RM Italy KL 503 Crunchy

[Handy Andy]

No...thank us ...

NZ8N and many others contributed...

To help answer the question regarding the inputs...

The "realm" of CB is a money maker and a stigma - for those that wish to dive into the market of such things.

If you make an amp purposely for 11 meter - you're gonna' get an X sprayed on your back - referring to what they do with hazards too close to main stream streets and roads...

Subject to removal - so RM Italy as well as many other - even T/S - install boards, kits' or extra components in the traces designed not to interfere - but augment the budding Ham enthusiast. But generates hardship and learning lessons designed to teach, which does not help the typical CB'er looking to stomp and interfere with other conversations as if he did up a bolt -on accessory - not saying anything to point fingers - but 3 falls out of four with the Rat in the rink - they often do it - and plead ignorance.

The mods are simple and not often taught - even to other techs working at the shop (- read this any way you want, but) even secrets are kept from others in the same room. So the environment out there, affects those in there too...

As time progresses though, you may have the SMD version of this amp - which may make this conversion even more difficult - so if you run into problems - don't ruin the work you've done to get him this far - take time, get pics document the problem and get the help you need.

 

[NZ8N]

My idea was to remove the driver transistor, and bypass that, having the Pi attenuator feed the interstage bandpass circuitry then to the outputs.

Your idea is to leave the driver intact, but change the low half of the bias (R19 6.8k) to a lower value, which does 2 things, lowers the input impedance to the Gate, thereby changing the Class of the Driver stage, then readjusting pot Trim1 to bring it back closer to Class AB (also higher current through the Bias circuit itself). Is there any way to trace the feed voltage trace to L12/C26 so to be able to insert a current meter, manually key the amp (no RF), and adjust the Driver Bias for idling current, like to 100mA (they are using IRF520's or equivalent).
Then, by removing the either or both of the Source resistor (R17) bypass caps (C21 and/or C22), which reduces the gain at RF frequencies.
I would start with the C21/C22 idea first, then maybe the R19 lower value.

 

[Greg T]

No...thank us ...

NZ8N and many others contributed...

To help answer the question regarding the inputs...

The "realm" of CB is a money maker and a stigma - for those that wish to dive into the market of such things.

If you make an amp purposely for 11 meter - you're gonna' get an X sprayed on your back - referring to what they do with hazards too close to main stream streets and roads...

View attachment 47684​

Subject to removal - so RM Italy as well as many other - even T/S - install boards, kits' or extra components in the traces designed not to interfere - but augment the budding Ham enthusiast. But generates hardship and learning lessons designed to teach, which does not help the typical CB'er looking to stomp and interfere with other conversations as if he did up a bolt -on accessory - not saying anything to point fingers - but 3 falls out of four with the Rat in the rink - they often do it - and plead ignorance.

The mods are simple and not often taught - even to other techs working at the shop (- read this any way you want, but) even secrets are kept from others in the same room. So the environment out there, affects those in there too...

As time progresses though, you may have the SMD version of this amp - which may make this conversion even more difficult - so if you run into problems - don't ruin the work you've done to get him this far - take time, get pics document the problem and get the help you need.

You're absolutely right, and I had no desire to slight the help of others. I thank all of you for weighing in.

This sure is a different time than when I talked on my first radio in 1964. There were 4 of us in town with radios, and nobody even thought of amplification. I talked on an RCA Mark VII !! I laid out of it for quite some time after the 70s and then returned in the 90s only to find everyone sounding distorted, crunchy and ugly. Being a musician all my life, I am an audiophile and HATE to hear these radios on the air where you can't understand a word they say. After researching a little to see what people were using I just shook my head. Traveling around as i did, I never took the time to license up, although I did grow very fond of the Amateur equipment. The quality difference remarkable, and is why I run a Yaesu today, and have for quite a number of years. I could never understand my friends' desires to spend $600 or more on a Galaxy Saturn, when a used HF rig in very nice condition was less money.

At nearly 68 years old and physically challenged, I still have a thirst for knowledge when it comes to this stuff. But I know my limits. I'm always excited when I find a way to improve something and have the ability to do it myself. Finding folks like you guys who are willing to share secrets and methods is extraordinary, and truly appreciated. It just saddens me that so many people have to jump on the band wagon and push junk into the market in the name of the almighty dollar. I'm still old-skool! I believe that if you sell a product it should work! LOL, maybe that's just me.

EDIT: OH! If any of you guys are, or thinking of building an old school small block chevy, i'm your guru! LOL

 

[NZ8N]

Addendum - With the amp keyed manually (no RF!), (jumper the Anode of D11 by RL1, to Ground), measure the voltage across R17, should be equal to or less then 4.7v. at exactly 4.7v, the Driver is drawing exactly 100mA.

Before you start making adjustments, though, measure this voltage to see what they set it at the factory, and report back to us.

 

[Tokin]

Well, that's a given. We all realize that. BUT my buddy is, shall we say, quite lacking in the coinage department? He's on the back side of 70 and post stroke, needs something to stay busy, and decent amplifiers today are nearly impossible to find without mortgaging the house. He had a nice running Texas Star DX-250 that was pretty clean and talked well until his radio decided to throw a 16 watt carrier into SSB. Tried to find him another one, new or used for a decent price. Not gonna happen in this economy. Most builders are not even building for lack of parts.
He had no choice but to grab what he could afford and now we just want to make it work.

Is his dx250 repairable? I have some used toshiba 2290's. If all it did was fry the pills i can help with that.

 

[DoctorAudio]

You bought the wrong one. You should have bought the
RM Italy KL 503 Creamy

 

[Greg T]

Is his dx250 repairable? I have some used toshiba 2290's. If all it did was fry the pills i can help with that.

I believe his would be repairable. It has SRF 2072 pills in it, though, which means everything would have to be rebalanced and matched. Thanx for the offer.

You bought the wrong one. You should have bought the
RM Italy KL 503 Creamy

LOL.... good one!

 

[Tokin]

I believe his would be repairable. It has SRF 2072 pills in it, though, which means everything would have to be rebalanced and matched. Thanx for the offer.
LOL.... good one!

I wont be stymied.
The mrf455 is a direct replacement for the rf parts srf 2072 https://www.worldwidedx.com/threads/old-mc-250-texas-star.249951/
I have a silver streak 150 with a pair of mrf455's ill donate to the cause. The amp works as it should or it did when i put it up so he can use it as it is or swap the pills into his texas star.
You can pm me an addy.

 

[Eldorado828]

I wont be stymied.
The mrf455 is a direct replacement for the rf parts srf 2072 https://www.worldwidedx.com/threads/old-mc-250-texas-star.249951/
I have a silver streak 150 with a pair of mrf455's ill donate to the cause. The amp works as it should or it did when i put it up so he can use it as it is or swap the pills into his texas star.
You can pm me an addy.

Now if only our country could pull together like that!

 

[Greg T]

I wont be stymied.
The mrf455 is a direct replacement for the rf parts srf 2072 https://www.worldwidedx.com/threads/old-mc-250-texas-star.249951/
I have a silver streak 150 with a pair of mrf455's ill donate to the cause. The amp works as it should or it did when i put it up so he can use it as it is or swap the pills into his texas star.
You can pm me an addy.

Mr. Tokin, you are a true gentleman. He will be home this weekend and I will tell him. He will be thrilled. His elder brother just turned 75 and is going to retire after 50+ years of driving. He is going to live about 45 miles away as the crow flies and he'd like to talk to him on the radio in the evenings. He really would be appreciative. I will PM you. Thank you, sir.

 

[Slowmover]

Mr. Tokin, you are a true gentleman. He will be home this weekend and I will tell him. He will be thrilled. His elder brother just turned 75 and is going to retire after 50+ years of driving. He is going to live about 45 miles away as the crow flies and he'd like to talk to him on the radio in the evenings. He really would be appreciative. I will PM you. Thank you, sir.

Hope you’ll update this as gear comes together.

 

[Greg T]

Hope you’ll update this as gear comes together.

Absolutely do my best. He lives a distance from me so I'll try to get it all working on MY bench before he gets it. My plan is for him to connect it up, turn his mic gain down and talk.

 

[Tokin]

Mr. Tokin, you are a true gentleman. He will be home this weekend and I will tell him. He will be thrilled. His elder brother just turned 75 and is going to retire after 50+ years of driving. He is going to live about 45 miles away as the crow flies and he'd like to talk to him on the radio in the evenings. He really would be appreciative. I will PM you. Thank you, sir.

No problem. I keep stuff around just in case. I don't mind helping as many here have helped me and are helping with getting my gear repaired and up to snuff.
I got your pm and Ill try to get it in the mail this week if not Monday for sure.

 

[Greg T]

No problem. I keep stuff around just in case. I don't mind helping as many here have helped me and are helping with getting my gear repaired and up to snuff.
I got your pm and Ill try to get it in the mail this week if not Monday for sure.

I'd at least like to comp you on the shipping costs!

 

[Tokin]

I'd at least like to comp you on the shipping costs!

We'll discuss that after you get the amp and get your friends amp running. Ill bet shipping wont be much more than $10