Murphy A146CM - UK Vintage Radio Repair and Restoration Discussion Forum

Nanozeugma · 26th Feb 2019, 1:10 pm

Hi all,
I am currently refurbishing the RF chassis of an A146CM batwing console.
Unfortunately (for me) L14 was in a somewhat delicate state and has now (it would appear) decided to go permanently o/c.
It did read about 12-13 Ohms before it failed.
It is described in the manual as a "diode choke" and a DC resistance of 12 Ohms given - but no inductance value.
I would imagine that a small modern axial RF choke would be a suitable replacement, but what value?
I do not currently have an LCR meter or bridge.
Any ideas?
T.I.A.

HamishBoxer · 26th Feb 2019, 1:37 pm

Not too critical I doubt.

Nanozeugma · 26th Feb 2019, 2:09 pm

N.B.
The service manual observes as follows...
"The i.f. harmonic filter:
To avoid whistles during the reception of certain stations - caused by feedback of i.f. harmonics to the frequency changer - the filter circuit L14, C31, C33 is connected in the cathode circuit of V3."

26th Feb 2019, 1:10 pm	#1
Nanozeugma Heptode Join Date: Nov 2017 Location: London, UK. Bury, Lancashire quite regularly :) Posts: 611	Murphy A146CM Hi all, I am currently refurbishing the RF chassis of an A146CM batwing console. Unfortunately (for me) L14 was in a somewhat delicate state and has now (it would appear) decided to go permanently o/c. It did read about 12-13 Ohms before it failed. It is described in the manual as a "diode choke" and a DC resistance of 12 Ohms given - but no inductance value. I would imagine that a small modern axial RF choke would be a suitable replacement, but what value? I do not currently have an LCR meter or bridge. Any ideas? T.I.A. Attached Thumbnails __________________ Thermionic Emission, warms the cockles of your tubes.

26th Feb 2019, 1:37 pm	#2
HamishBoxer Dekatron Join Date: Aug 2007 Location: W.Butterwick, near Doncaster UK. Posts: 8,935	Re: Murphy A146CM Not too critical I doubt. __________________ G8JET BVWS Archivist and Member V.M.A.R.S

26th Feb 2019, 2:09 pm	#3
Nanozeugma Heptode Join Date: Nov 2017 Location: London, UK. Bury, Lancashire quite regularly :) Posts: 611	Re: Murphy A146CM N.B. The service manual observes as follows... "The i.f. harmonic filter: To avoid whistles during the reception of certain stations - caused by feedback of i.f. harmonics to the frequency changer - the filter circuit L14, C31, C33 is connected in the cathode circuit of V3." __________________ Thermionic Emission, warms the cockles of your tubes.