Hiwatt DR504

[txbluesboy]

I think the ink marks shows that the solder joints have been inspected

[drew]

^ Yeah. You can read about it in Chapter 2 of http://mhuss.com/Hiwatt/history.html , and more here: http://www.harry-joyce.com/hjmilspc.htm .

[gldtp99]

Not sure if I have ever used the "snap in" caps before. Is it OK to solder these connections?
Thanks

Yes, you can solder the connections on "Snap In" cans----- If these snap-in cans were mounted on a PCB the lugs would be soldered----- just securely wrap the wire/resistor around the lug and solder it in place.
The JJ 220uF/385V cans you were looking at in the 1st place are also "Snap In" cans------- the only difference is that the lugs are spade-type instead of loop-type......................gldtp99

[mhuss]

This is what threw (throwed?) me. V3 is the phase inverter. V4 an additional gain stage made necessary by the less than unity gain of V3. If I read this right NFB is added both at the PI and again at the last gain stage. The MV before the 0 gain PI is interesting too. Technically this is a single tube PI but without the final 12AX7 it wouldn't be much of an amp I fear. A pretty piece of work. I'll bet this bit accounts for most of the Hi-Watt lauded cleans. Anyway, thanks for the clarification and the great site from Mr Huss.

Just catching up from a week long holiday...
The second half of V4 is a voltage reference for the PI, basically a buffered voltage divider. Note that there is no signal connected to its grid. This forces the PI to a predetermined grid (and by extension cathode) voltage, somewhat independently of the individual tube being used.

V3 is a modified long-tail "diff amp" style PI, nothing too mysterious there. Main difference is the 1M grid coupler which keeps both grids at the reference voltage at idle.

If the valve numbering seems odd, it's because the PI is not that last (physical) tube in a Hiwatt chassis.

--mark