Its been 3 years and now i´ve just finished a new tubeamp i started earlier this week.
Im not sure about output power but it can play insanely loud, it uses two EL38 in ULPP with an ECC83 as input stage and phase splitter.
Here are some pics: http://s136.photobucket.com/albums/q163/diymania/tubeamp/diy/mono/
Im not sure about output power but it can play insanely loud, it uses two EL38 in ULPP with an ECC83 as input stage and phase splitter.
Here are some pics: http://s136.photobucket.com/albums/q163/diymania/tubeamp/diy/mono/
Interesting design, but please put a cage on it or otherwise protect the plate caps and tag strip on the output transformer primary tag switch from accidental contact. As shown it is more than a bit hazardous..
How about a description of circuit topology and what dictated the choice of an ECC83 as the driver?
I am assuming you used a concertina style phase splitter. Cathode bias in output stage?
Building a second for stereo?
A schematic and some description of how it sounds beyond "insanely loud" would be cool too..
How about a description of circuit topology and what dictated the choice of an ECC83 as the driver?
I am assuming you used a concertina style phase splitter. Cathode bias in output stage?
Building a second for stereo?
A schematic and some description of how it sounds beyond "insanely loud" would be cool too..
I was thinking about a cage, tho the chassi is not connected to the amp ground, however this should not be relied on.
I´ll have to make a full schemo of this design. Why i chose ECC83 was simply because i have a pile of them, i´m not building a second one, however i am modding a tube radio to go with this amp.
The sound is comparable to a ss amp in the same power range, which to my ears is very good.
I´ll have to make a full schemo of this design. Why i chose ECC83 was simply because i have a pile of them, i´m not building a second one, however i am modding a tube radio to go with this amp.
The sound is comparable to a ss amp in the same power range, which to my ears is very good.
So heres the schematic of this amp:
An externally hosted image should be here but it was not working when we last tested it.
Corrected schematic: http://s136.photobucket.com/albums/...on=view¤t=tubeampel38recentcomplete.png
alittle more than a year have passed and i´ve done a few mods to this amp, before it was a 10W peak amp that liked to distort at moderate volume.
The mods that have been done is a new gain stage using a 12AX7, however i came up with a filament supply pinout switch to enable using a 6DJ8 as well without having to rewire the socket.
I also moved the volume control from after the gain stage to before the gain stage, as well as adding an additional transformer to the plate supply, raising the the VA from 80 to 160 and raising the plate voltage around 33 volts, just these simple mods made a big difference.
Now the amp can play insanely loud before clipping, of cource the distortion at low freqs caused by the opt is unavoidable, especially since this is a 60 year old opt from an old philips EL6411 PA amp.
Also the EL38´s left life on earth last spring/summer after for some reason the little pumpdown tube broke and let air into one of the tubes. The replacement tubes i got was a pair of Red Bank 6889´s for around 69 bucks on ebay.
However measurements and calculations on the opt shows that EL519 would be better suited for this plate to plate impedance, 3226ohms with a 4ohm load and around 6450ohms with a 8ohm load, which actually happen to be just right for EL34 or 6L6 tho.
Aight enuf talking, heres the schematic as the amp stands today:
I´ll make a video tomorrow.
The mods that have been done is a new gain stage using a 12AX7, however i came up with a filament supply pinout switch to enable using a 6DJ8 as well without having to rewire the socket.
I also moved the volume control from after the gain stage to before the gain stage, as well as adding an additional transformer to the plate supply, raising the the VA from 80 to 160 and raising the plate voltage around 33 volts, just these simple mods made a big difference.
Now the amp can play insanely loud before clipping, of cource the distortion at low freqs caused by the opt is unavoidable, especially since this is a 60 year old opt from an old philips EL6411 PA amp.
Also the EL38´s left life on earth last spring/summer after for some reason the little pumpdown tube broke and let air into one of the tubes. The replacement tubes i got was a pair of Red Bank 6889´s for around 69 bucks on ebay.
However measurements and calculations on the opt shows that EL519 would be better suited for this plate to plate impedance, 3226ohms with a 4ohm load and around 6450ohms with a 8ohm load, which actually happen to be just right for EL34 or 6L6 tho.
Aight enuf talking, heres the schematic as the amp stands today:
An externally hosted image should be here but it was not working when we last tested it.
I´ll make a video tomorrow.
Rewire you circuit into the PP1C and add a CCS at the output and get rid of those bias potentiometers and you'll have one of the best PP-amps available.
If you build the PP1C and send Allen a photo and your comments you can get the PP1CS schematic for free. I've used the PP1CS for years and it's an outstanding amplifier and outperforms about everything I had put against it. Instead of EL34 I use the JJ KT77. I can't really recommend the JJ tubes as they are not very reliable but do sound better than the EL34 I tried so far.
I'll upgrade the PP1CS to near the DPA300B using 6H30 & 300B tubes this year. FYI: the schematic for the DPA300B is not available.
The gain block im using is this one: http://www.angelfire.com/electronic/funwithtubes/Amp-Gain_Block.html
I´m not a fan of cathode biased no NFB amps, low power and high distortion.
I´m not a fan of cathode biased no NFB amps, low power and high distortion.
Get back on earth... ;-)The gain block im using is this one: http://www.angelfire.com/electronic/funwithtubes/Amp-Gain_Block.html
I´m not a fan of cathode biased no NFB amps, low power and high distortion.
The distortion in loudspeakers are way higher than that in any electronic circuit! I claim that the lower distortions you get with the shown circuit does not matter at all.
The PP1 input stage is balanced and will cancel some distortion. Adding 2 CCS to the inputstage and trimmers you can even trim it to optimal performance.
I'm not a fan of global feed-back. ;-)
Taste is like the butt, split. I prefer amps with feedback as they have much lower distortion than any non feedback or SET amp, not to mention that a no feedback amp doesent have anywhere near as flat freq response as a amp with feedback.
Now im not making any statements that my amp actually apply to said above as i have not done any measurements.
Now im not making any statements that my amp actually apply to said above as i have not done any measurements.
The freq response in a room is anything but flat so it does not matter that much in an amp to have a flat response.
That said you can obtain flat response with a NFB design as well.
Have fun with your low distortion FB amp.
Alittle more progress have been done on this amp. I rearranged the transformers on the chassi to make both fit, i also modified the circuit alittle.
New schematic:
Pictures:
And finally a 20Hz sinewave into a 4.6ohm resistor:
As you can see, there is no more 12AU7´s in there. The symmetry pot is to adjust the poutput waveform so its symmetrical as in both sides of zero looks the same.
The output power is about 40 watts and its flat from 20kHz down to pretty much 20Hz. I like it alot!!
New schematic:
An externally hosted image should be here but it was not working when we last tested it.
Pictures:
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.
An externally hosted image should be here but it was not working when we last tested it.
And finally a 20Hz sinewave into a 4.6ohm resistor:
An externally hosted image should be here but it was not working when we last tested it.
As you can see, there is no more 12AU7´s in there. The symmetry pot is to adjust the poutput waveform so its symmetrical as in both sides of zero looks the same.
The output power is about 40 watts and its flat from 20kHz down to pretty much 20Hz. I like it alot!!
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