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Old 31st December 2008, 05:44 PM   #1
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Default Ideas for a simple 6080/6AS7 Push-Pull amplifier

I have some 6080 valves which I would like to use in a simple-to-build yet good sounding P-P amp. I think this circuit from another thread fulfils these criteria:

http://www.excite-webtl.jp/world/english/web/?wb_url=ja1cty.servehttp.com/&wb_lp=JAEN&wb_dis=2

It uses a differential amplifier by a pair of Hi-gm of C3g. I have some hi-gm E180F pentodes which I think can replace the C3g. Is this so? As I'm not good at valve theory I would like to know what resistor changes this involves. Also, does such a circuit require a driver stage at the input in order to produce sufficient gain? I will be driving the amplifier from a separate 15-20dB linestage.

Thanks to all prospective helpers!

Best wishes and regards to all diy-ers.

Joe A
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Old 31st December 2008, 05:53 PM   #2
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Just noticed that the link is dead. Try this one:

http://ja1cty.servehttp.com/6080/60802.html

There is an english translation of sorts from the "Return to Home Page" link.
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Old 31st December 2008, 06:23 PM   #3
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Sorry if you've been trying to access the site. I just copied and pasted the link here hoping you will be able to copy-paste it

http://ja1cty.servehttp.com/6080/60802.html
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Old 31st December 2008, 06:36 PM   #4
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Hi,
i once built a simple little 6080 PP amp with a single ended front end driving an interstage transformer to do the phase splitting. I used a suboptimal interstage which compromised the top end somewhat. If you can afford a pair of Lundahl LL1660 I highly recommend this approach.
I have been toying with the idea of a new design using a direct coupled LTP into 6080 finals, with partial feedback to drive the output impedance down.
My experience was that 6080's work extremely well at 100V and 100mA, so a split rail design with about +/-130V would do the trick. If you are interested i could lash up a schematic of my ideas. The only thing I have not decided on is what driver valve would fit the bill. It would need to work comfortably at about 100V on the plate and sinking about 1-2mA of current and a gain of about 20.

Shoog
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Old 31st December 2008, 09:15 PM   #5
Jeb-D. is offline Jeb-D.  United States
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Here is my 6AS7 amp schematic. It's 2 stage and everything runs off a single supply, so it is easy. It clips at +/- 11Vpk, so that's a little more than 7Wrms output class-A into 8ohm. It uses about 6dB of cross-coupled g2 feedback and has an output impedance of about 1ohm. I am happy with the sound. It has been the primary amp in my system for almost half a year. I plan to add some kind of DC balance for the output stage, but haven't got around to it, nor found it absolutely necessary. It could be altered to use solid state rectification or a different input transformer. Also, hammond does make a universal primary version of this power transformer.

E180F would probably work really well adapted to this design. The current project I'm bread-boarding uses E180F. I could easily adapt them to this circuit, or the one you linked to if you need help with that.


Each channel
Click the image to open in full size.
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Old 1st January 2009, 01:33 AM   #6
ja2dhc is offline ja2dhc  Japan
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Default Re: Ideas for a simple 6080/6AS7 Push-Pull amplifier

Quote:
Originally posted by sonata149
It uses a differential amplifier by a pair of Hi-gm of C3g. I have some hi-gm E180F pentodes which I think can replace the C3g. Is this so?
Joe A
A Happy New Year to Joe & all,

I am so glad to discuss my circuitry of 6AS7pp. Here is a modified
schematic to use E180F/6688 instead of C3g. AS you can see,
the values of resistors are identical to C3g's. The key points
are as follows:

1: Adjust 190Kohm of G2 dropper to get 200-220V for both
plates of E180F/6688.

2: Confirm G2 voltage around 100-150V after above adjustment.

Because of Hi-gm of E180F, total amplifier gain from the signal
input jack to the speaker output will be more than 30dB which
is enough to get full power(9W) of the amplifier with less than
1Vrms signal input so that you don't need to use line amplifiers.
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File Type: gif 6080pp-6688.gif (21.5 KB, 1631 views)
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Old 2nd January 2009, 12:27 AM   #7
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Hi,

Just for info, you guys my also want to dig into the forum's archives.
The PP 6080 has been discussed before and I'm positive you'll find some interesting stuff in there.

I remember one amp in particular using an ECC88 to drive a pair of 6080s which I heard on Lowthers that stuck with me. It was made in Italy and nicknamed "Topolino".

Never mind me, carry on,
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Frank
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Old 2nd January 2009, 10:13 AM   #8
ja2dhc is offline ja2dhc  Japan
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Default Re: Re: Ideas for a simple 6080/6AS7 Push-Pull amplifier

I found similar construction amplifier in the below URL.

http://www.diyparadiso.com/sk6as7pp1.htm

The below lists comparison between mine & his.

_______________mine_______his
--------------------___-----------__-------------------
6AS7 P Voltage___160V_____170V
Differential Amp__C3g______EF86
OPT____________Custom___LL1664pp
_______________Made

Opt Imp. PP______2Kohm____3Kohm
Coupling_________Capacitor__Direct
CCS____________22Kohm___Transistor CCS
________________Resistor

According to his Web, this amplifier was exhibited
at the Paris Hi end Show.
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Old 2nd January 2009, 05:03 PM   #9
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Thank you all, guys for your suggestions. I'm still considering my options but your input has been much appreciated

Shoog wrote:

Quote:
I have been toying with the idea of a new design using a direct coupled LTP into 6080 finals, with partial feedback to drive the output impedance down. If you are interested i could lash up a schematic of my ideas.
If you can I would appreciate that.

Quote:
My experience was that 6080's work extremely well at 100V and 100mA, so a split rail design with about +/-130V would do the trick.
Can I ask ja2dhc and Jeb-D what is this voltage in their respective circuits (or the voltage at the cathode to ground)?

To Jeb-D

Quote:
E180F would probably work really well adapted to this design. The current project I'm bread-boarding uses E180F. I could easily adapt them to this circuit, or the one you linked to if you need help with that.
Your circuit looks nice too. Can you please work out the changes for using e180f's? Also, can you please quote the voltages at various points in the circuit for testing purposes.

Regarding the 10K:20K input transformer what type/voltage of toroidal trfx would fit in here? Judging by the results I would upgrade to the Jensen or other dedicated i/p trfx.

To: ja2dhc: In another thread you say that one can use a transistor CCS with about -15V instead of the -160V / 22Kohm bias for the LTP cathodes. As I'm not at all handy with transistors, can you please suggest a working circuit?

Thanks for your help so far.

Joe A
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Old 2nd January 2009, 06:52 PM   #10
Jeb-D. is offline Jeb-D.  United States
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Quote:
Can you please work out the changes for using e180f's?
Sure. I'll posted a schematic later today.

Quote:
Also, can you please quote the voltages at various points in the circuit for testing purposes.
Output stage: Aprox 290V B+, Cathode bias 90V, 60mA per triode.

Driver stage is 160V plate, and 150Vg2. However, Vg2 is going to come out to a different value for E180F.

Since the circuit is class-A, The approximated loading as seen per triode:
Click the image to open in full size.
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