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

Motorola 77FM
#1

All, I have a bad Silicon rectifier.. will replace with a 1N5408.. Question is do I need any additional resistance after the diode?

Here is schematic

[Image: https://live.staticflickr.com/65535/5072...5bf7_c.jpg]


Thanks

Skip
#2

I take it that you were replacing a selenium rectifier? ( I see that you stated silicon, which is what your replacement will be?). I would see what the voltage is after the last filter, then add resistance if necessary.

"I just might turn into smoke, but I feel fine"
http://www.russoldradios.com/
#3

There is 27 ohms in place now to limit the charging rate of the first filter cap.

Pliny the younger
“nihil novum nihil varium nihil quod non semel spectasse sufficiat”
#4

The original rectifier is a selenium. If you replace it with a silicon rectifier you should increase R33 by about 100 ohms or add a resistor. You will want to check the voltage chart for the 12AT7 plate voltage and adjust the resistor value accordingly. If someone already replaced the rectifier with a silicon then put your new one in and check if a resistor was added. FM front end amps are usually sensitive to variations in B+.




Users browsing this thread: 1 Guest(s)
[-]
Recent Posts
My last cabinet for this year
They are a nice looking radio, Stromberg. I have a small tabletop octagon-dial one. It sounds surprisingly nice. And t...morzh — 09:40 PM
Philco 41-608 changer coupler
Different years but the same idea.morzh — 09:38 PM
My last cabinet for this year
That’s a beauty! :thumbup:klondike98 — 09:24 PM
Philco 41-608 changer coupler
Hi Morzh, I've searched using Mondial as the user name with various keywords such as 'coupler', 'motor', 'idler', 'p...alangard — 08:31 PM
Philco 16B Parts
I think the chassis is painted.morzh — 08:13 PM
Philco 38-2 Automatic Tuning
Honestrly, the original is quite acceptable and, it seems to me, can be cleaned.morzh — 08:11 PM
Philco 41-608 changer coupler
Mondial left a thread about remanufacturing thois type coupler.morzh — 08:09 PM
IF can wire size and Rubber mounts?
Are you talking about rewinding or rewiring? For rewiring, meaning runnin wires to the coil from other components, the ...morzh — 08:08 PM
12' Philco
I wonder who would be able to "no stoop" with this one.morzh — 08:05 PM
IF can wire size and Rubber mounts?
Hello PHORUM members, I am still working on restoration of my PHILCO 37-640.  I want to start with rewiring the IF ca...georgetownjohn — 06:32 PM

[-]
Who's Online
There are currently 3341 online users. [Complete List]
» 2 Member(s) | 3339 Guest(s)
AvatarAvatar

>