Thread Rating:
  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5

Question about 118b
#10

There is a specific reason for use of the bleeder resistor in the 118. This radio uses a class AB triode output stage, and as such the plate current drawn from the power supply varies greatly with audio output level. Because the field coil of the electrodynamic speaker requires a fairly constant minimum level of current to maintain the magnetic field, the bleeder resistor was added to supply this minimum current through the field coil under all volume level conditions.

All the Philco radios using the triode connected 42 "Super class A" output stage also use this bleeder, 16B, 650 etc. As mentioned previously, there is no simple way to modify the circuit to eliminate the resistor unless you replace the field coil speaker with a PM type.


Messages In This Thread
Question about 118b - by fields 100 - 09-09-2014, 05:14 PM
RE: Question about 118b - by Steve Chambers - 09-09-2014, 07:39 PM
RE: Question about 118b - by SteveJB - 09-09-2014, 08:51 PM
RE: Question about 118b - by Arran - 09-09-2014, 10:25 PM
RE: Question about 118b - by morzh - 09-10-2014, 09:04 AM
RE: Question about 118b - by Ron Ramirez - 09-10-2014, 09:35 AM
RE: Question about 118b - by morzh - 09-10-2014, 03:04 PM
RE: Question about 118b - by fields 100 - 09-10-2014, 03:12 PM
RE: Question about 118b - by morzh - 09-10-2014, 03:21 PM
RE: Question about 118b - by Mondial - 09-10-2014, 08:12 PM
RE: Question about 118b - by Arran - 09-11-2014, 03:54 AM
RE: Question about 118b - by Ron Ramirez - 09-11-2014, 08:08 AM
RE: Question about 118b - by Mondial - 09-11-2014, 09:37 AM



Users browsing this thread: 4 Guest(s)
[-]
Recent Posts
trying to identify this wire type
The red wire is rubber covered wire. The others are cotton braid over rubber often in colors or a tracer, also strand...Chas — 02:43 PM
trying to identify this wire type
Greetings Phorum members, Hope you can help me identify this type of wire in the photo I have attached.  I am not sure ...georgetownjohn — 01:53 PM
Philco 60 Squealing
All correct shields must be in place, all tubes correct no subs of any kind. Check any soldered, riveted ground conne...Chas — 01:24 PM
Philco 60 Squealing
I have recapped and replaced out of tolerance resistors and so on. Radio plays nicely on fairly strong stations. The pro...dconant — 10:55 AM
Philco 46-420 Code 121 Reception issues
Welcome Eric, I agree with Bob and far as the two main electrolytic filter capacitors did you change them yourself or w...radiorich — 11:43 PM
Philco 46-420 Code 121 Reception issues
You mentioned the Philco manual and going through the check points...just to be sure we're on the same page here's the m...klondike98 — 08:13 PM
Philco 42-1008 conversion kit
Interesting. I haven't seen that before.klondike98 — 07:02 PM
12' Philco
Yes I had looked for it on the web as well some time back and could not find it. I was glad to see it turned up in Ron'...klondike98 — 06:59 PM
Shadow Meter Bulb
Now if you had a set with a tuning light then the bulb type is important to the circuit, some sets used those prior to t...Arran — 04:58 PM
Shadow Meter Bulb
Ok. Thanks for the correction.RossH — 03:09 PM

[-]
Who's Online
There are currently no members online.

>