Good Day all!
I have recently got one of these sets and am rapidly upgrading the original
design.
So far it has a Kokusai Mech filter, manual and AGC Rf gain control on the
RF stage. It has also had improvements to its AGC system and I am about to
update the RF stage FET.
One problem has arisen and someone might be able to help me here.
The Kokusai filter is NOT actually on 455 kHz, it's actual centre frequency
is 454.2 kHz (measured against a calibrated frequency counter), Since the
self excited BFO is NOT drift free I want to replace it with USB/LSB Xtals.
Can you still get the old time FT241 types, or does anyone know a source of
odd frequencies in the 455/465 kHz IF range?
I calculate that the the old FT241 channels I would need would be 328 and
326. That would give me BFO frequencies of 455.55 (should be 455.7) and
452.7 kHz that fits in with the odd filter.
That way one of the main sources of drift should be almost gone.
I have found that the FRG-7 has its problems, but, as someone who has
designed and built many communication receivers over the years IMO it is
the basis for quite a useful general coverage receiver and a VERY useful
bit of test gear with noise bridges etc.
Any suggestions gratefully received.
73's Cliff Wright ZL1BDA ex G3NIA New Zealand.

Some folks just can't leave well alone!

On Thu, 23 Sep 2010, Nikon D3000 wrote:

Some folks just can't leave well alone!

Another way of looking at it is that a commercial receiver makes
a good start at a semi-homebrew project.

I remember one article in QST in the late fifties where someone bought
a Knight Kit receiver and never built it as instructed. He used the
chassis and such and the variable capacitors and tuned circuits but
built up a different receiver. He saved on not having to do the chassis
work.

There were lots of receivers built that way around surplus equipment.

People rebuilt older receivers, pretty much starting from scratch,
either to put in miniature tubes or solid state the receiver. They
even admitted that at that point they might as well have started
from scratch, but the mechanical work in the receiver provided an
advantage.

I was agonizing earlier in the year about buying a Grundig 4000
when they were selling for under a hundred dollars (made more
tempting by having a gift card for the store, and at least at
one point they were tossing in a windup radio). In the end,
I decided it was too frivolous. But, I was tempted precisely
to use it as a project radio. As a portable, any portable for
that matter, there are some disadvantages, and merely putting it
in a bigger case and rearranging the controls, and adding a tuning
knob (it only has up/down switches) would make a fairly great
operational improvement. Add another switch so the IF bandwidth
switch doesn't control whether FM reception is mono or stereo.
Add a preselector for improved front end selectivity. Add an analog
s-meter. Add an RF gain control, or at least multiple levels of
attenuation in the front end. Move the BFO tuning to something
that is easier to use (it's a thumbwheel). Get a ceramic resonator
and add a CW bandwidth selectivity. Get some ceramic filters and
improve selectivity. Maybe add a synchronous detector. Once it's in a
bigger box, it's so much easier to add modifications.

I thought of it as a fun project, get a leap start on building a full
range shortwave receiver, but make it more functional and easier to use.
Even at a hundred dollars, it's almost at the range where people would
consider it throwaway, when it dipped under a hundred dollars it was
even moreso.

The problem was, I already have one, bought at the $100 level last fall,
plus a couple of better Grundigs that I bought at rummage sales for a lot
less. Out of the box those older Grundigs have more features, and if I
realistically, one of them would be a better choice for this sort of work.

So in the end, I didn't pursue the project, because as fun as it would
have been, the end product wasn't necessary to my needs.

Michael VE2BVW

"Michael Black" wrote in message
ample.net...
On Thu, 23 Sep 2010, Nikon D3000 wrote:

Some folks just can't leave well alone!

Another way of looking at it is that a commercial receiver makes
a good start at a semi-homebrew project.

I always start from scratch. I build my own PCB's, wind my own coils, metal
enclosures and chassis. If I was capable of making all my own components,
including tubes, I would sure would give it a go - real homebrew!

Nikon D3000 wrote:
"Michael Black" wrote in message
ample.net...
On Thu, 23 Sep 2010, Nikon D3000 wrote:

Some folks just can't leave well alone!

Another way of looking at it is that a commercial receiver makes
a good start at a semi-homebrew project.

I always start from scratch. I build my own PCB's, wind my own coils, metal
enclosures and chassis. If I was capable of making all my own components,
including tubes, I would sure would give it a go - real homebrew!


A FRG-7 from scratch would make a good project for you!

War story...many moons ago I saw a brand new FT-757 at a hamfest
disassembled to the fullest extent possible. They had just hit the
market at the time. The story was that it was an evaluation rig and the
teardown was part of the evaluation. They only wanted $100 for the
pieces and I was tempted to grab it. A 757 Kit - haha.

Then common sense clicked in. What if it is missing a couple of crucial
pieces?

-Bill

In message , Bill M
writes
Nikon D3000 wrote:
"Michael Black" wrote in message
news:Pine.LNX.4.64.1009232232010.18476@darkstar. example.net...
On Thu, 23 Sep 2010, Nikon D3000 wrote:

Some folks just can't leave well alone!

Another way of looking at it is that a commercial receiver makes
a good start at a semi-homebrew project.
I always start from scratch. I build my own PCB's, wind my own
coils, metal enclosures and chassis. If I was capable of making all
my own components, including tubes, I would sure would give it a go -
homebrew!
A FRG-7 from scratch would make a good project for you!

War story...many moons ago I saw a brand new FT-757 at a hamfest
disassembled to the fullest extent possible. They had just hit the
market at the time. The story was that it was an evaluation rig and
the teardown was part of the evaluation. They only wanted $100 for the
pieces and I was tempted to grab it. A 757 Kit - haha.

Then common sense clicked in. What if it is missing a couple of
crucial pieces?

The same caution should be exercised when buying second-hand jigsaw
puzzles.
--
Ian

Nikon D3000 wrote:

"Michael Black" wrote in message
ample.net...
On Thu, 23 Sep 2010, Nikon D3000 wrote:

Some folks just can't leave well alone!

Another way of looking at it is that a commercial receiver makes
a good start at a semi-homebrew project.

I always start from scratch. I build my own PCB's, wind my own coils, metal
enclosures and chassis. If I was capable of making all my own components,
including tubes, I would sure would give it a go - real homebrew!

http://paillard.claude.free.fr/

Rob wrote in
:

Nikon D3000 wrote:

"Michael Black" wrote in message
ample.net...
On Thu, 23 Sep 2010, Nikon D3000 wrote:

Some folks just can't leave well alone!

Another way of looking at it is that a commercial receiver makes
a good start at a semi-homebrew project.

I always start from scratch. I build my own PCB's, wind my own coils,
metal enclosures and chassis. If I was capable of making all my own
components, including tubes, I would sure would give it a go - real
homebrew!

http://paillard.claude.free.fr/


Well! Do some folks REALLY thing that an FRG-7 is good enough as it
stands!!!
First and most important problem, lousy selectivity, about 6khz BW with
very poor shape factor.
Secondly very poor AGC performance, this can easily be improved with an
HCD as AGC detector and better biasing of the AGC stage and detector.
Thirdly not very good RF noise and linearity performance. Easily improved
with a better FET, better biasing and introducing an RF gain control in
the G2 circuit, while keeping AGC action on the stage.
Finally too fast a tuning rate for easy SSB tuning. I am investigating
mods to the tuning mechanism to give me another 5 times slower rate.
BTW I have made 8 complete homebrew ham stations in my career and have
WAC and about 160 countries with them.
This INCLUDES receivers.
Admittedly an Xtal controlled CIO is a luxury, but I had found a not
inconsiderable drift in the original SEO oscillator that I had rather do
without. As has been said it makes the basis of quite a good receiver,
once a few bugs are removed.
After the RF stage my next target will be the first balanced mixer. It
looks to me as if the stage could be set up to reduce intermodulation
quite a bit.
However at my age starting right from scratch is not so easy so turning
a leather purse into a silk one is easier and quicker. My TS-820 has had
the same treatment and now runs ALL HF bands.
&#'s Cliff Wright

"Bill M" wrote in message
...
Nikon D3000 wrote:
"Michael Black" wrote in message
ample.net...
On Thu, 23 Sep 2010, Nikon D3000 wrote:

Some folks just can't leave well alone!

Another way of looking at it is that a commercial receiver makes
a good start at a semi-homebrew project.

I always start from scratch. I build my own PCB's, wind my own coils,
metal enclosures and chassis. If I was capable of making all my own
components, including tubes, I would sure would give it a go - real
homebrew!
A FRG-7 from scratch would make a good project for you!

I could quite possibly design and build a far better receiver than the FRG-7
anyhow!
Manufacturers build to a design price - so inevitably compromises have to be
made to keep within budget.
As a lone constructor, that restriction doesn't even enter into the equation
when I design and build. The only problem I sometimes find is when certain
components become obsolete and consequentially unavailable, so then it
becomes a case of "back to the drawing board!"

Bill M writes:
....[lots snipped]....
War story...many moons ago I saw a brand new FT-757 at a hamfest
disassembled to the fullest extent possible. They had just hit the
market at the time. The story was that it was an evaluation rig and the
....[more snipped]....

When I was in college (many moons ago), one of my HAM classmates
disassembled Collins transceivers to get parts for his hombrewing!
And when he was finished, they even looked nice (X-Y wiring, etc.)

Me? I take old TV's apart.

-- Myron A. Calhoun
--
-- Myron A. Calhoun.
Five boxes preserve our freedoms: soap, ballot, witness, jury, and cartridge
NRA Life Member & Certified Instructor for Rifle, Pistol, & Home Firearm Safety
Also Certified Instructor for the Kansas Concealed-Carry Handgun (CCH) license