10309	2014-09-27 10:12:43	peter_dl8ov	T2 Phasing Network capacitors
Message	Date	From	Subject
In the T2 schematic all of the capacitors in the phasing network are 0.001 uF apart from C23 wich is shown as 0.0027uF, is this correct? Peter DL8OV
10320	2014-09-28 16:26:42	iq_rx	Re: T2 Phasing Network capacitors
That is correct for the original T2 as published in QST more than 20 years ago. In later designs, as in EMRFD, all of the capacitors in the phasing network are 0.010uF. Best Regards, Rick KK7B
10321	2014-09-29 10:47:36	peter_dl8ov	Re: T2 Phasing Network capacitors
OK, thank you Rick. It looked unusual to see one capacitor in the set with an odd value so I thought I should ask. My next job is matching capacitors for both an R2Pro and a T2. 73 Peter DL8OV
10322	2014-10-01 18:15:36	radioaustralia123	Question about a potentiometer...with a tap....
Hi, I have a number ( a few hundred) of potentiometers that have a tap position. It is marked C 500k. The tap point is around 36K from one end (a) and 481k from the other end (b). My understanding is that on some old NOS potentiometers the “C” indicated logarithmic. The variable resistance slider at the 50% position is round 57K from end (a) and around 463k from end (b). It is not linear. Question: any idea for what application such a potentiometer would be used for? Thanks, Regards, Roderick Wall, vk3yc.
10323	2014-10-01 18:18:07	Jim Miller	Re: Question about a potentiometer...with a tap....
audio volume control jim ab3cv
10324	2014-10-01 18:21:47	radioaustralia123	Re: [emrfd] Question about a potentiometer...with a tap....
Ok on logarithmic being for a volume control. But what would the tap position be used for? Roderick.
10325	2014-10-01 18:27:25	Mike	Re: Question about a potentiometer...with a tap....
From your observation that at 50% rotation you have about 57K from one end and 463K to the other end, I believe your suspicion that it is logarithmic (or audio taper) is valid. (Although I'm unsure as to whether log taper is generally the same as audio taper- can someone comment?) On some audio (mono, or stereo) amplifiers the audio gain ("volume") control was provided with a tap at about mid-rotation; this tap allowed for connection of a capacitor that would alter the frequency response (in many cases, to boost the base frequencies at low volume level, but allow for "flatter" frequency response at higher volume). So maybe this is what you've got. Mike N4MWP
10326	2014-10-01 18:33:55	radioaustralia123	Re: [emrfd] Question about a potentiometer...with a tap....
Thanks Mike for your response. I should have also indicated that the tap physical position is not at the 50% position between the two ends. It is closer to end (a). OK
10327	2014-10-02 02:09:12	radioaustralia123	Re: [emrfd] Question about a potentiometer...with a tap....
Hi all, Jon sent a personal email indicating that the tap could be for what is called a “Loudness control” as shown at the bottom of this link. http://www.angelfire.com/electronic/funwithtubes/Amp-Volume.html J
10328	2014-10-02 12:15:36	Ephemeral	Small SMD trimmer capacitors with moderate temperature coefficients?
It seems that all the available small SMD trimmers in the 25pF range have ceramic dielectrics with temperature coefficients of the order of 1000 ppm.. Now I am concerned that my circuit may go off tune at temperatures outside the domestic range. Does anyone know a source of reliable and affordable trimmers with reasonable temperature coefficients? Thanks. Adrian, England.
10329	2014-10-02 13:48:32	David	Re: Small SMD trimmer capacitors with moderate temperature coefficie
I would look for a piston trimmer but while some are available in surface mount packages, they may still be too large. On Thu, 2 Oct 2014 20:16:41 +0100, you wrote: >It seems that all the available small SMD trimmers in the 25pF range have ceramic dielectrics >with temperature coefficients of the order of 1000 ppm.. Now I am concerned that my circuit >may go off tune at temperatures outside the domestic range. Does anyone know a source of >reliable and affordable trimmers with reasonable temperature coefficients? > >Thanks. Adrian, England.
10330	2014-10-02 13:58:25	Harold Smith	Re: Small SMD trimmer capacitors with moderate temperature coefficie
Generally the better tempco trimmers are smaller values. The dielectric constant of the more temp stable ceramics is smaller, so gives less capacitance per unit area. If you need NP0 or C0G trimmers, you'll usually have to settle for max C of no more than a few pF. de KE6TI, Harold