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RM KL-500: Convert to key line?

R

RogerTango

Member
Jun 20, 2008
5
0
11
The current VOX setting of the KL-500 works fine, mostly... but Id like to interface it with the key line from my HF radio. When working CW, the KL-500 likes to do a lot of VOX switching.

If I disabled VOX all together and manually switched the PTT relay in the amp, Id be happy. Of course I know I need an interface to isolate the amp keying from the radio.

My question is, how do I go about doing this?

I also do not know how to get the PCB out of the amp case, I never tried. I dont see any thread holes on the heat sink so I dont suspect there are any transistors held in place that way, so Id like to hear from someone else that took the PCB out of the heatsink/case.

Im guessing here, I need to cut some PCB runs to disable the VOX from energizing the PTT relay, then manually apply 12v to the relay to engage it. If so, that would be a simple mod, well suited for my simple mind! HA HA! The rig to amp interface I can manage on my own.

The amp is run strictly on HF, mostly 40m and mostly CW.

Thanks-
RT
 

No need to take it out of the case, rmovee the screws that hold thee slidable bottom plate in place and slide the bottom cover off it.

http://home.hetnet.nl/~l.van.lelieveld/

Click left on: Ombouw 27MC eindtrappen
And have fun

Rebuilding the KL500 for 1.6 to 30 mHz for 400 watts output
Including detailed instructions, pictures and also how to key the amp by the radio directly bypassing the HF keying

The amp already hass an transistor keying the relais, so you can use an small signal deleivered by your radio to switch the amp to rx/tx

Had an KL500 and did the modifications, nice to have with the FT 100 on hollidays and the switch mode PSU of 80 amps.
 
JustMe,

Thanks so much for a prompt reply.

My amp board is rel 4.0, and does not "match" the picture at the website.

I ran the website though Google language translation, but I still have some
difficulty understanding.

The best I can understand, the female RCA is connected between GND and the COLLECTOR of Tr3.

http://www.rmitaly.com/download/manuals/KL500-manual_rel_400.pdf

It appears a small voltage is applied to the base of Tr3 to switch it, as it appears the EMMITER is already at GND.

Please forgive me, my electronics is weak and I am learning as I go.

Would a close of the circuit/short between GND and COLLECTOR of Tr3 be what I am trying to accomplish?

Also there is mention of the capacitor, I do not understand the translation regarding it. I have a C1 and C5 at the ground of the input SO-239.

Than you so much,
RT
 
The collector of that transistor is used to pull down the relaiscoil to minus there.
Normally the transistor base will get an small voltage when the amp is driven by HF, the pickup C then feeds an small rectifier that will add the 0.6 volt needed to switch the transistor, that pulls the relaiscoil to minus.

Now you just add the switching line of your transciever directly on the spot of the collector, and thereby closing the relais by pulling the coil to ground there, it only takes 100 Milliamp or less to do so.

Contrary to my FT 847 that doees thee same of my SB-1000 from Heathkit, wich uses 300 Milliamps to close the tx/rx relais, wich is too much for the switching line in the FT 847, that is why i need an ARB 704 Switcher.

In the rebuildt KL500 the switching transistor is bypassed and the relais directly controled.
If you want to use it for SSB, do change the bias network as you can see on the pictures.
Donot forget to completely scroll down, lots of info and pictures.
The C he was writing about is directly soldered on the pad where the PL259 connector ends up, clip the lead there of the C but do not unsolder it, the wire of that C is soldered through the pcb and connected to an pad underneath.
That connection must not be broken.

Furthermore i beefed up the wires for DC, added fans on top, and in the lid to cool the new ferrite baluns.
The PL259 connectors had an extra ground wire connected and soldered to the ground plane of the PCB improving efficiency and grounding.

The fuses were altered to automotive fuseholders and 3 x 15 amp were put in there.

The fans are temperature controled, different as he did.

The rest of the rebuild is only interesting if you want to run the KL500 from 1.6 to 30 Mhz, the original is good for 12/11/10 meters.

The lack of an good Low pass filter means you need to switch passband filters for each band if you want to use it on 1.6 to 30 mHz.

I got my KL500 for free, and now it works fine 400 to 500 watts output on HF driven by the FT 100 on our hollidays with 10 to 15 watt input.

If you need more info, just ask.

73,
Cor
 
Thank you Cor, you have been both very helpful and friendly. I would like to do some more of these mods, you appear to be the most informative. Would you mind helping me as I do these mods please sir? With a little help, I am sure I can do what is needed to operate the amp without worrying about burning it up.

I am running it on 40m (7mhz) SSB & CW now and it appears to be doing fine, I can get 400w, but normally run it at 300w (300w Vs. 100w on CW is a big step up!), but Id like to get the amp in "proper" shape.

Many thanks-
RT
 
Justme said:
The rest of the rebuild is only interesting if you want to run the KL500 from 1.6 to 30 Mhz, the original is good for 12/11/10 meters.

The lack of an good Low pass filter means you need to switch passband filters for each band if you want to use it on 1.6 to 30 mHz.
Click to expand...

These are the areas I will need more help on sir, the rest I can do myself... Ive already dont the bypass fuse mod and have a 30a in line now. I also use computer power supply fans to cool the heat sink fins, another fan will be added soon to circulate air INSIDE the chassis.

I know nothing about passband filters in specific, but if you are willing to help, I am willing to try! This is something I very much want to learn also!

By the way, this is the Google translated page that I see:
http://translate.google.com/translate?u=http%3A%2F%2Fhome.hetnet.nl%2F%7El.van.lelieveld%2Fombouw%2FOmbouw.htm&sl=nl&tl=en&hl=en&ie=UTF-8

Thank you kindly,
RT
 
:wub:Normally the bias is derived directly from 12 volt line, we know that this voltage does change an lot under load, and some even crank up voltage to 15 volts.

What happens then is an excessive increase of bias, the transistors will pull an lot of amps in idle and since there is no good temperature tracking of the transistors the amp will "run away" thermally.
Pulling more amps, getting hotter, thereby pulling more amps etc.

He (i) prevented that by feeding the bias tee though an regulated source, an 7808 (8 volt) voltage regulator, so that the bias now is always the same voltage independent of the load.

You can see the changes made on his amp, since he put this on the net the factory adapted this change on the PCB.

http://home.hetnet.nl/~l.van.lelieveld/besturing lowpassfilters/besturing lowpass filters.htm

Here is how he changes the LPF's

Normally the PSU delivers the power through the output transformers, wich adds an extra load on the ferrite transformer taking the ferrite close to saturation.

The copper wound coils is the new way to feed the amp, without running the power through the ferrite balun.

http://home.hetnet.nl/~l.van.lelieveld/
Click on the left side on home

Here you can see his 1KW transistorised PA that delivers 1.2 KW at ease, with band Low Pass Filters
It will use 120 Amps at 14.4 volts measured at the transistors..

I run the KL500 in SSB without it getting war, he used an klixon temp switch to switch in the ventilators, i used an NTC with an LM317 and variable pot meter to run the fans from 0 to max depending the temperature sensed by the NTC that is mounted between the transistors.

I could pull 500+ watts from it in SSB at 80 meters, this is pushing the envelope an bit....

Normally i keep it at 400 watts from 160 to 15 then 350 to 300 up to 10 meters.

WARNING

USING these power in FM is leading to an certain death of the amp...

Keep it real and limit in FM power to 200 or 250 watts...

The transistors are rated for max 100 watts output, some losses in the combiner and low pass filters and with 400 watts output you are at the max.
To get an more even output from 160 to 10 we changed the output transformer for the new one you see in the picture.
The original was not good for the low frequencies, so adding some ferrite and other types ferrite took care of that and increased headspace for the increased power through the output transformer

The factory came out with 2 amateur HF PA's wich were derived from this design, automatic switching bandpass filters and all
HLA 300 is the amateur version, wich complies with all our European laws considering harmonic output etc.
http://www.rmitaly.com/scheda.asp?IDGr=1&cat=0&tipo=188
Here's the link to it, find the schematic diagram as given there for comparison

Or else you can try to make his 1.2 kw amp ;)
That one has 4 modules with each 2 transistors combined in one amp, switching LPF's and all.

I regularly have an QSO with him on 80 considering these amps, in wich we exchange our experiences.

Take care,

Cor
 
Last edited:
the bias mod is well worth doing, i prefere a 10 or 22 turn variable resistor in place of the 390ohm fixed resistor so you have the ability to set idle current to suite whatever beta transistors are fitted in your amp,
using the 7808 gives a failrly stable bias supply but the actual bias voltage at the transistors still drops as you drive the amplifier harder, it does not fluctuate with supply voltage variations like the factory unregulated setup,
the thermal tracking is also a very good idea, i use a different layout to the dutch guy, both methods work ok,

justme,
i dont understand what you mean by saying the factory adopted this change on the pcb,
the rev2 kl500 used by the dutch guy had the place for an undersized regulator that was unused, the later revisions dont have any place for a regulator leaving you with little option but bolting the regulator to the side of the amplifier,
the rev5 pcb uses a larger bias pass transistor which i have not tested for vdrop yet,
none of them use any form of thermal tracking from the factory.
 
Basically the owner of the site has worked on the red type, i have the black KL500 with the MRF transistors.

Basically the same, just very minor different input and output impedances to work with.

The first red KL500 he reworked didn't have the PCB islands to put in the regulating circuitry, the second one did have the circuitry or pcb tracks in place, maybe that was why he mentioned this, i'll have an qso on 80 with him this week and ask him.

Looking at the Motorola service bulletin in the RF book (1980?) where the first description was of an double MRF 454 (different transistor as in the KL500) i went from there to stabilise the bias.

Running an tracking diode between the transistors i can keep the bias very stable, and cold or hot, the amps pulled by the bias is within 20 milliamps the same.

Since i use regulated cooling the amp never gets hot, lukewarm in long qso's is all i get.

For an given amp i had an week of fun, getting it working within the spec's i need to comply with as ham here, since our country is densly populated an ham here better takes care of having an clean signal.

Somewhere on an mountainslope in France with the nextdoor neighbour 1 mile away it's all less critical ;)

But professional interest and just wanting to get the best out of it, i had it tested by our local FCC and it made the test perfect.

Another fun project done, the SB-1000 has an new 3-500ZG waiting to be put in,ending the restauration.


Take care,

Cor
 
cor the red one that he mods is the early rev2 which had the islands for the regulator, the second pic with the homebrew transformers is a later revision 3 or 4 i would guess,
i have been modding the rm amps to make them more stable/durable since they first came out, when i saw the dutch guys hf mods i realised i was not alone, he does some of the same mods as me and for the same reasons even though others have told me its a waste of time, at least two of us and all my local stations know its not a waste of time;),
not tried the bifilar wound dc feed to the collectors, motorolla say it improves the output waveform without hurting output power, that idea is used in the motorolla application notes and in some newer hf set pa stages,
hes an interesting guy, if you speak to him please ask him what regulator he used in the red amplifier, its a smaller package than the regular78xx series regulators and makes a much neater job if it has the current capacity,

thanks.
 
Since you are from the UK and liscensed? look for him on the Dutch net late at night PA3EKA
Another friend, also made some nice tube amps, http://www.xs4all.nl/~pa0fri/index-split.htm.

As far i know he uses the 7808 too, but i'll ask him this week when i'm on the net.

The basis of these RM amps is the engeneering bulletin from the 80's in wich Motorola made the first broadbanded amps for HF, i still have that RF Parts book here on the shelf.
Made an 2 meter lineair amp from 2 x MRF 247 20 years back, still working.

Nothing wrong with the basic design, but RM cut an few corners in their design, basically because the amps were for 10/11 meters, and every penny saved multiplied by the 10.000's amps is big money.

With the mods you did, or here on our side of the pond, you can convert them to decent amateur use amps, just the purists that know they come from the CB band will always find an reason to put them down.

That is why i had mine measured by our FCC to see if mine complied to all demands for pa's here, wich it did, without problems.
Basically when you have some understanding of PA's, be it tube or transistor or Fet amps, you all will come to the same mods.

Some amateurs with less time behind an workbench and lacking measurement
equipment and the will to bring an project to an good end will always have an disliking to these projects, and rather buy an Ham labelled amp.

I was liscensed in 1977, lacked money but had acces to parts, had an history of building (illigal) transmitters, amps, recievers etc.

So, in the start most my stuff was for those reasons homebrew..
Both my transcievers, FT100 and Ft 847 with Collins filters have seen modifications wich were tested and approved by the FCC (our version then) and did improve the transcievers considerably.

The Sb-1000 was bought as junker, and now is completely rebuild, working fine with the 23 year old Eimac tube but that one is now just 60% and the new 3-500ZG sits on the workbench to be put in.

Have an look here, he has English text translations too on most projects,
http://www.pa0fri.geerligs.com/

Looks like you and me are having the same fun in working the electronics ;)

Take care,

Cor
 
thanks for the links,
i have an as new ft100d in the spare room, its had 3 houres use at the most on low power from new,
have you looked at the lack of thermal tracking on the vhf/uhf pa?, i bought some higher flow fans to fit when i start using it, i would be interested in any mods you have done to your ft100,

also have a yaesu fl110 amp as featured on pa0fri's site, it could do with the input attenuator modding so my icom 703 drives it a little harder without having to use the compressor,

yes its fun experimenting, take away the soldering iron and radio is as interesting as watching grass grow:D
 
I added the Am filter, pita to do, but worth the work, performs fine in AM now, set the carrier at 25 watts modulated output should be 100 watts

Replaced the 40x40 x 10 mm fans by 40x40 x 20 mm fans double thicknesss, ballbearing type.

Cleaned the flux around the VHF/UHF fet PA added the standard circuitry i use to drive the fans i.e. 1K NTC LM317 and 2.2K potmeter with 2 1Nf C's for HF suppression.
Mounted the NTC on the sink near the power fet, and set the fans so that they run slow when the set is cold.

I initially wanteed to improve the bias for that fet, but other projects came up... and the FT 100 is used here for 2/70 on the repeaters we maintain as group.
On our hollidays in France i used the ft 100 and never had the Fet run away in this setup, even when the temperature was 35 degrees celcius in the shade.
Check the drains of the HF powerfets where they are soldered to the output transformer, there is an small gap bridged by solder, where problems can come from, cracks in the solder or not enough solder to keep the connection 100%.

Most problems of destroyed fets come from that....
http://groups.yahoo.com/group/FT100/
Here you can find some additional info,
Including mods, schematic diagrams, ESSB audiomods, doc's measurements, ATAS mods, settings etc.

http://www.k0lee.com/ft100faq.html#extrabands
Very informative site

That made the bias runaway mod less of an urgent project.
I did do some work on it, my ft100 had already some factory mods, extra grounding strips and copper flashing added.

I jujst replaced every screw in the set that held the pcb boards, added pointed washers after cleaning the chassis and set new screw in it wich had an copper layer on them.
That ensured an very good grounding of the PCB's.

My transcievers are switched on in the morning and off in the night, meaning they are on 16 to `18 hours an day.
Clean the inlet for the cooling airholes regularly, every 6 months i use an compressor to clean the insides out from dust.

Since the transciever is open then followed by an visual inspection and an quick basic measurement to see if it is still within specs.


Just glad i could be of some help,

73,
Cor
 
i have the sunon 10.8cfm fans from the usa and longer screws ready to go in,
not looked at my 100d but i have looked inside others and the output fets had no solder to the transformer endplates, the endplate goes through the board and solders on the underside then feedthroughs bring the connection back through the board to the fets ( terrible idea imho ) i saw the mod using small pieces of brass to bridge the gap, getting a soldering iron in there to solder them in a conventional manner without touching anything else wont be easy,
i dont have the am filter, they are hard to find here and expensive, if i wait long enough a scrap 100/d may come along that has the am filter fitted:D,
the fm filter is wide, i would prefer a 8kc filter and may change that in the future,
filtered compresed air and a soft brush is the method i use to keep my radios clean inside, i just cleaned out my jrc135, cleaned all the coaxial and edge connectors, its surprising how much dust gets in there after a while,
if i have any problems with the 100d grounding i will clean them all with caig deoxit and treat them with caig pro gold contact preservative, been using those products for years on hifi connections /mic switches ect and they work very well,

thanks cor(y)
 

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