[R-390] R390 RF Cap Confessions

[Roger Ruszkowski]

Cecil,
 
Consider also the assembly process.
You could set a new person down at a station and start them off.
You get an assembly that looks like this.
You need to install N of these one type parts.
Your finished assembly needs to look like this.
 
Do not send you two reference assemblies down the line.
 
Once there solder skills and speed get up to par, you could move them over
a station and let them do other parts.

You betcha, logistics trumps design every time.
I see what you want but this is what you are going to get from what is standard stock.
Only after our common value substitutes do not work will we go back to your original value.
Old designers will just call for stock values and wait for the prototype to be tested.
If some thing needs to be adjusted from a stock value then they can claim hay a stock value 
did not work in the prototype. 

Roger Ruszkowski AI4NI
 
 
-----Original Message-----
From: Cecil <chacuff at cableone.net>
To: Roger Ruszkowski <flowertime01 at wmconnect.com>
Cc: r-390 <r-390 at mailman.qth.net>
Sent: Sun, Nov 30, 2014 5:08 pm
Subject: Re: [R-390] R390 RF Cap Confessions


I suspect that's why every ceramic bypass and coupling cap in the SP-600 is the 
same exact value...not a design spec but supply chain efficiency.

Cecil

Sent from my iPad

> On Nov 30, 2014, at 3:48 PM, Roger Ruszkowski <flowertime01 at wmconnect.com> 
wrote:
> 
> 
> Fellows,
> 
> Not only have I been replacing the black or brown plastic tubular paper 
coupling and bypass caps
> referred to as black beauties, but some times I have installed new caps of 
different values.
> 
> Many of the caps were selected as from a preferred parts list of items in the 
supply chain
> and selected to maximize common values for procurement discounts  and simplify 
construction.
> 
> I have been using 0.001 UF for the 5000 PF by pass caps. 
> I use a 0.02 or 0.022 UF for C553 the blocking cap on the 1st IF stage.
> 
> I use 600 volt caps.
> I do not know why but I find the 600 volt caps have a better signal to noise 
ratio when I am done.
> Maybe its just the luck of the caps I was comparing back when, but the few 
times I have had
> a chance to install a 200 or 400 volt cap and then replace it with a 600 volt 
cap, the higher the
> voltage the better the signal noise ratio was. 
> 
> The difference is not dramatic use the lower voltage if its what you have.
> Use the original value if you feel the need.
> 
> But if you need to buy a dozen go for over 400 volt to 600 volt and bump the 
value up.
> I use a factor of 20 on the by pass filter caps and a factor of 2 for the 
inline signal passing DC blocking caps.
> I think on the inline blocking caps the higher voltage yields less popping so 
the meter needle has less jitter.
> You do get some stage gain so you need to be careful. You can get 
oscillations. You do let more noise pass 
> with the signal so consider if the extra noise is raising the noise floor or 
if you are working in a stage
> where the extra noise is still masked by other stages.
> 
> You get to back the IF gain down after you increase some inline values  
> 
> All subjective, as a sample of a few is not a significant statically 
meaningful value.
> 
> I can not say that my final signal to noise ratio has improved because I just 
replaced 
> a bunch of old poor caps or because I replaced a bunch of old caps with more 
filtering or both.
> 
> Exact before and after measurements of each cap was not done.
> And the few IF decks I have done is not meaningful as statistics.
> 
> The decks would not do 27 to 1 when I started and changing tubes
> did not get me to the signal to noise ratio. But after doing a change
> off all the usual suspects, I have been able to get every IF deck up to 27 to 
1
> and the receiver up to a good solid 20 to 1 from end to end on any and every 
frequency.
> 
> Roger Ruszkowski AI4NI
> 
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