Ceramic/foil

Philips Ag9015 used Philips Mustards, built in the 50-60’s. These are the best capacitors I ever heard. Smooth, bright sound, if you like such. Same valid for the dogbone types. Measured vales like a charm. Is not a soft cap, so microphony is also nice.

Please do not replace these as these do not degragade with the time. If you need to replace due to any reason (gets noisy because of heat stress while replacing some carbon resistors) or build up a new RIAA for this amp buy used or NOS.

They were built as Philips, Mullard, Bianchi, Miniwatt.

They were so good, that TAD started to build replica of the authentic foil-to-foil construction of the vintage 60s Mullard / Philips capacitors. I think this says it all.

The later 70’s Philips caps were less good. They are known as “Tropical Fish.” Not recommended by me.

Performance of Mustard

Just compare it to an electrolytic or anything else. Fabolous and frequency idependent performance. I picked this randomly, but you can easily face at some caps Q above of 3000 at 1kHz. (measured at an 100pF dogbone type)

Capacity(100Hz)
(higher better) 		Capacity(1kHz)
(higher better) 		Capacity(10kHz)
(higher better) 		Capacity(100kHz)
(higher better) 		Rp(100Hz)
(lower better) 		Rp(1kHZ) (lower better) ESR (10kHZ) (lower better) ESR (100kHZ) (lower better) Q(100Hz) (higher better) Q(1kHz) (higher better) Q(10kHz) (higher better) Q(100kHz) (higher better) Theta (100Hz) (-90 is the ideal ) Theta (1kHz)
(-90 is the ideal ) 		Theta (10kHz)
(-90 is the ideal ) 		Theta (100kHz)
(-90 is the ideal )
Philips Mustard 10nF 160V 10,671nF10.637nF10.559nF10.388nF 147.5 MOhm4.5Mohm11.15Ohm1.93Ohm1323307114.578.7-90-89.7-89.5-89.2

Generic knowledge on capacitors

Q = 1/D = tanΘ

Q = Xs/Rs = 2πf Ls/Rs = ½πf CsRs

Q = B/G = Rp/|Xp| = Rp/2πf Lp = 2πf CpRp

D=tan( δ )

Theta is sometimes Phi, same

What is a perfect capacitor alike?

-Values do not change with frequency

-Theta is -90degree, so is a perfect capacitor

-Has no leakage current (measured on operating voltage!)

Does such cap exist? No. But you can select one which suits most for the given task. Preamp coupler caps need to block DC (while conduct AC link), so low ESR is key, while low microphony, frequency neutral behaviour is also important. Very good page in this topic: https://www.instructables.com/id/Measuring-Capacitor-Health-tan-%CE%B4-vs-ESR/