My first attempt of the KT88 tube monoblocs have completed 4+ years now after they were first built in Oct 2020. This was originally designed for a driver tube 6FQ7 and final tube KT88, direct coupled and with LES power supply. It is a two stages amplifier. Last year i tried some adventures as below,
- Replace the driver tube with a high mu 12x7 driver tube and the final tube with a 300B with AC heating, direct couple. This had a more thumpy bass not requiring my subwoofer. But the mids and highs were not up to the mark of KT88. I used this amplifier for around 6 months and went back to the original KT88 design
- Replacing with the KT88, i had to go back to the subwoofer, but the mids and highs of the KT88 are very liquid and addictive. Since past 6 months i have been using the original design of 6FQ7 and KT88.
After discussing and exchanging ideas with my mentor, he suggested me to use a 6e6p tetrode connected as triode for the driver tube. As the 6e6p tetrode was a very inexpensive tube, i bought 4 of this tube - NOS for 22 usd including shipping which arrived yesterday. As i had already done a PSUD simulation of the schematic, it became very easy for me to migrate to this tube. I have now connected this 6e6p as my driver tube. I have used a more higher anode current for the driver (double than the previous tube) of around 9.2mA. This tube also has double the mu of the previous driver tube.
I am now listening to this modified setup since today morning and find them to be much better (atleast 15% to 20%) than the previous 6FQ7. I have not noticed too much difference with tube rolling from one brand to another brand of the same tube number. But chaning the tube number definitely has a solid impact as we now work with a much different bias current, amplification factor and topology of the tube.
This tube will definitely be for my keeps and looking at the cost of the tube, its the best mods that i have ever done for such a low price.
Thanks for looking.
- Replace the driver tube with a high mu 12x7 driver tube and the final tube with a 300B with AC heating, direct couple. This had a more thumpy bass not requiring my subwoofer. But the mids and highs were not up to the mark of KT88. I used this amplifier for around 6 months and went back to the original KT88 design
- Replacing with the KT88, i had to go back to the subwoofer, but the mids and highs of the KT88 are very liquid and addictive. Since past 6 months i have been using the original design of 6FQ7 and KT88.
After discussing and exchanging ideas with my mentor, he suggested me to use a 6e6p tetrode connected as triode for the driver tube. As the 6e6p tetrode was a very inexpensive tube, i bought 4 of this tube - NOS for 22 usd including shipping which arrived yesterday. As i had already done a PSUD simulation of the schematic, it became very easy for me to migrate to this tube. I have now connected this 6e6p as my driver tube. I have used a more higher anode current for the driver (double than the previous tube) of around 9.2mA. This tube also has double the mu of the previous driver tube.
I am now listening to this modified setup since today morning and find them to be much better (atleast 15% to 20%) than the previous 6FQ7. I have not noticed too much difference with tube rolling from one brand to another brand of the same tube number. But chaning the tube number definitely has a solid impact as we now work with a much different bias current, amplification factor and topology of the tube.
This tube will definitely be for my keeps and looking at the cost of the tube, its the best mods that i have ever done for such a low price.
Thanks for looking.
