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Old 25th November 2012, 04:01 PM   #81
aldovan is offline aldovan  Brazil
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Originally Posted by azazello View Post
I'm not agree about LF of H 125SE. 5-6 years ago seller offered this cheap tr. for SE 2A3, 300B, 6L6...I tried 300B with 125FSE and Freeq. band was more 20-30000 Hz with the sames amplitudes /+- 0 db!/. Now I don't believe that band is 70 or 150 - 15000 Hz . I don't understand seller's deals.....
If you do not use the transformer next to limits, you do not will have problems with the frequency response.
The major problem is the use of a BIG DC current.
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Old 27th November 2012, 07:49 PM   #82
iko is offline iko  Canada
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Originally Posted by aldovan View Post
Why you do not to buy the transformer ?
The Hammond in your country have a line of very good hifi output transformers( but not the 125E or 125SE, please).

Aldovan
This is what I got available.

Hammond Single Ended Tube Output Transformers - (1627 - 1642 Series)

No 10k at 150-200mA SE or ultralinear.

No schematic yet?
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Old 28th November 2012, 02:12 AM   #83
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Aldovan since this thread has come back to life, I would like to show what I built using your faith in the 6w6 variants. I posted this already in the gallery, but I got the idea to try these tubes from you and your YouTube video.

I went a little beyond simple in the power supply/filament area, using a well filtered/isolated voltage doubler with a rectifier/filter section for each channel. My "voltage doubler" ended up putting around 350 volts with no load, so I had to do some modification and got the voltage down to around 325. I also have separate supplies for the various filament requirements.

The amp circuit however is as simple as can be. I tried the LED biasing, but in the end I liked the resistor better. I also went from originally, a 12AT7, to a 12AT7B, and finally a 6N2P-EV.

I used simple Edcor 5 watt transformers. The transformers spec from 40 to 18k. I forget the number, but they are listed in the 10 watt section because of their expanded low end over their standard 5 watters.

The only tube amp I have to compare it with is my Tubelab SSE amp, and though different it compares very well with this amp. The 12W6 is sweater in a good way though. I have picked up over 30 of the tubes for less than 2 dollars each, so I now have a supply on hand to last me quite a while.
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Old 28th November 2012, 02:21 AM   #84
Bigun is online now Bigun  Canada
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Originally Posted by a95sonoma View Post
[...] I tried the LED biasing, but in the end I liked the resistor better. I also went from originally, a 12AT7, to a 12AT7B, and finally a 6N2P-EV.
very interesting!

Why did you prefer the resistor biassing, was it based on the sound, or on other things - please can you say a bit more ?

I have read that for LED bias to work well the LED must have enough current flowing through it to ensure it's operating away from it's non-linear region. Depending on which LED it might need 5mA or more and then it produces the best sound. What current flow did you have through the LED ? One thing to try if you want to mess with this any further is to string a resistor from the top of the LED to a +ve bias and let more current flow through it. Overall this could be cheaper because with the resistor bias you will be tempted to use only very high quality bypass capacitors.

I'm also really interested in your opinion on the input tube sound. How do you like the 6N2P-EV compared with the other tubes ? I realize the russian tube has a higher mu and other differences so I'm wondering if you have plans to compare with something of similar specifications like 12AX7 ?
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Last edited by Bigun; 28th November 2012 at 02:26 AM.
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Old 28th November 2012, 10:17 AM   #85
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Originally Posted by a95sonoma View Post
Aldovan since this thread has come I tried the LED biasing, but in the end I liked the resistor better. I also went from originally, a 12AT7, to a
Finally!! Someone else like the resistor biasing better. Sorry but I do not or will I ever like Led for bias. It looks pretty but to my ear the resistor is still king.
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Old 29th November 2012, 03:44 PM   #86
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Originally Posted by Bigun View Post
very interesting!

Why did you prefer the resistor biassing, was it based on the sound, or on other things - please can you say a bit more ?

I'm also really interested in your opinion on the input tube sound. How do you like the 6N2P-EV compared with the other tubes ? I realize the russian tube has a higher mu and other differences so I'm wondering if you have plans to compare with something of similar specifications like 12AX7 ?
Hi, I just thought to my ears anyway, the resistor just sounded more natural, the LED seem to push the upper mids and high range up were it didn't sound natural to me, but like it was going through a Graphic Equalizer.

I used DC on the heater voltage for the preamp tube, so its easy for me to change voltage from 12 volts to 6. Needless to say I tried the 12AT7, a Chinese 12AX7b and 6n2p, and the 6N2P-EV. I originally simmed the amp in LTSpice with the 12AT7, but when I built the amp the 12AT7 was slightly lacking in gain. So I started playing around with the other tubes and resistor values, both in LTSpice and with my ears until I got a combo I liked best.

What you see in the circuit is the about the 3rd version and final values I settled on. Its been a few months since I built the amp, so I've forgotten the exact measured current and voltage values. If you want I can run the spice program and give you values from that.
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Old 29th November 2012, 07:39 PM   #87
aldovan is offline aldovan  Brazil
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Quote:
Originally Posted by a95sonoma View Post
Aldovan since this thread has come back to life, I would like to show what I built using your faith in the 6w6 variants. I posted this already in the gallery, but I got the idea to try these tubes from you and your YouTube video.

I went a little beyond simple in the power supply/filament area, using a well filtered/isolated voltage doubler with a rectifier/filter section for each channel. My "voltage doubler" ended up putting around 350 volts with no load, so I had to do some modification and got the voltage down to around 325. I also have separate supplies for the various filament requirements.

The amp circuit however is as simple as can be. I tried the LED biasing, but in the end I liked the resistor better. I also went from originally, a 12AT7, to a 12AT7B, and finally a 6N2P-EV.

I used simple Edcor 5 watt transformers. The transformers spec from 40 to 18k. I forget the number, but they are listed in the 10 watt section because of their expanded low end over their standard 5 watters.

The only tube amp I have to compare it with is my Tubelab SSE amp, and though different it compares very well with this amp. The 12W6 is sweater in a good way though. I have picked up over 30 of the tubes for less than 2 dollars each, so I now have a supply on hand to last me quite a while.
Very nice amplifier !
But I prefer use a driver with good current capacity.
For me, the 6N2P do not is the best chice
In mode triode, a pentode need more current in grid, because the input capacitancy is high.
The 6N2P do not work fine with a led, because you need more current for linear operation of LED, normally 10mA or more.
In my opinion, if you use the 6N6P with 10-15mA, you amplifier will sound the best.
But this is my modest opinion, only.

Aldovan
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Old 29th November 2012, 07:46 PM   #88
aldovan is offline aldovan  Brazil
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Originally Posted by Original Burnedfingers View Post
Finally!! Someone else like the resistor biasing better. Sorry but I do not or will I ever like Led for bias. It looks pretty but to my ear the resistor is still king.
I do not verify differences between resistor and LED.
I prefer the LED because fixed the polarization.
The grid bias do not vary with LED.

Aldovan
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Old 29th November 2012, 08:50 PM   #89
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I prefer LED in cathode, and gyrator in anode. However it is hard to make a gyrator for such tube like 6Н2П with so high anode resistance. Any parasitic capacitance is significant. For such tubes probably resistors in cathode indeed are more optimal. I put oscillograms in the thread about my Tower project. One with 6Н2П, another with 6Н1П. With 6Н2П slew rate limit was clearly asymmetric.
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Old 3rd December 2012, 09:13 PM   #90
aldovan is offline aldovan  Brazil
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Originally Posted by Original Burnedfingers View Post
Finally!! Someone else like the resistor biasing better. Sorry but I do not or will I ever like Led for bias. It looks pretty but to my ear the resistor is still king.
Burnedfingers

More a music with NO bass for you listen !
In my "Samsung" box !

Cunninghnam 46 in triode mode. Class A - YouTube

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