Does it need to be SE? Did you want it to be a cathode follower?
Looking at your lists of tubes, I think that 6V6 is too small a tube to reach 8-10W SE. Are you open to using a bigger output tube? Also, I think your power transformer is going to put out more voltage than an SE 6V6 amp can take (because 6V6 will not be able to take much idle current at those voltages).
So you can stick with 6V6 and accept 2-3W max output in SE, go with push-pull, or you can try to work with something bigger like EL34, 6L6 or even KT88for more SE power.
No is not necessary considering the objectives. I was thinking to single ended due to the fact that they need a single output tube rather than two. However I recently learned that single ended amps tend to have greater distortion percentage, so what you suggest?
Use a 6L6 is not a bad idea if it is possible manage the distortion and the frequency response in SE.
See I bought that power transformer for another project that consist in a preamplifier with different sets of equalizations for records. If you want and considering the excess of voltage I can send to you via pm the schematic of the preamplifier stage (which use a 6SL7GT and a 6J5).
In any case it would be great keep the circuit direct-couplet while (if it is possible) fulfill the requirements. Doing so it is possible limits the number of components down and to i.e avoid grid-blocking of strong signals, short-circuiting of weak signals, transformer resonances etc..
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You can do about 9 watts with a 6L6GC (pentode connected). Then you could do a pentode driver with plate-grid feedback and get a pretty nice SE amp with low Zout and low distortion.
I'm picturing something really simple like an RH807 but I think it is possible to get much lower distortion with a pentode input. I'm working up a design. I think it will be a fun challenge even if it does not get used here.
I'm picturing something really simple like an RH807 but I think it is possible to get much lower distortion with a pentode input. I'm working up a design. I think it will be a fun challenge even if it does not get used here.
Nope.....Am I known for squeezing every last watt out of any given tube?
I built an SSE amp (conventional SE design) with 6V6GT's and an Allied 6K56VG power transformer, a cheap Edcor XSE 15 -5K OPT and a choke salvaged from a dead HP audio generator. It is wired in triode and produces the nicest 2 watts you can get short of building a 45 based DHT amp with expensive parts (got one of those too).
B+ is 325 volts with a 5AR4 rectifier. The little Edcor OPT's will go down to about 25 Hz at 2 watts before saturation shows up, and up to about 45 KHz, so why spend more money?
I tried several flavors of "6V6's" from the old metal tubes, some old 6V6G's, and various flavors of vintage tubes. The best sounding tubes were some old grey glass RCA's that were in one of my junk boxes.
You can squeeze about 3 watts from a trioded 6V6 by grossly exceeding the plate voltage ratings, but 3 watts isn't much louder than 2 watts, so I settled on 325 volts since I can get that with a cheap transformer. (It was $40 when I built the amp).
Some of the Russian (and certain old American) 6V6 type tubes will work up to 400 volts without issue, as Fender proved, but that is in pentode mode.
Note there are some direct coupled amp designs similar to this that do work well, but are not cathode follower outputs. Look for "Free lunch" and "monkey." There are some directly coupled cathode follower designs that work (I have built a few) but require a lot more parts and quite a bit of fiddling to make them work.
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I would suggest you look at the Mullard 20W EL34 amp.
To get what you want in SE, you'll either need to use feedback or build a 15+ watt amp to get those power/distortion figures. You'll also need to spend a decent amount of money on a high quality pair of output transformers that wouldn't be nearly as pricey or large in a push-pull amp.
When you said you were using this with a magnetic pickup, are you intending to build a guitar amp?
To get what you want in SE, you'll either need to use feedback or build a 15+ watt amp to get those power/distortion figures. You'll also need to spend a decent amount of money on a high quality pair of output transformers that wouldn't be nearly as pricey or large in a push-pull amp.
When you said you were using this with a magnetic pickup, are you intending to build a guitar amp?
Seems very interesting! In any case could you be so kind to explain me why a pentode as input tube can contributes to reduce the distortion? I prefer not use a pentode in any case of course if you managed to keep the distortion under 1.5%..
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Thank you for the suggestion. However, considering I was looking for an amp that used 6v6, 6j5, 6l6 etc just because I have already some of them for spare.
From the moment I started being interested in tube amp I noticed that there are really different opinions about the SE amp. I was thinking that they were yes more difficult to develop but much cheaper considering what I read etc. now I'm starting to be a little confused
(i.e. http://gabevee.tripod.com/setube.html)In any case, with a magnetic pick-up I mean the pre 60's record player pick-ups that have a winding coil and an armature that according to the record groove creates variations in the magnetic fields which is the output signal.
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Well now I'm just looking for a tube amp that can produces a really good sound in terms of frequency range and distortion while performing no equalization (if I'm not wrong is only a matter of resistors and capacitor in the input stage) and that I can build easily and learn from it (the amp of Mr.Bates is an example - unfortunately seems not so promising after you evaluations). I have already an amplifier that perform the RIAA and that I it use daily.
Regarding the voltage of the signal from the pickup, old ones like mines can produce a signal of higher voltage compare to modern cartridge due to the fact that old tube amps were less sensitive than modern ones as regard the input stage.
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This form of output stage local feedback makes a very linear current-to-voltage converter with low output impedance. It should be more linear and lower Zout than a triode output stage with the output power of a pentode.
This sort of output stage is best driven by a linear voltage-to-current converter. Pentodes make more linear voltage-to-current converters than triodes.
Yes, a pentode input works nicely for these circuits. Directly coupling is also helpful.
The higher distortion in SE amps is mostly second harmonic. While the number might be alarming at face value in real life, that is at your ears, the se sound with higher 2nd harmonic is very nice and natural in a well made amp. Push pull by virtue of its design, cancels this 2nd harmonic and the even ordered harmonics and the resulting distortion number is much less. But, the left over harmonics are 3rd and the other odd number harmonics, which to the ears sounds not so nice. In most speakers this remaining distortion may be hard to hear and is most often sensed as a hardness to the sound which becomes fatiguing to the ears after about 30 minutes or longer.
I am currently listening to an RH6L6 amp with 6sl7 driver using vintage Norelco tape recorder OPT (se el84), on Altec 19 speakers. Joni Mitchell from the "clouds" LP. Her singing and guitar playing is as if she is right in the room and portrayed with excellent tonal nuances. The low level tonal nuances can be lost in PP amps but are the sounds that bring your listening experience to a more personal and pleasurable level.
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Here is someone who built the Bates amp back in 2012 and liked it diytube.com • View topic - A Direct-Coupled Amplifier with Cathode Follower
Thank you for the explanation. I made some research and is right to say that is possible reduce the distortion in the input stage by increasing the the amount of inverse feedback already provided if the amp is direct-coupled? Or maybe biasing the tubes at the optimum point in each case?
Thank you so much for having shared the link. What you think now considering the obtained results? Does anyone is registered to the other forum and is so kind to ask how much is the obtained output wattage?
I'm working on a project as well, HMV130, and I also started with a cathode follower output but decided to go the 'usual' grounded cathode instead (mostly to avoid complicating the power supply). I came up with the following 6V6 direct coupled schematic inspired by the Free Lunch/Monkey/Loftin-White:
I haven't built this yet, but I have all the iron on hand already and may start wiring in the next couple of weeks. I think I've got all my bias points sorted out, but this is the first time I've tried designing something direct coupled, so any input is appreciated.
The 6V6 in ultralinear with 275V across it should be able to squeak out 4W. I'll probably also try it in triode to see what all the 6V6 triode hub bub is about. The 6DJ8 seems like the default choice for a lowish anode voltage, but I'm open to other suggestions. Only limit is the 8mA rating of the Hammond 156C choke.
I haven't built this yet, but I have all the iron on hand already and may start wiring in the next couple of weeks. I think I've got all my bias points sorted out, but this is the first time I've tried designing something direct coupled, so any input is appreciated.
The 6V6 in ultralinear with 275V across it should be able to squeak out 4W. I'll probably also try it in triode to see what all the 6V6 triode hub bub is about. The 6DJ8 seems like the default choice for a lowish anode voltage, but I'm open to other suggestions. Only limit is the 8mA rating of the Hammond 156C choke.
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