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 Post subject: GM-70 with 4P1L pentode DRD driver
PostPosted: Mon Jan 28, 2013 9:54 am 
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Joined: Mon Mar 22, 2010 1:10 am
Posts: 238
Trying to design a GM-70 amp with my limited knowledge. Hope to use a Loftin-White driver circuit - interstage - GM-70

This is a preliminary and I suspect will have many mistakes.

Please offer any feedback and corrections..


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 Post subject: Re: GM-70 with4P1L pentode DRD driver
PostPosted: Mon Jan 28, 2013 12:51 pm 
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Шаман, типа...

Joined: Tue Feb 10, 2004 12:30 pm
Posts: 7317
Location: Pleasant Hill, California
Looks fine on the first sight, except 10K on cathode when anode load is 7K. You definitely need either to shunt that 10K by capacitor, or apply negative bias to the screen from power supply, otherwise output resistance is huge and voltage amplification is less than 1. I did not check values of resistors, though.

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 Post subject: Re: GM-70 with4P1L pentode DRD driver
PostPosted: Mon Jan 28, 2013 5:22 pm 
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Joined: Mon Mar 22, 2010 1:10 am
Posts: 238
oops.. it should be 1k...


 
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 Post subject: Re: GM-70 with4P1L pentode DRD driver
PostPosted: Mon Jan 28, 2013 6:16 pm 
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Шаман, типа...

Joined: Tue Feb 10, 2004 12:30 pm
Posts: 7317
Location: Pleasant Hill, California
Now it looks better!

I will have soon PCBs available for power supply designed for Pyramid amps. Probably kits with all parts included will be available.

Here is schematic attached. One small PCB: soft-start limiter, second bigger: 400 and 800V rectifier, the 3'rd longer: +12V filament rectifier and sbabilizer, 270V for G2 stabilizer, 400V for driver stabilizer, -72V for bias rectifier and stabilizer (the later can be turned into -160V for MOSFET powerdrive). Also the last PCB contains star ground point and 22 uF film caps shunting 800V B+

As you understand, the PCBs can be used for other projects that need different voltages. Just change Zeners and some values of resistors. 800V is shunted by 10 uF film cap, so has "non-electrolytic" sonic quality of power supply, plus 240 uF of electrolytic filtering. It is more than enough for PP amp. For SE amp the stabilizer that is used for 400V here can be used, for example to get 700V stabilized, just add Zeners in the string.
Filament stabilizer sa well can be used for different voltages. Like, 5.6V Zener instead of 12V Zener will turn 12.6V output into 6.3V output.
If you don't need 270V for screen grids, don't install corresponding MOSFET and some other components. But you may find it usable to power preamp tubes by clean stabilized voltage that depends on Zeners used.

I plan to use this PCBs for other projects as well, that's why going to order more than I need for Pyramids. Such a way cost per PCB will be less: preparation of equipment costs more than $100, so if to order 100 PCBs it will be $1 per pcb additionally to it's cost instead of $100 per PCB if to order just one.


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-схема-пл-2.jpg
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 Post subject: Re: GM-70 with4P1L pentode DRD driver
PostPosted: Mon Jan 28, 2013 6:22 pm 
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Шаман, типа...

Joined: Tue Feb 10, 2004 12:30 pm
Posts: 7317
Location: Pleasant Hill, California
Here is PCB draft, one of the latest:

boards are made to fit into 1U enclosure. MOSFETs and Shottky rectifier screws to the chassis. However, can be screwed to a separate heatsink as well.


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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: GM-70 with 4P1L pentode DRD driver
PostPosted: Mon Jan 28, 2013 11:49 pm 
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Joined: Mon Mar 22, 2010 1:10 am
Posts: 238
I am interested in a few sets of the PCB... Smile


 
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 Post subject: Re: GM-70 with 4P1L pentode DRD driver
PostPosted: Tue Jan 29, 2013 10:51 am 
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Шаман, типа...

Joined: Tue Feb 10, 2004 12:30 pm
Posts: 7317
Location: Pleasant Hill, California
quikie22 wrote:
I am interested in a few sets of the PCB... Smile


I knew you would want some. Smile

The main problem now is in film caps. Digikey can sell for less than $10 / peace, but at the end of May. Mouser can ship now, but for more than $10.

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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: GM-70 with 4P1L pentode DRD driver
PostPosted: Wed Jan 30, 2013 4:59 pm 
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Joined: Mon Mar 22, 2010 1:10 am
Posts: 238
i can wait....


 
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 Post subject: Re: GM-70 with 4P1L pentode DRD driver
PostPosted: Wed Jan 30, 2013 6:32 pm 
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Шаман, типа...

Joined: Tue Feb 10, 2004 12:30 pm
Posts: 7317
Location: Pleasant Hill, California
quikie22 wrote:
i can wait....


I have all parts now, today got parcel from DigiKey with 950V MOSFETs, 60V MOSFETs, 220 uf/100V
and 10,000 uF/25V capacitors.

The next step is, to order PCBs. Found film caps on Alibaba, but the seller asks $13+ per cap, we need 2 of them per board. Too expensive, I think. I can get from DigiKey under $10, but at the end of May only if I pay now.

Image

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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: GM-70 with 4P1L pentode DRD driver
PostPosted: Fri Feb 01, 2013 1:24 am 
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Joined: Mon Mar 22, 2010 1:10 am
Posts: 238
Do you want me to make a payment first? Email me the amount and how to make the payment if yes.


 
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 Post subject: Re: GM-70 with 4P1L pentode DRD driver
PostPosted: Fri Feb 01, 2013 11:54 am 
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Шаман, типа...

Joined: Tue Feb 10, 2004 12:30 pm
Posts: 7317
Location: Pleasant Hill, California
quikie22 wrote:
Do you want me to make a payment first? Email me the amount and how to make the payment if yes.


Thank you, it would help!

I'll calculate. How many kits do you want?

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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: GM-70 with 4P1L pentode DRD driver
PostPosted: Fri Feb 01, 2013 8:58 pm 
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Joined: Fri Feb 01, 2013 8:26 pm
Posts: 3
Location: Australia
I would be interested in some PCB sets.


 
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 Post subject: Re: GM-70 with 4P1L pentode DRD driver
PostPosted: Fri Feb 01, 2013 11:05 pm 
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Шаман, типа...

Joined: Tue Feb 10, 2004 12:30 pm
Posts: 7317
Location: Pleasant Hill, California
Steve h wrote:
I would be interested in some PCB sets.


How many?

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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: GM-70 with 4P1L pentode DRD driver
PostPosted: Fri Feb 01, 2013 11:26 pm 
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Joined: Fri Feb 01, 2013 8:26 pm
Posts: 3
Location: Australia
I would buy 4 sets but depends on price or should i say how much my wife will let me spend.


 
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 Post subject: Re: GM-70 with 4P1L pentode DRD driver
PostPosted: Sat Feb 02, 2013 1:03 am 
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Joined: Mon Mar 22, 2010 1:10 am
Posts: 238
probably 4 sets


 
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