Hello, this is my frist post on this forum, I'm a 15yo italian hobbist.
Sorry for my bad English.
I built two se tube amp, and now i am looking for a more powerful project.
I've at home one ecc82, one ecc83 with one of the two triode broken and 2 el34. With these tubes i designed a schematic, but, because i never build a pp before, i don't know if this is a good design.
This is the schematic:
I did some errors in design?
The input is a CD player, has the driver enough gain?
Thanks for the helping.
Sorry for my bad English.
I built two se tube amp, and now i am looking for a more powerful project.
I've at home one ecc82, one ecc83 with one of the two triode broken and 2 el34. With these tubes i designed a schematic, but, because i never build a pp before, i don't know if this is a good design.
This is the schematic:
I did some errors in design?
The input is a CD player, has the driver enough gain?
Thanks for the helping.
Welcome to the forum, Giulio.
It looks good to me with the following notes:
I'd make the 270R cathode resistors 5W.
I would put the volume pot on the input to the first stage and make it 100k.
Also, you'll have A LOT of gain without a NFB loop. Either add one or get rid of the middle stage.
Over all it looks good though. Nice job.
It looks good to me with the following notes:
I'd make the 270R cathode resistors 5W.
I would put the volume pot on the input to the first stage and make it 100k.
Also, you'll have A LOT of gain without a NFB loop. Either add one or get rid of the middle stage.
Over all it looks good though. Nice job.
There is a trivial error on your drawing: the 375V B+ does go at the primary winding center tap of the output transformer. Your schematic reminds me of PA Geloso amplifiers, such as G227A: high gain ECC83 stage followed by volume/tone controls with high value potentiometers, then a voltage amplification stage and almost the exact same phase inverter. It may be OK for a guitar amp but it is not the best topology for Hi-Fi. If your CD player does have RCA line outputs, you don't need a lot of gain. I would put a 47K (or 10K) volume control potentiometer right after the input and I would remove the first ECC82 amplification stage. The end result will be greatly affected by the quality of the output transformer, do you have it already? If your current build experience is on the smaller 3-5W SE designs with 200-250V B+, be aware that 375V B+ at 30-50W power is the next level of danger. It absolutely requires proper tools and cautions.
Giulio, you'll definitely need some sort of feedback, either local or global, if you want pentodes to operate correctly into speakers.
I corrected the errors:
How can i add the negative feedback? With the feedback i must add another stage?
How can i add the negative feedback? With the feedback i must add another stage?
Search "plate to grid feedback" or "Schade"; this might be easier for you than designing a global feedback loop. You could thus reduce the gain of the output stage to about 3.
Here you go. Sorry the artwork is messy. Hand drawing with a mouse isn't my thing.
The NFB network is the 2000R || 500pf. The lower the resistor the more feedback. The cap value is a guess and real world testing with a signal generator and a scope is usually required to find it's proper value.
Koda
EDIT: If you get a high pitched squeal, the OPT is connected in opposite phase. Either reverse the secondary connections or the plate leads.
The NFB network is the 2000R || 500pf. The lower the resistor the more feedback. The cap value is a guess and real world testing with a signal generator and a scope is usually required to find it's proper value.
Koda
EDIT: If you get a high pitched squeal, the OPT is connected in opposite phase. Either reverse the secondary connections or the plate leads.
Attachments
Koda, you do mean the feedback to go to the 2nd stage, yes? (Actually that should be safer, I would think).
I've never put NFB into a concertina...
Here's an EL34 amp I drew last year... Different operating point than the OP is going for though.
I don't know. My guess is between 8 and 10db, maybe higher.
Attachments
Koda, of course not; the first stage is missing from the version of the schematic you have sketched on
The version I sketched on is the OP's new drawing. He's eliminated one of the gain stages as it was unnecessary.
It will reduce it. Not sure by how much, as I don't know the calculations, and I don't use SPICE. I'm a build, test, experiment kind of guy. It's more enjoyable as a hobby that way for me.
I like Artosalo's design above, too. I wonder if he can SPICE out your drawing with my NFB config and see how it is?
I like Artosalo's design above, too. I wonder if he can SPICE out your drawing with my NFB config and see how it is?
After I finish my preamp project a PP 6LU8/6LR8 is on my list so I am considering some of these same issues. I am leaning toward using the small signal triodes in the 6L_8s as drivers using plate to cathode local FB since I am not set up to deal with the stability issues involved with GFB.
The OPT I have available will give me 8k or 16k P-P which though not ideal shoild work OK for triode mode. Not sure about Pentode mode yet.
If you are running pentode mode I doubt that you would need much more than a low to medium mu triode for the voltage amplification stage.
The OPT I have available will give me 8k or 16k P-P which though not ideal shoild work OK for triode mode. Not sure about Pentode mode yet.
If you are running pentode mode I doubt that you would need much more than a low to medium mu triode for the voltage amplification stage.
I think i build this, but can i use the power amp circuit on the datasheet of el34 with the preamp of this circuit? I have a 3.5k output trasformer...
The inputs are a cd player (idk the voltage of the signal from it) and a vinyl preamp (250mV RMS)... this circuit can reach the full power with this input?
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