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

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

wrote:
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

---------------
The R2000 uses BA282 band filter switch diodes.

The RX Unit (X55-1340-00) in the R2000 sevice manual gives the
part number, which I just verified by looking at the stock diodes
that I saved when I upgraded both of my R2000s.

See http://www.vishay.com/diodes/list/product-85526/

For the 6MHz and 9MHz bands, good HP PINs give a slight but
noticable improvement. I expected a big improvement in the below
500KHz range but found nothing that I could hear.

I still lurk and will make the odd post when I have something usefull
to add. All prior Email accounts are abandoned and dead.

Terry

Oftentimes, it is the type of ferrite material used in the mixer baluns.
Also, it could be that low Q caps are being used in the lower bands. I have
both an NRD-515 and an NRD-91. Both of these receivers exhibit rolloff below
700kHz.
These comparisions are made, using a Drake R7, Palstar R30, Yaesu FRG-100,
Icom R-75, Lowe HF150, HF-225, and HF-250. I did repair a Kenwood R-2000 a
few years ago, and wondered if it had some sort of attenuation below 1.5MHz.
I noticed this same characteristic with a Kenwood R-5000 and an AOR-3030.

Pete

wrote in message
ps.com...

wrote:
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

---------------
The R2000 uses BA282 band filter switch diodes.

The RX Unit (X55-1340-00) in the R2000 sevice manual gives the
part number, which I just verified by looking at the stock diodes
that I saved when I upgraded both of my R2000s.

See http://www.vishay.com/diodes/list/product-85526/

For the 6MHz and 9MHz bands, good HP PINs give a slight but
noticable improvement. I expected a big improvement in the below
500KHz range but found nothing that I could hear.

I still lurk and will make the odd post when I have something usefull
to add. All prior Email accounts are abandoned and dead.

Terry