[TenTec] proper caps for Omni V?

[Steve Berg]

Would I be better off replacing the electrolytics with tantalum 
capacitors?  I would rather just do this once since I no longer have 
access to lab grade desoldering equipment.

Thanks,

Steve WA9JML

Dr. Gerald N. Johnson wrote:
> On Wed, 2008-02-20 at 01:21 -0500, Joe Roberts wrote:
>> Look for 105 deg C, Low ESR, High Frequency caps. Find caps designed for 
>> bypass and decoupling in digital circuits--switching power 
>> supplies,logic boards, and the like.
> 
> That's the right list of specifications. If the capacitors are recently
> made they should be far better than the 5 cent ones often used
> originally ever were. Miniature electrolytics age like power supply
> filter capacitors and always get poorer with age. Tantalums tend to
> always have better performance, but cost a whole lot more and when I
> used tantalums in a tube radio once their high frequency performance was
> so good I introduced VHF parasitic oscillations in the audio output
> stage.
> 
> The recommendation for replacing old miniature electrolytics can be
> applied to all solid state equipment in the house. If done correctly
> (good capacitors, good soldering, correct polarity every time)
> everything should perform better.
>> Check the Mouser catalog--I think they are currently listing some 
>> Chemicon brand parts of this nature. I also used a bunch of Nichicon 
>> Type PL which is a now obsolete series with decent specs.
> 
> I like to deal with Mouser but sometimes I wonder about them. They
> promise a new catalog four times a year and in each new catalog there
> are a bunch of new lines, and many quality lines missing. Did they buy
> surplus, inventory it and then not get any more, or did they not meet
> sales goals (themselves or the vendor) and so got dropped? Often
> searching their web site (not as fast as looking through the catalog for
> me) will turn up parts in stock that are no longer in the catalog.
>> Many manufacturers provide "motherboard" grade caps--Rubycon MCZ, Sanyo 
>> Oscon...best place to find these is ebay surplus. Search "motherboard 
>> cap" You won't find these in all required values but for some of the 
>> higher C decoupling caps, like at the input to the logic board, these 
>> would be great to use.
> 
> I'm no fan of surplus electrolytics. There's no way to control their age
> and often the date coding is very cryptic. I've bought NEW miniature
> electrolytics at a local distributor and rejected them when I tested
> them with my capacitor bridge and found poor power factor. Most bridges
> though don't test for power factor under 50 or 100 mf, I had to modify
> mine to do that.
>> There is often some leeway in cap value but this needs to be determined 
>> on a case by case basis. Obviously, QSK and AVC time constant caps, for 
>> example, must be the same value as the original (unless you want to 
>> change the time constants--not a bad idea for SSB AVC).
> 
> The capacity tolerance on electrolytics is large, I see none better than
> +/- 20% and some are -10% +75%.
>> While you are working on the IF/AF board, do the LOGIC BOARD and the 
>> DISPLAY DRIVER board. In fact I'd do those first. The reduction in 
>> internal noise when you redo these boards with good fresh modern caps is 
>> remarkable.
>>
>> These are a few electrolytics behind the heatsink...make sure you 
>> replace those also using good 105 deg C parts.
>>
>> A few other Omni V owners on the list have done this rebuild and all 
>> report fantastic results. With modern caps, you can make that radio 
>> better than new. Except for the recently discussed shortcomings in 
>> computer interface, I'd put the rebuilt Omni V on the table next to 
>> anything.
>>
>> Joe N5KAT
>>
>>
> 73, Jerry, K0CQ
> 
> _______________________________________________
> TenTec mailing list
> TenTec at contesting.com
> http://lists.contesting.com/mailman/listinfo/tentec
> 
> 
>