Replacing 5Y3-GT with 5V4GA in modified circuit

[miles2go]

First off, thanks to the many posters in this forum and others for helping to fuel my ever growing interest in electronics. I have learned much and hope to continue this adventure. In regards to my question of replacing the rectifier in a modified circuit based on a Marshall 1987 using push pull 6v6-gt's. As it sit's, the first B+ cap, a voltage dropping screen grid resistor, and leads from both the power and output trannies are attached to pin 2 of the 5Y3 and line voltage coming into pin 8. I have read that when using a 5v4, to run B+ from pin 8. Looking at the datasheet of both these tubes, there are differences. The general consensus seems to be that a 5v4 is a drop in replacement for a 5y3, with the obvious differences being less voltage drop hence higher plate voltage. I have also read that the 5v4 is more limited as far as filtering capacitance so it seems that it may require some slight modifications. I would appreciate more insight on this if possible. Thanks again...

[tubeswell]

You'll be okay with 16-22uF reservoir capacitance on the 5V4.

[miles2go]

Thanks for your reply tubeswell... Am I correct in assuming that pins 2 and 8 are internally connected filaments on the 5v4? When I compare the 5y3 to the 5v4, it appears the latter has what looks like an internal cathode connecting to pin 8. Is this what makes the 5v4 indirectly heated? Pardon my ignorance, but I am trying to make sense of the diagram.

[tubeswell]

5V4 has an indirectly heated cathode. Pins 4 and 6 are the plate pins, Pins 2 and 8 are the heater pins, with Pin 8 going directly to the cathode (So take the B+ off Pin 8 )

[miles2go]

Awesome man... Thanks for the reassurance. I switched the B+ and screen grid resistor along with the output tranny tap over to pin 8. I had 30 MFD as the first cap so dropped that to 10 MFD, but beefed up the filter supply behind that for the output and preamp tubes. I also switched out the cathode resistor and cap to compensate for additional current just to play it safe. Got her dialed in nicely and really think I will enjoy the tighter response of the 5V4.