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PostPosted: Jul Mon 31, 2006 3:45 am 
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From time to time I see push-pull designs with the screen grids of the output tubes connected to taps on the output transformer like they are in Terry's design above. What is the design objective for that? I'm guessing it is intended to improve the linearity of the output stage? Looks like it would provide some negative feedback.

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PostPosted: Jul Mon 31, 2006 4:13 am 
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It is called 'ultra linear' and does provide negative feedback. At one extreme is the triode connection and the other is the pentode connection. The UL connection has some of the advantages of both.
The design was patented in 1955 in the USA and much earlier in the UK.
http://patimg1.uspto.gov/.piw?docid=US0 ... PN/2710312

and a very good discussion may be found here. http://www.webace.com.au/~electron/tubes/ul.html

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PostPosted: Sep Thu 14, 2006 3:34 pm 
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Location: Salt Lake City, Utah, USA
Terry,

I was looking at your amp from 31 July, showing the Stromberg Carlson 1121PL Audio amp. Your idea of using 5V6's instead of 6V6's sounds like a great idea. I'm going to be building my first audio amp. If I used solid state diodes for the voltage rectifiers, that would leave the 5 volt winding from transformers made for tube rectifiers available. Wouldn't this work for subing 5V6's in this type of circuit?

Have you ever used 5v6's? How do they sound? I assume there would have to be some bias changes?

I'm going to build a tube amp for my R-391 Receiver. I will take the audio off of the diode load and use the home brew amp to listen to it.

Thank you for your time and help.

Best,
DW Holtman


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PostPosted: Sep Thu 14, 2006 5:45 pm 
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Location: Powder Springs,Ga. USA
future212 wrote:
Terry,

I was looking at your amp from 31 July, showing the Stromberg Carlson 1121PL Audio amp. Your idea of using 5V6's instead of 6V6's sounds like a great idea. I'm going to be building my first audio amp. If I used solid state diodes for the voltage rectifiers, that would leave the 5 volt winding from transformers made for tube rectifiers available. Wouldn't this work for subing 5V6's in this type of circuit?

Have you ever used 5v6's? How do they sound? I assume there would have to be some bias changes?

I'm going to build a tube amp for my R-391 Receiver. I will take the audio off of the diode load and use the home brew amp to listen to it.

Thank you for your time and help.



Best,
DW Holtman


5V6 is same as 6V6 except for heater voltage and price. I tried a pair of 5V6s and they worked fine and being NOS sounded better than the used 6V6s. I just made a short term test using the 6 volt filament supply (not recommended for long term!). The five volt rectifier winding should be fine for 5V6s. No bias changes are necessary since the tubes are identical except for heater voltage.

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Last edited by Terry Judkins on Sep Thu 14, 2006 7:13 pm, edited 1 time in total.

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PostPosted: Sep Thu 14, 2006 7:08 pm 
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Location: Buenos Aires, Argentina
future212 wrote:
Terry,

I was looking at your amp from 31 July, showing the Stromberg Carlson 1121PL Audio amp. Your idea of using 5V6's instead of 6V6's sounds like a great idea. I'm going to be building my first audio amp. If I used solid state diodes for the voltage rectifiers, that would leave the 5 volt winding from transformers made for tube rectifiers available. Wouldn't this work for subing 5V6's in this type of circuit?

Have you ever used 5v6's? How do they sound? I assume there would have to be some bias changes?

I'm going to build a tube amp for my R-391 Receiver. I will take the audio off of the diode load and use the home brew amp to listen to it.

Thank you for your time and help.

Best,
DW Holtman


I recommend you also consider 6AQ5 which is 6V6's little brother (miniature type). Same tube indeed, just slightly lower max ratings. Or the Jan 6005W which is mil. version. I have tried both and cannot tell the difference.

Mario


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PostPosted: Sep Mon 18, 2006 1:03 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 369
Yeah,the good old 6AQ5 really is an excellent tube.It never
got the proper respect from the audio equipment designers.
They probably always percieved it as a lowly television
tube and not suitable for hi-fi use.There is a vast amount of
these still available in NOS form with cheap prices.That makes
it very attractive for hi-fi homebrew projects.Many different
types and manufacturers to choose from.There is even a
European version of it,the EL90.
Regards,
Swanson


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PostPosted: Sep Tue 19, 2006 8:05 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 959
Location: Buenos Aires, Argentina
You can also find 5AQ5 and lately I purchased 10 NOS Tunsgram 12AQ5 with that sought after "dark grey smooth plate". Both are worth peanuts and they are wonderful tubes experiment and to enjoy.

Mario


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