Hi Frank,

That is a nice receiver, and the mods that you have done seem to cover
everything. The only thing that I can recommend....if this receiver uses
diodes to switch the input bandpass filters, I would replace them with
1N5767 PIN diodes. Bias them at around 60mA. I think that you can run up to
around 90mA, but that might be pushing them.
Philips also has some suitable PIN diodes, but you want to make sure that
you have a long enough minority carrier lifetime.
Congratulations on the new receiver! I haven't picked up anything new for
awhile, except that NRD-91.

Pete

wrote in message
oups.com...
Hi Pete; I just recently acquired an essentially mint Icom R70 off of
Ebay. It has the 500 kHz CW narrow filter included and came with the
manual and original box. After using this radio for a couple of weeks
I'm very impressed short of the weird ergonomics and the end of band
tuning anomalies. The sensitivity and selectivity are superb and the
BP shift and IF notch are among the best I've used. The audio is a bit
on the shallow side but I replaced a few of the electrolytic coupling
caps with film caps and the difference was very noticeable. I also
removed the LW/MW input attenuator and disabled the input rf amp defeat
for MW/LW. It can now be switched on and off from the front panel
switch. What is your experience with this radio and are there any other
improvement modifications that you know of?

Comments on this receiver from others are welcome.

Frank
K3YAZ
Tucson

Thanks for the info and advice Pete. I recently saw a comment that
standard 1N4002 type (60 Hz) diodes are actually good replacements for
the PIN diodes on the front-end band pass switching networks. Have you
heard of this?

Frank

Pete KE9OA wrote:
Hi Frank,

That is a nice receiver, and the mods that you have done seem to cover
everything. The only thing that I can recommend....if this receiver uses
diodes to switch the input bandpass filters, I would replace them with
1N5767 PIN diodes. Bias them at around 60mA. I think that you can run up to
around 90mA, but that might be pushing them.
Philips also has some suitable PIN diodes, but you want to make sure that
you have a long enough minority carrier lifetime.
Congratulations on the new receiver! I haven't picked up anything new for
awhile, except that NRD-91.

Pete

wrote in message
oups.com...
Hi Pete; I just recently acquired an essentially mint Icom R70 off of
Ebay. It has the 500 kHz CW narrow filter included and came with the
manual and original box. After using this radio for a couple of weeks
I'm very impressed short of the weird ergonomics and the end of band
tuning anomalies. The sensitivity and selectivity are superb and the
BP shift and IF notch are among the best I've used. The audio is a bit
on the shallow side but I replaced a few of the electrolytic coupling
caps with film caps and the difference was very noticeable. I also
removed the LW/MW input attenuator and disabled the input rf amp defeat
for MW/LW. It can now be switched on and off from the front panel
switch. What is your experience with this radio and are there any other
improvement modifications that you know of?

Comments on this receiver from others are welcome.

Frank
K3YAZ
Tucson

wrote:

Thanks for the info and advice Pete. I recently saw a comment that
standard 1N4002 type (60 Hz) diodes are actually good replacements for
the PIN diodes on the front-end band pass switching networks. Have you
heard of this?

Whatever happened to all those Schottky Diode mods that seemed to be the rage
years ago? Would this be something similar?

dxAce
Michigan
USA

In article ,
dxAce wrote:

wrote:

Thanks for the info and advice Pete. I recently saw a comment that
standard 1N4002 type (60 Hz) diodes are actually good replacements for
the PIN diodes on the front-end band pass switching networks. Have you
heard of this?

Whatever happened to all those Schottky Diode mods that seemed to be the rage
years ago? Would this be something similar?

That is a standard silicon power supply diode with something like .6 -
..7 volts forward voltage drop. The Schottky would be at least half that
and many are more like .25 volt.

If you don't bias the diodes into their linear range then it takes
signal power just to turn them on/off and that's where some of the
distortion comes from and the non-linear area contributes as well so the
smaller Schottky is an advantage.

--
Telamon
Ventura, California

I am not sure if the capacitance of the power diodes would be too high. This
could cause poor isolation, but if you reverse bias the unused filter
diodes, they might work.

Pete

wrote in message
oups.com...
Thanks for the info and advice Pete. I recently saw a comment that
standard 1N4002 type (60 Hz) diodes are actually good replacements for
the PIN diodes on the front-end band pass switching networks. Have you
heard of this?

Frank

Pete KE9OA wrote:
Hi Frank,

That is a nice receiver, and the mods that you have done seem to cover
everything. The only thing that I can recommend....if this receiver uses
diodes to switch the input bandpass filters, I would replace them with
1N5767 PIN diodes. Bias them at around 60mA. I think that you can run up
to
around 90mA, but that might be pushing them.
Philips also has some suitable PIN diodes, but you want to make sure that
you have a long enough minority carrier lifetime.
Congratulations on the new receiver! I haven't picked up anything new for
awhile, except that NRD-91.

Pete

wrote in message
oups.com...
Hi Pete; I just recently acquired an essentially mint Icom R70 off of
Ebay. It has the 500 kHz CW narrow filter included and came with the
manual and original box. After using this radio for a couple of weeks
I'm very impressed short of the weird ergonomics and the end of band
tuning anomalies. The sensitivity and selectivity are superb and the
BP shift and IF notch are among the best I've used. The audio is a bit
on the shallow side but I replaced a few of the electrolytic coupling
caps with film caps and the difference was very noticeable. I also
removed the LW/MW input attenuator and disabled the input rf amp defeat
for MW/LW. It can now be switched on and off from the front panel
switch. What is your experience with this radio and are there any other
improvement modifications that you know of?

Comments on this receiver from others are welcome.

Frank
K3YAZ
Tucson

"Pete KE9OA" ) writes:
I am not sure if the capacitance of the power diodes would be too high. This
could cause poor isolation, but if you reverse bias the unused filter
diodes, they might work.

Pete

I seem to recall reading that some of the 1N400X series have a structure
like PIN diodes, I think some of the higher voltage ones. This has been
stated in various places, though I have no idea about whether it's a valid
solution for this specific receiver.

Michael


wrote in message
oups.com...
Thanks for the info and advice Pete. I recently saw a comment that
standard 1N4002 type (60 Hz) diodes are actually good replacements for
the PIN diodes on the front-end band pass switching networks. Have you
heard of this?

Frank

Pete KE9OA wrote:
Hi Frank,

That is a nice receiver, and the mods that you have done seem to cover
everything. The only thing that I can recommend....if this receiver uses
diodes to switch the input bandpass filters, I would replace them with
1N5767 PIN diodes. Bias them at around 60mA. I think that you can run up
to
around 90mA, but that might be pushing them.
Philips also has some suitable PIN diodes, but you want to make sure that
you have a long enough minority carrier lifetime.
Congratulations on the new receiver! I haven't picked up anything new for
awhile, except that NRD-91.

Pete

wrote in message
oups.com...
Hi Pete; I just recently acquired an essentially mint Icom R70 off of
Ebay. It has the 500 kHz CW narrow filter included and came with the
manual and original box. After using this radio for a couple of weeks
I'm very impressed short of the weird ergonomics and the end of band
tuning anomalies. The sensitivity and selectivity are superb and the
BP shift and IF notch are among the best I've used. The audio is a bit
on the shallow side but I replaced a few of the electrolytic coupling
caps with film caps and the difference was very noticeable. I also
removed the LW/MW input attenuator and disabled the input rf amp defeat
for MW/LW. It can now be switched on and off from the front panel
switch. What is your experience with this radio and are there any other
improvement modifications that you know of?

Comments on this receiver from others are welcome.

Frank
K3YAZ
Tucson

In article ,
dxAce wrote:


wrote:

Thanks for the info and advice Pete. I recently saw a comment that
standard 1N4002 type (60 Hz) diodes are actually good replacements for
the PIN diodes on the front-end band pass switching networks. Have you
heard of this?

It's supposed to be the higher voltage parts in that series, (the 1N4007).

Whatever happened to all those Schottky Diode mods that seemed to be the rage
years ago? Would this be something similar?

Semiconductor-wise, they're pretty much the opposite.

A Schottky diode uses only one type of semiconductor and the junction
is silicon-metal. (The modern version of a cat's wisker detector).
Their feature is that they don't store a cloud of electrons or holes
inside their junction so that they don't have a feature called "reverse
recovery". (Executive summary, they don't look like a short circuit for
a few nanoseconds when the current switches direction). Reverse recovery
causes all sort of problems in switching power supplies, and is also
the cause of RFI from regular old transformer/rectifier power supplies.

A PIN diode uses both P and N type doping in the junction, but in
addition there is a layer of Intrinsic (neutrally doped) silicon
in the middle. This causes a bunch of stored charge to hang around
in the middle of the junction, so that for high frequencies it doesn't
look like a diode anymore. They're used for switches by forward
biasing them to turn them on, or when reverse biased the stored
charge eventually gets swept out of the junction and they look like
an open circuit (or really, a capacitor). As I understand it,
there's a tradeoff between storage time (and switching speed) and
capacitance. The designer would like as much storage time (sets the
low frequency response) and the minimum capacitance.

Mark Zenier
Googleproofaddress(account:mzenier provider:eskimo domain:com)

Now that I think of it Michael is correct. It was the 1N4007, the 1 kV
version of this slow diode that was recommended. It would tend to have
lower junction capacitance because of the wider depletion region due to
the heavier doping for the high voltage standoff. Once the diode is
biased on dc wise, the forward drop is not significant because it
doesn't "switch" with the signal current. I think the trend to
Schottky diodes was because of the lower intrinsic capacitance.

Frank

Michael Black wrote:
"Pete KE9OA" ) writes:
I am not sure if the capacitance of the power diodes would be too high. This
could cause poor isolation, but if you reverse bias the unused filter
diodes, they might work.

Pete

I seem to recall reading that some of the 1N400X series have a structure
like PIN diodes, I think some of the higher voltage ones. This has been
stated in various places, though I have no idea about whether it's a valid
solution for this specific receiver.

Michael


wrote in message
oups.com...
Thanks for the info and advice Pete. I recently saw a comment that
standard 1N4002 type (60 Hz) diodes are actually good replacements for
the PIN diodes on the front-end band pass switching networks. Have you
heard of this?

Frank

Pete KE9OA wrote:
Hi Frank,

That is a nice receiver, and the mods that you have done seem to cover
everything. The only thing that I can recommend....if this receiver uses
diodes to switch the input bandpass filters, I would replace them with
1N5767 PIN diodes. Bias them at around 60mA. I think that you can run up
to
around 90mA, but that might be pushing them.
Philips also has some suitable PIN diodes, but you want to make sure that
you have a long enough minority carrier lifetime.
Congratulations on the new receiver! I haven't picked up anything new for
awhile, except that NRD-91.

Pete

wrote in message
oups.com...
Hi Pete; I just recently acquired an essentially mint Icom R70 off of
Ebay. It has the 500 kHz CW narrow filter included and came with the
manual and original box. After using this radio for a couple of weeks
I'm very impressed short of the weird ergonomics and the end of band
tuning anomalies. The sensitivity and selectivity are superb and the
BP shift and IF notch are among the best I've used. The audio is a bit
on the shallow side but I replaced a few of the electrolytic coupling
caps with film caps and the difference was very noticeable. I also
removed the LW/MW input attenuator and disabled the input rf amp defeat
for MW/LW. It can now be switched on and off from the front panel
switch. What is your experience with this radio and are there any other
improvement modifications that you know of?

Comments on this receiver from others are welcome.

Frank
K3YAZ
Tucson

wrote:
Now that I think of it Michael is correct. It was the 1N4007, the 1 kV
version of this slow diode that was recommended. It would tend to have
lower junction capacitance because of the wider depletion region due to
the heavier doping for the high voltage standoff. Once the diode is
biased on dc wise, the forward drop is not significant because it
doesn't "switch" with the signal current. I think the trend to
Schottky diodes was because of the lower intrinsic capacitance.

There are better switching diodes than the 1N4007, though they are more
expensive and less commonly available. It's not a bad switching diode
for RF if you don't have anything else handy. If I'm not mistaken,
Ulrich Rhode wrote an article in QST some years back about the use of
such diodes in high performance receiver designs. His opinion was that
although cheap, the 1N4007 didn't have a place in higher performance
designs.

DE AB3A

There's no question that the 1N400X series is a poor switching diode
when it comes to speed and reverse recovery characteristics, however,
for switching in and out bandpass filters I think the reverse bias
junction capacitance is the major issue to prevent unwanted signal
coupling. I would definitely look for true PIN diodes if I were
upgrading the filter switching diodes rather than use 1N4007s. It's
just interesting that there have been articles on the fact that they
appear to work reasonably well in some cases. I know the Kenwood
R-2000 I had used the equivalent of 1N914s for these diodes in the
front end and they were horrible with all kinds of cross talk from
stronger, out of band signals.

Frank

Jake Brodsky wrote:
wrote:
Now that I think of it Michael is correct. It was the 1N4007, the 1 kV
version of this slow diode that was recommended. It would tend to have
lower junction capacitance because of the wider depletion region due to
the heavier doping for the high voltage standoff. Once the diode is
biased on dc wise, the forward drop is not significant because it
doesn't "switch" with the signal current. I think the trend to
Schottky diodes was because of the lower intrinsic capacitance.

There are better switching diodes than the 1N4007, though they are more
expensive and less commonly available. It's not a bad switching diode
for RF if you don't have anything else handy. If I'm not mistaken,
Ulrich Rhode wrote an article in QST some years back about the use of
such diodes in high performance receiver designs. His opinion was that
although cheap, the 1N4007 didn't have a place in higher performance
designs.

DE AB3A