Eddy -
I 'think' you're barking up the wrong tree unless you have already replaced the two 45 pF cap. If
the frequency of the PTO shifts several kHz or tens of kHz, that small, (probably less than 10% of
the total resonating capacitance,) isn't likely to correct it.
By the way, many small ceramic trimmers are temperature compensated, usually coded by color. Many
ceramic compression trimmers you see are N750, so be careful what you use.
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line
and TR-4/C Service Supplement CDs
<www.k4oah.com>
Eddy Swynar wrote:
Hi Guys,
Well, to-day I plan to "snip" that white tubular capacitor out of my PTO,& see
what might happen...
I'll note the frequency on my receiver AND the PTO before doing this, as the frequency from
the PTO climbs some 100-KHz in the absence of its "can": I'll then, probably,
temporarily install a small air trimmer in place of the tubular cap,& play with the
settings until the frequency might return to where it originally was, in the interest of
linearity.
I can then sub the trimmer with a fixed s.m. capacitor, perhaps in parallel
with a small ceramic trimmer.
Stay tuned---and wish me luck!
~73~ de Eddy VE3CUI - VE3XZ
*************************************************************************************************************************
On 2011-09-22, at 3:36 PM, Garey Barrell wrote:
Yes, that is a 'trim' cap and should be less than 10 pF or so. It's not likely
to have much effect on the stability of the oscillator. More likely are the
caps on the 'other' side of the board, shown further down, the two brown
tubular caps to the left of the Diode D13 are 45 pF each. That's probably a
'C-Line' Version 7 PTO. Probably a result of either a better buy on two 45 pF
caps over a single 90 pF, or a mechanical rearrangement of the board layout.
Those two caps are the most critical as far as stability of the oscillator is
concerned.
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line
and TR-4/C Service Supplement CDs
<www.k4oah.com>
Eddy Swynar wrote:
Hi Guys,
For a look-see at the suspect tubular capacitor that I am referring to in my
T-4X PTO, go to this website:
http://www.wb4hfn.com/DRAKE/DrakeArticles/TechTips/PTO-Repair.htm
Scroll down half the page to where you see the heading "ELECTRICAL FAILURES": the
photograph with the arrowed inscription marked "solder point" is immediately left of the
white tubular capacitor that I am referring to...
~73~ de Eddy VE3CUI - VE3XZ
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