RE:Slightly off top amp question (David Douglass)

[Vk2NU]

Firstly thanks to all who replied to my original post, if I didn't reply
personally..

On closer inspection I have so far found 2 ceramic door knob capacitors that
were falling apart !! These were not in the input coil alignment section,
but near the valves and band-switch in the amp.

For you RF guru's out there... I have a couple of questions..

1. Is it possible to solder these capacitors back together ? They are the
flatter type doorknob caps and basically what has happened with both of them
is that the one of the screw housings has fallen off the side of each cap
(hope this makes sense).

2. Secondly, if this is not advisable, can I just replace these with the
standard type (barrel shaped) door knob caps, as long as the KV rating is
greater or equal to that of the originals ?? Surplus sales have these for
under $20US each

Again apologies for the off topic post

Regards from a chilly Sydney..

David, Vk2NU

>Date: Tue, 27 Jun 2006 23:11:36 +1000
>From: "David Douglass" <[hidden email]>
>Subject: [Elecraft] Slightly off top amp question
>To: <[hidden email]>
>Message-ID:
        <20060627131135.KVTZ9971.omta01ps.mx.bigpond.com@customers8ycis>
>Content-Type: text/plain; charset="us-ascii"

>Apologies in advance for the off topic question!

>I've just bought an old FL-2100B amp to do up, and run with my K2 (I have
>the bits and pieces on order for the external keying
circuit!!).................


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[Vic K2VCO]

David Douglass wrote:

> On closer inspection I have so far found 2 ceramic door knob capacitors that
> were falling apart !! These were not in the input coil alignment section,
> but near the valves and band-switch in the amp.

These are probably padders to supply more capacity to either the tune or
load capacitors on 80 and 160 meters.  If they are broken, it might be
hard to resonate the output circuit on these bands which would cause
problems with input SWR and of course power output.

> For you RF guru's out there... I have a couple of questions..

> 1. Is it possible to solder these capacitors back together ? They are the
> flatter type doorknob caps and basically what has happened with both of them
> is that the one of the screw housings has fallen off the side of each cap
> (hope this makes sense).

I don't know, but I would certainly try, with silver-bearing solder!
Look carefully to see if the units are not otherwise damaged.

> 2. Secondly, if this is not advisable, can I just replace these with the
> standard type (barrel shaped) door knob caps, as long as the KV rating is
> greater or equal to that of the originals ?? Surplus sales have these for
> under $20US each

Probably yes.  There is both a current and a voltage issue, but in this
application the 5 KV types should be OK.  $20 seems steep, however.  Try
this guy: <http://www.mgs4u.com/RF-Microwave/doorknob-capacitors.htm>
He is honest and has reasonable prices.  Also you might check Fair Radio
Sales <http://fairradio.com/>, who are cheaper than the so-called
'surplus bandits'.
--
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco
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[peter gerba]

Did they have a resistor between them or at one side of a large RF Choke?

pete

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]]On Behalf Of Vic K2VCO
Sent: Wednesday, June 28, 2006 8:15 AM
To: David Douglass; Elecraft Reflector
Subject: Re: [Elecraft] RE:Slightly off top amp question (David
Douglass)


David Douglass wrote:

> On closer inspection I have so far found 2 ceramic door knob capacitors
that
> were falling apart !! These were not in the input coil alignment section,
> but near the valves and band-switch in the amp.

These are probably padders to supply more capacity to either the tune or
load capacitors on 80 and 160 meters.  If they are broken, it might be
hard to resonate the output circuit on these bands which would cause
problems with input SWR and of course power output.

> For you RF guru's out there... I have a couple of questions..

> 1. Is it possible to solder these capacitors back together ? They are the
> flatter type doorknob caps and basically what has happened with both of
them
> is that the one of the screw housings has fallen off the side of each cap
> (hope this makes sense).

I don't know, but I would certainly try, with silver-bearing solder!
Look carefully to see if the units are not otherwise damaged.

> 2. Secondly, if this is not advisable, can I just replace these with the
> standard type (barrel shaped) door knob caps, as long as the KV rating is
> greater or equal to that of the originals ?? Surplus sales have these for
> under $20US each

Probably yes.  There is both a current and a voltage issue, but in this
application the 5 KV types should be OK.  $20 seems steep, however.  Try
this guy: <http://www.mgs4u.com/RF-Microwave/doorknob-capacitors.htm>
He is honest and has reasonable prices.  Also you might check Fair Radio
Sales <http://fairradio.com/>, who are cheaper than the so-called
'surplus bandits'.
--
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco
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