LED Tuning indicator for 37-6xx Series - Printable Version

+- The PHILCO Phorum (https://philcoradio.com/phorum)
+-- Forum: Philco Radio Discussions (https://philcoradio.com/phorum/forumdisplay.php?fid=5)
+--- Forum: Philco Electronic Restoration (https://philcoradio.com/phorum/forumdisplay.php?fid=8)
+--- Thread: LED Tuning indicator for 37-6xx Series (/showthread.php?tid=733)

---

LED Tuning indicator for 37-6xx Series - AI2V - 08-14-2007

It may make the purists irate, but here's an addition to your Philco Frankenradio-

An extremely simple LED tuning indicator for the 1937 series - an LED in series with a 150K ohm resistor to ground; the other end of the LED connects to pin 1 of the 6Q7 AGC detector. You may want to adjust the resistor value; also a cap across the LED might improve it a bit.

DO NOT connect your LED/resistor to the AGC feedback line; doing so will cause distortion and a loss of sensitivity.

---

- Texasrocker - 08-14-2007

A12V, Thanks for sharing your info here!! I am no "purist" at all!! Never been, never had a reason to be!! I do not own any orig AK breadboards, so as far the "purists", all I can say is, unless you have a orig AK breadboard model,or orig Fada catalin sets (keep those orig if possible), ALL other brands are to-be-restored best we can!! Sounds like your findings replaces the bulky "shadowmeter-assy", and if so, I can still use my orig Philco spkr assy, in my Philco retrofit placing a model 37-630 6 tube chassis (missing its orig console cab), into a 37-610 shouldered tombstone cabinet had spkr included ( that didnt originally have shadow-meter) for a simple "retro-fit"!!?? You see, by not using the orig Philco shadowmeters "bulky parts", I may be able to use your idea instead and fit a simple-small LED just behind the escutcheons small shadow-meter slot!! If so, your new "invention" may be a better idea indeed, than me having to use a smaller PM-type spkr to accomodate for space to add a full-orig Philco shadowmeter into a Philco cabinet not designed for a shadowmeter in the first place!! Thanks very much, for sharing your valuable info here!! Fitting a 37-630 chassis from (orig mod X console cab) into a 37-610 shouldered tombstone cab fits perfectly, "except for the shadowmeter from the chassis", and doesnt allow enough space to use the orig Philco speaker "over top" of the orig "bulky shadowmeter escutcheon assy"!! Your idea may have solved my "retrofit" probs!!! Many thanks again for sharing your info!! Sincerely, Randal

---

Shadow meter still is best - AI2V - 08-15-2007

Randal-
I still use the shadow meters where ever I can. This mod is just something is did to my very Franken-ish 37-620 and will work for any Philco's in the 1937 chassis (an more). Since the 37-620 doesn't have a shadow meter, I replaced my escutcheon with a very large console type with the shadow meter window (some minor wood cutting necessary), and placed a high intensity 5mm 8K LED behind it.

Something else noteworthy on Philco's with the balanced antenna connections (screws): reception is greatly increased with a simple 8-turn bifilar 1:1 toroid ring transformer on the input. I did this only to make connection to a coaxial antenna line but it has proven superior even with a single antenna connection.

---

- Terry Judkins - 08-15-2007

Pin 1 of a 6Q7 is the shield/ground. I am a bit puzzled how a led would light connected from ground to ground.... : :

---

Correction in connection - AI2V - 08-15-2007

The correct connection is to the point where the two 1 Meg resistors #44 and #50 come together- Pin 4 of the 6Q7. It was late last night and I traced the wrong wire. In my actual circuit I don't use the pin 4 detector but use a solid state detector in it's place- that shouldn't make any difference.

Sorry about any confusion. My 37-620 was a junker at one time and was brought up from that condition. It could be much neater, but that's not a priority.

---

- Texasrocker - 08-15-2007

...I havent cut the wires to my shadowmeter yet! Always glad to hear new "ideas"!! A12V, can you put up a schematic of your working circuit "replacement shadowmeter LED light" here? Thanks, Randal

---