Ryan
6550 & 8417 are pin interchangeable as long as Pin #1 isn't connected. In 8417 it's a second plate connection. If you have a wire on pin #1 it could be moved to pin #3.
8417 has higher transconductance giving the tube higher gain using lower negative grid bias. A 6550 in the socket could draw too much current without increasing grid bias. You would need to measure voltages and current.
Norm
: I was also wondering, on a completely different project, what is involved with swapping an amp designed to run with 8417 outputs, to the more common 6550's ??? Is it even possible ? The amp is a 200 watt mono PA jobber. Im looking to buy it, but it has no tubes. Possibly going to convert it to 100w stereo amp, as there are two output xfmr's in series..... Thanks again for any help !
: Ryan
As Ned mentioned, the 8417 has higher transconductance - read higher gain. When subbing the 6550 you may, probably will, have to increase the control grid drive signal to the 6550. Many amps with the 8417 used split load phase inverter as you only had to provide about 25-30 volts p-to-p to fully drive the 8417. IMHO the 6550 doesn't sound like the 8417 but few tubes do - sorta reminiscent of the 7591s.
Rob
: I was also wondering, on a completely different project, what is involved with swapping an amp designed to run with 8417 outputs, to the more common 6550's ??? Is it even possible ? The amp is a 200 watt mono PA jobber. Im looking to buy it, but it has no tubes. Possibly going to convert it to 100w stereo amp, as there are two output xfmr's in series..... Thanks again for any help !
: Ryan
The 6L6GC would also need a greater drive signal. In addition, the 8417 has a plate dissipation rating of 35 W (very conservative) while the 6L6GC is only 30 W. This design appears to push the 8417s "gently" - you can get 100 W out of a pair so you might get away with the 6L6GC but be aware that the 8417 has a maximum plate voltage of 600 V as opposed to the 500 V for the 6L6GC. It depends on the circuit. Generally Hi Fi designers avoided most 6L6 family tubes after the 5881 favoring 7591s, 6550s, 8417, etc. I build sound production equipment (guitar amps) not reproduction equipment so I'm not much of a Hi Fi expert - my old Scott 300B uses 7591s though.
: Ok thanks for the help... now- another question. Is it possible to use the famous 6L6gc in place of the 8417 ? The amp is rated 200 watts with 8 tubes.... Isnt the 6l6 also rated the same way ? I dont know if the pinouts are the same though. Which tube is the best quality sound for hi-fi applications ? Thanks again. Ryan