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New in the original box, untouched ARC-5




 
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KC4VWU
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« Reply #25 on: September 22, 2017, 02:06:45 AM »

Does it have that "smell"?
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ka1tdq
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« Reply #26 on: September 22, 2017, 05:30:36 PM »

I don't really know... I didn't put my nose down there.  Sometimes it's best not to.  One surprise though was opening the rear cover on top.  My wife said, "Oh, a mirror!"  And I'm like, that's for calibrating the VFO with the seeing-eye tube, not for putting on makeup. 

Jon
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K6JEK
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RF in the shack


« Reply #27 on: September 22, 2017, 11:03:41 PM »

It's a work of art. I bet many of you think so too even if you have a four module class E rig sitting in the background. I've never been able to explain to someone not similarly enchanted why pieces like these or other cleverly designed and carefully constructed pieces are things of beauty.
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KC4VWU
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« Reply #28 on: September 23, 2017, 08:48:47 AM »

Your right, sometimes it's best not to put your nose down there, but it's just radio equipment in this instance, so it's O.K.

I don't know what it is about old Military electronic gear, but it has that smell. I've learned it over the years, and it is unmistakable. Don't know what it is; varnish, MFP, or maybe some toxic substance, but it does signify that said equipment is of major coolness. And no, it's not the smell of damp basement, mouse pee saturated Hallicrafters S-40. Consumer electronics of the same period does not have "the smell", although they do have a certain scent especially when the toobs are lit.

Who knows? I doubt if any modern US mil. equipment has "the smell", since most of it, or the majority of it's parts, is made in Asia. And we know what Asian electronics smells like, right? Plastic.    
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W2JBL
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« Reply #29 on: November 07, 2017, 06:47:23 PM »

    All my ARC-5 stuff has that smell, or variations on it. By the way I rencently powered up an unmodified 5.3-7 MC Navy unit and at 650 on the PA and 300 on the oscillator with a 22K PA screen resistor got a paltry 35 watts out. The bypassing is not so good either- Touching the power cable coming out of it actually pulled the vfo. So much for running un-modified.

     I have two complete ARC-5 transmitter setups here: one fixed, one mobile. Both easily put out a 100 watt carrier. They are plate modulated."Navy" ARC-5's are using a shunt fed tank circuit and were designed to be plate modulated. The mobile rig uses a modulator built on an ARC-5 transmitter chassis. It uses a pair of 6883's (12 volt 6146) with the grids grounded and the screens driven by a Valiant driver transformer and 6V6. Mobile power is form  GE Mastr-Pro mobile power supply strip. The mod transformer in both rigs is an ART-13 unit. The base uses a pair of 807's resistance coupled in AB-1. Both use inverse feedback around the entire chain and are full on HI-FI audio. It's power supply/modulator is built in an old Wasco AM marine radio cabinet.

  To get 100 watts out of an ARC-5 I update the bypassing on all the tube cathodes, screens etc with ceramic caps, using the shortest leads possible soldered to the tuning cap frames. I shunt the PA plate choke with a National 2.5 MHY choke to cure a voltage drop issue, and add a bypass cap at the bottom. Note that you MUST replace the plate blocking cap with a good ceramic of 500 pF to .001 at 1.2 KV or higher. The stock cap will EXPLODE otherwise (It happened to me more than once). Get rid of the fuse link between the top of the plate choke and tank coil. Next I resonate the coupling link with a large Arco mica trimmer cap of around 1200 PF in paralell with the link located as close as possible to the terminals on the link (this is important). Unlock the PA tune cap and juggle it along with the added trimmer and the coupling control to get to max RF out. With 700-725 on the PA plate 300-325 on the screens and 300 on the oscillator. Use a 22k screen resistor (per the RCA tube manual)and if all is right and you have good tubes you get to 100 watts. The tubes show no color and I have had no issues running them like this. 

     The pictures are of this setup in my 78 Chevy Caprice. Power is from a GE Mastr-Pro power supply strip. The system works flawlessly even on old buzzard transmissions. I stopped using the Icom 718 as a receiver in favor of a Drake SPR-4. So nice to have a world class receiver with noise blanker in the car. The CB with converter it tried didn't cut it in the real world due to really bad image rejection on 75.   


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