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Teflon capacitors

Posted by sser2 (A) on April 25, 2017 at 21:28:02

In Reply to: Let's start with mica capacitors posted by sser2 on April 25, 2017 at 16:19:03:

Older types

ФТ-1, ФТ-2, ФТ-3 (FT-1, FT-2, FT-3, Ftoroplast high Temperature). Same construction, but FT-1 have axial silver-plated wire leads; FT-2 and FT-3 have silver-plated brass tabs. Electrodes are aluminum foil, and insulation is either 2 layers (200 V) or 3 layers (600 V) of 20-micron film of Ftoroplast-4 (equivalent to DuPont Teflon). One layer of Ftoroplast is never used because it is impossible to produce film without spot irregularities. Capacitance range is 560-0.01 (FT-1), 0.027-0.047 (FT-2) and 0.01-0.68 (FT-3). Maximum temperature 200C. FT capacitors have considerable series inductance. Foils are connected to tabs or wires by thicker aluminum strips; these strips are riveted to tabs, but not welded or soldered to foils. For this reason, FT caps may not perform well at very low voltages, and, if used as coupling capacitors at low signal levels, need at least 10V of DC bias. FT capacitors are non-magnetic.

ФЧ (FCh) - Ftoroplast high frequency. Non-inductive winding, rated for RMS voltage at specified frequency, usually 5 or 10 kHz.

ФГТ-И (FGT-I) Ftoroplast Sealed in Tubular ceramic case, Impulse duty. These are high voltage (kilovolts) capacitors for pulse generators. High voltage rating is achieved by series connection of sections stacked inside the case, and filling the case with nitrogen pressurized at 6 atm. Large sizes preclude their tube DIY use, although there are claims that they are the best-sounding teflon caps.

Newer types

K72-8 Grounding capacitors. One of the leads is threaded for connecting to chassis. Aluminum body, non-magnetic, values in thousands of picofarads.

K72-9. I could not find any difference between this type and K72П-6, other than different manufacturing plants (K72-9 St. Petersburg, K72П-6 Novosibirsk).

K72-11 Kings of Russian teflon caps. Beer can size, steel case with axial screw terminals. The highest values are 4.7 uF 125 V and 2.2 uF 250 V. Some are rated for high frequency, and those may have the lowest tgδ (<0.0008 vs. 0.0015 of regular teflon capacitors).

K72П-3 (K72P-3) Feed-through capacitors designed for filtering off high frequencies. Due to their construction, have virtual zero series inductance and can pass frequencies in the gigahertz range. Body, which serves as grounding electrode, is bolted to the chassis.

K72П-6 (K72P-6) Similar to FT, but have tightly sealed steel body with glass insulators, and silver-plated steel connection pins. Internal leads are 999.9 silver, a capacitor may contain up to 0.45 grams of it.

Foils of all K72 capacitors are welded to leads, so there are no restrictions on minimum voltage.

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