I am serious in wanting to understand my hobby and have been studying in my spare time & have a fare understanding on what is going on inside the chassis, but I definitely lack experience when it comes to judging what I am seeing on my test instruments, as with radios I am having to study / gain experience on how to use the tools I am working with.
I have been slowly purchasing test equipment and have found radio swap meets are a grate source for used equipment, to date I believe I have almost everything needed to start my adventure.
Due to a recent post I have read & starting to plug things in I have the following questions.
Test meter / Rider manual,
If I understand correctly when Rider put their manuals together during that era, affordable test meters were of the mechanical movement type, which put a load on the circuit in test, so Rider wrote in their test data what the voltage readings would be under a load. Using vacuum tube or digital meters today due to their high resistance will not load the circuit in test thus showing higher voltage readings. Am I correct in my understanding?
Electrolytic capacitors,
For some reason I got it in my head a little bigger is better, recently during first powering of a Zenith 6-S-229 using a variac I was satisfied everything was OK, I left the variac at 117V and switched the radio on. The electrolytic’s charged beyond the 450 volt rating (around 520V) before going down to operating voltage as tube emissions took place. I had replaced the originals during restoration C-16 8MFD and C-17 14MFD with 10MFD and 16MFD. After the test I replaced C16 & C17 with 6MFD and 12MFD (Its what I had available at the time) and repeated the test, what I saw was both capacitors initially charged to about 438 volts before dropping down.
Am I correct in assuming the following?
For safety, an electrolytic capacitor should never be allowed to charge beyond its rated voltage, even if it is temporary.
Modern electrolytic capacitor’s due to advance material technology are smaller in physical size but can be a little more potent on charging / current draw then the originals made back around the thirties.
I should pretty much stick to original values when replacing old caps.
One question for the above, I have purchased from several venders and found capacitors of the same value come in different size packages from different manufactures, are manufactures alike or do some manufacture products emulate better the characteristics of vintage capacitors then others, or is this of concern.
Concerning safety of my family and to the radio’s that I will eventually repair, would a thermistor of the correct value be an appropriate modification to reduce initial stress when a vintage radio is first turned on. If so which is more practical installing on the 117V primary transformer winding or on the radios B+ side before the electrolytic capacitors.
Thank you for reading my post, and a belated Merry Christmas to you and your family.
Larry Goldy
Test meter / Rider manual,
Precisely…… on the test readings. The worst case of circuit loading might be is the older 1000 ohms per volt
sensitivities of VOM’s. Then as development of ever more sensitivities of meters were developed, 10,000-
20,000-50,000 Ohms per volt units were permissible with their decreased loading factors. Upon the advent of
the VTVM and its gain and isolated loading….. isolations shot up to the 1 meg and 10 meg ranges. Likewise
with the advent of solid state replacement of bipolars, FET’s and op amp inputs, the loading made yet another
quantum jump in lessening.
Electrolytic capacitors,
True, keep right at the capacitor values or a smidge above it in respect to the sets initial design parameters.
Until those tubes warm up about the only thing holding down the peak power supply voltage being developed
is a bleeder resistor across the power supply, if incorporated, or the actual leakage within electrolytics, being
inherently less on fresh/new electrolytics, as compared to the old units.
“For safety, an electrolytic capacitor should never be allowed to charge beyond its rated voltage, even if it is
temporary.”
That’s certainly something that we ideally would like to see happen…..sometimes only getting that margin by
upping the voltage ratings of new units a smidge.
I have purchased from several venders……..
My definitive test on like capacitive value / voltage rated electrolytics of different manufacturers is to compare
in the sets in their specific circuit . One test is having a series connected DC milliameter function of a VOM-
Digital meter in line with the cap, but it being shorted across with a test lead, until initial charge is accumulated,
then un short to permit measuring the leakage current..(Being set off station, as to not catch any change from
audio output stage variance in responding to AF modulation peaks). The other test is to measure AC ripple
current across the capacitor with a DVM. Opt for the units that provide the less leakage current along with
the less AC ripple voltage reading.
would a thermistor of the correct value be an appropriate modification to reduce initial stress when a vintage
radio is first turned on………..(Fortunately your rectifier tube is also delaying B+ development time equally
as other tubes warm up) Instant power, selenium rectifier circuit utilization, that was another story.
The thermistor certainly was a good buffer in commercial applications, military equipment and later on, in
tubed televisions.
Each application would need a bit different selection in the hot/cold resistance as well as its currenting capabilities.
I have seen many, many more thermistors used on the secondary than on primary input. An absence of
secondary voltages, with the filaments warming up was also provided by delay relays/tubes also on test
equipment and commercial equipment.
I certainly remember, on two situations, of building up and hiding under chassis, a peak voltage bleeder circuit.
One item, a priceless old MC Intosh tubed amp that I never would be able to find some parts for if they
crashed.
Likewise, a large Classic 15 inch + 15 inch Fender amplifier. The protection was incorporated by merely
utilizing a large metal cased
TV horizontal output transistor with a current limiting/bleeder resistor-to-Collector-to-emitter-to-ground and
then its base receives a minute voltage sampling of the raw B+ thru a high value resistor. A zener diode to
ground completes the circuit , with its value selected to the voltage value/peak that I don’t want to see the
initial B+ ever rise above. After warm up, the decreased normal voltage just leaves that circuit quiescent
until next power up time.
73’s de Edd
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
:I started collecting vintage radios about a year and a half ago. Currently I have three projects that have been cleaned, rewired and resistors & capacitors replaced. To an earlier post I wrote, I was instructed how to power a chassis and what to look for and have done so successfully with out smoking or damaging components. (Or maybe I just gust lucky) Currently I have limited myself to transformer type radios thirties & early forties mainly due to the learning stage & safety.
:
:I am serious in wanting to understand my hobby and have been studying in my spare time & have a fare understanding on what is going on inside the chassis, but I definitely lack experience when it comes to judging what I am seeing on my test instruments, as with radios I am having to study / gain experience on how to use the tools I am working with.
:
:I have been slowly purchasing test equipment and have found radio swap meets are a grate source for used equipment, to date I believe I have almost everything needed to start my adventure.
:
:Due to a recent post I have read & starting to plug things in I have the following questions.
:
:Test meter / Rider manual,
:If I understand correctly when Rider put their manuals together during that era, affordable test meters were of the mechanical movement type, which put a load on the circuit in test, so Rider wrote in their test data what the voltage readings would be under a load. Using vacuum tube or digital meters today due to their high resistance will not load the circuit in test thus showing higher voltage readings. Am I correct in my understanding?
:
:Electrolytic capacitors,
:For some reason I got it in my head a little bigger is better, recently during first powering of a Zenith 6-S-229 using a variac I was satisfied everything was OK, I left the variac at 117V and switched the radio on. The electrolytic’s charged beyond the 450 volt rating (around 520V) before going down to operating voltage as tube emissions took place. I had replaced the originals during restoration C-16 8MFD and C-17 14MFD with 10MFD and 16MFD. After the test I replaced C16 & C17 with 6MFD and 12MFD (Its what I had available at the time) and repeated the test, what I saw was both capacitors initially charged to about 438 volts before dropping down.
:
:Am I correct in assuming the following?
:
:For safety, an electrolytic capacitor should never be allowed to charge beyond its rated voltage, even if it is temporary.
:
:Modern electrolytic capacitor’s due to advance material technology are smaller in physical size but can be a little more potent on charging / current draw then the originals made back around the thirties.
:
:I should pretty much stick to original values when replacing old caps.
:
:One question for the above, I have purchased from several venders and found capacitors of the same value come in different size packages from different manufactures, are manufactures alike or do some manufacture products emulate better the characteristics of vintage capacitors then others, or is this of concern.
:
:Concerning safety of my family and to the radio’s that I will eventually repair, would a thermistor of the correct value be an appropriate modification to reduce initial stress when a vintage radio is first turned on. If so which is more practical installing on the 117V primary transformer winding or on the radios B+ side before the electrolytic capacitors.
:
:Thank you for reading my post, and a belated Merry Christmas to you and your family.
:Larry Goldy
:
What I do understand is,
Using and older style 1000 ohms/volt meter will put me in line with older test documents, when comparing voltage reading, however I also understand using an older style meter is not for all circuits.
For safety I will not accept a capacitor charging at or above rated voltage, instead I will look for the cause and if need be replace the capacitor with a higher voltage rating.
Testing capacitors in their operating circuit, I want to try that. It would be good for me to experience the test results, as I know not all things are manufactured equally. Also this will give me a better feel on the circuit as well as the components under test.
Good point! The rectifier tube does delay capacitor charging so installing a thermistor on the primary side of the power transformer makes less sense now, so I will study more on the possible use on the B+ side to minimize peak voltage.
Again thanks for taking your time to help out.
Regarding electrolytics, it always is ideal to have electrolytics which can handle the no-load voltage. However, if the manufacturer originally used 450 volt electrolytics, you probably can get by using them as replacements. If the originals shorted out, this may or may not be the cause of the short. Electrolytics develop leakage over time sometimes even if not overstressed. Usually electrolytics have a momentary overload threshold to work with anyway.
Regarding electrolytic size, as you and Ed agree upon, bigger is usually better. When dealing with high voltage AC radios, though, especially those with rectifier tubes which have close spacing between the cathode and plate (6X5, for example), too high a value can cause arcing between the cathode and the plate during turn-on, especially when the radio is already warm and both the load of the charging electrolytic and the rest of the radio are imposed upon the rectifier at the same time. 6X5 tubes are fried easily this way. Zenith often used two of them in parallel and still had a lot of trouble. With AC-DC radios, often you can go as high as 100 MFD, though unless you have a high output amplifier (push-pull or double push-pull mono or stereo), going higher than about 60 is unnecessary unless a higher value is given in the schematic. Even with these radios if you go higher than 100, you may fry the 35Z5 or 35W4 tube. With selenium rectifiers you must be EXTREMELY cautious with over valuing the electrolytics. With AC radios I advise you not to go over 40 MFD unless a higher value is given in the schematic. If you are using a 6X5 or 84/6Z4 tube, use exactly what is given in the schematic +/- 5 MFD. You may experiment with slightly higher values, but you may damage the tube.
Regarding different types of condensers, I've used paper, ceramic, metalized film, and mica condensers in radios, and have noticed little difference in performance. Try to stay away from paper condensers. Otherwise the rest perform almost equally when used in tube radios. Metalized film condensers have a unique characteristic. Since there is a film of metal on the di-electric, if a short occurs, the film burns away easily, often eliminating the short. They call this "self healing."
Thomas
You are correct, the schematic did point out a 1000 ohm per volt meter should be used and sorry to say I did not understand that and let it blow right by me.
I feel a little foolish because the relating questions I had were based on using a digital meter and of course coming up with the wrong conclusions.
My objective is to be responsible to my hobby and to the forums I post on, what I learned from this is I should not be afraid to ask simple questions and leave out speculation, at least until I can back them with better testing methods.
I would like to address the replies you gave,
Regarding voltage readings I am currently looking for a Simpson 260 meter and hope to find one soon. I understand for people with a lot of experience using a digital meter is no problem but for a beginner like me the Simpson 260 will make life a little easier to compare voltages of the schematic.
I understand now electrolytics have a momentary overload threshold, and understand larger capacitors do give better filtering. However in replacing capacitors its probably safer for the radio if I stick with the print, if I have problems later someone like you with extensive experience can help in determining if larger values would be beneficial or not.
Self healing, I was wondering what that really meant. Thanks. If I understand correctly when the metal film burns away due to an internal the problem is fixed and this is sort of a onetime deal.
Thomas I do have a simple question which I will post separately.
Thanks your reply was much appreciated.
Larry
Regarding self healing, this can happen again and again. Of course if it happend too often, the condenser would be destroyed. A condenser of this type is made by putting a metal film on each side of two special plastic "ribbons" such as mylar. This plastic varies in thickness depending upon the voltage requirements for any particular condenser. Generally the plastic is as thick or thicker than a plastic sandwich baggy. Usually it's a bit thicker. The two ribbons of plastic with the metal film are wound into a cylinder. Each metal film faces the uncoated side of the other plastic ribbon so that the two films do not touch electrically. They are insulated by the plastic. The capacitance depends upon the thickness of the plastic and upon how much of this is wound around it self. If the plastic must be made thicker for more voltage threshold, then more of this material must be wound around in order to get the same capacitance as could be achieved with less when the plastic is thinner. Leads are attached in a special way unknown to me (for the most part), so that each lead touches its metal film. One lead touches one film and the other touches the other film. The leads are then used for connecting to your radio. Should an arc temporarily occur through the plastic, causing a short, metal film in that area on the pastic will melt away. Since it melts away from the faulty zone, the arc cannot continue unless the insulative plastic breaks down elsewhere. In this way the condenser is self-healing.
With paper condensers, when an arc forms through the paper, a carbon trail is left in the paper. Actual metal foil is used between the paper, and this foil doesn't melt as readily as the metal film. If the condenser shorts out, it tends to retain leakage after the short, and is thus useless. Also, with age, paper condensers absorb moisture in the paper even though the paper is oil soaked. Also, the aluminum tarnishes even though it is soaked in oil. Most petroleum oils actually contain sulfur, which, when converted to sulferic acid by various means (again, moisture, etc.), will corrode the aluminum on its own. The corrosion is not much, but microscopic bits of aluminum, whether corroded or not, work their way into the paper, with the oil as their vehicle. This is also how a paper condenser becomes leaky. Such leakage isn't repairable. Aluminum particles may also be moved through the oil due to polarity differences in the condenser--one side is positive and one is negative. There are many reasons for the failure of paper condensers.
The sulfurs in some motor oils and in gasoline are one of the reasons why moisture, developed in the crank case of a cold engine from gasses which blow by the piston rings, rusts out and damages the inside of the engine. This is why it is important to take long hot trips. Cold short trips do not evaporate this moisture. The moisture combines with the sulfur and creates sulferic acid. The sulfur, when in the motor oil, is otherwise harmless. Better oils contain very little sulfur. Hopefully this somehow relates to how paper condensers break down.
Thomas
Thomas
Thomas
Thomas