Built-in Intercom

[lowNslow]

Finally getting around to putting in a built-in intercom. Tired of the wire mess with the portable. Was wondering how others worked in the push-to-talk switch. I am trying to decide if is better to hard wire it in or to put in an addition plug below the panel so it can be removed easily . Any other problems to think about? This is a Sigtronics SCI-S4 unit.

[doug8082a]

Mine are hard wired and work great. I like not having to worry about any extra wires hanging around. I used two Telex PTTs. I mounted them "backward" on the yokes - i.e. with the switch on the back side of the yoke so I can hit it with my index finger. We drilled a hole through the panel overlay, installed a grommet, and ran the wire through there. Here's a pic:

[GAHorn]

I did something similar, except I didn't want to drill a hole in my panel so I just routed the coiled lead into the opening between my floating instrument panel and the fixed panel. It took me about 3 seconds and that's about the same amount of time it took me to convert to using my thumb instead of my index finger to press the mic button. (sort of like pickeling off a few rounds from the cannon) This also allowed me to drape the cable over the top of the center-shaft and avoid too much hangin down in the way (as you can see.) I recommend you avoid any serious modification to your yoke, for several reasons. (No approval basis, and risks condemnation of your increasingly-valuable original yokes.)

[lowNslow]

Mine are hard wired and work great. I like not having to worry about any extra wires hanging around. I used two Telex PTTs. I mounted them "backward" on the yokes - i.e. with the switch on the back side of the yoke so I can hit it with my index finger. We drilled a hole through the panel overlay, installed a grommet, and ran the wire through there. Here's a pic:

I like the idea of running the cord as close as possible to where the yoke comes thru the panel to avoid the "hang down". Since I have a '53 I'll probably do it as George did since there is no convenient place to put a hole and grommet as in your installation. Did you just buy the standard PIT and cut off the plug or do the come without the plugs?

I recommend you avoid any serious modification to your yoke, for several reasons. (No approval basis, and risks condemnation of your increasingly-valuable original yokes.)

Thanks George, I actually was thinking about drilling into the yoke, but came to the same conclusion.

[doug8082a]

These were regular Telex PTTs with the plug attached. We cut if off and hard wired it.

[cessna170bdriver]

My particular intercom does not automatically connect the headset straight through when powered off, nor does it carry the push-to-talk line through. Therefore, I installed phone and mic plugs on the intercom output to which I have access. I also have phone and mic jacks on the input to my audio panel. That gives me a way to reconfigure in case of an intercom failure. (Hasn't happened yet). If you make sure the intercom you buy has automatic fail-over, you won't need to do that.

The PTT has both a mic plug and a mic jack. I plug the PTT male plug into the audio panel mic jack, then plug either the intercom or headset mic plug into the PTT mic jack. That saves me from having to dig into the wiring when the PTT fails (happens about every 10 years). This also makes it very easy to use my hand-held back-up mic with PTT in the event of a headset failure (hasn't happened) or I forget to bring a headset to the airport (happens occasionally).

Miles

[markeg1964]

I installed an intercom but I still have a mess



I installed two plugs at both ends of the panel and just plug the PPT into the mic plug. You can just see the pilot’s mic and head plugs in the photo. I got the idea from looking at other 170s. If I was to do it again I think I would hardwire the PTT switch to clean things up some.

[Bruce Fenstermacher]

That Mark is an outstanding rats nest but not the worst I've seen.

[blueldr]

Looks like you need to buy a flute and take some lessons as a snake charmer.

[GAHorn]

Karl, just out of view to the left (in my pic) at the very edge of the fixed panel, is the mic and phone female jacks. I bought a genuine Telex* PTT and kept it intact. I simply routed the male plugs thru the opening at the floating panel immediately left of the column, and brought the male plugs back out the far left side and plugged them into the females. The coiled cord is sufficiently robust to keep it's place and not fall out from between the shock-panel and the fixed panel. The excess coiled cord (about a foot) simply rests on top of the radio to the extreme left, a KLN-88 Loran. You can stuff as much or as little behind the floating panel to allow whatever length to "hang down" as you do or do not wish. The coiled cord remains fixed due to the coils holding themselves between the panels, and does not interfere with any controls movement.

* I recommend the genuine Telex brand because of it's quality of PTT switch. The chinese copies do not last. The back of the actual switch has a piece of thin, foam-tape adhesive. Place the swith where you want it, and compress the foam as you tightly wrap/fixate the velcro strap, and the switch will remain properly placed.

I have a PS Engineering II, 1000 intercom. I hard-wired a seperate, hand-held microphone for emergency and crewmember's use, according to the intercom's instructions/schematics. It will over-ride the headset mic and bypass the intercom internal transmit relays. Therefore, in case of any intercom or other likely failure of a headset, the hand mic will directly operate the transmitter(s). My hand mic is mounted in the mfr's original location and properly clears the flap handle.

[jrenwick]

That's one beautiful panel, George. I admire your originality!

[lowNslow]

Thanks all, I think I'll go with Marks suggestion and just wrap any excess wire around the yoke.
The intercom I got does say it has a "fail-safe" feature that allows you to send and receive with an intercom failure or loss of power to the intercom, it also has connections to the the handmike jack, but I'm not sure why.
George, are you saying that you use the PTT double jack feature and do not have it hard wired?

[GAHorn]

Thanks all, I think I'll go with Marks suggestion and just wrap any excess wire around the yoke.
The intercom I got does say it has a "fail-safe" feature that allows you to send and receive with an intercom failure or loss of power to the intercom, it also has connections to the the handmike jack, but I'm not sure why.
George, are you saying that you use the PTT double jack feature and do not have it hard wired?

My Intercom (PS Engineering) also claims it is "fail safe" and will also "always" revert to manual control and cannot prevent transmitting/receiving in case of Intercom failure. Capital "B". Capital "S".

That statement, and a phone call to PS Engineering (their "engineers" absolutely swore their unit was not my problem) cost me a week and a couple hundred dollars.

My problem: On freezing days I could receive, but could only transmit a carrier... no modulation. The tower became quite agitated after a few attempts to contact clearance delivery. (DWH tower, which has a reputation for short tempers.) Only after a 20 minute period of idling with the avionics on, ... then suddently all was just fine. A few days later, the symptoms reappeared on a frosty morning.
I called PS Engineering and they made all their assertions it absolutely was NOT their equipment, because their intercoms ALWAYS fail to a "by pass" mode by DESIGN. (and I guess their opinions of their design team is infallible.) They quite convincingly blamed my Narco 810+ radio.
I called Narco, who gave me shipping instructions for factory service, and I shipped it to them. Two days later their technician "Don" called and reported he'd frozen, baked, and shaken my radio incessantly, and they could find absolutely nothing wrong with it: "...it's probably your intercom."
I was pretty non-plussed at Narco. They returned it overnight (but included a 1 year warranty as part of their $120 invoice.)
I removed the PS Engineering II intercom and sent it to PS Engineering and told them to bench check it in cold conditions. They removed the offending relay, installed a replacement, made an unauthorized modification (completely removed a diode I'd only clipped to provide side-tone in accordance with their instructions ... but I'd only clipped it because I thought I might wish to retain the option of re-attaching it... now they'd killed that option without asking).... and returned it a week later, freight COD, and an invoice for $80.

"Fail Safe" means they only THINK it should revert to by-pass in case the particular failure mode they've designed for occurs. Their thinking does not consider actual failure of their design-thinking.

[HA]

George, as a sim instructor who sits at work thinking up creative ways to get the poor unsuspecting saps up front in trouble you oughta know that "fail-safe" only really means "for what we thought of"

just like emergency procedures that only save your bacon if the proper failure mode occurs, otherwise you're out of luck ("smoke in the cockpit" in a King Air, for example - fine, unless it isn't the environmental fan, then good luck)

I've managed to get around the "fail-safe" provisions of countless things in my flying career, maybe I'm just talented

[PaddyM]

Good morning all from the now melting side of the 49th parallel!
This is an old post but with some searching found it and seems to speak to my problem--maybe!
There has been intermittent radio issues , but only transmitting-- receiving was fine.
I think the problem is the pilots ptt and not the radio.
So, here is where I am at.
Pulled the pilot's seat out yesterday to get coiled up under the instrument panel to locate the ptt wire that comes through panel .
Looks very similar to George's a small hole through the panel and feeding the coiled Telex pt300 cable through.
I then traced the lead and discovered a joint with 3 wires coming from the joke switch coloured ( Canadian spelling!) black,red, and a white.
The red was broken/ not used?.
Opening up the ptt I found the red and white connected to contact points and what appears to be a shielded brass fitting that squeezes down into the round opening in the plastic at entry point.
Still with me?
So back to the joint-- seeing the red not wired in, and what appeared to be a red and white striped wire attached-- I thought walla! an easy fix just re-attach the reds together and problem solved.
Well with my readers on, what appeared to be red and white wires wrapped together , turned out to be a white wire plastic coated with a single red stripe , but only 1 wire inside.
With separate contact points in the switch it didn't make sense to connect the red and white to a single wire, so that's when my wife came back to the hanger to pick me up and so I left --scratching my head.
There must be another wire up in there that the red was attached to is my guess.
The ptt is old , but I can't find a wiring diagram so far.
Any ideas?

Further info--- do have an intercom--works fine, tuned in a frequency and could still hear other ac-- quite far away, have a co-pilot's ptt that when depressed I can hear clicking.
So I think -- back to pilot's ptt and that broken red!

Thanks for any ideas!
Wife and I have booked a room in Bardstown hoping we can get down.
Cheers, and happy Easter!
Pat