06-27-2008, 12:40 AM
Part of the logic here is since the B+ is so low the total current draw thru a single-choke, like a 1-2K speaker field coil, would cause an unacceptable amount of voltage drop and swing. I suspect thats the flutter being referred to.
This 37-604 is a good example. Its a small radio with a small speaker and that precludes having a big honking field coil. Note that the speaker FC is 2400 ohms. That says small wire. While the inductance *could* be good for filtering the voltage drop would be too much so they used it as the speaker field and nothing else. In essence it provides no substantial function in filtering as is typically expected. Moreover it doesn't drop voltage to the rest of the set.
The 2250 ohm choke feeds the 6A7 and the 78 screen. They don't draw any substantial current nor do they fluctuate in current draw so the voltage drop isn't significant.
The 400 ohm choke handles the output stage and the 78 plate. While the 78 IF amp doesn't play much of a role the 43 output certainly does. The 2250 ohm drop wouldn't be suitable there.
So its a creative juggling act to balance the current draw/voltage drop accordingly. The tubes are being run at their bare minimum voltages in this scheme so that was their way of distribution what little voltage they had to work with. Just another way to skin the cat.
This 37-604 is a good example. Its a small radio with a small speaker and that precludes having a big honking field coil. Note that the speaker FC is 2400 ohms. That says small wire. While the inductance *could* be good for filtering the voltage drop would be too much so they used it as the speaker field and nothing else. In essence it provides no substantial function in filtering as is typically expected. Moreover it doesn't drop voltage to the rest of the set.
The 2250 ohm choke feeds the 6A7 and the 78 screen. They don't draw any substantial current nor do they fluctuate in current draw so the voltage drop isn't significant.
The 400 ohm choke handles the output stage and the 78 plate. While the 78 IF amp doesn't play much of a role the 43 output certainly does. The 2250 ohm drop wouldn't be suitable there.
So its a creative juggling act to balance the current draw/voltage drop accordingly. The tubes are being run at their bare minimum voltages in this scheme so that was their way of distribution what little voltage they had to work with. Just another way to skin the cat.
