[jph14]

Recently went back to work on Philco 90 with single 47. Have quite a bit of hum. Electrolytics were replaced with 10 mfd. All the Bakelite caps were rebuilt. Also the metal multi cap boxes were redone with the correct values(as per this site) also the tone control was redone. All tubes very good.
Out of spec resistors replaced.
How large of electrolytics can I use? Any other thoughts on possible hum causes on this old guy?
I did everything this site suggested. 
Thanks

[Mondial]

Do you have the shield plate installed on top of the chassis between the rectifier 80 tube and the 27 audio amp? Without this shield the 27 will pick up hum from the large AC voltage on the plates of the 80. Later models may have a regular tube shield on the 27 instead of the metal plate.

You can increase the capacitance of the second filter cap after the choke to a higher value like 20 or 30 uF. Do not increase the first filter cap right after the rectifier as it will raise the DC output voltage.

Keep in mind that there will always be some residual hum due to the use of AC to heat the filament of the 47 output tube. You might try another 47 which may have better match between the two halves of its filament, better cancelling the filament induced hum

[morzh]

What Mondial said.

Also: Check your ground on the audio preamp, and wiggle the tube (27, isnt it?) , and also others, see if hum gets choppy or disapear when you do it. Also, just pick the chassis with both hnds while it is working (be careful not to touch inside or you will suffer painful/ lethl consequences) and flex it (it is thin) and see if the hum does the same, gets choppy or disappears.

This would point to a bad rivet or bad tube soket contact.

[jph14]

Thanks guys,
Shields are all in place. Replaced first audio tube-27- this helped a little. Replaced 47 and this reduced hum. Will check rivets etc. will trying upping the 2nd electrolytic- maybe 22 mfd.
Might just have to live with a little hum.
Thanks again,
Joe