Icom IC-720A

[KA9MOT]

I don't know if we could call it a boatanchor but it is old so here goes.....

I was given a non-working Icom IC-720A. I was able to get it to work for about 20 seconds on 40M and then back to no RX or TX. A quick google search lead me to check the band switch and I think that is where the problem lies.

Anywho, I've deoxed the switch and still no happiness. I did find a mod online which uses relays and a few IC's to resolve the problem. I also found a mod for the mod.

The Mod:

http://www.hayseed.net/~jpk5lad/IC-720/IC-720%20Rotary%20Switch.htm I am unable to find anything from anybody who has actually done this and says it will work.

The Mod for the Mod:

http://zaverio.com/~asbesto/ic720amod/ The 2 links on the bottom right of the page have very good detailed pictures, but there is little text explaining what has been done.

I could disassemble the switch and clean it as is shown at http://zaverio.com/~asbesto/ic720amod/rotary-switch-images/ but I think I'd rather do the mod.

Could you guys take a look at the mod and help me decide if this will actually work and be worth the expense (14 relays aint gonna be cheap, and I am thinking about using Solid State Relays) and I have no clue if that board is available or what it would cost to have it reproduced. I am going to email F5IKI and see if he has any boards left, assuming the only email I was able to find is still good.

Sorry for being so needy guys.

[N8YX]

First, you want 2A reed relays - not solid-state.

Next, this is the same type of circuit which Kenwood, Cubic and a number of other manufacturers have employed to switch the bandpass or lowpass filters in their HF transceivers. I would have to look at the '720 mod info but it should be fairly close to the other designs: That is, a decoder (3-to-7 or 7-to-7, depending on the band control word), buffering logic and a set of relay drivers.

It's not that big a deal to construct - the hardest part will be finding the correct relays. I'll examine the info during the next couple days and offer additional comments as needed.

[KB3LAZ]

First, you want 2A reed relays - not solid-state.

Next, this is the same type of circuit which Kenwood, Cubic and a number of other manufacturers have employed to switch the bandpass or lowpass filters in their HF transceivers. I would have to look at the '720 mod info but it should be fairly close to the other designs: That is, a decoder (3-to-7 or 7-to-7, depending on the band control word), buffering logic and a set of relay drivers.

It's not that big a deal to construct - the hardest part will be finding the correct relays. I'll examine the info during the next couple days and offer additional comments as needed.

Is that in the same era as the 271? If so I wonder if it too may have eprom issues. Both my 271a and 271h needed new eproms when I got them. Simple fix, decent price. Sadly I dont think the man is still in business that makes the after market replacements.

[KA9MOT]

First, you want 2A reed relays - not solid-state.

Next, this is the same type of circuit which Kenwood, Cubic and a number of other manufacturers have employed to switch the bandpass or lowpass filters in their HF transceivers. I would have to look at the '720 mod info but it should be fairly close to the other designs: That is, a decoder (3-to-7 or 7-to-7, depending on the band control word), buffering logic and a set of relay drivers.

It's not that big a deal to construct - the hardest part will be finding the correct relays. I'll examine the info during the next couple days and offer additional comments as needed.

See, that is why I asked the experts! Thanks!




Is that in the same era as the 271? If so I wonder if it too may have eprom issues. Both my 271a and 271h needed new eproms when I got them. Simple fix, decent price. Sadly I dont think the man is still in business that makes the after market replacements.

No eprom issues with this one and I sent an email to the guy who makes them and he still has a few available. He is the one who told me there was no back-up battery for the eprom.
I don't know if this rig will actually work when I get the bandswitch issues resolved, but I am crossing my fingers and hoping it doesn't cost allot to find out. The rig came with a Heil Hand Mic that looks like a CB mic. It looks pretty crappy. I plan to build a pre-amp (probably copy the Astatic Pre-amp that comes with a D-104) and use something else. Probably the same computer mic and footswitch I used with my TS-480SAT. I really miss that radio.

[W2NAP]

incase you need it.
User Manual http://www.w2ibc.com/modules.php?name=Downloads&d_op=viewdownloaddetails&cid=72&lid=2292&ttitle=IC-720a_Instruction_Manual#dldetails
Service Manual http://www.w2ibc.com/modules.php?name=Downloads&d_op=viewdownloaddetails&cid=72&lid=2293&ttitle=IC-720A_Service_Manual#dldetails

[W1GUH]

I've got a 720A. There's a yahoo group on them with lots of information. (http://groups.yahoo.com/group/IC720/) You'll probably get all the info you want there. That's a great radio -- it's a "vintage rice box classic." Lots of information on the infamous rotary relay.

[N8YX]

That '720 is missing a couple things:

5225

5226

The EX-7072 allows one to slave an IC-720(A) to an R-70, which incorporates a number of interference-fighting features that the transceiver does not.

Icom's omnipresent Molex plug is used to daisy-chain the control facilities of a number of their accessories...the IC-2KL amplifier, AT100/500 tuners, EX-1 expansion accessory and EX-627 antenna switch to name but a few.

I have an R-70 and an EX-7072 in the shack. I also have an IC-745, which does not offer the data I/O on its Molex connector that is needed to slave it to the R-70. Thus, I'm going to design and build an I/O converter...

[KA9MOT]

incase you need it.
User Manual http://www.w2ibc.com/modules.php?name=Downloads&d_op=viewdownloaddetails&cid=72&lid=2292&ttitle=IC-720a_Instruction_Manual#dldetails
Service Manual http://www.w2ibc.com/modules.php?name=Downloads&d_op=viewdownloaddetails&cid=72&lid=2293&ttitle=IC-720A_Service_Manual#dldetails

Thank You! I needed the Service Manual!




I've got a 720A. There's a yahoo group on them with lots of information. (http://groups.yahoo.com/group/IC720/)You'll probably get all the info you want there. That's a great radio -- it's a "vintage rice box classic." Lots of information on the infamous rotary relay.

Thanks Paul! I'll check them out!





That '720 is missing a couple things:

5225

5226

The EX-7072 allows one to slave an IC-720(A) to an R-70, which incorporates a number of interference-fighting features that the transceiver does not.

Icom's omnipresent Molex plug is used to daisy-chain the control facilities of a number of their accessories...the IC-2KL amplifier, AT100/500 tuners, EX-1 expansion accessory and EX-627 antenna switch to name but a few.

I have an R-70 and an EX-7072 in the shack. I also have an IC-745, which does not offer the data I/O on its Molex connector that is needed to slave it to the R-70. Thus, I'm going to design and build an I/O converter...

That is cool. I'll bet it is not easy to find one of them. I'll have to see what other accessories were available for this rig. I'm not a huge Icom fan... I had an IC-730 that I really liked but it had the dirty relay problem for the pre-amp. I contacted Icom and they had a relay, but they wanted $85 for it. I found a numbers matching relay at RF Parts for $9.99.....That turned me away from Icom. I don't mind people making a dollar or 10 from me, but I refuse to be raped. lol

[KB3LAZ]

That '720 is missing a couple things:

5225

5226

The EX-7072 allows one to slave an IC-720(A) to an R-70, which incorporates a number of interference-fighting features that the transceiver does not.

Icom's omnipresent Molex plug is used to daisy-chain the control facilities of a number of their accessories...the IC-2KL amplifier, AT100/500 tuners, EX-1 expansion accessory and EX-627 antenna switch to name but a few.

I have an R-70 and an EX-7072 in the shack. I also have an IC-745, which does not offer the data I/O on its Molex connector that is needed to slave it to the R-70. Thus, I'm going to design and build an I/O converter...

You have an addiction! :P Seeing your thoughts on a few things of this matter. I still think it would be neat for them to come out with a modern day twin set.

[N8YX]

Seeing your thoughts on a few things of this matter. I still think it would be neat for them to come out with a modern day twin set.
I would love for Icom to come out with a transceiver which matches the R-9500 and offers all-mode capability on everything through 1.2GHz...inclusive of 222 and 902MHz. Yes, I would buy one.

[KB3LAZ]

I would love for Icom to come out with a transceiver which matches the R-9500 and offers all-mode capability on everything through 1.2GHz...inclusive of 222 and 902MHz. Yes, I would buy one.

No no no. I want a transmitter and receiver not a transceiver and receiver. :D True modern day twins. :D

[N8YX]

No no no. I want a transmitter and receiver not a transceiver and receiver. :D True modern day twins. :D

A transceiver plus receiver is the way modern-day "twins" are implemented. Think SO2R with the transmitter section capable of being controlled by either receiver.

[KB3LAZ]

A transceiver plus receiver is the way modern-day "twins" are implemented. Think SO2R with the transmitter section capable of being controlled by either receiver.

Right but Im saying they should build something retro. :D Im willing to bet I would not be the only one buying it. :D

[N8YX]

Right but Im saying they should build something retro. :D Im willing to bet I would not be the only one buying it. :D

Unless they gave them away, I'd be willing to bet you would definitely be in the minority. The last days of the amateur-market "discretes" ended with the 75S-3/32S-3, HR1680/HX1681 and R4C/T4XC series. What followed was the KWM380/(planned)451-S1, TR7/R7 and TS-820S/R-820. Each was a transceiver/receiver pair. Remember that on many operating desks, space came at a premium. Collins, Drake and Kenwood's marketing departments were aware of this.

One might opine that the IC-720/R70 along with the later '751/R71 combo were designed as a "set" but in actuality the receivers were introduced several years later than the transceivers. Neither is as fully integrated as the 7-line or '820 series is: Full transceive capability and an antenna distribution scheme which allowed both receivers to operate at once.

[KB3LAZ]

Unless they gave them away, I'd be willing to bet you would definitely be in the minority. The last days of the amateur-market "discretes" ended with the 75S-3/32S-3, HR1680/HX1681 and R4C/T4XC series. What followed was the KWM380/(planned)451-S1, TR7/R7 and TS-820S/R-820. Each was a transceiver/receiver pair. Remember that on many operating desks, space came at a premium. Collins, Drake and Kenwood's marketing departments were aware of this.

One might opine that the IC-720/R70 along with the later '751/R71 combo were designed as a "set" but in actuality the receivers were introduced several years later than the transceivers. Neither is as fully integrated as the 7-line or '820 series is: Full transceive capability and an antenna distribution scheme which allowed both receivers to operate at once.

Minority but not alone. However, its not likely to happen. Therefore my thoughts are to at some point put together a R4-T4 station. Ofc my dreams of a KWS-1 and 75A-4 will always be in place for my AM station. :P (32v-? and 75A-4 are more likely or something similar.)

[N8YX]

Minority but not alone. However, its not likely to happen. Therefore my thoughts are to at some point put together a R4-T4 station. Ofc my dreams of a KWS-1 and 75A-4 will always be in place for my AM station. :P (32v-? and 75A-4 are more likely or something similar.)
I know where a set is located and will be coming available in the near future. If you're interested, I'll put you in touch with the person.

[KB3LAZ]

I know where a set is located and will be coming available in the near future. If you're interested, I'll put you in touch with the person.

Lol. I bet the shipping to Spain would be erm..yeah a car might be cheaper. :P They are not in my future for another 3-5 years at the least.

[KK4AMI]

I'm selling off half a dozen hobbies on ebay to get the money to buy a discrete AM Transmitter. I want to use it with an R71A modified for AM reception with a 10 kHz filter. I love the sound of AM. I'm trying to stay out of the tube era. How is the Yaesu FL-101 on AM? I like the discrete twin idea to. Most have built in power supplies.

[N8YX]

I'm selling off half a dozen hobbies on ebay to get the money to buy a discrete AM Transmitter. I want to use it with an R71A modified for AM reception with a 10 kHz filter. I love the sound of AM. I'm trying to stay out of the tube era. How is the Yaesu FL-101 on AM? I like the discrete twin idea to. Most have built in power supplies.
The FL-101 is very nice when run on AM - use a D-104 with the rig for best results. Remember not to exceed 100ma IC when transmitting AM, and adjust the mic gain for a slight flicker on voice peaks. Best way to set the audio level with the transmitter is via an inline monitor scope such as a YO-100/101.

What I would do if I were you is to find an FR-101S and pair with the transmitter.

Caveat:

The Yaesu receiver has no notch filter or PBT control but on AM you aren't going to need them. I would choose the "S" model over the "D" because the analog readout needs no special treatment when plugging in extra band crystals.

[KK4AMI]

The FL-101 is very nice when run on AM - use a D-104 with the rig for best results. Remember not to exceed 100ma IC when transmitting AM, and adjust the mic gain for a slight flicker on voice peaks. Best way to set the audio level with the transmitter is via an inline monitor scope such as a YO-100/101.

What I would do if I were you is to find an FR-101S and pair with the transmitter.

Caveat:

The Yaesu receiver has no notch filter or PBT control but on AM you aren't going to need them. I would choose the "S" model over the "D" because the analog readout needs no special treatment when plugging in extra band crystals.

That sounds good. If I can get the pair cheap, then I'll get both. I was going to use the R-71A with ICOM FL-33 (9.010 MHz) cuz I had it, but I know it would be better to have the matched set. Richmond Frostfest is on the 4th of Feb.. I plan on going armed with a fist full of dollars.

[KB3LAZ]

I used to use a pair of Yaesu 101s. :) Loved them. I had the opportunity to buy a restored set cheap. Still kicking myself in the ass for not doing so.

[N8YX]

That sounds good. If I can get the pair cheap, then I'll get both. I was going to use the R-71A with ICOM FL-33 (9.010 MHz) cuz I had it, but I know it would be better to have the matched set. Richmond Frostfest is on the 4th of Feb.. I plan on going armed with a fist full of dollars.
Here's one set:

http://swap.qth.com/send-to-friend.php?counter=958646

Another:

http://www.eham.net/classifieds/detail/357788

The receiver itself:

http://www.ebay.com/itm/Yaesu-FR-101-Digital-Ham-Radio-Receiver-Amateur-FT-101-FL-/180799813733?pt=LH_DefaultDomain_0&hash=item2a18823865

[KB3LAZ]

Here's one set:

http://swap.qth.com/send-to-friend.php?counter=958646

Another:

http://www.eham.net/classifieds/detail/357788

The receiver itself:

http://www.ebay.com/itm/Yaesu-FR-101-Digital-Ham-Radio-Receiver-Amateur-FT-101-FL-/180799813733?pt=LH_DefaultDomain_0&hash=item2a18823865

The set I had available to buy was sexy. A friend of mine had them. W9QNE. I think before that KXQ had them or used them or bought them or something but I dont remember. The first set I ever used belonged to W4CLM. Ofc if you know the call you know they were showroom.

[N8YX]

I had two "sets" back in 2004-2005:

An FR-101D/FL-101; the receiver had the digital display, 2/6M converters, FM board and several of the SW BCB crystals and the transmitter had the accessory speech processor.

An FR-101S (analog) and an FT-201. The latter was a redesigned FT-101 whose ergos and cosmetics were identical to the FR-101, but you couldn't transceive with the set - the IF frequencies were slightly different so it wasn't possible for one to supply reference signals to the other. This particular 101 just escaped Katrina and when I got the thing I equipped it with all the spare AUX/WARC/SWBCB crystals I could find. It had both converters and the FM board as well. Both receivers had all available filters.

I sold both plus a lot more Yaesu gear to a guy from Indiana in 2006.

Nice rigs. They did some things which my Drake and Kenwood twins didn't.

[KK4AMI]

I'm looking for the best post Boat anchor (minimum tubes) for transmitting Amplitude Modulation. I want to take up the full 6 kHz bandwidth using a high fidelity speech processed voice :soapbox:

[N8YX]

I'm looking for the best post Boat anchor (minimum tubes) for transmitting Amplitude Modulation. I want to take up the full 6 kHz bandwidth using a high fidelity speech processed voice :soapbox:

Kenwood 940.

Remove the predriver emitter ballasting resistor, sub an R/S 273-1374 audio transformer (secondary in place of the resistor) then drive the primary via the speech amp.

AMWindow has details. I'm getting ready to mod one of mine and will post pics.

[KK4AMI]

Kenwood 940.

Remove the predriver emitter ballasting resistor, sub an R/S 273-1374 audio transformer (secondary in place of the resistor) then drive the primary via the speech amp.

AMWindow has details. I'm getting ready to mod one of mine and will post pics.

Thank you again Sir. I read the AMwindow mod to the 940. I like the simpler external mod to the 940. I like the idea of installing a fancier commercial speech modulator/processor. I figured you for an ICOM user/Cubic Collector, but you really don't seem to have any brand loyalty. Your radio knowledge seems to border on "Commercial Repair Facility". Is that what you do?

[N8YX]

Thank you again Sir. I read the AMwindow mod to the 940. I like the simpler external mod to the 940. I like the idea of installing a fancier commercial speech modulator/processor. I figured you for an ICOM user/Cubic Collector, but you really don't seem to have any brand loyalty. Your radio knowledge seems to border on "Commercial Repair Facility". Is that what you do?
Nope, just a tinkerer/RF enthusiast who has the majority of their amateur radio "fun" on the test bench. Whichever piece of equipment best fills a specific role is what I'll place in the lineup.

[KK4AMI]

Nope, just a tinkerer/RF enthusiast who has the majority of their amateur radio "fun" on the test bench. Whichever piece of equipment best fills a specific role is what I'll place in the lineup.

Well that's too bad! I figured with all the radios you have experience with, you must be the official tester at "Fair Radio Sales" or something. :)

[N8YX]

Well that's too bad! I figured with all the radios you have experience with, you must be the official tester at "Fair Radio Sales" or something. :)
All of my "rescues" get used and eventually passed on to other hams. While I love rebuilding and collecting older gear I am limited in terms of space, so the current iteration of the shack is probably what will endure. A few Cubics and Drakes will stick around, though.

[KA9MOT]

I heard from F5IKI today. He made me some boards and mailed them.....for free! I'm excited now! He absolutely refused any sort of payment. I just cant get over how generous so many hams are turning out to be.

[W3WN]

Right but Im saying they should build something retro. :D Im willing to bet I would not be the only one buying it. :DYou're probably right, but I suspect that the market for true twins these days is so small as to be below the threshold where the costs of designing, building, and marketing the rigs would make it worthwhile.

[W3WN]

All of my "rescues" get used and eventually passed on to other hams. While I love rebuilding and collecting older gear I am limited in terms of space, so the current iteration of the shack is probably what will endure. A few Cubics and Drakes will stick around, though.I wish I had the repair bench you do. My biggest problem right now is that until I finish the shack (or scrap the half-assed job I've got so far and start over), I have no real good place to work on equipment.

[N8YX]

I wish I had the repair bench you do. My biggest problem right now is that until I finish the shack (or scrap the half-assed job I've got so far and start over), I have no real good place to work on equipment.
Most of my repair work is done atop a spare dining-room table, and I set up various test equipment on it as required. I too wish I had a proper bench. :lol:

[WØTKX]

I'll put in a plug for my Flex 3000 on AM. With the SAM mode on RX and plenty of DSP bandwith and EQ/Compression toys, it rocks.

Yakking with 75m and 10m AM enthusiasts, they have all said "nice audio"... usually before they know what radio it is. The boat anchor AMers were a little shocked that a radio without KNOBS can do AM well. :lol:

My TS-850 does a decent job of it, but I need to do the mic preamp bypass mod, and fire it up via my Tascam board. Which I need to do anyway, to extend the capabilities of that rig with the DSP-100 on (E)SSB. Really enjoy messing with enhanced and slightly wider audio, making SSB sound "life-like" is great for ragchewing.

[KB3LAZ]

You're probably right, but I suspect that the market for true twins these days is so small as to be below the threshold where the costs of designing, building, and marketing the rigs would make it worthwhile.

Simple fix. They already force us to buy what they put out or buy used. xD

[KB3LAZ]

I'll put in a plug for my Flex 3000 on AM. With the SAM mode on RX and plenty of DSP bandwith and EQ/Compression toys, it rocks.

Yakking with 75m and 10m AM enthusiasts, they have all said "nice audio"... usually before they know what radio it is. The boat anchor AMers were a little shocked that a radio without KNOBS can do AM well. :lol:

My TS-850 does a decent job of it, but I need to do the mic preamp bypass mod, and fire it up via my Tascam board. Which I need to do anyway, to extend the capabilities of that rig with the DSP-100 on (E)SSB. Really enjoy messing with enhanced and slightly wider audio, making SSB sound "life-like" is great for ragchewing.

Computer without tubes rather. =P

[W5IEI]

I'll put in a plug for my Flex 3000 on AM. With the SAM mode on RX and plenty of DSP bandwith and EQ/Compression toys, it rocks.

Yakking with 75m and 10m AM enthusiasts, they have all said "nice audio"... usually before they know what radio it is. The boat anchor AMers were a little shocked that a radio without KNOBS can do AM well. :lol:

My TS-850 does a decent job of it, but I need to do the mic preamp bypass mod, and fire it up via my Tascam board. Which I need to do anyway, to extend the capabilities of that rig with the DSP-100 on (E)SSB. Really enjoy messing with enhanced and slightly wider audio, making SSB sound "life-like" is great for ragchewing.

Same deal with the Orion , Orion II.
The processor does all the work in AM.
Switch modes to AM,key up,and watch the 100 watts automatically drop to 15 or so.
Modulation runs up to around 30 watts.Drives an AL-1500 real good.
People I have talked to in person say it sounds great.

[KA9MOT]

I received the boards and they are a work of art. Beautifully done. Now I need to source some parts and the fun begins!

[W1GUH]

Most of my repair work is done atop a spare dining-room table, and I set up various test equipment on it as required. I too wish I had a proper bench. :lol:

Mine's my cocktail table. Only problem is setting it up for whatever activity I want to do, but once that's done, it's perfectly fine! But of course I live alone, nobody to pester me about anything. Wouldn't have it any other way.

Added advantage of that is that if I had a "proper bench", it'd probably be a mess usually. This way I'm forced to neaten up afterwards.

[K7SGJ]

Plus it's probably easier to clean off the long hippy hairs that fall out.

[KB3LAZ]

Plus it's probably easier to clean off the long hippy hairs that fall out.

I had long hippy hair once. Now I have very little hair. That was due to choice not nature.

[K7SGJ]

I did too, once upon a time. Now, the hair is pretty thin, but as they say, who wants fat hair.

[KA9MOT]

I traded the rig off. One dead IC-720 is worth a very nice antenna analyzer.........who knew? 1 old Icom = 1 AUTEK VA-1

[W1GUH]

Plus it's probably easier to clean off the long hippy hairs that fall out.

Been a few falling out lately. But there's plenty left!