Thank you both! I'd be satisfied with 5 - 30 Watts. I'm very experienced with solid state, and I've built tube kits, but this would be my first scratch-built tube project.
Your input is much appreciated.
Mike
P.S. I already have a fair stock of 6080's I'd like to put to use, but since it's my first scratch built amp, I've been looking for something as simple as possible.
Your input is much appreciated.
Mike
P.S. I already have a fair stock of 6080's I'd like to put to use, but since it's my first scratch built amp, I've been looking for something as simple as possible.
Konnichiwa,
A simple and inexpensive solution would be to build Menno Van der Veens "Maurits".
http://www.plitron.com/PDF/PB/Article/Atcl_13.pdf
The advantage is that due to it's fairly low internal impedance you can actually get away in the case of the 6AS7/6080 with using a normal torroidal Mains Transformer (115V+115V : 6V+6V with the 6V windings parallel will give a 8KCT:6R Transformer) witout running into saturation or other troubles.
Torriods by inheret design have rather low leakage inductances, which helps the high frequency response, the low impedance of the Output Valves helps with the low end, you cannot misuse EI mains transformers that way, BTW.
The powersupply could be improvised from a 115V+115V : 115V+115V mains insulation transformer with a few added turns for the heaters and also a few for the HT to be added. A nice 330VA or bigger mains insulation torroid would fit the bill. You can usually find neat looking diecast metal enclosures to enclose your Tooridal Output and mains transformer, giving the Amp a clean and simple appearance.
If you slightly re-adjust the output stage operation (based on the Svetlana Datasheet) you need around 370V +B (can be gotten with a little extra work from a 230V AC voltage and a few turns added by hand), make the common cathode resistor around 750 Ohm, use a 50VA or larger 115V+115V : 9V+9V as 5K-CT : 8 Output Transformer and you will have around 6 - 10W RMS available from this modifed "Cheapo Maurits".
This should give you a simple and inexpensive start to schratch building. After that you can consider how you feel about a more complex Project, with many 6AS7 Output valves (you need a lot to get the output impedance in OTL operation to anything sensible) and you will be better able to judge if you actually want to do that kind of thing or not.
Anyway, this would be my take on a simple "beginners amp", that could be build for very little money.
Sayonara
mrothacher said:
A simple and inexpensive solution would be to build Menno Van der Veens "Maurits".
http://www.plitron.com/PDF/PB/Article/Atcl_13.pdf
The advantage is that due to it's fairly low internal impedance you can actually get away in the case of the 6AS7/6080 with using a normal torroidal Mains Transformer (115V+115V : 6V+6V with the 6V windings parallel will give a 8KCT:6R Transformer) witout running into saturation or other troubles.
Torriods by inheret design have rather low leakage inductances, which helps the high frequency response, the low impedance of the Output Valves helps with the low end, you cannot misuse EI mains transformers that way, BTW.
The powersupply could be improvised from a 115V+115V : 115V+115V mains insulation transformer with a few added turns for the heaters and also a few for the HT to be added. A nice 330VA or bigger mains insulation torroid would fit the bill. You can usually find neat looking diecast metal enclosures to enclose your Tooridal Output and mains transformer, giving the Amp a clean and simple appearance.
If you slightly re-adjust the output stage operation (based on the Svetlana Datasheet) you need around 370V +B (can be gotten with a little extra work from a 230V AC voltage and a few turns added by hand), make the common cathode resistor around 750 Ohm, use a 50VA or larger 115V+115V : 9V+9V as 5K-CT : 8 Output Transformer and you will have around 6 - 10W RMS available from this modifed "Cheapo Maurits".
This should give you a simple and inexpensive start to schratch building. After that you can consider how you feel about a more complex Project, with many 6AS7 Output valves (you need a lot to get the output impedance in OTL operation to anything sensible) and you will be better able to judge if you actually want to do that kind of thing or not.
Anyway, this would be my take on a simple "beginners amp", that could be build for very little money.
Sayonara
Hi Alex
A 6AS7 or 6080 pp is a superb sounding amp. I've attached a schematic of my own take on the 6AS7 pp idea.
I use low current drive in my amp and love the sound it makes. Others might prefer higher current drivers but either way the 6AS7 can be made into a stunning sounding push-pull amp.
Mine uses differential amps with constant current sinks in the tails of both the driver and power stages. The driver uses a simple LM317 as a sink with an STC 12E14 regulator tetrode as the sink for the output stage.
It is a work-in-progress and I'm thinking about reducing the number of stages to 2 by putting a 6SL7 or similar as a driver and removing the first stage. By doing this I'm trying to take full advantage of the low Miller capacitance of the 6AS7 by using a high gain low current driver. That's for the new year.
As it is though the amp sounds simply beautiful.
On another thread Shoog has done the opposite to me and used high currents and interstage transformer coupling. Also, his constant current sinking arrangements are a bit more sophisticated than mine.
Both approaches are equally valid and will produce an amp that sounds superb. I can guarantee you won't be disappointed whichever option you choose.
Steve.
A 6AS7 or 6080 pp is a superb sounding amp. I've attached a schematic of my own take on the 6AS7 pp idea.
I use low current drive in my amp and love the sound it makes. Others might prefer higher current drivers but either way the 6AS7 can be made into a stunning sounding push-pull amp.
Mine uses differential amps with constant current sinks in the tails of both the driver and power stages. The driver uses a simple LM317 as a sink with an STC 12E14 regulator tetrode as the sink for the output stage.
It is a work-in-progress and I'm thinking about reducing the number of stages to 2 by putting a 6SL7 or similar as a driver and removing the first stage. By doing this I'm trying to take full advantage of the low Miller capacitance of the 6AS7 by using a high gain low current driver. That's for the new year.
As it is though the amp sounds simply beautiful.
On another thread Shoog has done the opposite to me and used high currents and interstage transformer coupling. Also, his constant current sinking arrangements are a bit more sophisticated than mine.
Both approaches are equally valid and will produce an amp that sounds superb. I can guarantee you won't be disappointed whichever option you choose.
Steve.
Attachments
An OTL from scratch would be very difficult for a first time tube builder.
You may want to consider an OTL headphone amp. Or a kit from http://www.transcendentsound.com/ The prices are very reasonable, it would honestly probably cost you more to build one of equal quality from scratch using a schematic for reference. I know it's not 6as7 based, but the T-16 stereo kit looks to fit your requirements.
You may want to consider an OTL headphone amp. Or a kit from http://www.transcendentsound.com/ The prices are very reasonable, it would honestly probably cost you more to build one of equal quality from scratch using a schematic for reference. I know it's not 6as7 based, but the T-16 stereo kit looks to fit your requirements.
Steve Cresswell said:
Thanks Steve.
I have been reading the progress of your build on another forum last night.
I will source an appropriate input transformer to do the phase inversion, maybe have a winder custom wind a pair for me.
BTW, I forgot the bookmark the other forum that you narrated your progress, can you please email it to me: alexg_ht (at) yahoo.com
Thanks.
Hi Steve,
Forgot to mention, am driving my 6080 parafeed with a 12at7, the 12at7 cannot drive the 6080 into full power. I have a 5670 preamp with a lot of gain, paired with the 12at7/6080 parafeed, then I am getting decent power.
Am thinking of doing the 6080 PP using a 6n1p or 5670 driver into a center tapped choke phase inverter (just like the Seth Amplifier of Jean-Francois Lessard, which I have tried on a PP 832A with excellent result) then into 6n1p voltage amp, then into the 6080. B+ for the 6n1p at 400VDC and B+ for the 6080 180 to 250VDC.
This might give me enough voltage swing on the first two stages to drive the 6080 to produce adequate power.
Forgot to mention, am driving my 6080 parafeed with a 12at7, the 12at7 cannot drive the 6080 into full power. I have a 5670 preamp with a lot of gain, paired with the 12at7/6080 parafeed, then I am getting decent power.
Am thinking of doing the 6080 PP using a 6n1p or 5670 driver into a center tapped choke phase inverter (just like the Seth Amplifier of Jean-Francois Lessard, which I have tried on a PP 832A with excellent result) then into 6n1p voltage amp, then into the 6080. B+ for the 6n1p at 400VDC and B+ for the 6080 180 to 250VDC.
This might give me enough voltage swing on the first two stages to drive the 6080 to produce adequate power.
There is around 50mA going through each triode section plus around 35mA set aside for the sink.
The 12E14 sink is pulling approx 135mA to ground.
50mA per triode might not seem much for a 6AS7 to be passing, but as I said, this is a deliberately low current design, which I like the sound of.
Halving the cathode resistor on the sink will of course double the current passing through the 6AS7s and gives a more forward sound. This setting for the output tubes is more suited to commercial speakers. The low curent setting suits my Fostex driven Metronomes better.
Steve
The 12E14 sink is pulling approx 135mA to ground.
50mA per triode might not seem much for a 6AS7 to be passing, but as I said, this is a deliberately low current design, which I like the sound of.
Halving the cathode resistor on the sink will of course double the current passing through the 6AS7s and gives a more forward sound. This setting for the output tubes is more suited to commercial speakers. The low curent setting suits my Fostex driven Metronomes better.
Steve
Hi all,
I've just started another thread looking for anyone interested in group buying some Lundhal LL1517 output transformers to use as input/interstage transformers. These would appear to be ideal for my 6080 amp design (see attached schematic), and a bargin at about £20.00 per pair.
Shoog
I've just started another thread looking for anyone interested in group buying some Lundhal LL1517 output transformers to use as input/interstage transformers. These would appear to be ideal for my 6080 amp design (see attached schematic), and a bargin at about £20.00 per pair.
Shoog
Attachments
Bringing up an old thread.
I'd like to start an OTL project (as I have no access to any transformers here, not even toroidal!!!).
Was looking at the 6C19P tube. they have a 120 ohm plate resistance and are fairly cheap. Better option than 6AS7 no?
I guess I could use these in an OTL design. Not sure which one yet. Just doing some research.
Also to detect DC on the outputs, could I use a simple LED connected to ground (along with fuse protection and possible relays of course for large failures)?
If the LED is connected to the output it will illuminate if there is any DC present no?
I realise a small amount of DC can be present in SS amps, I had 300mV on one channel I had to fix. But anything up to 15mV can do no damage to speakers.
I'd like to start an OTL project (as I have no access to any transformers here, not even toroidal!!!).
Was looking at the 6C19P tube. they have a 120 ohm plate resistance and are fairly cheap. Better option than 6AS7 no?
I guess I could use these in an OTL design. Not sure which one yet. Just doing some research.
Also to detect DC on the outputs, could I use a simple LED connected to ground (along with fuse protection and possible relays of course for large failures)?
If the LED is connected to the output it will illuminate if there is any DC present no?
I realise a small amount of DC can be present in SS amps, I had 300mV on one channel I had to fix. But anything up to 15mV can do no damage to speakers.
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