[R-390] R390 RF Cap Confessions

[Cecil]

Yep...I agree.

The trick is what are better values for those since we are now replacing them during our restoration.

Cecil

Sent from my iPad

> On Nov 30, 2014, at 4:31 PM, Roger Ruszkowski <flowertime01 at wmconnect.com> wrote:
> 
> 
> 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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