Icom IC-735 ALC

[KC2TAU]

I've decided to put my IC-735 on the air on AM and have built the commonly found circuit that allows one to apply a negative voltage to the ALC jack in the back of the radio. I have been able to successfully use it to set the resting carrier level. When I watch the output wattage on my meter it seems that as soon as I have finished modulating the carrier level dips and then rises back to its original resting level. This is also shown when I watch the scope. The radio seems to modulate to about 95-100% positive but the external ALC voltage seems to do nothing with regards to preventing this downward power dip. Is there some sort of internal adjustment that is causing this?

[Pete, WA2CWA]

Some info:
http://amfone.net/Amforum/index.php?topic=13932.0;wap2

http://www.mattesini.com/IC-735/AM-MOD.html

[N2DTS]

I had one when they were new, very nice looking, simple and small radios, very well made as well.
You can make them general coverage TX, and I adjusted the ALC pot inside the radio so it would put out 150 watts. I did not run it there, but did try it a number of times and nothing blew up. It likely gets dirty at those power levels and something would likely fail eventually, but you could run it on AM at 25 watts out without the ALC kicking in.
Since its just a pot adjustment, you can mark it and put it back if you sell the radio, otherwise you just have to adjust the power output control to only 100 watts out.

I did mods to the audio, but it never sounded good.
The RX has a lot of noise/hash, high wide 1st IF lets any close by signal overload the radio, but the passband tuning does work on AM and the filters are ok.
The AM carrier output is not stable with temp and it varies over time making it a pain to use as an exciter.

Its actually quite a bad radio, but it looks good and its solid.

[flintstone mop]

The ALC adjustment should be done extremely careful. The 150watts will eventually take out the RF final. But you DO need that 'headroom' for nice positive peaks. I would assume you are going to amplify this radio, so try to adjust for legal limit AM from the linear, and keep the Icom below 25Watts.
If you have the schematic you could get hi-audio from your station mic and any processing equipment right to the balanced modulator chip.
This trick was done in my Kenwood TS850. You'll need a good isolation transformer for the balanced audio from your audio equipment to go unbalanced into the chip.
 
Here's a link from AMFONE about your radio

http://amfone.net/Amforum/index.php?action=printpage;topic=25323.0

There does not seem to be any tricks online to bypass any filters to achieve hi-fi audio for ESSB or hi-fi AM.
There were for my TS850 and I love the audio reports for MOPRADIO!!

Fred

[KC2TAU]

What confuses me, though, is that why have others who have done this mod to their radios reported great success through the lack of ALC activation whereas my radio still seems to have this issue? Doesn't running a negative voltage to the ALC jack in the back completely remove the ALC activation from the equation?

[Pete, WA2CWA]

Actually, I remember trying the mode on my IC-756 PRO II a number of years ago, and it didn't change the characteristics in the AM mode. However, no one at the receiving end could tell the difference so I removed the mod. I'm sure Icom has changed ALC circuit designs over the years in their rigs so it's also possible you might have component or adjustment issues within their ALC circuitry. In a way I like Icom's ALC design on AM because it's very difficult to over drive a linear with nasty positive or negative peaks.

[N2DTS]

I had the same (non) results with a pro 3 when I tried it.
I thought I was doing something wrong.

I think trying to make most of these radios work well and sound good is often much more trouble then its worth.
The receivers are filled with noise and distortion, the filters are no good, the 1st IF's are wide open, the output power is low, if you want to drive an amp, get a dx60 and mod it for good audio and use a nice old receiver or an SDR.

You can adjust the ALC pot in the 735, and you just have to control the power output, just like any old tube AM rig. You can not just turn the power all the way up and run the radio at 150 watts out, at least not for long.

Some rigs can sound very good on AM stock, with a limited high end, but with the right mic/voice/processing they sound good, but icom is not a brand known for that.

Actually, I remember trying the mode on my IC-756 PRO II a number of years ago, and it didn't change the characteristics in the AM mode. However, no one at the receiving end could tell the difference so I removed the mod. I'm sure Icom has changed ALC circuit designs over the years in their rigs so it's also possible you might have component or adjustment issues within their ALC circuitry. In a way I like Icom's ALC design on AM because it's very difficult to over drive a linear with nasty positive or negative peaks.

[Pete, WA2CWA]

On my PRO II, I feed the audio through the ACC jack in the rear that goes directly to the modulator. Haven't used the front mike jack in many years. Heil mike into a homebrew equalizer into the PRO II modulator. I remember working you on 40 meters with the rig. It was driving a SB-200.

[N2DTS]

I have heard them sound good, I never got mine to sound good, but never worked hard at it.
Did you have the ALC mod at the time?

I have had all three, a 1, 2 and two pro 3's.
I still have the cables to use the line out, ptt and the line input.

On my PRO II, I feed the audio through the ACC jack in the rear that goes directly to the modulator. Haven't used the front mike jack in many years. Heil mike into a homebrew equalizer into the PRO II modulator. I remember working you on 40 meters with the rig. It was driving a SB-200.

[Pete, WA2CWA]

I have heard them sound good, I never got mine to sound good, but never worked hard at it.
Did you have the ALC mod at the time?

I have had all three, a 1, 2 and two pro 3's.
I still have the cables to use the line out, ptt and the line input.

Tried the mod; didn't do anything worthwhile so didn't waste anymore time with it. For my taste, the PRO II sounded fine. Never had any complaints with it unless everyone I worked was being polite. Been using the Heil into the home brew equalizer since the early 90's on several different rigs.  I've also used the W2IHY equalizer which also works well. Since I'm not obsessed with Hi-Fi sounding AM with well-rounded positive peaks, shrinking negative peaks, etc. I just like making contacts and having a QSO. I don't need or want to sound like Barry White.

[Opcom]

Yes for a regular QSO they are OK. I'm OK with the receiver for SSB but am not so picky. I remind myself it was not a high end radio, it was a rather cheap one with simple innards. I prefer the older Kenwood TS430-S.

The one here is a possible target to be hacked or parted for its power stages and used in a rackmount black box to boost a 10mW, 'laboratory signal generator' for an easy no-tune way to drive a class C stage here. A special input on the PA of the IC-735 tells me it should be good for those long winded transmissions.