[morzh]

MrFixr55


Valid suggestions.

Let's see.

1. I did not increase the output cap C2. I tried increasing it, with absolutely no effect, so I took it off, and it is 10uF again.
Speaking of icreasing the current - no, it would not. The load after LC filter draws current which is constant.
Also, in general, the ripple current from the inductance with a constant value of the output Volatge really depends on the inductance, not capacitance. And the inductance is a current source, so there will not be "inrush" type charge, as the one that occurs with the first cap where the current is only limited by the plate resistance of the 80 rectifier. However the output ripple voltage will decrease with increasing the C2 cap.
Also the ripple voltage will decreas with using a low impeadance cap, as the output ripple voltage has a Ir*ESR component (in DCDC concverters this is the only significant component).

Now as for increasing the input (C1) cap - yes it could be safely (for the 80 rectifier - up to 32uF) raised to that value. However the value of the B+ then will aso increase, as the input ripple before the inductance will be much less. So your tubes will run hotter. The difference could be quite significant. COnsidering the radio is already plugged into 120V AC, it is something to consider.


2. Yes, many folks agree the direct heated tubes with large heater current are spurces of extra hum. The technique goes from replacing them with different tubes to using DC for heating.
Thing is, I try to be as original as possible, so if a capacitance increase was a consideration for the C2 (if it worked, which it dod not), a schematic change for me is not an option.

3. One way they used to compabt extra ripple (which is not necessarily what causing it all in my case) - putting 0.15uF or so cap across the choke (field coil) to compensate the ripple through the inductance. But many think it does not work well, and even remove igt altogether from places where it i used. Like Philco 20 and such.

4. I have a Philco 70. It uses a very similar tube line-up. 24As and 47 at the Audio. (I specifically do not mention the 90 I have as it is a P-P output one, and the 20 as it is also P-P, both are direct heated tubes, 45 and 71A). It does not have as strong a hum. However, it has a different scheme for powering the tubes.
They use one winding to power the 4x 24A, dial light and the 27, and another separate winding to power th 47 tube. And it is a separate centertapped winding with the tap Grounded.


So to summarize, were it some very common tube radio that I wanted to make a musical exibition piece, I might rework the schematic, bring it to a near hifi level (would probably also require changing the speaker) and then marvel at its acoustical performancel however the AK82 is rare and beautiful enough radio that to me is worth keeping as original as possible.
So are my Philcos 20 (have three of them) and the 90 (the more rare version with 2x45 output).