But it requires a DC down shift to bring the grids to 0V. I've seen folks do this (DC coupling, no grid bypass on second triode). But after closer inspection, I see that it's the standard way to connect a differential pair that is direct coupled (meaning the second triode's grid is AC coupled to ground, as expected). I thought that's how it was originally configured from the schematic posted on post #3. It seems to me that a simpler design would have allowed them to use better parts (such as PS caps with the appropriate voltage rating and higher quality resistors - see 's videos) and produce an even better amp at the same or maybe even lower price.Ĭlick to expand.One use of a cathode follower in this manner would be to allow a DC coupling of the stage it's connected to, without needing to AC couple or bypass the grid of the second triode in the differential pair. Of course, if it doesn't degrade the sound, then most people will just say "no harm, no foul" even if the added complexity offers no benefits. That would allow one less 6SL7 to be used on the input and eliminate the extra 6SN7 they added to the power supply to deal with the voltage issue. If it does cause reliability problems, it seems like a far simpler solution would be to cap couple it, which eliminates the issue. I've never noticed any comments that this creates reliability or performance issues in the Eico. Interestingly, the Eico also puts high voltage on the grids of the 6SN7s since the 12AX7 is directly coupled yet they don't bother to do anything to eliminate it. The additional tubes are also costing owners who get into tube rolling more money, even if they realize that changing the 6SN7 in the PS is unnecessary and leave it alone. Use one octal tube and socket instead of three and the additional parts and labor required. It seems they could have just as easily done the same using a single 6SL7 (mu 70).
#6sn7 cathode follower driver
The Eico HF-87 schematic that I posted uses a single 12AX7 (mu 100) as input to its 6SN7 driver / phase inverter section. The bean counters are most often accused of diminishing the quality of a design but in this case I wonder if they should have been given more influence than the designers. But doing so in a commercial product just cuts into profits. I sometimes add things to DIY builds just because I want to try them. It just seems like this aspect of the amp is over engineered, which is not something we usually associate with Chinese amps.ĭesigners usually claim added complexity has some benefit. The decision to add the cathode follower led to the decision to add the 6SN7 in the PS to eliminate the high grid voltage. If the following stage was hard to drive then the use of a cathode follower would solve the problem but, as far as I know, it's not difficult to drive. If it doesn't, why would they want to add one? Which is why I'm wondering if a cathode follower provides any sonic benefit or advantage when used in that position. By adding the cathode follower they created the "problem".
Click to expand.As I see it, they had the "extra" triode, which is configured as a cathode follower, because they chose to add it.
0 kommentar(er)
