Line cord Re: [Hammarlund] HQ-129

[Roy Morgan]

At 09:00 AM 2/6/2007, RJ Mattson wrote:
>Dave,
>I just completed a HQ-129x restoration and installed a 3 conductor line
>cord. ... I removed the old leaky line paper caps and put one 0.05 mfd 1 
>KV ceramic on the hot conductor (protected by the switch and fuse) to chassis.

Best to put one cap from line to neutral and one from neutral to 
chassis.  Safer.

>I looked through my collection of 0.05's caps but could not find any marked
>Vac.

Some caps are rated for line bypass application.  I quote part of my 
diatribe on line cords and bypassing:

>RF Bypass caps should be installed as follows:
>
>One from Line to Neutral, after the fuse.
>One from neutral to chassis.
>
>When our boatanchor equipment was made, it was common to use both a 
>two-wire, ungrounded line cord and two bypass caps, one from each side of 
>the line to the chassis.  DO NOT re-create this situation when you install 
>the three wire grounded line cord.  This causes a danger of fire should 
>the line to chassis cap short but not draw enough current to blow the 
>circuit breaker, and this arrangement also causes the chassis to be at 
>half the line voltage if the safety ground is not present (such as in a 
>two-wire outlet used with an adapter, or in an outlet improperly wired or 
>faulty.)
>
>There are currently available "Safety" capacitors meant for line bypass 
>applications. You can tell them from normal caps in the catalogs because 
>they cost about 5 times as much as normal caps.  If you take apart 
>computer power supplies or junk TV sets, you will wind up with one or two 
>from each unit.
>
>A reasonable review and discussion of caps used in older radios and line 
>bypassing is at:
>http://www.justradios.com/safetytips.html
>"ABC's of SAFETY Capacitors for Tube Radios"
>That web page does not, however, discuss the method of installation.  The 
>authors are in Canada and offer a number of services for old radios, 
>including technical information, and capacitors.
>
>April, '05:  Caps suitable for line bypassing can be had at Mouser and 
>other large parts suppliers.  Also the company with the "ABC's" article 
>has both the caps and additional information about them:
>http://www.justradios.com/capacitors.html

(Complete diatribe emailed to anyone who asks for it.)

Roy

- Roy Morgan, K1LKY since 1959 - Keep 'em Glowing
13033 Downey Mill Road, Lovettsville, VA 20180
Phone 540-822-5911   Cell 301-928-7794
Work: Voice: 301-975-3254,  Fax: 301-975-6097
roy.morgan at nist.gov --