July 25, 2009 at 1:46 pm #1320scoobydoo391965Forum Participant
I am trying to find someone who may know or have the values of autolite capacitors. I have a few radios with them in
but dont know the values of them I am new to replacing caps and am still new to reading the diagrams so not always good
at tracing them out. I have a rogers 11/95 with 2 6f6 tubes with 2 autolite caps number 33108 that I cant find the value for. I also have others in this radio number 33108,33102 come to mind any help would be appercitated thanks again.July 28, 2009 at 1:15 am #1451philForum Participant
I too am not that good at it, But Ill try to explain I will try to explain simply and others can pipe up if you have questions or if what I say is too elementary.
first off read this, it is very well written ,(not by me) :https://www.antiqueradio.org/recap.htm
Make sure what you are doing is safe. I will eave out any suggestions about that ,but make sure you read up on safety if you are unsure of anything. be extra careful if you can’t read the schematic. do you have an isolation transformer?
Get the schematic and print out the tube data for each of the tubes from https://www.nostalgiaair.org/
Print out the base diagram for each tube in the set, example: https://www.nostalgiaair.org/tubes/6f6.htm
lay or prop the chassis upside down and prop it up so it is safe and unplugged.
pick a capacitor and mark it on the schematic.
write down what parts the cap connects to. probably you can follow it to a pin on one of the tubes or maybe a transformer or something. it may well go to more than one part.
use the base diagram to help you determine which pin you are looking for in the radio. It will read the same way around as you are viewing the radio when it is upside down on the bench. Pins are numbered clockwise from the key in the base.
It’ll take time at first to find each pin and follow the wire to the cap, but then you will at least know where the part is on the schematic. When you know that you can usually see the value written either beside the cap on the schematic or it will give a callout number and you refer to the parts list on the schematic. That will give you the value. note the voltage and the capacitance.
test the radio to make sure it still works properly between each part.
I assume you have some sort of digital voltmeter. see if it has a setting for capacitance. if it does, try reading a few new ones of that value.
you can unsolder one leg of the cap and check it for capacitance to see what it measures. It may or may not be relevant if the cap is leaky, but good to write it down anyway, and keep track of the old part.
the cheap digital meters won’t really tell you if the cap is leaky, but you could try to check if it is completely shorted by measuring resistance.
I am not sure about the numbers you gave, which was the original question.
careful with the electrolytic caps , discharge them with a screwdriver before you zap yourself or the meter.
Are these electrolytic caps you are referring to? If they are , keep track of their polarity, else they blow up, and note that some may be isolated from the chassis.
ok , that’s about all I know 🙂
PhilJuly 30, 2009 at 1:32 am #1436Gerry O’HaraKeymaster
I have attached the schematic for the 11/95 model. As Phil suggests, locate the Autolite caps on the schematic by tracing the circuit, identifying the correct part(s) and then replace them with similar values as per the schematic. If ever you cannot find the value of a part (capacitor or resistor), it is possible to make an educated guess at approximate values unless they form part of a tuned circuit (then it is rather more problematic, though you will find you don’t have to change these too often anyway as they are almost always silver mica types that tend to be much more reliable than paper or electrolytic types). The part(s) selected by ‘rule of thumb’ (see below) may not be perfect but it will most probably get the set working to a point you can experiment a little to optimize the values – most tube circuits tend to be fairly tolerent of resistor and capacitor values that are not exactly as designed (most parts used had a tolerence of +/-20% anyway), however, exercise some caution as component values in more innovative circuits can vary significantly from the ranges given below:
Capacitor ‘rule of thumb’ for tube sets:
– Power supply smoothing and audio frequency (AF) decoupling: 10uf electrolytics, 450vw (or at least 10% higher than the plate supply voltage).
– Decoupling of plate/filament supply, screen or cathode at radio frequency (RF): 0.01 to 0.05uf, at intermediate frequency (IF): 0.05 to 0.1uf, Mylar, polycarbonate or polypropylene, 630vw (or at least the plate supply voltage of the set plus 10%, unless used as a cathode decoupler, then it can be much lower, though at least 50vw, though if in doubt use 630vw). 0.1uf caps may also be used for AF stage cathode decoupling if the original cap was not an electrolytic.
– Inter-stage coupling: at RF: 0.0001 to 0.005uf, at IF: 0.005 to 0.05uf, at AF: 0.01 to 0.1uf Mylar, polycarbonate or polypropylene, 630vw.
– Tone: 0.01 to 0.25uf (use a range if there are several different switched tone positions – higher values give more bass cut), Mylar, polycarbonate or polypropylene, 630vw.
– Only use silver mica caps (or polythene caps if you can find high-voltage ones if needed) in IF an RF tuned circuits. IF tuned circuits at ~460kHz often use 100 to 150pf.
Resistor ‘rule of thumb’ for tube sets:
– Cathode: 150 to 470 ohms, 1w.
– Screen dropper: 47k to 100k, 1w.
– Plate (if used): 1k to 4.7k (RF and IF stages), 47k to 270k (1st AF stage).
– Grid bias: 470k to 1M, 0.5w.
– Volume control: 0.25M to 2M, audio (log) taper.
– Tone control: 50k to 250k, linear taper.
Download Rogers Majestic 11_95 small.jpg. (Caution: This file may not be virus scanned.)
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