[Milsurplus] CV-157
John Vendely
jvendely at cfl.rr.com
Wed Dec 23 09:19:57 EST 2015
Nick provides excellent advice on the CV-157. A few points may be worth
adding--if at all possible, check the response of the sideband filters
before purchase. Degraded passband response is not unusual, usually due
to aged crystals. Of course, this can be a problem with all the old
gear, including the insanely overpriced CV-591. For some reason, the
CV-157 LSB filter seems be more failure prone than the USB, though I
really can't think of any obvious reason why this should be the case.
As Nick points out, the CV-157 was always used in pilot carrier AFC
mode, so its 555 kc LO is not not as stable as the crystal controlled
LO in the simple CV-591 converter. The CV-157 will therefore drift
noticeably during warmup. Speaking of temperature, these things
naturally generate a lotta heat, so running the blower is a must, or the
unit will overheat badly in a rack.
The only "problem" tube may be the 5751 dual triodes in the AFC motor
drive system. The 5751 has become all the rage amongst guitarists who
believe it will give them a "gutsy" tone their original 12AX7s cannot.
The formerly cheep 5751 is therefore now priced at a premium. The
primary reason for using the 5751 in the AFC was that its two triodes
were very closely matched, permitting very good motor drive amp
balance. You could probably substitute well-matched 5814s or 12AX7s
with no problem.
When properly aligned, with good filters and the sideband demods tweaked
per the book, the CV-157 provides beautiful audio. It was designed for
the low in-band intermod distortion necessary for multitone modulation.
Sweep alignment of the IFs is the way to go, since certain IF
transformers must be adjusted for controlled "tilt" for the overall IF
response to come out right.
73,
John K9WT
On 12/22/2015 12:37 PM, Nick England wrote:
> The CV-157 is surprisingly un-modular! Even though it looks like the
> power supply lower section is easy to separate, it isn't. It pulls out
> *almost* far enough to work on.
>
> It has been several years (and other silly projects) since I restored
> my CV-157 but I'd say, technically, if you can repair and align an
> R-390A, then you can certainly do the same for a CV-157. A scope is
> probably necessary for any troubleshooting. The TM is clear and
> complete of course.
> http://www.militaryradio.com/manuals/CV-157/cv-157-tm11-266.pdf
>
> Basically it is three parallel sections -
> 1) a USB IF amp and product detector
> 2) a LSB IF amp and product detector
> 3) a carrier IF amp and motor drive circuit for the AFC
>
> Here's another thing to consider -
> The sideband filters are 6kc wide so that will may be an issue in a
> crowded band. The CV-591 is the more usual 3.2kc so there is less
> adjacent signal interference.
> The 6kc width is because the CV-157 was really designed for
> multi-channel AFSK RTTY - like 32 TTY channels in each sideband.
>
> Repair parts - well if a 100kc IF transformer or filter is blown, only
> another CV-157 will have those parts. Otherwise it is the usual caps
> and resistors. There are a zillion IERC tube shields (well 40 or so)
> which probably are worth more on eBay than a CV-157. IIRC, the tubes
> are regularly available military types, no oddball ballast or regulators.
>
> Overall it is an excellent unit for its intended use, but way
> complicated for just regular voice SSB.
> It will probably be an interesting and moderately challenging project,
> which you may or may not enjoy. Or if it hasn't been messed with or
> been stored in bad conditions, you may not have to do much at all.
>
> And you'll probably be the only kid on your block running one.
>
> 73 & Have Fun
> Nick England K4NYW
> www.navy-radio.com <http://www.navy-radio.com>
>
> On Tue, Dec 22, 2015 at 10:55 AM, Reuben Popp <reuben.popp at gmail.com
> <mailto:reuben.popp at gmail.com>> wrote:
>
> Hey Nick,
>
> So what you're really saying here is that for the
> quasi-experienced technician it would most likely require some
> serious study as well as the help of a more experienced elmer ;)?
>
> I see that at least one manual (TM11-266) is available. How
> difficult is it to acquire parts? Is it modular like the
> R-390As? Just curious to see if I'm potentially getting myself
> into deeper water than I care to wade at this point. Then again,
> I would hate to miss out on a piece of equipment that others rate
> highly and I might be able to acquire at a decent price.
>
> Thanks again
> Reuben
>
>
>
> On Tue, Dec 22, 2015 at 7:00 AM, Nick England
> <navy.radio at gmail.com <mailto:navy.radio at gmail.com>> wrote:
>
> The CV-157 spec says 105 lb but it seems much heavier. It is
> a great ISB converter (simultaneous USB and LSB) which
> includes a motor drive AFC for tracking reduced pilot carrier
> ISB transmissions. It has 44 tubes and lots of circuits to
> align. I really enjoyed spending several weeks learning how it
> works and getting mine running. Acquisition cost is low
> because sane people don't want something that big and heavy.
> Anywhere from $10-100 is reasonable. Hard to beat if you want
> an interesting and challenging project. I enjoy projects but
> YMMV.
>
> The TMC CV-591 is much much smaller, lighter, easier to
> use, and more expensive.
>
> There aren't any ISB or pilotcarrier signals to copy anyways
> so audio performance is about the same for regular SSB voice.
>
> OR just switch your rcvr to CW and MGC, offset the BFO, turn
> down the RF gain, and turn up the AF gain and SSB voice sounds
> just fine.
>
> Cheers
> Nick K4NYW
>
>
> On Tuesday, December 22, 2015, Reuben Popp
> <reuben.popp at gmail.com <mailto:reuben.popp at gmail.com>> wrote:
>
> Hey gang,
>
> Quick question here. I might have an opportunity to get
> my hands on a CV-157... maybe. The current owner said
> he's had it now for some years now and never used it.
> Question is, what are they worth in good unused shape?
> Are there any gotchas for them (hard to find parts or
> tubes) as opposed to the much smaller TMC CV-159? That
> said, are they as good a performer as the -159 or just
> mediocre?
>
> Thanks again, Merry Christmas (or Happy Holidays if you
> prefer) to all and 73
> Reuben
>
>
>
> --
> Nick England K4NYW
> www.navy-radio.com <http://www.navy-radio.com>
>
>
>
>
>
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