From amargosaent at iscweb.com  Tue Jan 29 17:05:35 2008
From: amargosaent at iscweb.com (amargosaent@iscweb.com)
Date: Tue Jan 29 17:03:45 2008
Subject: [HBR] Negative temp compensation capacitors
Message-ID: <479FA32F.8070407@iscweb.com>

Has anyone on the reflector identified a source for negative temp 
coefficient capacitors in the N750 range available in small capacitance 
ranges (e.g., 1 pfd through 20 pfd in 1  and 2 pfd steps)?  I am aware 
of one US  manufacturer (Presidio Products) making a wide range of those 
components, but apparently only through contract with defense and 
aerospace manufacturers, nothing available (according to their local 
rep) through distributors or mail-order houses (Newark et al).

These caps are used in the HBR 11/13 Hartley oscillator design to 
stabilize frequency drift caused by temperature rise on start-up.

73 de W6HHT  
 
From hbrnut at suddenlink.net  Tue Jan 29 19:42:08 2008
From: hbrnut at suddenlink.net (WA5VGO)
Date: Tue Jan 29 19:45:20 2008
Subject: [HBR] Negative temp compensation capacitors
In-Reply-To: <479FA32F.8070407@iscweb.com>
Message-ID: <5.2.0.9.2.20080129183815.00bf7ac8@pop.suddenlink.net>


>Has anyone on the reflector identified a source for negative temp 
>coefficient capacitors in the N750 range available in small capacitance 
>ranges (e.g., 1 pfd through 20 pfd in 1  and 2 pfd steps)?

Surplus Sales Of Nebraska had a pretty good selection at surprisingly 
decent prices a few years ago. You might want to check them out.

http://www.surplussales.com/


73,
Darrell, WA5VGO



From N2EY at aol.com  Wed Jan 30 07:37:44 2008
From: N2EY at aol.com (N2EY@aol.com)
Date: Wed Jan 30 07:41:02 2008
Subject: [HBR] Negative temp compensation capacitors
Message-ID: <c5b.25914c5e.34d1c998@aol.com>

In a message dated 1/29/08 5:00:57 PM Eastern Standard Time, 
amargosaent@iscweb.com writes:


> Has anyone on the reflector identified a source for negative temp 
> coefficient capacitors in the N750 range available in small capacitance 
> ranges (e.g., 1 pfd through 20 pfd in 1  and 2 pfd steps)? 

Not really, but I do know a trick, learned from master receiver builder W2LYH 
and others.

I presume the temp comp is for an oscillator. 

The trick is to first get the oscillator working without temperature 
compensation, and see that it drifts downward in frequency with increasing 
temperature, which would mean it needs negative temperature compensating capacitance.

Then add "too much" negative temperature compensating capacitance so that it 
drifts the wrong way.

The trick is that an air trimmer cap is then installed in series with the 
temperature compensating capacitor so that the amount of compensation can be 
adjusted. Of course a fixed NPO capacitor can be substituted once the exact value 
is known, but that's an extra step which requires a wide selection of NPOs.

73 de Jim, N2EY


**************
Start the year off right.  Easy ways to stay in 
shape.
     
http://body.aol.com/fitness/winter-exercise?NCID=aolcmp00300000002489
From tshoppa at wmata.com  Thu Jan 31 09:16:39 2008
From: tshoppa at wmata.com (Tim  Shoppa)
Date: Thu Jan 31 09:20:31 2008
Subject: [HBR] Negative temp compensation capacitors
In-Reply-To: <479FA32F.8070407@iscweb.com>
References: <479FA32F.8070407@iscweb.com>
Message-ID: <47A191F7020000370001F8BA@gwiavs.nservices.wmata.com>

W6HHT asks:

> Has anyone on the reflector identified a source for negative temp 
> coefficient capacitors in the N750 range available in small capacitance 
> ranges (e.g., 1 pfd through 20 pfd in 1  and 2 pfd steps)?  I am aware 
> of one US  manufacturer (Presidio Products) making a wide range of those 
> components, but apparently only through contract with defense and 
> aerospace manufacturers, nothing available (according to their local 
> rep) through distributors or mail-order houses (Newark et al).

> These caps are used in the HBR 11/13 Hartley oscillator design to 
> stabilize frequency drift caused by temperature rise on start-up.

I just went to www.newark.com and searched for "n750" and
they seem to have some Vishay, Dale, Sprague, etc. N750
ceramic disk parts in stock in the 10pF -low hundred pF range.

Put a couple of these in series and you can synthesize any
value you want from low pF on up. I know, it's not as
nice having every pF value from 10 to 20 in a drawer.

Try widening your search so you don't just get Presidio.

Also, Digikey lists AVX and BC N750 parts in their database
as special order, when I've ordered similar parts in the past
it took "only" a few weeks to get them.

Allied lists some nominal-N750 tempco ceramic trimmers from AVX
and Murata which are not the perfectly traditional way of doing this
but are used for tempco trimming in more modern equipment.

Tim.

