(09-06-2015, 07:27 PM)Mondial Wrote: Yes, as Terry said electrolytics will not hold up long in this application.
Small value electrolytics are not rated for the ripple current they will be subjected to in a tube power supply filter. The lower the capacitance, the lower is their ripple current rating, and a modern 2 uF electrolytic was not designed to be an input filter in a vintage tube power supply. They will overheat and eventually fail.
Back when the 511 was designed, capacitors were expensive and so they used the smallest capacitance paper caps possible. These caps could however handle the ripple with no problem.
Today, the best option for replacement is a film type cap. They are designed to handle such service and will basically last forever. These are the type I use and have been very happy with their performance.
Thank you both for letting me know about this! I never knew about such a thing. I will be sure to get film type cap replacements. So these are not electrolytic wet style caps? Are these are modern dry caps? I have several early AC sets, would you guys recommend these type of caps for all early AC filament sets with power supplies designed close to this model 511 such as Radiola, Zenith, ect?
Thanks
Jon
"A Minute of Care is Worth an Hour of Repair" circa 1930.
(09-06-2015, 07:27 PM)Mondial Wrote: Yes, as Terry said electrolytics will not hold up long in this application.
Small value electrolytics are not rated for the ripple current they will be subjected to in a tube power supply filter. The lower the capacitance, the lower is their ripple current rating, and a modern 2 uF electrolytic was not designed to be an input filter in a vintage tube power supply. They will overheat and eventually fail.
Back when the 511 was designed, capacitors were expensive and so they used the smallest capacitance paper caps possible. These caps could however handle the ripple with no problem.
Today, the best option for replacement is a film type cap. They are designed to handle such service and will basically last forever. These are the type I use and have been very happy with their performance.
Thank you both for letting me know about this! I never knew about such a thing. I will be sure to get film type cap replacements. So these are not electrolytic wet style caps? Are these are modern dry caps? I have several early AC sets, would you guys recommend these type of caps for all early AC filament sets with power supplies designed close to this model 511 such as Radiola, Zenith, ect?
Thanks
Jon
Hi Jon,
> So these are not electrolytic wet style caps?
Yes that is correct.
>Are these are modern dry caps?
Yes again. They are NOT electrolytic wet or dry.
They are non polarized film caps. Much like your
yellow mylar caps used the replace bypassing
and coupling cap, only much larger in capacity.
Generally I would recommend using them in older
sets that have small capacity filters.
Yes, that's pretty much it. Until about 1930-31, most AC powered radios used paper filter capacitors. Electrolytics were just being commercially developed, like the early Mershon caps.
Any time you have a filter cap right after the rectifier of less than say 8 uF, I would recommend using a film replacement. Its especially important at this circuit location because the input cap sees the most ripple current. After the filter choke or field coil it not as critical because the ripple level is much lower.
Thanks guys for the help in understanding why! I never knew this as I am used to wet electrolytic's. This 511 is the oldest radio I have ever worked on (I have not started on any of my pre 1931 Philco's/RCA's yet). I will remember this critical lesson for all my future pre 1931 radio restorations.
A friend is mailing me some Non-polarized film caps. They will be on their way tomorrow morning. I hope to get them in a few days so we can call this project a wrap!
Jon
"A Minute of Care is Worth an Hour of Repair" circa 1930.
The final part of the electrical restoration has arrived. Since the new dry caps are quite large and will be taking up a lot of room, I have decided to re-stuff the filter condenser can. Just now, I was able to rid the can of it's old filter caps. Plenty of tar in this one! My method, if any of you were wondering: I first gently pulled off the can lid were all the solder connections were. Next I cut each wire to separate the can from its lid. With the lid off I was able to take a cork screw, attach it to the filter block and pull it out as one piece after heating up the can to soften the tar within. This process did take about 15 to 20 minutes. It works well for me though.
In the 3rd picture you will see my replacement caps. All these caps are rated to at least 600V. Values are close but not exact. You will see the actual MFD values that will be used, on picture 3.
The schematic calls for values MFD as: 0.4mfd 4.0mfd 2mfd 1mfd 2mfd .015mfd
My values: 0.5mfd 5.0mfd 2.5mfd 1.25mfd 2.5mfd .015mfd
Will this work?
Also I take lug number 5 as being a true ground? I am having a troubled time trying to figure out how to wire up each cap to it's lug. For example: Would lug 6 and 8 be connected together (one side of .015 on lug 8 and the other side of the cap on lug 6?)
"A Minute of Care is Worth an Hour of Repair" circa 1930.
I have started on the main filter block. I am re-wiring the new parts in exactly as they are shown on the filter block diagram Ron provided on that excellent schematic.
Jon
"A Minute of Care is Worth an Hour of Repair" circa 1930.
I finally finished the main filter block. I followed the wiring diagram to a "T". Here is a picture of the end result. Everything was tested and double checked, a successful repair! If you look on the can within this picture you will see that I essentially wrote with a grease pen that the can was "Re-Stuffed" for any "future radio restorers". I was able to just snap the lid with all the parts attached, to the rest of the can. Friction held it on originally, and I was able to replicate a very similar process without damaging the can itself.
Next I hooked up a fully restored Heathkit T-2 Signal tracer (with universal output trans to use as a test speaker) to the speaker jacks correctly via the Heathkit owners manual (no output trans on this receiver it's self). The original speaker is missing from this set and I do not have another magnetic speaker on hand. I turned on the set first with a dim bulb. Power trans has no shorts, bulb lit and dimmed very nicely. Next I powered the set up at 110VAC via a variac. All the tubes lit including the pilot lamp, but no sound despite the variable condenser and knobs manipulated every which way. I have a 70 ft outside antenna connected properly. No ground connected though.
I next tested what voltages I could on each of the tubes, they seem normal, results below. I tested all three chokes, results not recorded, but all tested around 200 OHM, I would say they are good. I also tested 1st and 2nd AF trans, results below. No opens, but the secondary on the 1st AF (one side to ground, other to the grid of the 26 tube) read 1.41 MEG OHM while all other primary/secondary readings on the AF transformers read in the thousands.
I am thinking the secondary on the 1st AF trans is open due to this 1.41 MEG OHM reading, thus causing no sound out of the receiver. I am only a novice at this stuff and it took me this last week with the help of books/reading and several friends to figure this out. What do you guys think????
Thanks
"A Minute of Care is Worth an Hour of Repair" circa 1930.
Two ways to go. One the replace the transformer AES a has a suitable unit 1:3 ratio. Or connect .01 cap from pin 2 of the 27 to pin 3 of the 26 and a 250k to ground. Connect a 100k resistor from pin 2 of the 27 to B+
The transformer is a bit better way as it adds volt gain between the detector stage and 1st audio.
Terry
(This post was last modified: 10-08-2015, 09:26 PM by Radioroslyn.)
(10-08-2015, 09:11 PM)Radioroslyn Wrote: Two ways to go. One the replace the transformer AES a has a suitable unit 1:3 ratio. Or connect .01 cap from pin 2 of the 27 to pin 3 of the 26 and a 250k to ground. Connect a 100k resistor from pin 2 of the 27 to B+
The transformer is a bit better way as it adds volt gain between the detector stage and 1st audio.
Terry
Terry,
I am thinking I will go with another transformer. Is there one available, small enough to sit inside of the old clam shells for aesthetics? I have never done this before. What type of unit and ohms rating should I go for from AES?
Thanks for the help
Jon
"A Minute of Care is Worth an Hour of Repair" circa 1930.
I think I will do the RC-Coupling as the customer does not care either way. I already have my parts on hand.
Do I need to fully disconnect the interstage transformer from the other wires going to it? Do I solder the new parts to the existing lugs with wires still attached (as it sit's now? )
Jon
"A Minute of Care is Worth an Hour of Repair" circa 1930.
)