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
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
100k is way to much for the 6sn7.
/Olof
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.
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.
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!
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!
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.
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?
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
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...😕
OK, another embarrassing old guy moment. The 6550 SE has a 6SJ7 driver, not a 6SL7, as the schematic clearly shows. I had 6SJ7s on hand so I used them instead of D3As.
I used a 6SL7 as an LTP in a 7591 pp e-linear. Brain fog rolled in just before I posted and I mashed up the two designs.
The e-linear design relies on high Rp in the driver. At 44k and a mu of 70, the 6SL7 works well with an easily driven tube like the 7591 and I think it might drive a 6550, too, but don't know for sure.
I found that, for some reason, a 6SJ7GT sounds much better in this amp than the metal version. Another guy who built the amp found the same thing.
I used a 6SL7 as an LTP in a 7591 pp e-linear. Brain fog rolled in just before I posted and I mashed up the two designs.
The e-linear design relies on high Rp in the driver. At 44k and a mu of 70, the 6SL7 works well with an easily driven tube like the 7591 and I think it might drive a 6550, too, but don't know for sure.
I found that, for some reason, a 6SJ7GT sounds much better in this amp than the metal version. Another guy who built the amp found the same thing.
Attachments
.BMP){kind=link}
Basicly I`ll have to `word it``(This is the original design )-The power supply gives 390 v then goes through a 20k resistor to the plate,which is referenced to ground by a 470 k resistor...Rk is set at 6.8k! .Then it simply goes to the coupling cap(.22uF), and to a 1k resistor to the 6550,triode connected.The way it is,according to plan needs like 5-6 volts if not more to acheive full output power(10-11 watts@5% distortion)This a guess.I`m still experimenting with different skeems of operation.I tried a 6sl7wgt and I find it saturates easy.Maybe a two stage 6sn7 ,current source or cathode follower ect. I think I have my work cut out for me...Two stages, Hum...
6550 single-ended amplifier
Oups, I failed to mention that just after the coupling cap, there is a ground connection throught a 270k resistor and then to the 1k resistor to the grid of the 6550...
Oups, I failed to mention that just after the coupling cap, there is a ground connection throught a 270k resistor and then to the 1k resistor to the grid of the 6550...
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