HQ-120-X Filter Capacitor

[k3msb]

Hello all --

C19 In the power supply filter stage is a 3 stage capacitor: 16uF / 450V, 16uF 350V and 8uF 450V.   The capacitor case specifies the color of wire for each stage.

The colors on the C19 wires are so old and blackened that neither I nor my wife can read them and I'm not sure about two of the stages;  the schematic does not specify which stage is which.

I think the 16 uF 450V connection goes at the junction of L18 and L20. This is because there was a replacement capacitor for this section of the 3 stage capacitor installed in the radio.

I would expect the 8uF section to be at the end, but since it has a 450V rating perhaps it goes to the junction of the 5V4 and L18?

Thanks!

[WQ9E]

Mark,

The 8uf is the input capacitor (junction of rectifier cathode and filter choke), the 450 volt 16 section is intermediate, and the the 350 volt is the output section.

For replacement if you cannot find the exact value as original either a 10 or 12uf @ 450 is fine for the input filter then use 22uf@450V for the remaining two sections, use 105C replacements.

The RBG (military variation) uses a 4uf input and a pair of 4uf for each of the remaining two, probably to keep the consumable spares simpler.

[k3msb]

Thanks Roger.

I already have the exact value replacements, and they will fit nicely inside the original housing.

[KC4VWU]

True dat!

Seriously though, I know it's a pain but if you dismount the chokes it makes it a lot easier to trace the wiring and figure out the sequence. the HQ-129x is basically the same.

...Phil

[k3msb]

True dat!

Seriously though, I know it's a pain but if you dismount the chokes it makes it a lot easier to trace the wiring and figure out the sequence. the HQ-129x is basically the same.

...Phil

Phil:

The legend on the capacitor casing is
16 / 450 - Red
16 / 350 - Green
8  / 450 - Blue

What I have is

16 / 450 - cut
16 / 350 - black
8 /  450 - black

So, even though I know where the two black wires connect in the circuit (both physically and on the schematic), I have no idea what one goes to the 16 and which one goes to the 8.

There's a lot of well cooked parts in that area of the radio.  I received my parts order from JustRadios and everything is going to be replaced.   The majority of the resistors are way out of spec which I didn't find unusual in the least.

Both chokes and the transformer tested good;  I did that before I started on the restoration.

[KC4VWU]

Mark,
          I have 3 that are packed up and awaiting attention, although I know one has a cooked transformer which was removed along with the chokes so as to study the situation. That was several years ago and the project was put on the back burner to move on to something else. The chokes are probably different values, so don't get them mixed up.

I may have to revisit those receivers this weekend, if so I'll try to take a few detailed pictures.

...Phil

[k3msb]

Phil

Thanks for the offers on the photos.  I took a lot of them before I started on the radio, so I don't need more, except.....

What I would like is a photo or two of how the rear most choke is attached to the chassis.   The power transformer on mine is not original, but I have an original one inbound, and the rear most choke was mounted with some funky brackets and the power transformer mounted with some big sheet metal screws.      I don't know if the power transformer on top of the chassis and the choke on the bottom of the chassis were mounted together, or separately.   

I have not yet measured the inductance on the chokes yet -- I'll have to yank out the IT-28 this weekend -- but the DC resistances of the two chokes are indeed different.    If I remember I'll post my measurements here over the weekend.

I also have an HQ-129-X.   I used to use it every now and then, but the caps are all original so I've been hesitant on using it lately for obvious reasons.