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: 2 Guest(s)
[-]
Recent Posts
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
Model 28L
For 28 you will probably need to buy a Hammond 125CSE. Or any of the series of the power you need, with SE suffix. Then ...morzh — 02:09 PM
37-60 revision 6
I am restoring a Philco 37-60 and it shows run 6 they removed the ground from G3 of the 6K7G and put the G3 to -2.5v for...bobbyd1200 — 01:01 PM
Shadow Meter Bulb
Mike is correct on the bulb connection, two separate circuits. I found that by rotating the bulb and sliding it forward ...RodB — 12:19 PM
Hickok AC51 tube tester
Cleaned ann contacts, switches and sockets, works great now.martinj — 11:32 AM

[-]
Who's Online
There are currently 6095 online users. [Complete List]
» 1 Member(s) | 6094 Guest(s)
Avatar

>