HRO-60 Cap question

[WV9R]

I'm replacing all of the paper caps in my HRO-60 receiver. My question is about the mica cap that is across the transformer from pin 4 to pin 2. The manual calls it a filter cap, but from the way it looks and from what I read if this cap shorts out, the transformer can go with it. So, my question is, can I replace the .0022 mica with a .01 cap of the same voltage rating and connect it from pin 4 to ground, I realize pin 2 is ground, but I'd rather put it to the chassis, so if something happens it wont short across the windings of the transformer, or am I missing something easy here?   Thanks in advance.

[WQ9E]

Ray,

That cap is not necessary and is of value only to sellers of replacement transformers.  Just remove it and don't replace it.  That is the reason a number of HRO-60's and other similar vintage Nationals are running with replacement transformers.

Rodger WQ9E

[WV9R]

Hi Rodger,
       Thats what I was thinking too ...I just dont trust myself yet ...hihi   Thanks  once again.

[Jim, W5JO]

Hi Ray,

Pin 4 to Pin 2 of what?  Are you referring to the transformer or the rectifier socket?  On the schematic there is a .1 from pin 4 of the rectifier socket to ground not pin 2.  Pin 2 is the filament of the rectifier and the pick off point for HV, so I wonder what the deal is?

What does the capacitor look like?  Is it a round tublar cap like others in there or is is a square  cap about the size of a postage stamp?  If it is the square thing it will have 6 dots on it.  These can be mica or paper and denoted by the first dot on the line where the arrow is located.  I can't remember just off hand but think a white dot indicates paper and another color is mica reading from left to right  in the direction of the arrow.

If you have a mica from pin 2 to pin 4 of the rectifier tube, look for other modifications or deviations from the standard diagram.  I have one purchased by a telephone company and there are significant differences.  Fortunately I have the manual supplied and have been able to identify the mods and revese them.

[WV9R]

Hi ..the cap I am referring to is C-63 on the schematic. It shows on the print from neutral to ground. In the pic in the manual you can see what I'm referring to. The cap is across the primary and the secondary of the transformer. I was going to try and include that page of the manula but I have not had any luck.   

[KM1H]

The cap was designed there for a purpose which was to keep any noise spikes from getting into the B+ . You can remove or replace with something that will outlive you and your grandkids. There are actually 2 in that circuit, C-63 and 64

Go to Mouser and get a pair of .0047 AC Safety caps.

Carl
KM1H
National Radio 1963-69

[WQ9E]

OK Ray,

That is a line bypass cap and the replacement should be a modern one rated for this (AC) service.  They are available from Mouser and Digikey.  The one on the "hot" side of the line should be mounted on the device side of the fuse to offer additional protection in case of short.

The cap I originally referred to (which I mistakenly thought was your first question) is C-118.  Remove this cap if you have not done so already.

Rodger WQ9E

[Jim, W5JO]

Those are mica types and under controlled circumstances will probably outlast us all, but since you are not sure of the lineage of the receiver, do as Carl suggested and buy replacements.  If they short it should take out the circuit breaker or fuse so nothing "should go wrong.  Just to be safe use modern caps there.

[KM1H]

The mica cap which was once thought to last forever is failing rapidly these days. Those of us who service these old sets on a regular basis are finding more and more micas with high leakage, intermittents (crackling and static sounds) and even open circuits. It is almost 100% related to circuits with a voltage involved.

And then there is SMD, Silver Mica Disease, in IF cans that use silvered mica on ceramic substrates in place of a real mica cap. This process started in 1951. Some of those can be fun to replace

Carl
KM1H

[Gito]

Hi


I believed that C 63 and C64  is used as an line filter  it also  bypass for RF feedback  ,that is(RF) induced into the electric power  line by RF from your  Antenna,So Changed/replaced it with a high voltage  C ,for safety.

When Rf gets back into your Transmitter ,it caused the audio section not working as it should be,it also can caused hum.

Gito

[N3DRB The Derb]

if you are going through the radio anyway, just use suitably rated and typed modern caps everywhere.

[Gito]

hi

In my opinion the voltage rating of Caps is very important ,yes now we can have modern caps ,which is usually small sized compared to old caps ,but with higher voltage ratings.
At least to me ,when we  need for instant 0.01 ufd 450 v,and there's a 0.01  1 kv   caps with the "same" Size.I choose to use the 0.01   1kv caps.Since Caps broke when its voltage rating is passed.Naturally The higher voltage rating Caps is more reliable .

A 200 ufd 450 Cap today is one half to one third  the size of the old  200 ufd cap .

Gito