This month I finish the EL152 pentode single amplifier. Telefunken power tube is glorious and balance sounding, compared with the 300B amplifier. Bass is not emphasized. Currently EL152 is driven by ECC88. Later ECC88 will be replaced by ECC82.
Currently EL152 is pentode wired, 300V plate and 250V g2 -24V g1 as data-sheet recommends. Fixed biased
EL152,
Great looking amplifier!
I like the schematic too (*).
What speakers did you use when you listened to the amplifier?
Welcome to diyAudio!
(*) One of my latest amplifier designs is a 2 stage push pull, with beam power output tubes, and no negative feedback.
That probably "breaks the rules" of 95% of the readers of Tubes / Valves.
Happy Listening!
Great looking amplifier!
I like the schematic too (*).
What speakers did you use when you listened to the amplifier?
Welcome to diyAudio!
(*) One of my latest amplifier designs is a 2 stage push pull, with beam power output tubes, and no negative feedback.
That probably "breaks the rules" of 95% of the readers of Tubes / Valves.
Happy Listening!
From the theorethical point of view it is better to add a capacitor of large value from screen to cathode.
But in any instance I suggest to try a voltage divider from screen to 88's cathode, DC decoupled via a big C in order to use the AC voltage at the screen in a positive form.
But in any instance I suggest to try a voltage divider from screen to 88's cathode, DC decoupled via a big C in order to use the AC voltage at the screen in a positive form.
Why don't you use any cathode resistor for biasing? You could lower the distortions and provide some safety to the tube.
Thank you so much for you appraising!
I ever posted my 300B amp in diyaudio.
Your amp design really breaks the rule.
My aim is discovering the big sound of classic tubes, beyond 300B and 211/845.
I use EL152 amp to drive the notorious Dynaudio BM15.
I don’t use cathode resistance for EL152 because the plate voltage is under 300V in the initial design. I will try to add cathode resistance later when plate voltage is sufficient.
Take into account that for a pentode, optimal plate load is nearly the voltage at the anode (Ebb) divided the anode current (Ib). This is the DC resistance for it and don't get confused with its anode resistance ra several time larger. So, each time you move the grid bias, you will move toguether the Ib, thus every grid bias will requiere proper anode load and vice-versa.
Looked into el152 datasheet...indeed, there's an indication for 300v anode voltage at 130mA, but that's how you get the highest distortions and to the heat dissipation limit of the tube.You should seriously consider cathode resistors especially because your Anode load looks to be lower than needed.
They were probably ment to be used as rf amplifier in class C...
https://www.diyaudio.com/community/threads/el152-gu50-and-el156.162697/#post-2110260
https://www.diyaudio.com/community/threads/el152-gu50-and-el156.162697/#post-2110260