TheRadioBoard

K
BCB conditions have been up and down. Signals are there,to be sure, but so is the QRM/N. Last night the noise level was 40 over...even covering WSM. Lots of storms to the south-but no rain here-and no relief from the heat! The QRN was even bad on 20 meters, dont often hear static crashes that high in frequency...
-31 meters has been good to great, however. Logged Austria and The Voice of Turkey--signal quality is fair to very good.
-My radio is a work-in-progress. To many details to post, but I will hit a few of the high points:
--It all started with loosing a bid for an R392 on Ebay...I had owned both the '390 and 390A in the past, and had always wondered what the 'little brother' to those rigs would be like. I down-loaded the manual and the more I read, the more I wanted one! Quite a radio!
--So I decided to build my own. So far, I have the RF stage and mixer working -and working very well! I am using an IF strip with three 6EH7's working into an LM318 precision rectifier (detector)-this from a previous radio. I have yet to build the R392 IF /agc/det strip.
-The RF stage in the '392 uses 2 26A6's. The signal corps hot-rodded the front end by changing the 26A6s to 26FZ6's. The 'FZ6 is not listed anywhere. It was made for, and used in the R392-no where else!
-It took a bit of effort to find the 'FZ6-and some data on same. Jim Cross (vacuum Tubes,Inc.) provided both the tubes and some info on them....I built my RF amp per the '392 manual, except I am using a variable cap for tuning and toroidal transformers. I built it using the 26A6's. It worked extremely well. Tuning was very sharp and precise. Just what I had hoped for. Then I plugged in the FZ6's....WOW!
The measured gain was a good 50 to 60 % higher!
-I have a good deal of work ahead of me, to be sure, but indications are that this rig will out perform just about anything. My tuning range is from 500kc to 15.7mc in four bands. The BCB is split into two bands. 500kc to 880kc-780kc to 1712kc..
-This is one hot radio. I have a Hammarlund HQ180 I use to check for images -I dont have a dial calibrated for the RF stage yet. So far the homebrew 392 equals or beats the '180.
-The Mixer uses a 26D6. Same as the VFO in the 392, but coils are switched to change bands. Frequency readout is via a N3ZI digital dial.
Rf stages are tuned separately. No tracking error, but one more knob to turn!
---updates to follow, sorry for the long post
de wb0rai Don in Nashville

_________________
"Love is grand...divorce is about a hundred grand"

WB0RAI de N1NQC- WOW !

To actually BUILD anything in the R390 league ! I certainly take my hat off to you sir.

I kind of hang out on the LOW end scale of things as far as scratch building goes - single tube/transistor regens, very high Q crystal sets,antennas, etc.

I'm simply a lifelong "tinkerer" and have never had any formal electronics training. No really serious test gear here either.

Probably the most ambitious project I'd ever take on would probably be on the level of be a rebuild of an AA5 ,etc. To redo an existing set is one thing, but to scratch build /design something R-390 level complicated-YIKES!

But I have my fun with no/single/low active component count designs.Some have worked incredible (like the WN6Q mentioned earlier in this thread) or my SERIOUS big litz crystal sets . So it keeps me out of trouble-usually, HI .


Anybody else out there?

dah di dah

k
---Most of the heavy lifting-the circuit design-of course, was done by Collins-so I an just borrowing from a proven design--with a LOT of help from Langford Smith's book "Radiotron Design Handbook, and a bit 'try this and see what happens..." So building a ten-tube radio is not that much different then building ten-one tube radios.
-Now my homebrew392 differs from the real thing in many ways, I have only one conversion to a 455kc IF, the R392 is triple conversion. Also my rig only tunes up to 15.7mc--the R392 to 30mc. I didnt think that with a 455kc IF it would work very well above the BCB, best I had hoped for was-maybe -80 meters. It works amazingly well up to 15.7mc-and I could push it above that, but I ran out of contacts on my band switch. No room for more coils.
All the inductors in the radio are wound on T-157-6 and T-187-6 cores with #20 and #16 wire. Very high Q. The RF tuning cap is a 3 gang silver plated mil spec ebay treasure...no idea what it came out of...so the RF unit is built with the same design criteria as your crystal set---high Q low loss. The result is image rejection that is very impressive, indeed. Tuning is not at all difficult. The LO/mixer uses high -side injection. The digital readout accounts for the IF and reads out the frequency minus the455kc IF.
Simply tune to the wanted frequency--say 6170.0kc--Radio New Zealand-on the air right now...and then peak the rf stage for max signal. The bias for the (2) 26a6's is set by a 10-turn 1 k pot which serves as the RF gain control---allows you to set the gain for the best s/n level. It is possible to set the gain to a point on the edge of oscillation....just like a regeneration control. You can hear the signal narrow to the point of cutting off the sidebands-again much like a regenerative detector. On CW it gives single signal reception. The self-excited mixer is a 26D6. Maybe four or five parts in the whole thing. The oscillator coils are also wound on T157-6 cores with the largest wire I could fit on the core. The cores are also large and #6 material. Frequency stability-both long term and short is very good. 100cycles from cold turn on to 15 min.-then +/- no more than 10 cps drift. No temp comp caps are used.
My other vice is metal working. I have a lathe and milling machine, so for me, its almost more fun doing the metal work, making the dial drives, knobs, RF tight enclosures and so forth. The L.O. is worm -gear driven with a 100:1 ratio, very smooth. No backlash. The RF tuning cap is driven by a hardened and ground .125 shaft, driving the rim of a 5 inch disk-the disk taken from a computer hard drive. All moving parts are set in ball bearings. The tuning shafts have fly-wheels, so tuning is much like a Hammarlund SP600.
The RF stage tunes VERY sharp. Even with the reduction, it takes the touch of a safe-cracker to tune-but once its there--it is rock stable.
--I am starting work on the IF /agc/det stage. The R392 has SIX IFs!
My radio is build in modular form, so I can change/optimize as I go along.
--So far, it weighs in at 43lbs.....and, like the '392, the plate voltage is only 28v....!
73
de wb0rai Don in Nashville

_________________
"Love is grand...divorce is about a hundred grand"

Hey Don,

Impressive. My other vice is wood working, which is much easier to pull of that metal working in my tiny shop.

K

I feel kind of sheepish saying this -- but for this years Summer Homebrew Contest I built a kit radio - a Small Wonder Labs SW40+, qrp 40m transceiver. It’s a tiny little superhet that puts out CW at about 1.5w on the 40 meter band.

Well, it’s a “little bit” home brew. I added a second band segment, linearized the varactor tuning, added a zero-beat indicator and a Tayloe SWR bridge.

The reason I wanted to build and play with this design/kit by Dave Benson was because of the extensive circuit analysis and documentation on the web. I’m learning a lot from the “Elmer 101” series and the McMaster Univ. pages devoted to the SW series.

It’s still on a breadboard but its stable and works really well.

As Dick Kliejer said: it’s all “for fun and for learning”.

73, Dan

One thing about an analog radio -- you can spin the dial and rapidly go from one band to another. So this morning I was spinning the dial and overshot the 31 M band and found a station at around 10300 kHz. Sounded like Chinese music. It was a strong signal and lasted from 7:20 am PDT to 7:40 when it faded into the noise. I listened closely on the half hour in hopes of getting an ID on it but no such luck. The music continued without interruption. What is an AM broadcast doing up there? Anyone have any idea?

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Tom

Maybe you were hearing the infamous Firedrake jamming signal:
http://en.wikipedia.org/wiki/Radio_jamming_in_China

Thanks Bob. I found firedrake audio clips online, and that's not it. What I heard was something played by a modern-sounding orchestra, although the composition sounded rather Chinese (but I'm certainly no authority).

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Tom

The Sound of Hope transmits from Taiwan at 10300 KHz. It only puts out 100 W, so if that's what you heard, it was a good catch!

George

HOLY COW!!!!!!!
my hat is off to you sir--heck, if i build a decent xtal set i feel proud--i sat in front of a pair of R-390s for four years--they were Really good radios--my job was operating them--uncle sam knew better than to turn me loose with pliers and screwdrivers

73
jerry-----k5psh

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TB
In GOD we trust,
all others we monitor!

Jerry
Thanks for the kind words!
It all started with a 1n34 and a crystal earphone...alligator clip on the finger stop on the telephone for an antenna...my older brother built this-radio(?) while I watched. I was eight at the time. The first thing I heard was "Dragnet".....I've been hooked ever since........that was in 1957,btw....that 1n34 moment lead to a life long fascination with radio, Ham license, commercial first phone at 18.....and some 45 years in broadcast engineering.
-I retired in '09 so now I have the time to build...and make use of all the priceless-useless things that have found there way into my junk box over the years.....
God has been very good to me over the years,and I have been able to own/use some of the 'high end' receivers...SP 600's-the R390 and R390A.
I also owned a Watkins Johnson HF1000.....and a Kenwood R70....and -not to forget my first 'real radio'......a Knight-kit Ocean hopper in 1960......
I also have built just about every form of regenerative circuit I could find...
They all worked. Some better than others...each and every one offered a great learning experience.
-I think of all the radios I have built thru the years...the one that out preformed them all was Bob Weaver's 6me8 double reflex superhet. It could hear everything my HQ180 could hear (BCB). Really a remarkable radio.
My current project is a real challenge. The front end is built/working and I am now in the design stages of the IF /detector /AGC stage(s). I am using an IF / detector from an other radio at present, to test the RF front end, and so far I am very pleased with the results.
-I will try to post pics when I get it beyond the 'clip lead' stage.....
-Sorry for the long post....more info than you wanted!
73's
wb0rai Don in Nashville

_________________
"Love is grand...divorce is about a hundred grand"

ok Don

sounds like we are about the same vintage--i think i have a few years on you--my radio began with an xtal diode set also----actually it began in 1950 when i commandeered the family BCB AA5--have always been fascinated by unseen voices and signals--ham tiket in '58 and morse intercept op in the army in '66--never made a career out of it tho--probably a big mistake, but it's too late now--

just hanging around and havin' fun--been inactive this summer--last qso was in june--gotta get busy when fall comes and the qrn abates--

see ya

73
jerry

_________________
TB
In GOD we trust,
all others we monitor!