I did some sim studies, this time using 39Vrms for a source.
I just did two versions of the circuit, and scoped them both in parallel, as below.
Bias Study 1.JPG
First one shows the difference in capacitor attachment, whether before or after a 220K dropping resistor. Top trace (c in the voltage list) is attachment before the 220K resistor, second one down is d, the voltage at the 25K; 52.7V, and 12.358 out at the 14 second mark. The third trace down is the voltage at the first capacitor when connected after the dropping resistor, and fourth is the voltage at the top of the 25K, 5.2V and 4.255V at 14 seconds. What I took from this is that the 220K severely limits the charging on the first filter cap.
The "instant" value of voltage on the fast charge looked funny, so I changed the time scale, as below. Indeed, it does do the rachet-up thing on the first few cycles after turn-on.
Bias Study 2.JPG
The suspicion on the thread was that the 220K should be vastly smaller. I changed that to 220 ohms, and got the pic below.
Bias Study 3.JPG
Sure enough, now the raw bias voltage on the first cap and the voltage at the top of the 25K now get much larger than when choked off by the 220K. But it's still not as big as the cap-before-resistor case. My theory was that the resistor was choking off charging pulses, stretching them out and not letting the cap charge as quickly and hence not to as near the peak of the incoming AC. So I put current probes on the two diodes; sure enough, the probe on the resistor-before-cap line was much wider, indicating a longer charging time.
Bias Study 4.JPG
I increased the series resistor from 220 to 4.7K to see the difference that makes.
Bias Study 5.JPG
Sure enough, the cap-after-resistor case took even longer to charge, but there was no effect on the charging pips for cap-before-resistor.
So I think the sim shows what the theory predicts: diode-resistor-cap setups charge faster when the resistor is low. In this case, putting the cap right after the diode charges the cap to a usable bias voltage fastest. This lets one get bias on the tubes FAST, and tinker it with resistor dividers to the necessary level.
You do not have the required permissions to view the files attached to this post.