Welcome Guest! Be sure you know and follow the Phorum Rules before posting. Thank you and Enjoy! (January 12) x

Thread Closed
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
Gloritone 27 Radio
I have a model 27 that someone painted the cabinet brown. I've been trying to sell it for awhile but the cabinet paint m...Jim Dutridge — 02:30 PM
Restoring Philco 96
Joseph Yeah. The situaction is complicated by me living with my family in NJ while mom is in FL. Were it not for my ...morzh — 10:55 AM
Restoring Philco 96
Best of wishes for your mother. I hope she recovers well. My mother struggles with sciatic pain as well, so I am familia...jrblasde — 10:41 AM
Restoring Philco 96
Well, because I am away, I cannot check it. Hope mom becomes better enough for me to get back. I think I will be here f...morzh — 10:27 AM
Restoring Philco 96
Nice find! I hope it completes your console.jrblasde — 08:45 AM
Gloritone 27 Radio
Hello john, That, is the first time I have have seen or heard of that brand and model. Welcome to the party !! Sincer...radiorich — 08:08 AM
370 Norman Bel Geddes trim pieces
Thank you! I’ll probably use the half-round molding and tone it to match the original. Thanks for the replies!Max T — 06:34 AM
Gloritone 27 Radio
I'm kind of late to this thread, but Buzz1151 has a 3 part restore series on the model 27: A little bit of extra t...Eliot Ness — 05:48 AM
370 Norman Bel Geddes trim pieces
You can get half-round moulding in various diameters at any home improvement store. That way the flat edge is uniform. ...GarySP — 12:03 AM
42-345 Resistors
Great comments. I have a tinkering bench at my office, and that's where Little Phil is right now. I will have to comb ...proftrussell — 11:12 PM

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

>