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 Post subject: GE 221 Electrolytics
PostPosted: Apr Wed 08, 2020 2:45 am 
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Location: Townsend, MA
This radio appears to be unmolested. However, it has a 3 section electrolytic can containing values that differ from the factory documentation.
Both Riders and Sams state is should contain 50/50/40 (Uf).
The installed cap has 250/200/10 (uF), which were verified when measured.
These values are marked on the cardboard sleeve. The can is unmarked.
The radio plays well and without hum.
I measured 103 volts on the B+, on 122VAC in.
The common negative is isolated from B- and the can is riveted to the chassis via a phenolic isolation spacer.
Its under-chassis wiring is clean and consistent with the rest of the chassis.
If this wasn't factory installed, then someone did a damn good job.

So the obvious question is...should I use the installed values, or go by the documentation?


Attachments:
GE Cap.jpg
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IMG_5609.JPG [ 582.96 KiB | Viewed 342 times ]
Schem.jpg
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 Post subject: Re: GE 121 Electrolytics
PostPosted: Apr Wed 08, 2020 2:54 am 
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It seems to be a factory replacement part, the part number is different than the number on the schematic.

Since GE used them as replacements, either value should work.

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 Post subject: Re: GE 221 Electrolytics
PostPosted: Apr Wed 08, 2020 2:58 am 
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Notice on the caps a range of capacities. These were made as replacement to cover many different electrolytic values. Date code is 1971.

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 Post subject: Re: GE 221 Electrolytics
PostPosted: Apr Wed 08, 2020 3:29 am 
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It's likely that the rivets holding the phenolic insulating wafer to the radio chassis are "factory original" but the capacitor itself is not factory original.

When the original capacitor was replaced, the technician straightened (or cut off) the "common negative" tabs on the original filter capacitor can so that it could be removed without damaging the phenolic wafer. Then the new capacitor was inserted into the existing phenolic wafer.

The uF tolerance on vintage electrolytics was typically quite wide, often stated to be -20%/+80%.

So a capacitor labeled with the original factory schematic value, 50uF, would be considered in-spec if it measured between 40uF and 90uF.

This is the result of applying a similar tolerance range to the replacement capacitor:

100 to 200uF corresponds to: 120uF
125 to 250uF corresponds to: 150uF
5 to 10uF corresponds to: 6uF

I'm curious as to which section of the capacitor is wired as C7A (input filter) and as C7B (after 1200 ohm resistor).

This replacement capacitor is a very large filter capacitor for a 35Z5 rectifier tube. But one advantage is it will reduce the amount of background hum level heard when the volume control is at minimum, compared to the factory-original 50uF/50uF.
.
Note that the 35Z5 is NOT wired to route the B+ plate current through the "pilot lamp" tap of its heater. That was probably a good idea in this case. The much larger capacitance of the replacement capacitor would likely make the surge current high enough to open the heater of the 35Z5 if the radio was on and warmed up, and then switched off for just a few seconds, and immediately switched back on while the tube heater was still hot.

Instead, this radio has a small series resistor for "inrush current limiting" connected to the plate of the 35Z5. It would probably be a good idea to check that resistor to verify it hasn't increased in resistance from repetitive surges.

-EB

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 Post subject: Re: GE 221 Electrolytics
PostPosted: Apr Wed 08, 2020 4:07 am 
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Location: Townsend, MA
So it was indeed a replacement. Nice work.
I know that these had wide tolerances, but again, they're quite far from the original spec.
So, if I'm to replace them and considering electricboyo's points, what would be the ideal values to use?


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 Post subject: Re: GE 221 Electrolytics
PostPosted: Apr Wed 08, 2020 4:08 am 
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The capacitor specifically states "Service Designed". It's a replacement.

In answer to the original question, go with the schematic values.

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 Post subject: Re: GE 221 Electrolytics
PostPosted: Apr Wed 08, 2020 5:24 am 
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i exclusively have collected/restored hundreds to maybe slightly over 1000 AA5 sets over the past 40 years. i now have 70, lol.

i don't think i have never seen that high of a value in the filtering section of the standard AA5/6 set that was factory original.

if it were me, i would install the correct value capacitors based on the schematic.

i say when this radio went in for repair 50 years ago and that was the capacitor they had on hand to get the set out of the shop.

they used it, it worked, grandma paid up, and got her radio back that week.

steve

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 Post subject: Re: GE 221 Electrolytics
PostPosted: Apr Wed 08, 2020 12:02 pm 
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Looks like the mystery's been solved and I've learned a few things to boot.
I'll go with the original values.
Thanks for all your help! :P


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 Post subject: Re: GE 221 Electrolytics
PostPosted: Apr Wed 08, 2020 3:10 pm 
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It looks to me like that capacitor was removed from something else prior to being installed in the radio. The center portion of the cap appears had a mounting ring crimped around it, similar to caps that are mounted to a chassis sideways. As someone else mentioned, I'm sure it was "get it fixed and get it gone".

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 Post subject: Re: GE 221 Electrolytics
PostPosted: Apr Wed 08, 2020 3:24 pm 
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Yes, it does appear to be so Jim.
It even has a marked area where the mounting band should go.


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 Post subject: Re: GE 221 Electrolytics
PostPosted: Apr Wed 08, 2020 5:18 pm 
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A Sound Mind wrote:
So it was indeed a replacement. Nice work.
I know that these had wide tolerances, but again, they're quite far from the original spec.
So, if I'm to replace them and considering electricboyo's points, what would be the ideal values to use?
What size is the speaker in this radio?

Larger speakers produce more audio output at low frequencies. This makes their residual 60Hz hum louder.

Small AA5 or AA6 radios with 3” or 4” speakers are usually OK with their “original design value” 50uF filter capacitors. Typically you will need to hold your ear close to the speaker to hear the background hum from these smaller radios. The residual hum becomes inaudible when you are more than 3 or 4 feet away from the radio. Both the radio manufacturers and radio listeners accepted this small amount of background hum at that time in history.

For larger radios with 6”, 8”, or oval speakers, the traditional B+ filter circuit with 2x 50uF capacitors may not totally quiet the residual hum.

In the traditional AA5 or AA6 circuit design, the audio output tube (50L6, 50C5, etc.) gets its plate B+ from the first 50uF filter capacitor. This capacitor receives pulsating DC from the cathode of the rectifier tube (35Z5, 35W4). The AC ripple at this location can be as large as 3 to 6 volts. This is large enough to generate an audible background hum from larger speakers.

I have several radios that have larger speakers and cabinets, along with a somewhat louder background hum than I would like. I’m working out a (slightly modified) B+ filter arrangement in hope of getting them to be completely hum-free.

I have two Wards Airline radios which are relatively “hum-free” already, compared to my other AA5 and AA6 table radios. I plan to model my “improved” B+ filter design on them since they already work so well. These Wards Airline radios have a 3 section B+ filter system. It uses a total of three 50uF capacitors. There is also one added resistor: This is placed between the positive terminals of the first and second 50uF filter capacitors. Value is from 100 to 220 ohms. The B+ for the audio output stage is taken from the positive terminal of the second 50uF capacitor. The AC ripple still present at this point is .5 to 1V. Considerably less. Finally, there is a 1k ohm resistor in series between the second and third 50uF capacitor. The 90V B+ from this third 50uF capacitor feeds the RF and IF sections of the radio, and also the first audio amplifier stage (12SQ7, 12AV6). The residual AC ripple at this point is only 10 to 50mV.

I hope to post the results of my experimentation very soon.

-EB

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 Post subject: Re: GE 221 Electrolytics
PostPosted: Apr Wed 08, 2020 5:51 pm 
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electricboyo wrote:
I have two Wards Airline radios which are relatively “hum-free” already, compared to my other AA5 and AA6 table radios. I plan to model my “improved” B+ filter design on them since they already work so well. These Wards Airline radios have a 3 section B+ filter system. It uses a total of three 50uF capacitors. There is also one added resistor: This is placed between the positive terminals of the first and second 50uF filter capacitors. Value is from 100 to 220 ohms. The B+ for the audio output stage is taken from the positive terminal of the second 50uF capacitor. The AC ripple still present at this point is .5 to 1V. Considerably less. Finally, there is a 1k ohm resistor in series between the second and third 50uF capacitor. The 90V B+ from this third 50uF capacitor feeds the RF and IF sections of the radio, and also the first audio amplifier stage (12SQ7, 12AV6). The residual AC ripple at this point is only 10 to 50mV.

I hope to post the results of my experimentation very soon.

-EB


Philco used three filter caps in many of their radios, yes hum should be 99+% gone.

GE used a 100 mfd in some of their large speaker radios, 70 & 80 mfd were fairly common.

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 Post subject: Re: GE 221 Electrolytics
PostPosted: Apr Wed 08, 2020 6:14 pm 
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35Z5 wrote:
Philco used three filter caps in many of their radios, yes hum should be 99+% gone.

GE used a 100 mfd in some of their large speaker radios, 70 & 80 mfd were fairly common.


i have done this.

per your suggestion years ago on an AA6 that had a larger 6" speaker, i added that extra 3rd capacitor as per a philco schematic. it added a 22 mfd capacitor and a 120/130 ohm resistor in the filtering network.

the hum was 99% gone and i only lost 3-5 vdc in the B+.

edit: thinking back, this was the project,

viewtopic.php?f=12&t=336427

steve


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philco.jpg
philco.jpg [ 34.95 KiB | Viewed 234 times ]

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 Post subject: Re: GE 221 Electrolytics
PostPosted: Apr Wed 08, 2020 6:34 pm 
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The GE QT line stood for "Quick Turnover" and was a series of aftermarket replacement electrolytics. They indicated you could use a few capacitor values to replace ones within the "range" of values marked on the parts. But this one is way out of the range that should have been used to replace the original part in that set.

The capacitor in the photo with a 7126 date code is significantly newer than the radio. It's quite possible that a professional technician did a really neat installation without causing damage to the original phenolic insulator or wiring.

Many if not all of these QT caps originally came with a metal mounting strap attached, which could be removed if you were installing it onto a phenolic insulator or a punched chassis.

Here's a link to an eBay listing, for a reference photo of what this capacitor looked like when it came out of the GE box. Note the presence of the metal strap.......

https://www.ebay.com.sg/itm/NOS-NIB-Vin ... SwXvRc9DPf

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 Post subject: Re: GE 221 Electrolytics
PostPosted: Apr Wed 08, 2020 7:58 pm 
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Back when replacement twist-lock electrolytics were common, off the shelf items, any good technician would break the tabs off the old one and remove it, salvaging the phenolic or metal mounting ring for the new can. As others have noted, this was not a factory installed capacitor, it was a universal replacement sold aftermarket to radio and TV repair shops. That it ended up in a GE radio was probably a coincidence.

One could argue that 1971 was 49 years ago so the capacitor seems to have lasted a long time, despite the fact its uF values are higher than necessary. It is to be noted that GE put an 18-ohm resistor in series with the plate of the 35Z5 which probably added enough impedance to the circuit that the higher capacitance did not damage the tube. Or if the radio did eat tubes after that, nobody did anything about it. But since 35Z5 tubes are not as readily available or cheap today as they were 50 years ago, I would put the capacitors back to the schematic values and check the 18-ohm resistor (R12 on the schematic) to make sure it hasn't gone down in value.

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 Post subject: Re: GE 221 Electrolytics
PostPosted: Apr Thu 09, 2020 11:42 pm 
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Dutch Rabbit wrote:
35Z5 wrote:
Philco used three filter caps in many of their radios, yes hum should be 99+% gone.

GE used a 100 mfd in some of their large speaker radios, 70 & 80 mfd were fairly common.
i have done this.

per your suggestion years ago on an AA6 that had a larger 6" speaker, i added that extra 3rd capacitor as per a philco schematic. it added a 22 mfd capacitor and a 120/130 ohm resistor in the filtering network.

the hum was 99% gone and i only lost 3-5 vdc in the B+.

edit: thinking back, this was the project,

viewtopic.php?f=12&t=336427

steve
In light of today’s higher AC mains voltage in the USA, that reduction of 3-5V for the B+ voltage feeding the plate of the 50L6/50C5 is “no problem at all.”

The next resistor to the right can be reduced in value slightly if needed to maintain >90V on the B+ rail that feeds the RF/IF/first AF and 50L6/50C5 screen grid.

I’m gonna try this out on the very next radio that goes across my workbench.

-EB

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 Post subject: Re: GE 221 Electrolytics
PostPosted: Apr Fri 10, 2020 3:20 am 
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it works.

steve

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