ALC OVERSHOOT IN RM ITALY AMPLIFIER

[long night]

Hi Shockwave and the others here. You are all far more knowledgable than myself on this subject and extremely helpful. A little background on me. I enjoy radio and have had a stroke so I am limited as to what I can physically do. Radio is something I can do. I live in Vancouver Wa. There used to be Radio repair shops here, but sadly no longer. I am unable to drive so traveling to one is out. Without any nearby radio repair shops I thought I would try to make repairs myself. This is very fun for me especially when a repair goes right! Not always the case for me. Sending equipment out for repair is quite costly with today's shipping prices. So liking to work on radio equipment gives me great pleasure. Enough on me. Currently I have two amplifiers that need repair. One is an Italy 703. If I understand correctly from schockwave the RM3s are gone in it. I need to find a good replacement mosfet transistor if you can recommend one that is available for the RM3. My second amplifier uses EFR9530 transistors which I also ca not locate. If you know of a good available replacement transistor for this too I would greatly appreciate it. My memory sometimes does not cooperate so I may search for the correct word or term without success. Forgive me for this when it happens. I am slowly learning and you are all so very helpful. This is a great radio forum to belong to! Any tips and knowledge you wish to pass along I am very greatful for. Remember I am a beginner and a simple explaination is helpful to me.
Thank you all again Chuck Saylor

 

[long night]

If the rest of the group has not informed you enough...

When you "spike" a MOSFET - you have two things to concern with...

Saran Wrap and Surge Arrestor.

Saran Wrap - being even thicker than what is in the devices' package.

But the concept - of using thin material to insulate the Gate from the mess it has to control underneath it you only have so much insulation and if too thick affects the devices maximum useable frequency bandwidth

Surge Arrestor part; is in the Mess that in itself is designed to self destruct and blow a fuse, itself or a whole string of parts connected to it That is built into the device itself.

Ever use Saran Wrap in a Microwave? It'll eventually get too hot and melt onto your food - or worse...

View attachment 48112
Keep fresh batteries for the Smoke detector handy...
​

The Surge Arrestor is in the substrate itself - too much current is one thing - too much voltage - you can cause it to "backfire" - the power generated by the circuit - even if it's fed by less than 50% of it's maximum RATING for Reverse Breakdown - the EMF and EMP caused by overdriven Gates and the pulse generated by the mess on the opposite side - will cause the "surge arrestor" the design is, to fail - in a conducting condition - and either blow a fuse - melt a wire, burn a trace - melt lead or see above...

As you search for MOSFET ratings - one thing you do need to pay attention to is the Datasheet...

View attachment 48113
Too much of a good thing - usually is...
​

Some power supplies come with "overload protection" but are only as good as the ability to sense such conditions.

The problem with MOSFET's are their inherited "Zener" ACROSS (it's built this way) and how long it can stay "triggered" - a recovery issue - so as you put RF out there - any VSWR issues reflect their condition onto the leads of this device - and if excessive - will begin to clamp and keep clamping until it self destructs.

Hi Handy Andy. Please read my new post to see my level of experience and background with radio equipment. I am pretty new, but trying ti understand and learn from you and others who have far more experience than myself. Any explaination is helpful and simple instructions are too. If I don't understand I will let you know. If you then wish to explain further that would be great.
Thank you Chuck Saylor

 

[Handy Andy]

Ok! Welcome aboard...

Didn't want to alarm you but I also didn't wish for you to consider you're being brushed off...

IF it's necessary - I apologize if it seemed a bit too rough.

You deserve a good strong explanation to help you get to know your radio. We are here to help and many of us are quite passionate about our equipment.

Many consider a radio as an "electronic accessory" and even as a toy for a form of entertainment - until they realize it can help save lives - including their own.

It's not necessary to let us know you have a medical condition, but I am glad to know the post did not offend you.

 

[AudioShockwav]

As far as I know, Rocket Box electronics sells ERF 9530 in a 4 pack for 36 bucks.

73
Jeff

 

[long night]

Ok! Welcome aboard...

Didn't want to alarm you but I also didn't wish for you to consider you're being brushed off...

IF it's necessary - I apologize if it seemed a bit too rough.

You deserve a good strong explanation to help you get to know your radio. We are here to help and many of us are quite passionate about our equipment.

Many consider a radio as an "electronic accessory" and even as a toy for a form of entertainment - until they realize it can help save lives - including their own.

It's not necessary to let us know you have a medical condition, but I am glad to know the post did not offend you.

No need to apologize sir. You are not in the least bit rough either.Thanks

 

[long night]

As far as I know, Rocket Box electronics sells ERF 9530 in a 4 pack for 36 bucks.

73
Jeff

Seams like they are always sol out!