A 1 Watt battery powered elctron tube audio power amplifier in class A

At your risk. Use suitable fuse in series with batteries etc. Using a PCC84 double triode electronic valve. Both triode sections can be paralleled as on EMI BTR2 replay amplifier output stage using a B65. PCC84 or ECC84 can operate at 100V Vb. This can be made from 2 4AA battery holders holding 12 6V 4LR44 batteries. Grid input voltage needed seems small, of the order of 3V so an input transformer can be used and no other tube. The output transformer which should have an air gap or (be made from a ferrite ring core?) can double the power efficiency from 25 per cent to 50 per cent since the induction at the primary doubles 100V to 200V, see load lines - Applied Electronics - Gray - MIT. 14mA are possible from each triode. A 4000ohms to 4ohms output transformer ie a 30:1 ratio would make this current x30. Other class A Pleiades lab considerations are a downscaled Musical Fidelity A1 using a BD139 driven by a BC549 emiter follower, load the speaker itself (at your risk), feedback from collector to driver transistor base, a resistor from driver base to ground as on K. Jones amplifier, see previous posts. Or for push pull class A adding a BD140, BC559 pair below. Or istead of feedback adding a output transformer at the output and an input transformer (Langenvin style) and using just 2 BD139 or if needed another 2 BC549, . Single ended has the advantage of not cancelling even order harmonic generation which is octaves really. See previous posts on BD138 single transistor power amplifier with output transformer. No feedback makes a gentle curving curve with no abrupt overlod distortion. Distortion tends to 0 as the signal gets smaller which is very important for music signals. Just one amplifying device creates small order distortion products which are not further multiplied by other cascaded active devices. How would the PCC84 sound like?

A Solar Powered Amplifier of Exceptional Sound Quality

Yesterday 10 years old Ionas was given the task to design the box of the class A single ended audio power amplifier. To surprise he drew on his ipad a blue solar panel on top of the box and a the sun above! Today last posts (grounded collector or emiter follower) were taken over from daybefore yesterday and yesterday where CC was changed to common emitter. Sound was louder, Rs=20Kohm, Ia=100mA. An output 10:1 transformer on a ferrite toroid was placed between 4ohm speker and transistor collector in order to improve efficience. At same Vb=8V it was a surprise to find optimum IC to be just 10mA! Loudeness was a bit higher, sound very smooth with amazing detail on treble, oercussion, female or male 60's Italian voice. Class A operation can sound so nice and smooth our sence opens up. Little power output is needed to make the miracle. Solar powering is possible with a small panel when impedance matching is used for max power transfer. More experimemts needed for a step down ratio of less than 10 to 1 for the @N3055. Would 10 to 1 be optimum for BC550? What would optimum be for BD438?

Aknowledging Dr. Rutter for giving the very interesting book : Audio Amplifiers - Ed. J.R. Davies

It contains on page 41 the brilliant article 2-Transistor Miniature A.F. Amplifier by K. Jones which formed perhaps 2 decades ago the basis of the Pleiades single transistor amplifier by removing one by one most components. These amplifiers sound very nice as expected from pure class A (electrons flowing all the time) circuits. Using just one transistor creates simple harmonic distortioon components when it starts gently overloading.

Correcting previous post. Using the output impendance of music source to bias the power amp. Single transistor audio class A power amplifier with no other components part 2

Yesterday the Sony CD Walkman line output had been accidentaly connected between collector and base of the Pleiades 2N3055 power amplifier instead of between emmiter and base. It worked showing that the source of music can be used instead of the collector to base bias resistor. Today the CD walkman was connected between emmiter ground and base and a 56Kohms biasing resistor for best perceived bass was used. The sound was louder and still smooth. Both options are very interesting and yesterday's unusual.

A single transistor audio power amplifier with no external components except a 9V battery

At your risk. Speaker may be blown since there is class A current passing though it. A protective fuse must be in series with battery for fire hazard protection too. Other equipment connected may be blown too. This is the Pleiades 2N3055 amplifier in a 2 cigarette packet size box. Today the 10K bias resistor from collector to base was removed. It immediately worked much better as there was overbias due to direct coupling to the Sony CD Walkman line output. Purely by chance due to the particular 2N3055 Hfe, no series resistor is needed for volume reduction. So no capacitors are used, no resistors, just a 9V batterry, actually 8V due to use. Quiescent current through speaker when said series resistor is 0Ohms is 47mA. Sound quality although of low volume is amazing on voice and many instruments including percussion. When Rs=10K is used to reduce volume, Ic becomes 33mA which is handy for saving battery energy. Signal path: Ingenue - KD Lang CD - Sony D-EJ758CK sn5048123 CD Walkman line out -Pleiades 2N3055 - Pleiades linoleum Auratone type 5C speaker with Tesla 5in drive unit fullrange