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 Post subject: Re: Gubernator - 8: parallel SE GU-50 amp
PostPosted: Thu Jun 02, 2011 11:59 am 
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Шаман, типа...

Joined: Tue Feb 10, 2004 12:30 pm
Posts: 7312
Location: Pleasant Hill, California
Today I finally figured out how to correct sad construction mistake I made. I've found a donor for heatsink for power supply and fixed it on chassis: 40W of power dissipated by PS MOSFETs would be too much to dissipate by chassis itself.


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hsink1.jpg
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hsink2.jpg
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 Post subject: Re: Gubernator - 8: parallel SE GU-50 amp
PostPosted: Fri Jun 03, 2011 2:15 am 
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Joined: Mon Mar 22, 2010 1:10 am
Posts: 238
Looks good. Waiting to know how it sounds Smile

BTW, hope you don't mind us asking, what construction mistake? Is it the heatsink for the power transistors? It cannot fit under the chassis? I need to know so that I don't repeat it. I am considering building this same amp as well due to the success of the previous GU-50 amp.


 
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 Post subject: Re: Gubernator - 8: parallel SE GU-50 amp
PostPosted: Fri Jun 03, 2011 8:55 am 
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Шаман, типа...

Joined: Tue Feb 10, 2004 12:30 pm
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Location: Pleasant Hill, California
quikie22 wrote:
Looks good. Waiting to know how it sounds Smile

BTW, hope you don't mind us asking, what construction mistake? Is it the heatsink for the power transistors? It cannot fit under the chassis? I need to know so that I don't repeat it. I am considering building this same amp as well due to the success of the previous GU-50 amp.


My construction mistake was, I underestimated power that chassis would need to dissipate. I usually don't add heatsinks to tube amps since perforated aluminium chassis is enough. This time it is not enough.

This time I need to get 600V stabilized from 800V I have, and both stages will draw constantly 200 MA total. Add here possible 10% increase of voltage in household outlet...

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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: Gubernator - 8: parallel SE GU-50 amp
PostPosted: Sat Jun 04, 2011 3:13 pm 
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Шаман, типа...

Joined: Tue Feb 10, 2004 12:30 pm
Posts: 7312
Location: Pleasant Hill, California
Power supply with all stabilized voltages is ready. Forgot about bleeding resistors, it is not good when rectified voltage is 800V!


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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: Gubernator - 8: parallel SE GU-50 amp
PostPosted: Wed Jun 15, 2011 11:55 am 
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Шаман, типа...

Joined: Tue Feb 10, 2004 12:30 pm
Posts: 7312
Location: Pleasant Hill, California
Laboratory work: testing bunch of randomly selected 12L6 tubes to find statistics of their parameters, to set an optimal idle current and trimpot ranges to properly bias GU-50 tubes.

Stabilized 12.6V for filament, stabilized 120V B+, stabilized 26.5 mA cathode surrent. Measure voltage drop between ground (1'st grid is grounded) and cathode.

The procedure: insert a tube, wait 5 minutes, number it and record the measured voltage.


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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: Gubernator - 8: parallel SE GU-50 amp
PostPosted: Wed Jun 15, 2011 12:18 pm 
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Шаман, типа...

Joined: Tue Feb 10, 2004 12:30 pm
Posts: 7312
Location: Pleasant Hill, California
All tubes continued slowly drifting at the end of 5 minute heat-up, so I decided to bake all 20 of them on today's hot sun, inside of their boxes and sleeves several hours before repeating the experiment. Of course, they are all NOS, and need to be backed! But I don't bake anymore tubes with bakelite sockets in the oven.

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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: Gubernator - 8: parallel SE GU-50 amp
PostPosted: Thu Jun 16, 2011 9:09 pm 
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Joined: Mon Mar 22, 2010 1:10 am
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wavebourn wrote:
All tubes continued slowly drifting at the end of 5 minute heat-up, so I decided to bake all 20 of them on today's hot sun, inside of their boxes and sleeves several hours before repeating the experiment. Of course, they are all NOS, and need to be backed! But I don't bake anymore tubes with bakelite sockets in the oven.


In this type of cases, I let the filaments do the work, connect to filaments and leave a few hours till the tubes get really hot... same technique as the 6S33S users practice.... other methods of heating may not be as reliable...


 
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 Post subject: Re: Gubernator - 8: parallel SE GU-50 amp
PostPosted: Fri Jun 17, 2011 9:21 am 
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Шаман, типа...

Joined: Tue Feb 10, 2004 12:30 pm
Posts: 7312
Location: Pleasant Hill, California
I found one more problem: all case of IRF730 transistors I bought cheap on epay are far from specs. Fried few of them before making this discovery. The next week I am going to return back to the project, and redesign power supply completely. It was PITA to unbolt all the assembly in order to replace one MOSFET and resistors/diodes around it.

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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: Gubernator - 8: parallel SE GU-50 amp
PostPosted: Fri Jun 17, 2011 3:07 pm 
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Joined: Mon Mar 22, 2010 1:10 am
Posts: 238
wavebourn wrote:
I found one more problem: all case of IRF730 transistors I bought cheap on epay are far from specs. Fried few of them before making this discovery.


As I mentioned in my post before, they are selling a lot of fake parts, I suspect they are labelling lower spec parts as higher ones to sell at higher prices. Certain batches of my MOSFETS kept blowing in my regulated power supply too as mentioned in my post in the other thread.

wavebourn wrote:
The next week I am going to return back to the project, and redesign power supply completely. It was PITA to unbolt all the assembly in order to replace one MOSFET and resistors/diodes around it.


I could not agree more.


 
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 Post subject: Re: Gubernator - 8: parallel SE GU-50 amp
PostPosted: Fri Jun 17, 2011 5:28 pm 
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Шаман, типа...

Joined: Tue Feb 10, 2004 12:30 pm
Posts: 7312
Location: Pleasant Hill, California
What is strange, I can't find what is inside: transconductance is much lower, but break-down voltage it keeps well. Well, at least 400V is still fine for them. Looks like some kind of failed attempt to make a copy. Or, some low current high voltage dies inside that I don't know about. They worked like a charm while I did not need currents from them higher than 20 mA.

I am going to use some pull-offs from computer power supplies.

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


 
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