Comments on: Lost to time: Check out the Fairchild 627 Equalizer circa 195nvr https://www.preservationsound.com/if-you-thought-the-fairchild-660670-was-rare-check-out-the-627-equalizer-circa-195nvr/ information and ideas about audio history Wed, 06 Apr 2022 18:19:19 +0000 hourly 1 https://wordpress.org/?v=6.9.4 By: chris https://www.preservationsound.com/if-you-thought-the-fairchild-660670-was-rare-check-out-the-627-equalizer-circa-195nvr/#comment-620739 Wed, 06 Apr 2022 18:19:19 +0000 http://www.preservationsound.com/?p=8602#comment-620739 In reply to DaveP.

Please keep us informed of your progress!

]]> By: DaveP https://www.preservationsound.com/if-you-thought-the-fairchild-660670-was-rare-check-out-the-627-equalizer-circa-195nvr/#comment-620728 Wed, 06 Apr 2022 14:26:16 +0000 http://www.preservationsound.com/?p=8602#comment-620728 I have been asked to make one of these and it will appear on Groupdiy under “627 from scratch” later this year (2022). The last post got the pots right 10k/5k and 50k/25k, the other resistors have to be a quarter of these values to get the range specified. I managed to work out a way of using ordinary pots with gear wheels connecting the three pots together. The 6E5 has limits of 125/250V but I think the optimum HT is around 230/240 V. The cathode follower draws 10mA at this voltage. The 6SG7 is a variable impedance with its cathode voltage set by the HT divider R47 and the 25k Pot, it loses the top end through the C7. What concerns me is the setting up procedure, there are lots of parts marked “select”. I guess this is to get the response curves shown above.

]]> By: Michael Callahan https://www.preservationsound.com/if-you-thought-the-fairchild-660670-was-rare-check-out-the-627-equalizer-circa-195nvr/#comment-590617 Mon, 02 Sep 2019 23:05:21 +0000 http://www.preservationsound.com/?p=8602#comment-590617 Hi

Quick calculation using f = 1 / 6.28 x R x C shows R21a and R21c to be somewhere around 10K for the hf EQ. R21b is half of that so 5K. For the low end EQ R22a and R22c around 50K and R22b 25K. As I recall, Fairchild was a major manufacturer of precision pots, so odd ball assemblies would not have been an issue for them…
Mea culpa: this is of course a Twin Tee circuit, not a bridged tee as I stated earlier.

]]> By: Michael Callahan https://www.preservationsound.com/if-you-thought-the-fairchild-660670-was-rare-check-out-the-627-equalizer-circa-195nvr/#comment-590272 Fri, 30 Aug 2019 00:15:41 +0000 http://www.preservationsound.com/?p=8602#comment-590272 HI

On the three section pot R21a R21b R21c, R21b should be one-half of the other two sections. Also note that C15 is twice the value of C13 and C14. These correspond to the ratios of the classic Bridged Tee circuit. 100k for R21a and R21c, with 50k for R21b might be an interesting place to start

]]> By: ZEZ https://www.preservationsound.com/if-you-thought-the-fairchild-660670-was-rare-check-out-the-627-equalizer-circa-195nvr/#comment-584438 Sun, 30 Jun 2019 19:20:21 +0000 http://www.preservationsound.com/?p=8602#comment-584438 In reply to Zhiguang E Zhang.

Please ignore this comment, I made a correction below:

]]> By: Zhiguang E Zhang https://www.preservationsound.com/if-you-thought-the-fairchild-660670-was-rare-check-out-the-627-equalizer-circa-195nvr/#comment-584401 Sun, 30 Jun 2019 05:54:09 +0000 http://www.preservationsound.com/?p=8602#comment-584401 The T2 transformer is wired as such because for this EQ, the frequency cuts are low and high rolloffs and not ‘band-reject’ -style attenuation cuts.

]]> By: Zhiguang E Zhang https://www.preservationsound.com/if-you-thought-the-fairchild-660670-was-rare-check-out-the-627-equalizer-circa-195nvr/#comment-584400 Sun, 30 Jun 2019 05:46:25 +0000 http://www.preservationsound.com/?p=8602#comment-584400 Regarding T2, the transformer is wired as such because the high and low rolls are not frequency cuts (look at any modern EQ), merely ‘Q’ width adjustments.

]]> By: DIY AML Fairchild Tube Equalizer and its Magic Eye magic – maxpro.audio https://www.preservationsound.com/if-you-thought-the-fairchild-660670-was-rare-check-out-the-627-equalizer-circa-195nvr/#comment-554508 Wed, 21 Nov 2018 17:29:01 +0000 http://www.preservationsound.com/?p=8602#comment-554508 […] Most of the information on the Fairchild 627 Equalizer I could find online, comes from this link: https://www.preservationsound.com/?p=8602 […]

]]> By: Steve Calver https://www.preservationsound.com/if-you-thought-the-fairchild-660670-was-rare-check-out-the-627-equalizer-circa-195nvr/#comment-416723 Wed, 28 Jun 2017 11:11:25 +0000 http://www.preservationsound.com/?p=8602#comment-416723 I was looking through American Broadcast History website in the Electronics magazine section under Annual buyers guide and came across an Advert from 1951 by Fairchild, it is on Page 246, this might shed some light on the 3 gang potentiometer, I suspect it is Type 746 which is linear type with a value of 100K.

Here is the link: http://www.americanradiohistory.com/Archive-Electronics/Buyer-Guide/Electronics-Buyers-Guide-1951-06.pdf

You will find the original article on the equaliser in Audio Engineering 1951 on the same site. Hope that helps!!!

]]> By: Steve https://www.preservationsound.com/if-you-thought-the-fairchild-660670-was-rare-check-out-the-627-equalizer-circa-195nvr/#comment-387060 Sat, 21 Jan 2017 14:20:22 +0000 http://www.preservationsound.com/?p=8602#comment-387060 Hi Chris,

probably expensive as hell if you can even get a small qty, but there are options for the triple-taper pot it seems:

http://www.potentiometers.com/seriesS127.cfm

Any mention of what value they should be?

Thanks a lot for posting this; looks like a very cool piece!

By the way, i really dig your videos on Youtube, would love to see you do more; especially regarding equipment builds and studio techniques!

Cheers,
Steve

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