The AM Forum

Hello everyone,

I had a few questions that maybe someone could assist me with. I started work on converting my Harris Gates MW-5 for opperation on 160M and have been working a few issues out with the OSC/IPA. Being that this machine works in the range of the broadcast band I need to adjust my exciter a bit. My question is if I bypass the dual oscillator board and feed the IPA amp with 160m signal from a VFO will the IPA amplify this signal being that it is slighlty above the range of 1640 kc? On the IPA there is a set of four coils with a strip of adjustable ferrite rods that may control the matching? Any help or insight would be greatly appreciated.

Thanks
-Ben

Since BAMA doesn't have a schematic` of the MW-5, could you scan one in so we can help?

Phil - AC0OB

Sure,

Here is a block diagram of the IPA chain. Its located in the upper right hand of the drawing. I have also included a picture of the IPA section if it is of any help. The final transistors or Motorla SJ7349's in the picture.

Thanks

One more schematic.

And here is the text portion.

Those are not really what we call block diagrams but it appears a 30 V P-P sine wave from the oscillator is feeding the broadband IPA that is peaked by L1 and associated caps.

The broadband IPA appears to be a switch-mode amp for higher efficiency. The output of the IPA is filtered by L2 and associated caps to turn the pulses back into a sinewave.

The C1 cap in the IPA may would have to be modified for a change in frequency.

Some questions are:

1. is your VFO capable of supplying a 30 V P-P since wave into the BB IPA switcher
2. Does your VFO have a low enough impedance to drive it
3. Are you going to change components in the Final as well to tune to a higher frequency
4. Do you have the test equipment and an electronics background sufficient to make these changes

Phil - AC0OB

Feed the VFO input thru a .01 cap or so to the base of one of the oscillator transistors.  You might have to play with the level a bit so as not to overdrive the transistor.  It doesn't appear that there are any tuned circuits between the oscillator and the driver output.  Tune L2 for max on the inputs of the IPA modules.  If you run out of room, you'll probably have to trim the inductor and/or remove one of those C3 capacitors.

It appears all the coils on the IPA outputs are ganged together.  Since you're going for a frequency well above 1640 they should most likely be all the way out (ie min inductance) or close to it.  I'd guess you'd then tune the slugs for max signal out of the IPA.  If that coincides with absolute min inductance, you'll probably have to trim the inductors a bit.

What are you going to do about the JK FLip FLop divider (U1)?

You might be able to inject a 3-5 volt TTL signal into R19 with the strap removed if the VFO has a digital output.

Phil - AC0OB

You run the oscillator at 2X the carrier, or whatever the divide ratio of the flippy flop is.  A good strategy anyway, to keep RF leakage from the xmitter into the VFO.  

But yes, you could certainly feed 5V or so into that jumper arrangement.  I don't think it would need to be a TTL square wave, but a TTL Schmitt trigger would easily solve that.

The more stages isolating the input from the output the better, and it's generally easier to use the existing signal shaping and level circuits.  However I point out that all of this is edumacated conjecture as I've never seen, much less converted, a MW-5.

Thanks for the varrious ideals so far. I finallialy got a chance to run 3 phase ac into the garage this evening so now some real work can start. For the sake of simplicity, and just for a good experiment I think I will try to feed 5v into the jumper setup to get an ideal what what this thing wants to do. If its comes down to brass tacks Im sure I could buid a simple oscillator/amplifier with all the tube junk around here to act independently of the existing setup.

-Thanks!

WOW lucky guy......3-phase power at your fingertips!

This would be interesting to read your progress of a solid state TX, and a big one, to the ham bands.
Reading the circuit description, you could get legal limt from the solid state part of the TX. They mentioned something about the tube final. Where is the modulation taking place?
Some operating tips and stuff

http://www.oldradio.com/archives/hardware/MW-5tips.htm

Little more gooogling reveal the MW5 might be a smaller cousin to the MW50. Hence a similar technical configuration. Watch out for the 15KV supply
Fred

Hey Ben,

Congratulations on your acquisition of the Big Harris.  Hope to hear you on the air again with your Valiant while you work on getting the Harris up and running.  It was nice talking to you the other day on 75m AM.

73, John KX5JT

Here is an interesting 4-part read on the Harris/Gates years in Quincy:

http://www.thebdr.net/articles/prof/history/Quincy1.pdf

Phil - AC0OB

Believe this is a PWM rig, Fred.

Hi Ben!

I just became the proud owner of a Harris, Gates 2 Transmitter. I think it may be a more modern version of what you have.

Converting it to 160 or 80 is also a project of mine. I plan to feed a VFO into the crystal osc. area and take it from there. In checking for RF-frequency sensitive components....they are only after the IPA and in the PA and Final matching circuits. With parts changed out they are spec'd to 1.705mHz so it souldn't be too too hard to convert.

I have gotten some excellent reading info from the "Class-E" transmitter group. Please google them!

Good luck! I'll Keep you posted.

Mike VE3BNB

Great read!!

Hi Ben,

I powered up the low level sections of my Harris Gates 2 transmitter and found that the metering, oscillator board and IPA are working. Since I don't have a 1N4056 I couldn't get the high power or the modulator tested.

But I did test the oscillator board and the IPA with a crystal that I have that works out to 1,926.6665kHz and found that the osc. board works and the IPA puts out around 15watts and gets warm. I brought the signal up a fair amount by tuning the IPA output roller inductor that is located before the power divider. I believe your MW-5 is similar in layout and board stages. On the schematic for the IPA it shows the output tuning is the first stage of frequency sensitive components. Specifically there are about 5 doorknob type capacitors that bring the roller inductor into resonance. Later on this week I'll try and remove some of them to try to get the unit up in frequency.

My transmitter was factory tuned for the bottom of the AM band and I'll be reducing a lot of "C" to bring it into the 160m band.

The crystal I used was from an FM lowband radio. Let me know and I'll send you one. At least then you can test and modify your TX chain before you hook up a synth. to it.

Take care. Mike VE3BNB


 

Hello again,

Its been a bit since Ive got a chance to re post due to studying for another enginnering test for work so I havent be able to really tinker with the MW5a. I hit a small snag in the 3 phase and my AC unit so I may have to go another route as far as powering this thing up. Luckly the rest of the transmtter is powered just by 240vac with the exception of the B+ transformer. With a quick rewire of the xfmr I think I can have it opperate from 240 as well, just need to move a few things around.

Mike,

Thanks for the information and Im about at the same step your at with this machine here at the house. The MW5a was built in 78 so your Harris Gates II is a few years younger but from what I can tell about its has similar circuitry for the most part. The transmitter here was tunned up on 1300kc and there are a few things they changed around in the pi networks from the IPA and amp section. For instance on the OSC/IPA deck there are locations for three caps in varrious areas. The transmitter only has 2 caps in the input and output stages for matching at the frequency, furthermore I have found a list of parts to be change in determining frequency. So Im going to have to mess around with that next. I may have to take you up on the offer for the xtal. I tore appart my shack last night looking for a crystal that might work and set me up on 160 but that didnt work out as well as I hoped. Ill include the scan of the list that I found. Hearing that your having luck with the Gates II makes me motivated to work on this machine again.

Thanks again to everyone and Ill get more pictues and junk like that up soon.

-73
Ben

Would this work with out burning the house down?

73
-Ben

MW5a pictures

More pictures

Even more pictures.

VERY nice looking transmitter.
the TX audio should be unbelievable!!!
WBCQ 7415 audio, even though shaped for short wave transmission is about the best I have heard. Probably the only MW50 ever converted to short wave!!!!

Just get those solid state guys to behave.

Get whatever power you can out of it. Coz we need static crushers and QRM crushers on the bands

Fred

Thanks alot!
Hopefully if all goes to plan 160m will be alot more interesting. Getting mosfets working is half the battle.


-Ben

Wow, congrats on the MW-5 At one time I had three that I kept in service, two 5A and one 5B but now down to just one as a backup for a DAX. The PDM modulation system works great in the MW but if you have not ever worked on one before you will find that the power control and start up systems will be a task to master. Reducing power for "ham" services may allow you to get away with a smaller HV supply then the original three phase 10 kV monster. Also keep in mind that the PA deck is in series with the PDM modulator tube and floats at that potential above ground so be careful!

Thanks for the headsup on the PDM deck. Have you ever had any issues with the mosfets dying on you? Last night I got around to buiding and doing a quick tests on a phase converter. Ill take a look at it on the scope tonight.

-Thanks
Ben

I have not had much history with IPA failures, the stupid class D modulator driver tends to fail but have not had any issues with the IPA. Running them at 5 kW they do go thru a modulator tube every year and a PA tube every other, also have seen the choke in the PDM stage burn out,  replaced plate transformers and best of all the two solenoids that short out the HV supply will sometimes fail and its very colorful when that happens. I may have a IPA deck from a MW-5 that I squashed up with a backhoe, that was a particularly nasty bad tempered and highly modified by a past engineer MW-5b and it deserved to die but did save lots of the innards first so if you need parts I may have them.  If you have a strong stomach take a look at:  http://staff.salisbury.edu/~rafantini/gates&collins.htm

Nice!

That'll teach it!!!!!!!!

BTW Timtron might have some tips about the MW5. He solved a very expensive problem in the WBCQ MW50 with damper diodes. Harris wanted $5000 for the diode stack. Timmy uses 4 tubes (?) to act damper diodes.

FRED

SORRY the link below would not save the pic from this link:
http://www.flickr.com/photos/28334187@N07

Hey any more news on this?

I got around to tinkering with the MW5a today. To start I had ordered a 80 meter xtal at 3.6700 kc from ebay last week for 4 bucks and got it friday. After doing a quick conversion to run everything with the exception of the HV transformer I hit the filliment button and the machine came to life. I checked all the filliment readings with a VOM and everything was where it should be. In the manual it states to run a clip lead from ground to pin 5 on the OSC pcb to start the oscilator devider. The first test was on the original 2600 xtal from where it lived (1300) Kc broadcast band. I also had connected my frequency counter to the IPA and it read out 1300 kc. Next trick was to run my 80 meter xtal and see if I could get out 1.835 which I was aiming for. I used another set of clip leads from the xtal socket to my FT-243 crystal , flipped over the switch and watched the frequency counter display read out 1.8347! I made a a few adjustments to the trimmer cap to relight the led to full brilliance and called it good.


The next trick is to get the phase converter and HV xfmr up. Or find a line distrobution transformer.

Thanks
-Ben

New Pictures

Updated pictures

Glowing 3cx2500

Harris developed a phase monitor kit that attaches to the front panel of the power supply cover that is a three phase detector. This kit looks at the ripple frequency on the HV (30 kV) supply and if it does not see the correct frequency it will turn off the plate contactor. It’s a PC board that mounts right on the front panel and you can easily bypass this because if you don’t you may have some issues getting the transmitter to keep the plats contactor locked in when you push the HV on, being that you do not have real three phase. Also remember that everything in the PDM/PA compartment is at extremely high potentials and although it’s a huge hassle do not operate the HV with the back cover removed! On the PDM control board will be power controls for high and low power, start with them turned all the way down. This will allow you to turn on the plate with no output from the PDM stage and no RF out but will give full grid drive to the PA tube and you should see grid current and be able to peak the grid then if your anywhere near resonance. The oscillator and IPA deck always run at full power regardless of the output power and all power control is a function of the PDM amplifier, the two little pots on the PDM control board. The little lights behind the window for the PA deck are 115 vac although they look like 12 volt car bulbs. They should come on with the filament power; let me know if you need any.
Ray Fantini KA3EKH

The glowing 3CX2500 would get some juices flowing as the excitement builds. Sounds like your taking a nice, thought-out approach to get the TX up to 160M. Hopefully it's smooth sailing.
It's gonna be hard to keep the ole girl tamed down, though. Build strong antenna components and tuner............hi

Fred

I would like to thank everyone again for the support, parts and help.

I have been asking everyone for there ideals and insight on getting this machine up on 160 so I have a better understanding of pit falls that may be advoided and the fact if I crunch a tube im done ha!

Fred, thats the next stunt is the tuner. I get chills thinking about it.

Thanks again Everyone, half the fun has been updating this page.

more to come

73
-Ben
-Ben