Quad ESL Cap mods

William, I have no experience with Mundorf Tube caps, because Tube caps are designed for high voltage tube gear power supplies, not coupling.

Regarding Face's Mundorf cap, it is a great choice if the original cap is rated for 250 Volts or less, however, I maintain my recommendation to bypass any large film caps with a Mundorf 4.7 uF silver / oil. This will provide speed and transparency in the treble range, which large film caps tend to lose due to high internal inductance (side efects of the soda can size).
224.7 uF as compared to 220 uF means that your speakers bass response will extend a couple of Hertz down, not really a factor given the usual 5% tolerance of large film caps and any resistors used within the speakers.
Good luck

I have been researching the same options for replacing the electrolytics in my Quad 2905s. FYI the 220uF cap is in series with the input and it does have a 1.5 ohm resistor in parallel with it (which could also use an upgrade to a Mills or something similar). I have read several of the capacitor comparisons including some comments specific to Quad 2905s over on the Audiocircle website. My observation is that for very little extra cost you can get 2-100uF Mundorf MKP 400V. And for a little more again you could get 4-47uF of the same 400V MKPs. With the 2905s any shift toward a heavier balance is not what I want. So with four caps instead of one I have the flexibility to try various values and see if the increased resolution and speed(expected from smaller values with higher voltage ratings) are what I like better. My big decision is whether to spend more on Auricaps which I understand have a slightly nicer midrange and apparently are a step up from the Mundorf MKPs. Their premium price at two to three times the Mundorfs would certainly indicate this. I would definitely appreciate comments from anyone who has compared these two. Another big plus with the Mundorfs is the availabilty of a nice selection of blend/bypass capacitors such as the Supremes or the Silver/oils as someone pointed out. I think its likely combining MKPs with their premium capacitor lines would really improve the sound. I'm not sure if the Auricaps sound would improve being bypassed for extra performance. From reading the Auricap datasheet, its actually discouraged. I would like to know if anyone has had good results doing this also.

I spoke to a moodder and he says F & T MPP caps with a Harmony cap bipass are the best way to go for the price. He feels the F & T MPP caps give a better result than the Mundorf MKP.

He sais the only appropriate cap for this (Quad esl) application is MPP type (Metallised Polypropylene) and of course they have to be of adequate voltage -- because of this, suitable candidates are limited and pricey...

Any comments?

Any experience or comparison of F & T MPP caps?

thanks,
William

The Mundorf is rated at 250V, which should be more than enough.

HI
I have Auricaps and Mundorf PP caps in my tube amps (not the same application, I know). I prefer Mundorf Supreme to Auricaps IMS.
Mundorf caps are metalized polypropilene.
Munforf silver and oil is a significant step forward in transparency as compared to M. Supreme or M. tube cao, but it is only economically feasible as a bypass cap.
Many high-end speaker manufacturers are switching to Mundorf caps for their top model's crossovers: BW 800D, Magico, ZU Definition and some others I forget.
Any cap smaller than 220uF will attenuate deep bass response.

Regarding the paraleel resistor, find out its value and power rating (usually written in the transistor body).
Mills MR12 is widely well regarded as a neutral, non inductive resistor up to 12 Watts per resistor. You can use several in paralell to reach the correct ohmic value and power handling. E. G. ten 80 ohms 12W resistors in paralell will add up to 8 ohms and 120 watts.
Dale makes aluminum-clad non-inductive resistors in 20W and 50W ratings.
DO NOT install the resistor flush with the cap(s), because it will get very hot on music peaks and may damage the caps.
Any PP or MKP cap will certainly sound much better than an electrolytic cap, but if you can avoid the cheapest ones, it will be a wise investment, given the Quad ESL's transparency and midrange naturalness.
Good luck

I hope this helps