[Milsurplus] RT-70

Thu Jan 5 17:10:16 EST 2017

The big issue with all that forties and fifties design stuff was its super wide band. Netting with similar stuff from that generation was ok but the wide design of the receivers makes it difficult if not imposable to hear the new narrow band stuff and the transmitter deviation is such that you can easily over modulate and be distorted on newer radios. Have netted with those old tube sets and things like the VRC-12 and PRC-25 but still the tuning rate tends to be an issue. Also you do not have the sub audible tone for working the squelch with newer sets. The power to weight ratios are a bit too much for my taste also. Look at this YouTube Video and it shows the comparison between those old sets and the VRC-12 family along with the divisions for working frequencies of armor, infantry and artillery.

https://www.youtube.com/watch?v=aUh2jSvvBVM

Ray F/KA3EKH

-----Original Message-----
From: Milsurplus [mailto:milsurplus-bounces at mailman.qth.net] On Behalf Of Bruce Gentry
Sent: Thursday, January 05, 2017 4:52 PM
To: Milsurplus at mailman.qth.net >> Milsurplus <Milsurplus at mailman.qth.net>
Subject: Re: [Milsurplus] RT-70

I will ultimately find the needed parts to get the big VRC setup together and working. It used an RT-70 and the amplifier along with an RT 67 or 8, a PP-109 or 112 power supply, and a standalone R-108 or 9 reciver on a common mount. I can imagine the combinations of RTs were almost endless. Why were different corps of the Army on different bands? 
Were there too few channels? I was a small guy when you worked on these, but I had a screwdriver and pliers in my hands already. These rigs are built to last, and seem to be nearing the ultimate in tube design. How aware were military radio techs at the time about transistors? I wonder if that entire range of VRC/PRC gear was regarded as being the last stand for tubes  with full expectation the next family of replacements would be solid state.

    Bruce Gentry

On 1/5/17 2:26 PM, CWH wrote:
> They were also used  in tanks for communication between infantry and 
> tanks. The AM 65 was used as an interphone amplifier.  I was a radio 
> repairman in a M48 tank company 1953-1955.
> 73 Charlie W8CFO
>
> -----Original Message----- From: Dennis DuVall
> Sent: Thursday, January 05, 2017 1:50 PM
> To: Jack Antonio
> Cc: milsurplus at mailman.qth.net
> Subject: Re: [Milsurplus] RT-70
>
> Have several of these.  Don’t recall any particular problems getting 
> the things running but it’s been a while now.
> Vibrator supplies come in 6, 12 & 24 volt flavors.  Very low power and 
> short range but fun to play with.  Understand they wee used for local 
> area coms until telephone wire could be strung.
>
> Dennis D. W7QHO
>> On Jan 5, 2017, at 9:34 AM, Jack Antonio <scr287 at att.net> wrote:
>>
>> On 1/4/2017 2:42 PM, Bruce Gentry wrote:
>>> I'm getting a couple RT-70 transceivers and the matching audio 
>>> amplifier/power supplies working, and need connectors. I also have 
>>> the
>>
>>
>> Problems I had with my RT-70 and AM-65:
>>
>> Either relay K1 or ballast tube R-32 were bad in the AM-65. Maybe 
>> both. This is from 10 year ago memory, and any notes I took have gone 
>> AWOL.
>> These two components are in an over-voltage protect circuit, and it 
>> was intermittently protecting when it didn't need to. Of course it 
>> worked fine on the bench, and only cropped up when I took the radio 
>> to MRCG to play with. I found exact replacements, but from where I 
>> don't recall. Possibly Fair or eBay.
>>
>> Vibrators sticky, but a bit of tapping and use got them working 
>> again. I think I was lucky there.
>>
>> Intermittent squelch in RT-70. Found a number of leaky paper or film 
>> type caps in audio section, replacing made squelch a little less 
>> flaky. As I remember there were two different types that looked the 
>> same, but one was physically larger than the other. The large ones 
>> were good, the small ones were all leaky.
>>
>> Finally found that the tip of the tip of the last limiter had broken 
>> off, was hard to see visually.
>> I think that particular tube was a bit taller than the normal size, 
>> and it had broken off when the radio was pulled out of the case.
>>
>> Strange thing is that the receiver still functioned, although volume 
>> was down and squelch just didn't work right.
>>
>> Last problem is that the 1Mc calibration crystal was missing, I 
>> replaced it with another from the "box du junque", it sort of works, 
>> but the cal signal is weak.
>>
>> Hope this helps you get your set running.
>>
>>
>>
>> Jack Antonio WA7DIA/4
>>
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