Does anyone know the values of the electrolytic filter caps in a Philco model 80? The schematic shows these as #34 and #35 with 8 and 4 near them. Is 8 and 4 the mfd rating, and what should the voltage be? I am thinking of replacing it with a 10/10 at 160v

Using a 150 volt electrolytic in the power supply is a good way to blow up your rectifier. Save the 150 volt electrolytics for AC/DC radios. The schematic clearly shows 250 volts at the plate of the output tube. Check between one of the plates of the rectifier tube and the center tap of the high voltage winding with an AC volt meter. Remove the rectifier tube when you perform this. The AC voltage across here is approximately the DC voltage you will see at the rectifier--between the rectifier cathode and the center tap of the power transformer...this DC voltage measured here can only be accurately measured with new electrolytics in place, so measuring it now is useless. Your electrolytics should have voltage ratings at least 30 volts above this. I will assume that you will want 350 or 400 volt electrolytics. Your power supply uses a transformer that puts out from 300 to 350 volts most likely. 8 and 4 MFD are pretty accurate for a set of that vintage. 10 or 20 will really improve things. Anything above 20 MFD is excessive. Don't go over 50 or 60 MFD with a #80 type tube. My Philco model 60 has a 10 and a 20 MFD replacement, and there is absolutely no hum at the speaker. If you use a 10 or 20 MFD condenser as a replacement for either, this is fine. If you use two condensers of different values, the higher value condenser should be closest to the rectifier. Do not use values below the original ones specified.

Actually I checked out your diagram again:

www.nostalgiaair.org/PagesByModel/843/M0013843.pdf

Below the first schematic is a second page that lists a lot of information including voltages. It says that from one of the rectifier plates to the high voltage center tap you should see about 340 volts AC. That said, use electrolytics rated at 375 volts DC or 400 volts DC. Many other voltages and data are given, which you will find very useful. Print these pages out.

Thomas

:Does anyone know the values of the electrolytic filter caps in a Philco model 80? The schematic shows these as #34 and #35 with 8 and 4 near them. Is 8 and 4 the mfd rating, and what should the voltage be? I am thinking of replacing it with a 10/10 at 160v

Thanks for the info. Luckily I think I have some 22mf 350v or 400v that will work caps of Sorry I was tired and got the voltages mixed up with an AA5 I had been working on.

:Using a 150 volt electrolytic in the power supply is a good way to blow up your rectifier. Save the 150 volt electrolytics for AC/DC radios. The schematic clearly shows 250 volts at the plate of the output tube. Check between one of the plates of the rectifier tube and the center tap of the high voltage winding with an AC volt meter. Remove the rectifier tube when you perform this. The AC voltage across here is approximately the DC voltage you will see at the rectifier--between the rectifier cathode and the center tap of the power transformer...this DC voltage measured here can only be accurately measured with new electrolytics in place, so measuring it now is useless. Your electrolytics should have voltage ratings at least 30 volts above this. I will assume that you will want 350 or 400 volt electrolytics. Your power supply uses a transformer that puts out from 300 to 350 volts most likely. 8 and 4 MFD are pretty accurate for a set of that vintage. 10 or 20 will really improve things. Anything above 20 MFD is excessive. Don't go over 50 or 60 MFD with a #80 type tube. My Philco model 60 has a 10 and a 20 MFD replacement, and there is absolutely no hum at the speaker. If you use a 10 or 20 MFD condenser as a replacement for either, this is fine. If you use two condensers of different values, the higher value condenser should be closest to the rectifier. Do not use values below the original ones specified.
:
:Actually I checked out your diagram again:
:
:www.nostalgiaair.org/PagesByModel/843/M0013843.pdf
:
:Below the first schematic is a second page that lists a lot of information including voltages. It says that from one of the rectifier plates to the high voltage center tap you should see about 340 volts AC. That said, use electrolytics rated at 375 volts DC or 400 volts DC. Many other voltages and data are given, which you will find very useful. Print these pages out.
:
:Thomas
:
::Does anyone know the values of the electrolytic filter caps in a Philco model 80? The schematic shows these as #34 and #35 with 8 and 4 near them. Is 8 and 4 the mfd rating, and what should the voltage be? I am thinking of replacing it with a 10/10 at 160v

I put in a pair 10 mfd 450v electrolytics, and the radio works. I don't think it will need an alignment, although the strongest station in my area comes in very loud. I have to turn the volume all the way down to tune past it. The other stations seem to come in all right. Does this radio have an AVC? If so, is it the cap and the resistor marked 5 and 10 respectively on the schematic? It also has a "sensitivity" control on the back of the chassis. I don't know if this might correct the volume quirk

This radio blows me away! It is amazing in construction, and the note they made on page 5 of your schematic about whistles is hillarious. Your radio does not have an automatic volume control. Amazingly it is a superheterodyne. It uses one intermediate frequency transformer (IF) and the detector is a triode, and uses regeneration. The regeneration part has to be the wildest part! This radio uses a little bit of everything to make a very small superheterodyne. The sensitivity control you see on the back of your set is actually the regeneration control. Since the regenerative detector is only working with one frequency all the time (the IF frequency), there is no need to retune it for each station. You simply set it for maximum reproduction, and that's that. The note about whistles warns about setting the regeneration too closely to the point where the detector would break into oscillation. A shift in component values due to temperature and weather change can easily make this detector break into oscillation. Basically what you have is a superheterodyne front end that conveniently converts all stations to one frequency (the IF frequency), and then you have a one tube regenerative set in the middle. The benefit of the regenerative detector is that regenerating the same frequency over and over again tends to amplify that frequency much more than other frequencies that happen to reach the detector. By this very nature, very selective tuning can be achieved without a second IF transformer to further filter the IF frequency. The regeneration that takes place in the first IF takes care of this. Furthermore, because regeneration makes a signal louder, no first audio amplifier tube is needed. Two birds with one stone. Quite the trick radio! Still, the regeneration section can lead to instability, which is probably why this idea did not last too long.

When setting up this radio, follow all of the instructions carefully, and read them over and over again. Go over the schematic, and you will get to know this radio's strange and very interesting design.

Resistor 11 simply feeds B+ to the screen grid of the oscillator/converter tube. This resistor would seem almost to be an AVC resistor by how it's attached so-to-seem to the screen grid of the output tube. Remember that the second filter condenser is also connected to the screen grid of the output tube, though, so all that exists here is pure filtered DC. The condenser (#10) serves to filter the DC after the resistor (#11). Otherwise the current draw fluctions would be imposed on the current after resistor 11 by the oscillator tube. These current fluctions after resistor 11 would in turn set up unwanted feedback oscillations. In detail this can be explained as: tube is oscillating as wanted, which causes fluctions in the screen grid current simply by natural tube operation. An increase in the screen grid draw at any given moment reduces the voltage available to the screen grid from resistor 11. This reduction in current makes the screen grid slightly less positive, which throws off tube operation slightly at that given moment--causes it to conduct less. Because the tube is now conducting less current, now the screen grid has more current available to it, which causes the tube to conduct more, and so on....at radio frequencies, which sets up an unwanted oscillation. With condenser #10 present, the fluctuations are filtered out--the condenser holds a charge longer than any given fluctuation, and fills in the lows, causing the screen to receive a constant voltage. When visualizing this, one must also always take into consideration that even though electricity moves very fast, it does have inertia, and likes to stay going or to stay stopped, like any other matter, which aids in causing feedback when adequate filtering is not available. This is why direct current, which flows in one direction, is able to conduct an arc across two ponits that are slowly moved apart, than alternating current is. You will readily see this at voltages of about 60 volts or higher.

Anyway, away from all that detail....since your radio has an oscillator converter and an oscillator detector, and no other simple RF amplifier, it is not really practical to have an AVC circuit. This is perhaps another reason why you do not see your radio ciruit used in many radios. If AVC was applied to the antenna grid in the oscillator tube (grid one, #36 tube), this grid is in the path of cathode to plate flow which is also used for the oscillator. Fluctuations in grid bias at anything other than radio frequencies would severely affect the oscillator performance, and would tend to throw off the tuning of your radio. Tuning would be like playing football with a baloon. Same holds true with the detector. Though this would not throw off tuning, bias shifts would affect how much regeneration would happen, and in some cases could cause the tube to spill into oscillation, which is unwanted in regenerative circuits.

As for the reason why you cannot turn down the volume on some local stations, Norm explained it quite well. Stations were not as powerful when your radio was made--there were not as many of them, etc. No need for all the power. Your radio was not shielded for this. Your volume control is on the antenna circuit. Strong radio stations can make it into the radio chassis (without you even having an antenna wired up), and can make it into radio circuits further down the line. To remedy this, make sure that the antenna coil is in a shielded can. Try placing either a thin metal plate under the chassis (mounted securely to the cabinet) or try gluing down aluminum foil. A wire must be attached to whatever you use, and should be attached to the chassis, or the chassis must somehow rest on the metal sheet and make contact. Make sure that no components or exposed wires touch this sheet. This sheet of metal should be able to keep most strong stations out from under the chassis. Also make sure that both of your RF tubes are shielded.

There is a way to put a volume control before the audio amplifier, but this will alter your set, which is not a good thing to do unless absolutely necessary. See if the metal won't do the trick, first.

As always, read this over again thoroughly. It will help you understand your radio better.

Thomas

:I put in a pair 10 mfd 450v electrolytics, and the radio works. I don't think it will need an alignment, although the strongest station in my area comes in very loud. I have to turn the volume all the way down to tune past it. The other stations seem to come in all right. Does this radio have an AVC? If so, is it the cap and the resistor marked 5 and 10 respectively on the schematic? It also has a "sensitivity" control on the back of the chassis. I don't know if this might correct the volume quirk

I must add something to what I said about the filtering network to the #36 screen grid. Resistor #11 passes B+ to the screen grid. Condenser #10 filters it. Resistor #9 reduces B+ to the screen grid somewhat by bypassing some of it to the chassis.

If you also happen to notice condenser #5 and resistor #6, these are not AVC components, either. They are in series with the primary coil of the oscillator circuit, which is in turn in series with the oscillator/converter cathode. The resistor and condenser serve to bias the cathode slightly positively with respect to the first grid, which feeds RF in from the antenna, to be mixed with the oscillator frequency.

Thomas

Thanks for the help Thomas. The radio does have the metal sheet under the chassis. My radio is actually a model 81 comparing the tube complement to the schematic. I didn't notice the difference in tube lineup when I first looked at the schematic. It has an 80 rectifier, 42 output, and 2 77's. Only one of the 77's is shielded, so I'll try to find a shield to put on the other

The shield should help. Having the metal wrap around the sides of the chassis will help, too--usually Philcos of that era had open sides, because the cabinet covered the sides. Make sure that no wires or components touch the metal. Any grid leads that are exposed on top of the chassis can be shielded with a long metal spring or some other shielding material. For the time being, if you still have trouble with the radio, try wrapping aluminum foil around the grid leads and make the foil long enough so that it contacts the chassis wherever the wire goes into the chassis (metal cans, etc.). The foil, and springs, if springs are eventually used, must not touch the grid wire itself or the grid clip. The foil or spring should cover only the insulated part of the wire, and should be clamped down in some way so that it cannot work its way up to the bare wire. With the spring, this is a simple matter of crimping the end turns just a bit so that they grab the insulation.

For the time being, you may also try wrapping the unshielded tube with aluminum foil. Keep the foil away from the tube pins. Allow a chunk of foil to hang out at the bottom so that it may rest against the chassis somehow. Philco type can shields can occasionally be found on eBay. The radios they come from are common, and unfortunately are occasionally scrapped.

If trouble is still had, a tandem control must be obtained that has two potentiometers connected to the same shaft, as well as a power switch. Good luck finding such a device. One potentiometer must be a 20,000 ohm device, like the original, and should be wired like the original, and the other should be a 1 meg device. The second should have the contact at the extreme counter-clockwise position grounded (chassis). Condenser 25 is disconnected at 26 and the #42 tube 1st grid. Condenser 25 is then connected to the extreme clockwise position terminal. The center terminal is connected to one side of a .05 MFD condenser (400 WV), of which the other side of this condenser is connected to resistor 26 and the 1st grid of the #42 tube.

Thomas

:Thanks for the help Thomas. The radio does have the metal sheet under the chassis. My radio is actually a model 81 comparing the tube complement to the schematic. I didn't notice the difference in tube lineup when I first looked at the schematic. It has an 80 rectifier, 42 output, and 2 77's. Only one of the 77's is shielded, so I'll try to find a shield to put on the other