The AM Forum

Hi!

Just had my Collins 618S-1 up and running, so far only simple tests has been done.
Will have to check the settings for the modulator assy, it is supposed to do at least 95% but I'm seeing less than that.

It's an Amazing pice of work the all the servos tuning the circuits.
Unfortunatly, I have only a rough home made control head, have to do something about that.
I have the dynamotor power supply, so with the fan and servo circuits in the radio and the dynamotor, it's not the kind of radio that you would have in the bedroom, trust me...

Anyway, are there any other 618S-1 users here?

If you are not familiar with the 618S-1, it's an aeronautical tranceiver 2-25 MHz AM/CW making 100W.
XTAL controlled and completly automatically tuned.

Glad to hear the news on your 618S-1! Slight misadjustments of the RF stage can change the modulation. It always expects a 50 ohm load - there is really no loading cap/adjustment. How much modulation do you get on for example a frequency in band 1 or 2?

I have three of them. One is operable but not hooked up presently. I have repaired them as well. I have used the VFO from the SSB version instead of crystals. I had to make also a rough control, after figuring out the truth table, posted what I have on bunkerofdoom.

There are some for sale in NZ or AU from what I hear. They were recently retired from the local airlines and probably super clean, I was told this was discussed on mauldroppers message board by one of the NZ members, I think the handle was 4-400 or something. I don't use that board so know no more.

Anyway I love the 618S-1 because of all the servo action. not to mention actual RF tuning, as usual in Collins and others of the day.

There is one standing upright (stored) next to my desk with the cat's pillow on it. She likes it too.

BTW on band 4, Don't try to use a crystal or oscillator up to go past 25Mhz on band 4.

I spent a couple years getting one running, YouTube video at:

https://www.youtube.com/watch?v=2tP3Bkek-EM

This is one I did on the ARC-38, not a 38A USB radio but a real AM version:

https://www.youtube.com/watch?v=NDMRC-Plow0

This is the latest one at:

https://www.youtube.com/watch?v=HD2Y-zEcvKE

So as you can tell I wasted lots of time on that family of radios. Couple things that are real helpful. First you don’t have to run the fan with the case removed. Second and this is real helpful is remove the 115 volts 400 cycle after the radio reaches its tuning solution. If not the transmitter tends to hunt a little when keyed and also things are a lot quitter with the tuning voltage removed. And last but not least don’t waste time trying to use the original dynamotor power supply unless you somehow think you have to. The receiver, SMO or crystal deck was originally powered by use of a half wave doubler from the ships 115 volt 400 cycle bus. The dynamotor only ran when you keyed the transmitter to provide the HV for the PA and modulator. I used old GE Master base station power supplies being they provided the bias, +250 for the receiver and +650 for the HV and that works well for me.
Will also say that the most time and biggest problems were not the electrical systems but all the servo system had mechanical issues being all the little synchro motors were frozen, the gear box systems had frozen bearings, things like the little two direction motor in the 180L tuner would stick and the mechanical choppers would be bad. They would vibrate but the contacts would fail and they won’t track correctly.
You got to have several of these radios in order to get one to work.

An addendum, are you using the 180L antenna tuner with it? The tuner is an important part of the radio considering that it is not just a tuner but also the T/R switch. When it’s all configured correctly the tuner and the transmitter work together, but I will come back to the thing about pulling the AC Servo voltage after the transceiver and tuner reach a solution. A friend of mine who flew with that transceiver back in the old days on the C-141 tells me that it was common practice to pull the circuit barker that feed the servo/antenna tuner after the radio was set and tuned for a new channel just for that reason.
I have a three phase 120 volt 400 cycle power supply for that radio that was used by the commercial airlines that fits in the regular DC power supply rack that you can have for the cost of shipping.

Thank you Ray! I learned so much from your videos and advice when trying to get my stuff running, esp. the tuner.

'regular' DC to 400Hz inverters work but make very harsh tone in the motors. I have to wonder if it is worse for them. Have you used sinewaves such as from a MG or dynamotor?
I still totally agree with turning the servos off when done with tuning.

Have you done any more with it?
I just have not had time to revisit mine.

Hej!

Patrick, so far I have had it on the air for quite a few hours, as a matter of a fact I replaced the dynamotor the other day.
Detected an unwanted noise from one(?) of the ball bearings, so I just replaced the dynamotor, will repalce the bearing some other day.

I still have to make some kind of (improved) "control box" and solve the problem with feeding the X-tal oscillator with a"VFO signal".
The funny thing is, if I feed it with a VFO signal, the servo tunes the racks in to a position that is less than optimal, resulting in low grid drive and somewhat poor reception.
AND, I need two tuning slugs, since two of them are broken off.