here's the schematic: http://www.simpletube.com/databank/SingleEnded/KT88_PSE_12AX7_Andrea_Ciuffoli.jpg
also can I replace the 12ax7 with 5842 (or 5687)? what resistor/cap values need to be used?
thank you.
also can I replace the 12ax7 with 5842 (or 5687)? what resistor/cap values need to be used?
thank you.
jarthel said:
The front stage is SRPP, of course you can use 5842 or 5687 for the job, but I think the B+ of about 430V is a tat too high for 5842 and 5687, may have to drop the B+ to about 300~350 if you don't wish to exhause the tbes too quickly.
I recon the Rk should be depend on which operating point you wish to operate the tubes.
Hope this help...
Cheers
The 5687s gain is too low, though running 210V across it is no problem for it. Rating is 330V.
The 5842 rating is 200V, and it prefers less volts with more current.
If using a single tube, one will have to be careful of heater to cathode considerations, as designed the amp avoids the problem by giving the top pair of triodes their own elevated heater winding.
The 5842 rating is 200V, and it prefers less volts with more current.
If using a single tube, one will have to be careful of heater to cathode considerations, as designed the amp avoids the problem by giving the top pair of triodes their own elevated heater winding.
Hi,
12AX7/Ecc83 mu=100, very high rp, very low current normally about 1ma or less... normally a bad choice to drive anything at all, but very common as voltage gain stage.
12AT7 mu=60
5842 mu=45
5687 mu=15
6n1p mu=35
The othe tube are just not direct substitution in this circuit. You must do some adaptation.
Why not look at 12BZ7 high gain higher current, but its uses octal socket. 6SL7 is another possibility.
Cheers
12AX7/Ecc83 mu=100, very high rp, very low current normally about 1ma or less... normally a bad choice to drive anything at all, but very common as voltage gain stage.
12AT7 mu=60
5842 mu=45
5687 mu=15
6n1p mu=35
The othe tube are just not direct substitution in this circuit. You must do some adaptation.
Why not look at 12BZ7 high gain higher current, but its uses octal socket. 6SL7 is another possibility.
Cheers
12AT7, sections parallel: resistor 75ohm/envelope. Bypass capacitor: 2,200uF- 16V. Panasonic FM or other low impedance type, next higher or lower size ok.
Im leary of the 2.2ohm cathode feedback resistors, wouldnt this lead to excessive current through the KT88s as cathode current through the secondary? Misprint of 2.2K? Whatever the value is, if 12AT7 does not quite produce enough gain, one could increase the value of these resistors and reduce the fixed bias voltage to compensate.
Im leary of the 2.2ohm cathode feedback resistors, wouldnt this lead to excessive current through the KT88s as cathode current through the secondary? Misprint of 2.2K? Whatever the value is, if 12AT7 does not quite produce enough gain, one could increase the value of these resistors and reduce the fixed bias voltage to compensate.
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