I connect the output tubes in triode mode , for simplicity ( don't need stabilized power supply for the screens ) and sounds better , the minus is half the power of pentodes . about 26-28 Watt .Variation of Futterman - I mean that the outputs of the phase spliter is interchanged with resprct to output tubes , also known as Technics variation , the same topology circuit you have biuld .
Interesting,
Is your power supply using floating gnd ie balanced resistor or to centre tap of power transformer? Single fullwave rectifier?
It would be interesting to hear your thoughts on supply hum and noise rejection..ie do you take any special precautions to reduce hum in your amps on the power rails?
Regards
M. Gregg
Non floating , I connect the center tap straight to the capacitors with a single fullwave rectifier , it's better with two full wave rectifiers . I use chokes on the power rails and large capacitors , exept this it is important to take good care of ground loops .
Thank you , you can read my comments about the schematic ,on the related video -Youtube
Evxaristw poly , thank you very much , soon i will have news .Poly wraio, Dimitri!
Very nice, Dimitri! Welcome to the DIYAudio Forums! I can't wait to see what else you come up with
In last Sunday i finished the two channels of the amp , i have a little hum on the right channel but yesterday i solve the proplem , it was one PCC85 noisy tube , and i remove it . The sound is more clean , with better bass and better high frequency and more detailed than that of the Futterman topology and it sounds more powerfull , but i think this has to do not only with the differences in topology - schematics but with usage of better components , like better quality power supply capacitors , ultra fast soft recovery Hexfred diodes , special quality EI power transformers , and better designed differential stages to minimize harmonic distrotion . The -3db point in high frequency is at 170 Khz , I will make more measurements the next days , I will keep you in touch ,Thanks .
I measure 35 Vp-p with 1Khz sine wave into 8Ω load before the amp start cliping , wich means around 20 W , well its not too powerful because the PL36 is triode connected , but it sounds very nice , and maby in the future I will make some modifications . The output impedance (measured at 10 Vp-p into 8Ω load ) is 1,6 Ω . What do you think guys about these measuraments ?.
Hi banat , thank you very much , I don't try pentode mode because it needs stabilized power supply and more windings on the trafos and it would be more complicated , so I choose triode mode for simplicity , and I think it sounds better because the tube is more linear in triode mode , what do you think ?
No , you don`t need any stabilized extra circuit to run PL36 in pentode mode , just swap B1/B2+ supply lines ONLY for each group (bank) of PL36 g2 resistors , for pentode mode of operation they have to be connected to opposite B+ PSU line , ( or opposite anode line ) , g2 load resistors have to be remain on the same value as for triode conected tubes .
Sorry that I can not attach schematic now , it is very simple modification , but my scanner is run out , I will try tomorrow again for sure .
Best Regards !
Sorry that I can not attach schematic now , it is very simple modification , but my scanner is run out , I will try tomorrow again for sure .
Best Regards !
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You can double the output power even now running 10 x PL36 triode connected Circlotron only with simple rising of the load(speaker) impedance from 8 to 16 ohm ( or even slightly more, up to 32 ohm ) , this will improve the Amps sonics timbre Significantly to , your Amps will run much cooler to , relative small OTL Amps as yours simple love the higher load(speaker) impedance !
