Hello!
This is the last circuit I have developped around a push-pull of EL84.
The intention was to make a simply solution with a very good OT trafo.
In attach the schematic: it use a 6922 with the first section at gain and the second as cathodyna.
Then the output stage with fixed bias and a pentode connection ( my preferred).
The OT trafo is a double C core, laminated 0,1 mm, with 39:1 ratio.
The secondary is one fixed at 6 ohm nominal; the ratio is very high this because the intention was to fix the bias point in full class A until the max power.
The second image is the proto of the OT trafo and it is possible to see one chassis this because the entire project is a mono amp so there are two chassis.
The third photo is the pcb with all components on board included the tubes.
At the test the output power is 10 w.
The Vdc is 300 volt and bias current is 40 mA each 84; the filter caps are 1000 uF total.
The diagram of the freq. answer is without feedback that in this project is 9 dB. The power is 1 watt/8 ohm.
At -3dB the cirve is good; 15 Hz to 85 kHz
The other diagram is the response with feedback; - 1 dB at 10 Hz and 120 kHz ( around).
The third response is with a 0,22 uF in parallel to 8 ohm; also a good response.
The feedback is applied without any compensation cap and this is a good results.
The lasts are the wave taken at the 1 ohm resistor of the 84 so it show is this circuit works in class A.
One is at 1 watt, the other is around 10 watt, close to the switch in AB.
Last is the square wave 20 kHz, a good results ( I have taken other screenshot at differetn frequencies, always fine).
NOTE: this is a project Simulation FREE!! and Solid state FREE!! ( there is only the diode bridges)
🙂
Walter
This is the last circuit I have developped around a push-pull of EL84.
The intention was to make a simply solution with a very good OT trafo.
In attach the schematic: it use a 6922 with the first section at gain and the second as cathodyna.
Then the output stage with fixed bias and a pentode connection ( my preferred).
The OT trafo is a double C core, laminated 0,1 mm, with 39:1 ratio.
The secondary is one fixed at 6 ohm nominal; the ratio is very high this because the intention was to fix the bias point in full class A until the max power.
The second image is the proto of the OT trafo and it is possible to see one chassis this because the entire project is a mono amp so there are two chassis.
The third photo is the pcb with all components on board included the tubes.
At the test the output power is 10 w.
The Vdc is 300 volt and bias current is 40 mA each 84; the filter caps are 1000 uF total.
The diagram of the freq. answer is without feedback that in this project is 9 dB. The power is 1 watt/8 ohm.
At -3dB the cirve is good; 15 Hz to 85 kHz
The other diagram is the response with feedback; - 1 dB at 10 Hz and 120 kHz ( around).
The third response is with a 0,22 uF in parallel to 8 ohm; also a good response.
The feedback is applied without any compensation cap and this is a good results.
The lasts are the wave taken at the 1 ohm resistor of the 84 so it show is this circuit works in class A.
One is at 1 watt, the other is around 10 watt, close to the switch in AB.
Last is the square wave 20 kHz, a good results ( I have taken other screenshot at differetn frequencies, always fine).
NOTE: this is a project Simulation FREE!! and Solid state FREE!! ( there is only the diode bridges)
🙂
Walter
Attachments
Hi Andrew
the OT are custom made from a little company near me. They wound only trafo on C nucleus laminated 0,1 mm; for 300B (also s.e.) , EL34/KT88 and 84
The idea is to offer the kit.
Walter
the OT are custom made from a little company near me. They wound only trafo on C nucleus laminated 0,1 mm; for 300B (also s.e.) , EL34/KT88 and 84
The idea is to offer the kit.
Walter
waltube,
A C-Core transformer, but enclosed with traditional E-I End Bells?
Right?
That is a great idea!
A C-Core transformer, but enclosed with traditional E-I End Bells?
Right?
That is a great idea!
Hi 6A3,
yes. I found two types of bells that fit good , one for this OT ( around 15 watt at 30Hz) and other for 300B s.e. and EL34/KT88 around 40 watt at 30 Hz
Walter
yes. I found two types of bells that fit good , one for this OT ( around 15 watt at 30Hz) and other for 300B s.e. and EL34/KT88 around 40 watt at 30 Hz
Walter
waltube,
Congratulations,
Looks great!
I bet it sounds great too!
With a square wave that looks that good, with only a resistor for negative feedback and no comp cap across it . . .
That means the output transformer is Superb.
i would like to have a pair of those transformers, and 'matching' end bells.
Too expensive, especially with shipping.
Congratulations,
Looks great!
I bet it sounds great too!
With a square wave that looks that good, with only a resistor for negative feedback and no comp cap across it . . .
That means the output transformer is Superb.
i would like to have a pair of those transformers, and 'matching' end bells.
Too expensive, especially with shipping.
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@ Walter.
would you like to start a small pcb production?
I have a lot of EL84 and good output transformers in my stock.
would you like to start a small pcb production?
I have a lot of EL84 and good output transformers in my stock.
to 6A3,
thx for appreciation.
The sound is very fine.
About OT I will give, for info the specification and the costs with p&p
Walter
thx for appreciation.
The sound is very fine.
About OT I will give, for info the specification and the costs with p&p
Walter
hi walter ... how does it sound compared to well known EL84 amplifiers (eg Leak Stereo 20 I've heard some months ago)? thx
to huggy
the pcb are arriving soon.
They cost 25eu. each + p&p
to brimax
I know very well the Leak that is a reference , but also other stuff.
Due the OT trafo with an high ratio I lost just few power ( 8 ohm resistive load) but it is capable to drive complex loudspeaker with a good efficency.
The sound seem to be very complete from bass to high with more "life" respect the Leak (p.e.)
to Kevinkr
The OT is very good stuff as the test lab says.
The little company who wound thse types of trafo use a beautiful machine comes from a hiend brand in Switzerland; I consider it is the best machine ( it is old ) to wound perfectly the bobbin. This is one of the major step I have seen.
Also the C core 0,1mm laminated helps. ( I use only C core on OT trafo)
I have ready also a s.e. for 300B and is coming a p-p for EL34/KT88
The costs are not low ( also because the numbers of production are not high)
All OT for p-p are always with one single tap on secondary and no UL connection ( only under request); in my opinion the tetrode/pentode connection is more exiciting.
I am preparing also a internet page to list the stuff with all real test lab.
With a help of my friend in Audioelettronica
Walter
the pcb are arriving soon.
They cost 25eu. each + p&p
to brimax
I know very well the Leak that is a reference , but also other stuff.
Due the OT trafo with an high ratio I lost just few power ( 8 ohm resistive load) but it is capable to drive complex loudspeaker with a good efficency.
The sound seem to be very complete from bass to high with more "life" respect the Leak (p.e.)
to Kevinkr
The OT is very good stuff as the test lab says.
The little company who wound thse types of trafo use a beautiful machine comes from a hiend brand in Switzerland; I consider it is the best machine ( it is old ) to wound perfectly the bobbin. This is one of the major step I have seen.
Also the C core 0,1mm laminated helps. ( I use only C core on OT trafo)
I have ready also a s.e. for 300B and is coming a p-p for EL34/KT88
The costs are not low ( also because the numbers of production are not high)
All OT for p-p are always with one single tap on secondary and no UL connection ( only under request); in my opinion the tetrode/pentode connection is more exiciting.
I am preparing also a internet page to list the stuff with all real test lab.
With a help of my friend in Audioelettronica
Walter
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You say the response -3dB is 15Hz for the low frequency but in my opinion, and a lot other technician* is far to high.
A push-pull transformer should be easely below 5Hz otherwise the induction is far to less and so the transformer has not the right design.
* see radiotron designers handbook
Hi Mr. 80 mV
The response you mentioned is the entire circuit, open loop with the 84 in pentode mode
Look to other graph, if you can’t understand I will explain
Bye
Walter
The response you mentioned is the entire circuit, open loop with the 84 in pentode mode
Look to other graph, if you can’t understand I will explain
Bye
Walter
Then your circuit is bad, 15hz is poor results.
Btw your “circuits” is not of any use because there are no values of any components
Btw your “circuits” is not of any use because there are no values of any components
