Single Ended Amplifier Design
PostPosted: Thu Mar 24, 2011 8:51 pm 
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Шаман, типа...

Joined: Tue Feb 10, 2004 12:30 pm
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Location: Pleasant Hill, California
They may be bent: made from soft metal.

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 Post subject: Re: GU-50 Single Ended Amplifier Design
PostPosted: Thu Mar 24, 2011 11:46 pm 
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Joined: Mon Mar 22, 2010 1:10 am
Posts: 238
Sockets are very tight. My GU-50 have gone in and never to come out again!! (or so it seems). Mine are the second type too.
Removal requires a bit of ingenuity and mostly force ( try to imagine the creative use of some rope and a wall post).

I think the pin holders are designed to provide tight contact with the pins of the tube hence the difficulty in insertion and removal.


 
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 Post subject: Re: GU-50 Single Ended Amplifier Design
PostPosted: Fri Mar 25, 2011 9:42 am 
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Шаман, типа...

Joined: Tue Feb 10, 2004 12:30 pm
Posts: 7312
Location: Pleasant Hill, California
quikie22 wrote:
I think the pin holders are designed to provide tight contact with the pins of the tube hence the difficulty in insertion and removal.


Yes, for mobile military equipment.

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