Can someone tell what I would need to do to use Kt88 with this schematic
6th Street Bridge: Review: Eico HF-60 tube monoblocks or where I may obtain the information. If I can't use Kt88 with it, is there a similar schematic.
6th Street Bridge: Review: Eico HF-60 tube monoblocks or where I may obtain the information. If I can't use Kt88 with it, is there a similar schematic.
EICO took a significant step in using the 6SN7, instead of the 12AX7, in the LTP role. High gm and low RP are quite important. Perhaps the best "vintage" implementation of Mullard style circuitry is found in the Harmon-Kardon Citation V. Notice the 12BY7 voltage amplifier, which also is a high gm type, and the 6CG7 is electrically equivalent to the 6SN7.
The 12BY7 is getting scarce and is (IMO) best reserved for already existing units. I've provided a 6922 cascode that will substitute quite well for the 12BY7, in the voltage amplifier role. Switch to the ECC99 as the LTP and you will have the small extra amount of drive that KT88s require.
Replacing the LTP tail resistor with an 10M45S constant current sink (CCS) is refinement (forced symmetry) that was not available circa 1961.
The 12BY7 is getting scarce and is (IMO) best reserved for already existing units. I've provided a 6922 cascode that will substitute quite well for the 12BY7, in the voltage amplifier role. Switch to the ECC99 as the LTP and you will have the small extra amount of drive that KT88s require.
Replacing the LTP tail resistor with an 10M45S constant current sink (CCS) is refinement (forced symmetry) that was not available circa 1961.
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The important thing is to get the cathode resistor right. I did this quite a few years ago and triode connected the KT88s and changed the cathode resistor so each tube drew about 60 ma. KT88s are too expensive to run at full dissipation. Plate voltage was 440 volt and the power available at the secondary was about 19 watt. The pin out is the same as el34
Take a look at this.
Modifying the Eico HF-60 to Use 6550s
There's an EF86 version, and near the bottom, there's a 6CG7 version.
Modifying the Eico HF-60 to Use 6550s
There's an EF86 version, and near the bottom, there's a 6CG7 version.
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When making a 5-20 clone, here are good info:
Lundahl Transformers • Old fashioned 30W Push Pull amplifier
Lundahl Transformers • Old fashioned 30W Push Pull amplifier
"Iron" suited to EL34 category tubes will not do, when the "finals" are KT88s. 60+ WPC is easy enough to get, when "fixed" bias is employed.
Mullard style circuitry is quite tolerant of O/P "iron" that is not creme de la creme. Edcor's CXPP100-3.3K is quite well suited to this project. Magnetic headroom is a must, when GNFB is employed, to avoid core saturation. Both Mullard and Williamson style circuitry employ GNFB loops.
Edcor "iron" is a good value and getting better performance entails an outlay of more $.
Mullard style circuitry is quite tolerant of O/P "iron" that is not creme de la creme. Edcor's CXPP100-3.3K is quite well suited to this project. Magnetic headroom is a must, when GNFB is employed, to avoid core saturation. Both Mullard and Williamson style circuitry employ GNFB loops.
Edcor "iron" is a good value and getting better performance entails an outlay of more $.
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