Thread Rating:
  • 1 Vote(s) - 5 Average
  • 1
  • 2
  • 3
  • 4
  • 5

model 20 hum (detector circuit?)
#15

(10-25-2015, 12:01 AM)Steve Davis Wrote:  It looks the problem is after the 24 but before the 27. It could be lead dress. Try moving the 27 grid lead to see if that makes a difference.

Steve

I have already thought about that. In fact I changed out the lead from the .01 coupling capacitor block and the grid of the 27. I tried moving it around first, nothing really changed. I think the problem is the fact that the grid of the 27 is running at -7VDC, which is far too high for this tube. One person told me to try different values of grid bias resistors to lower it. However why, what caused the voltage to get so high in the first place? Further proof is when I put a small electrolytic with the + end to ground and the - end to the grid, the hum drops and I can hear the station to which the radio is tuned. However the capacitor does drop the volume to a low level at the same time it removes the hum. I was suspecting the voltage divider/bias resistor, but disconnected all of the terminals and checked the resistance and all sections tested correct according to the Philco schematic. Tubesforme


Messages In This Thread
model 20 hum (detector circuit?) - by Tubesforme - 10-19-2015, 01:11 PM
RE: model 20 hum (detector circuit?) - by OZ4 - 10-19-2015, 06:23 PM
RE: model 20 hum (detector circuit?) - by OZ4 - 10-20-2015, 10:01 AM
RE: model 20 hum (detector circuit?) - by Tubesforme - 10-25-2015, 12:46 AM
RE: model 20 hum (detector circuit?) - by OZ4 - 10-25-2015, 10:57 AM
RE: model 20 hum (detector circuit?) - by OZ4 - 10-25-2015, 11:39 AM
RE: model 20 hum (detector circuit?) - by morzh - 10-25-2015, 11:08 PM
RE: model 20 hum (detector circuit?) - by OZ4 - 10-26-2015, 10:18 AM
RE: model 20 hum (detector circuit?) - by OZ4 - 10-26-2015, 10:34 AM
RE: model 20 hum (detector circuit?) - by OZ4 - 10-26-2015, 11:24 AM
RE: model 20 hum (detector circuit?) - by OZ4 - 10-27-2015, 08:43 PM
RE: model 20 hum (detector circuit?) - by OZ4 - 10-28-2015, 11:52 AM
RE: model 20 hum (detector circuit?) - by OZ4 - 10-28-2015, 03:36 PM
RE: model 20 hum (detector circuit?) - by OZ4 - 10-30-2015, 06:13 PM
RE: model 20 hum (detector circuit?) - by OZ4 - 10-31-2015, 10:40 AM
RE: Low continual hum in model 21 - by Tubesforme - 10-23-2015, 11:19 PM



Users browsing this thread: 58 Guest(s)
[-]
Recent Posts
37-690 Bass Choke Replacement
Ah, now where to find one. I've into this before on smaller sets, I now recall. Hammond makes one that is only rated...Radiodial — 03:27 PM
Philco 38-7 Speaker
Ask the admins to put them together. As for the renaming, while inside the thread, you simply press "New reply&quo...morzh — 02:23 PM
37-690 Bass Choke Replacement
This is the parts catalog. 32-7528 choke is 65H, 10mA, 2,250 Ohm inductance. Find a suitable one.morzh — 02:18 PM
37-690 Bass Choke Replacement
While troubleshooting the no bass amplification issue, I think I found the culprit. The choke #104 is reading 164K ohms....Radiodial — 01:42 PM
Philco 60 Squealing
Your IF transformers are tuned to the resonant frequency they were designed for. When you observe the bell curve they di...RodB — 01:35 PM
identify very thin wire for replacement on 37-640
Thanks so much for your help!  I really could not have gotten this far without the kindness of you and other members.  T...georgetownjohn — 11:50 AM
Philco 38-7 Oscillation
Will do, thank you.tludka — 10:26 AM
Philco 38-7 Oscillation
As to your oscillation issue I would align the IF transformers. That may solve the problem. You also would want to check...Radioroslyn — 10:22 AM
Philco 38-7 Speaker
Thank you, I will check this out, I do have some shields I can place around the specific tubes. I searched the four que...tludka — 10:18 AM
Philco 38-7 Speaker
Also, check if any wires going to Grid Caps of the tubes that are supposed to be INSIDE of their respective shields (if ...morzh — 09:54 AM

[-]
Who's Online
There are currently 3442 online users. [Complete List]
» 3 Member(s) | 3439 Guest(s)
AvatarAvatarAvatar

>