philco 49-602 B+ Voltage Too High, No Life

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philco 49-602 B+ Voltage Too High, No Life

Post by linuxrunner on Mon Jan 29, 2018 11:53 pm

First i have little to no electrical knowledge, i was gonna scrap everything in this radio and use the case but i figured might as well try to get it to work and maybe learn something first.

i replaced all the caps in this radio (except the Mica ones) before I did anything. upon powering it up i get no signs of life, no noise, no smell and no glowing of any tubes. I went through the wiring schematic the best i could and i didn't change any wiring when i wired up the caps (but i am not sure if it worked before). The diagram shows i should be getting 125v dc after the selenium rectifier but i am getting 156v dc. then after some resistors it should be 120v then 55v then 7.5v. I am getting 150v DC everywhere.

From what i can tell the expected failure mode of a selenium rectifier is higher resistance so i would expect a lower voltage if it were going bad?

I know it's probably pretty obvious for some, but could you point me in a direction? does this sound like bad wiring? faulty tubes? a bad rectifier or caps? not sure even where to start.

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Re: philco 49-602 B+ Voltage Too High, No Life

Post by willy3486 on Tue Jan 30, 2018 8:05 am

I don't do too much with these types where they have batteries or AC but I do have a few questions. First off it looks like the tube filaments are in series. Do you get a resistance reading in ohms across the tubes? I am wondering if a tube has a open filament if this would cause it to no drop the voltage giving you the voltage you see. Also what about the switch reading with the ohm meter. I have designed power supplies that run higher than the design but once a load gets put on it the voltage drops to the voltage it should be. Also if it does have a tube burned out and it was fine before you may want to bring the voltage up slowly or use a dim bulb tester. If you are not familiar with a dim bulb tester you can do a search on them and they are easy to build.

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Re: philco 49-602 B+ Voltage Too High, No Life

Post by Chas on Wed Jan 31, 2018 12:06 am

Go here to get the schematic if you do not already have it...

http://www.nostalgiaair.org/Resources/download.asp?FN=\M0013666.pdf

Print it oversize and paste it together.

Look at the battery/AC transfer switch and be sure all the contacts and circuit routings are working correctly. Check resistors R100, 101a, 101b and 102 for correct resistance. Also some of these battery sets have a electrolytic capacitor across the filament circuit. If a tube is found open, do not plug in a good tube unless an hour has past to allow that cap to discharge... See C202...

Never, ever, remove/replace a tube in a battery set with the power ON...

Since the set has been powered you are already past the "dim-bulb" step...

Do use a 10k ohm/volt analog meter. A DVM draws very little power from the circuit and readings taken from the schematic won't agree with a DVM. The DVM will say they are high...

Be sure the installation of new components did NOT cause a large blob of solder or wire snips to short.

Without splicing copies of the schematic it is difficult to find a power supply load or bleeder resistor, if there is one, it may be open causing the supply voltage to go high...

I do advise following up on the radio as letting get the best would mean a troubleshooting lesson not learned...

BTW Linux spoken here...

GL

Chas


Last edited by Chas on Wed Jan 31, 2018 12:12 am; edited 1 time in total (Reason for editing : More to say...)
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Re: philco 49-602 B+ Voltage Too High, No Life

Post by linuxrunner on Wed Jan 31, 2018 12:58 am

Thanks for all the suggestions,
I went ahead and built the dim bulb tester so at least now i won't fry new stuff when i get to the point of testing again. (i thought i had to buy a variac, didn't know there was a cheaper option.)

i do have the schematic and i did test each of the resistors in the power supply section of the schematic and they all tested within around 10ohms so they seem to be good.

i looked up each of the tubes for the pinout and i am not sure i know what i am doing here, but as far as i could tell it looks like on all of them pins 1 and 7 are the filament?
If so a few of them have open connections between pins 1 and 7 (the 3v4 and 1t4).
I attempted to get some resistance readings on the heaters but i didn't get resistance on any other pins (besides between 1 and 7).

for example in this pinout of the 1R5, should I be able to read resistance between pins 3,6 and 4? are these the heater?

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Re: philco 49-602 B+ Voltage Too High, No Life

Post by Chas on Wed Jan 31, 2018 10:05 am

I do have the schematic and i did test each of the resistors in the power supply section of the schematic and they all tested within around have 10ohms so they seem to be good. Take a good look at the schematic... The resistors in question, R100, 101a, 101b and 102 are: 60, 1125, 1125, 2200 ohms each. You may be reading them incorrectly. At 10 ohms the tubes and rectifier would be destroyed...

The tube diagram shown, pins 3,4 & 6 are all grids signals general go "in" there... The filament is 1, 7 & 5, there is a jumper inside the tube between 1 & 5.

Resistance of the heater (filament) can be read between 7 & 1 or 7 & 5. The jumper will always be zero ohms.

See: https://frank.pocnet.net/

Also: http://antiqueradios.com/archive.shtml

Download all of "The Elements of Radio Servicing"

BTW the filaments of this type of battery tube will not be seen to glow, possibly in a darkened room, very dull red.

GL

Chas

Spend some time with vacuum tube theory, it will help.


Last edited by Chas on Wed Jan 31, 2018 10:16 am; edited 1 time in total (Reason for editing : Left out info...)
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Re: philco 49-602 B+ Voltage Too High, No Life

Post by linuxrunner on Wed Jan 31, 2018 10:55 am

Sorry, i ment the resistors all tested within around 10ohms of their correct values. 63, 1131, 1123, 2211 to be exact.

I did not realize the heater and filament were the same thing, silent I will check out those links and download The Elements of Radio Servicing.

It sounds like 2 of my tubes are probably bad as there is no connectivity between the filament pins.


no connectivity between 1 and 7 on both of these tubes...
3V4
1T4

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Re: philco 49-602 B+ Voltage Too High, No Life

Post by Chas on Wed Jan 31, 2018 12:42 pm

Most battery tubes are relatively inexpensive from many vendors. Avoid "boutique" tube vendors.

The selenium rectifier could still be a problem. Check its forward and reverse resistance with an analog VOM. Expect about 30 ohms forward and near infinity reversed.

You can check the power supply by removing all the tubes. Locate the B+ and the A- B- connections at the power supply. Calculate a resistor for the B+ for a load of about 10MA at 90 volts and a resistor for the A+ for a load of about 30ma at 7.5 volts. Use ohms law to determine the resistor value and wattage. Tack solder the resistors to the the respective circuits. Use the dim bulb or a variable transformer and apply power while monitoring the "A" voltage. when the voltage reaches 7.5 or the variable transformer is at full output, there should be agreement or 90 volts and 7.5 volts.

Use an analog meter to make the measurements. If the selenium rectifier is failing the voltage will be low. If a DVM is used the voltage may appear high as there may be AC leakage that the DVM can detect that a VOM would ignore. That AC would make the radio hum and raise havoc with the new filter capacitors...

Replacement of the selenium with a silicon diode requires more math to install a suitable resistor in series to reduce the output voltage. So to avoid the headache take the "educated" guess...

That diode HAS to be installed correctly, no second chance, the wrong way will take out the filter condensers.

Either add a resistor in series with R100 or replace R100 with a value, to start 150 ohms higher. Then take new readings with the existing load resistors.


BTW please take resistance readings of the IF transformers, the antenna and oscillator coils, these should all be low values. If any are high then there is a problem with that coil.

Find a web site that has a glossary of electronic jargon, old and new terms as well as a few foreign terms for devices and circuits will get mixed in text as well as schematic symbols.

GL

Chas
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Re: philco 49-602 B+ Voltage Too High, No Life

Post by linuxrunner on Wed Jan 31, 2018 6:41 pm

Thank you Chas for all your help.

I will see if i can get my hands on an analog VM before I get too much further. I went ahead and ordered some replacement tubes. I will let you know how i make out with these tests once i get an analog VM.

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Re: philco 49-602 B+ Voltage Too High, No Life

Post by Chas on Wed Jan 31, 2018 9:11 pm

You cannot go wrong with a Simpson 260. Taken care of it will resell. FWIR it is 10K/ohms/volt, that is the load resistance when measuring volts. Most common radio schematics where measured at that load.

There are some variations in the model line but three ohms/volts/current scales should be present. There may be a High voltage input or a db scale. The db scale is at 600 ohms load and is blocked by a capacitor making it useful for measuring the audio level when aligning a receiver.

There were optional cases, one with a roll-up door, another with a leather exterior case.

https://www.simpsonelectric.com/products/test-equipment/vom-multimeters/260-8-260-8p

The case is insulated Bakelite can take abuse, but do not drop it...

If you buy one used be sure it is recently calibrated and all ranges working, no battery damage. As a noob, messing with precision resistors can get awkward...

One more caveat about DVM's, though they serve their purpose, some types cannot measure capacitance of a leaking capacitor. Some cannot measure the DC resistance of an inductor, like a choke, or transformer. It has to do with how the processor works...

I lament that I have several Simpsons, actually lying about, one in the attic, one in the shed another on the bench. Having the opportunity to buy them cheap used from Ham estates and yard sales...

GL

Chas

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Re: philco 49-602 B+ Voltage Too High, No Life

Post by easyrider8 on Wed Feb 07, 2018 5:35 pm

Chas wrote:The selenium rectifier could still be a problem. Check its forward and reverse resistance with an analog VOM. Expect about 30 ohms forward and near infinity reversed.
You cannot check a selenium with a VOM , the VOM does not supply enough voltage to turn it on. I find it hard to believe you were able to measure 30 ohms in the forward direction, none of my Simpsons will do that.

I have been working on these radios for over 60 years and yet to find a failed selenium although I have replaced many in television sets.

Having high voltage on the B+ indicates lack of a proper load due to the tubes not conducting and the lack of the filament load due to a bad tube filament. Once the defective tubes, capacitors and electrolytics are replaced everything should fall into place.

I would definitely not suggest replacing the selenium at this point, that would really open up a can of worms.

Chas wrote:Do use a 10k ohm/volt analog meter. A DVM draws very little power from the circuit and readings taken from the schematic won't agree with a DVM. The DVM will say they are high...
This is a low impedance circuit and using an analog or digital meter will not make a difference.

Dave
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Re: philco 49-602 B+ Voltage Too High, No Life

Post by Chas on Wed Feb 07, 2018 8:03 pm

Linuxrunner wrote:Thank you Chas for all your help.

I will see if i can get my hands on an analog VM before I get too much further. I went ahead and ordered some replacement tubes. I will let you know how i make out with these tests once i get an analog VM.

How is the project going?

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