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Old 5th August 2011, 08:07 PM   #1
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Default 6550 SINGLE-ENDED AMPLIFIER

Hi,has anyone built or seen the `6550 single-ended amplifier`` from AudioXpress sept.01...I`ve built it in 2004, and I wonder.After leraning more about pre-amps and drivers I`m a bit un sure about R4 ,20k driving a 6sn7 at the plate with 280 volts seems to be a lot of current at 14 ma.I`ve modified it putting 100k on the plate along with mandatory changes on Rk.More gain but Ijust can`t put my ear on it but...something is missing.p.s.I use nos tungsol 6550 marconi and rca 6sn7`s.so the tubes aren`t the cause and neither the iron,Hammond... Thank`s
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Old 5th August 2011, 10:01 PM   #2
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If you have 280V b+ at the driver stage 20k seems just fine. It should give you 6-8 mA idle current.
100k is way to much for the 6sn7.

/Olof
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Old 6th August 2011, 01:17 AM   #3
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Well, you've just experienced that different operating points sound different even when dealing with the same tube.
Sometimes you see that from the curves, sometimes not. Good thing you have ears, isn't it
In general, tubes as 6SN7 need some current for a gound sound. Only a few tubes sound still good even in starvation mode. E.g. 12AX7/ECC83 and EF86.
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Old 6th August 2011, 04:41 PM   #4
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As subjective as this sounds, I actually built that amp and was very, very disappointed in the results, even though I used the newer Hammond 1628SEA's. I did everything I could to try and actually like it before cannibalizing it for parts. The power supply components were used for the RH84 I am using now - which I like much better.

To be fair, the same designer also published another article in AX that same year for a PP 12V6/12SL7 amp. It was my first scratch-built amp, and it sounded absolutely great!
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Old 7th August 2011, 09:44 PM   #5
dtut is offline dtut  United States
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This feels a bit like piling on. I built this amp because I was interested in Pete Millet's e-linear 6550, but wanted to try something easier. I wound up building a 6SL7/6550 e-linear that I'm quite happy with.
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Old 8th August 2011, 12:04 AM   #6
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So,Ihave to change the operation points and maybe tubes.The application notes that come with tube data seems to starve the tubes.What will change the sound from what it is to something much more acceptable,given the cost.From the coupling cap to the output of the transformer is good.modified with 1800uF450v and120,000 20v so it is pretty hefty .The power supply was It`s like most of the single-ended amplifier back end.So what is needed is a new front end.And the choice is rather limited in octal`s 6sn7 or 6sn7. the tubenut
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Old 8th August 2011, 12:12 AM   #7
ttan98 is offline ttan98  Australia
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Quote:
Originally Posted by tubenut33 View Post
So,Ihave to change the operation points and maybe tubes.The application notes that come with tube data seems to starve the tubes.What will change the sound from what it is to something much more acceptable,given the cost.From the coupling cap to the output of the transformer is good.modified with 1800uF450v and120,000 20v so it is pretty hefty .The power supply was It`s like most of the single-ended amplifier back end.So what is needed is a new front end.And the choice is rather limited in octal`s 6sn7 or 6sn7. the tubenut

Can you show us the circuit diagram so that those with no access to it can understand your situation better?
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Old 8th August 2011, 04:39 PM   #8
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Click the image to open in full size.Click the image to open in full size.
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Old 8th August 2011, 05:03 PM   #9
tinitus is offline tinitus  Europe
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Old 8th August 2011, 06:41 PM   #10
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This is copyrighted material,or I am having a hard time to attach the image.Iwill draw MY circuit and will try harder to post it...
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