N3IBX Collins S/Line AM Modification Page

This is the N3IBX Collins S/Line AM modification page. The articles I have listed came to me through the generosity of the Collins reflector members when I posted a query on an AM modification to my 32S-1.I have not tried any of the mods listed. They are posted as a reference for those who may want to attempt it. If anyone has information or has a modified S/Line please let me know and I'll post your listing. I plan to modify my 32S-1 for AM in the future. Good Luck and Happy AMing!

Many thanks to those who contributed to my query for this modification. Without them this would not be possible.

I just purchased a 32S-1 and in the manual is an addendum with the circuit details for the

modifications for am. It lists 3 additional parts, .001 cap, 10k pot w/sw, and 40 uufd

cap. Add the parts between plate of bfo tube and grid of mixer.

This modification will permit normal am operation by bypassing the mech. filter.

Load same as per instruction book.

Then keep knobs in lsb or usb.

Use the 10k pot and mic gain to load the transmitter up to about 150 ma plate current.

Speak into the mic and adjust so that the plate current needle will just wiggle.

Turn switch off to go on ssb.

Use phone patch on xtr for mic input.

Use ptt, (j4 on xtr) for ptt.

Put pot/switch in place of mic jack on front on xtr.

I have not tried to use this radio in am as I do not have a mic yet and . This modification

is by KH6DK and is dated April 1961.

I would be happy to scan this document for you if you like. It has a diagram of the

2)I'm the one who put this mod out on the Reflector several months ago. It was originally obtained from Floyd Soo, CCA.

I have used this mod in my 32S-3 for a year or so. The audio reports have been excellent and most people don't even know that you are transmitting on only one sideband. They are amazed that a Collins S-line can transmit AM!!

3)FYI I did this mod. to a spare 32S-3 and it works very well! I use it

every now and then even though I have a 32V-3. I built it in a small mini

box and attached the mini box to the PA cage ( no holes required! )

4)just purchased a 32S-1 and in the manual is an addendum with the circuit details for the

modifications for am. It lists 3 additional parts, .001 cap, 10k pot w/sw, and 40 uufd

cap. Add the parts between plate of bfo tube and grid of mixer.

This modification will permit normal am operation by bypassing the mech. filter.

Load same as per instruction book.

Then keep knobs in lsb or usb.

Use the 10k pot and mic gain to load the transmitter up to about 150 ma plate current.

Speak into the mic and adjust so that the plate current needle will just wiggle.

Turn switch off to go on ssb.

Use phone patch on xtr for mic input.

Use ptt, (j4 on xtr) for ptt.

Put pot/switch in place of mic jack on front on xtr.

I have not tried to use this radio in am as I do not have a mic yet and . This modification

is by KH6DK and is dated April 1961.

I would be happy to scan this document for you if you like. It has a diagram of the

The major difference in the two units is how the 32S-3 is designed for

CW operation. In that unit the balanced modulator is grounded and in

the 32S-1, a tone is generated into the audio circuitry.

6)I have a 32S-3 and have thought about trying something like that myself.

I would appreciate it if you could keep me posted. I presume they would

allow the carrier to pass along with one sideband. My concern would be what

would happen to the PA and or the power supply trying to handle the extra

power going into the carrier. You would probably have to reduce your drive

quite a bit to allow for that. I had thought about playing around with

reduced carrier which would ease the burden onthe equip.

7)here are large differences between the 32S1 and the 32S3 but not in the

area of the AM mod. It works great. Many of us have done the mod with great

results.If properly done there are no non reversible or obtrusive changes to the rig.

The mod does not change the SSB operation.

Go for it. You will like it. ( That is if it is the mod that we all use. )

8)It can be done, but you can only load it up for 30 watts or so.

9) I have had excellent audio reports. Even though only half a side band is transmitted. (I have

had better reports using USB than LSB.)

10) Collins 32S-3 AM Conversion:

Using small coax, like RG-174, connect the center conductor of the coax to

Pin 12 of S8J (emission sw). This is the point where the BFO output coming

from Pin 6 of V2. C92 (.01) and L28 (2 mh) can be found here. In series

with the center conductor of the input coax, will be a .01 cap and 5k pot to

In series with the wiper of the 5K pot, is a SPST switch and another .01 cap

and the center conductor of another piece of RG-174. This output coax goes

to Pin 7 of V4. The coax shields should be grounded. Tune and load

transmitter in SSB mode.

To operate, set emission sw to either USB or LSB, close the SPST switch, key

the xmtr and adjust the pot for 100-125 ma Plate Current maximum! Back mic

gain down so that only the highest audio peaks will cause a VERY SLIGHT

movement of the plate current needle!

That's it! Good luck!

11) I mounted all my components on a small bracket and

attached it to the final tube cage. No holes were drilled.