Thread Number: 70108  /  Tag: Ranges, Stoves, Ovens
Another Vacuum tube application soon to go solid state?
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Post# 930275   4/3/2017 at 01:45 by kb0nes (Burnsville, MN)        

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The LDMOS-FET technology continues to march on. Most radio and many TV transmitters today are being made solid state, and thanks to increases in frequency soon the microwave oven may no longer have a magnetron.

It will likely be a few years as Asian magnetron's are darned inexpensive but there are advantages to going solid state too.

A magnetron is a high power oscillator which simply starts to oscillate when it is energized. The frequency is determined by it's physical construction and really isn't all that stable. When the load in the oven cavity changes the frequency will drift around. Using a solid state power source the frequency is derived by a low power frequency variable oscillator then is amplified up to cooking power levels by these new transistors. Operating frequency is completely stable and can be varied over a relatively wide range.

All common microwave ovens have some form of carousel or stirrer to attempt to break up the standing waves in the cavity which cause hot and cold spots. By using a solid state power source the frequency could be varied at will which will cause the nodes and anti nodes in the cavity to vary. No stirrer needed.

Different foods could potentially benefit from being able to alter the frequency of the heating energy too. Frozen foods may respond better to a different frequency then microwave popcorn for instance.

This link is an interesting look as a number of ways that solid state power could improve microwave cooking.

Will be interesting to see how this technology progresses!

  View Full Size

Post# 930281 , Reply# 1   4/3/2017 at 02:20 by rp2813 (The Big Blue Bubble)        

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I'm on board whenever it happens!  I'm easily annoyed by burnt popcorn before all kernels have popped, which is how my Panasonic inverter likes to render it -- on the "Popcorn" setting to add insult to injury.


Yes, I own a fabulous space age avocado Penncrest popper and it does a beautiful job, but microwaving is so much faster and provides a disposable container.  Besides, if I'm going to invest that amount of time and trouble, I might as well toast up some blanched almonds.

Post# 930292 , Reply# 2   4/3/2017 at 06:27 by tolivac (greenville nc)        

TV transmitters have been solid state for the past 25yrs in the low and high band VHF.Only UHF is still tubed-Klystrons,and Klystrode tubes.Harris made the first solid state TV transmitters in anolog-now digital.The klystron type tubes handle powers for each tube-from 20Kw to 65Kw.And the tube only needs 5w to drive it to full power.The solid state "magnetron" s very interesting-will have to see how this come out and how soon.Maybe those UHF TV transmitters then will be SS.

Post# 930300 , Reply# 3   4/3/2017 at 07:51 by combo52 (Beltsville,Md)        
Solid-State Magnetron Replacement

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Great news Phil, Question can we retrofit this to the 1958 Hotpoint Electronic cooking-center at the warehouse ?

Post# 930308 , Reply# 4   4/3/2017 at 09:05 by panthera (Rocky Mountains)        
If they have the lifespan

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Then, great - the power loss to run a magnetron is easily 30-40%.

BUT - we've all seen the super short lifespans of so many appliances. I'd want a SS microwave oven to last longer than the two years max. we have gotten out of the Panasonic Inverters.


Post# 930321 , Reply# 5   4/3/2017 at 10:42 by kb0nes (Burnsville, MN)        

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Keven - I'd surmise that these should have a longer lifespan then a magnetron assuming decent design. Solid state electronics don't wear out so they could last. Of course the life span of a magnetron is pretty impressive too. The bane of any magnetron design is the need for >3Kv high voltage. In the olden days when it was done with a big transformer the HV supply was very reliable, but heavy, inefficient and expensive. The early model Panasonic inverters have proven to be a little fragile, but this was due to the HV instability in the inverter itself. The later models have been better judging from the ones I have worked on.

John - While a resto-mod would be cool it would wreck that classic. That needs to have a fully functioning original RF system to preserve the history.

Rex - Take a look at Fully solid state LDMOS UHF TV transmitters are available NOW. Except for the highest frequency/power applications I can't imagine any station buying a tube any longer today.

Post# 930495 , Reply# 6   4/4/2017 at 01:01 by tolivac (greenville nc)        

GatesAir has made improvements in their TV transmitter designs-now you can get high power SS UHF.So goodbye to Klystrons and Klystrode tubes.Normally I don't like SS transmitters because they can be more complex than tubed models and have higher parts count-those GateAir mode3ls show promise.Have seen earlier then Harris SS Platinum analog TV transmitter on Ch#8 in Richmond,VA.These newer GatesAir ones are much more advanced.If I were shopping for a transmitter would consider this.SW transmitters are adiffrent matter-they STILL have tubes!

Post# 930497 , Reply# 7   4/4/2017 at 01:18 by LordKenmore (The Laundry Room)        

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Audiophile types often still prefer tubes for audio equipment. And so...I wonder if a solid state microwave will find acceptance in audiophile circles. Or will audiophile types feel magnetron microwaves have warmer, smoother food?




Although.. more seriously, one tube amp maker has used the example of microwaves to show that tube technology isn't dead. So much for that example. LOL

Post# 930500 , Reply# 8   4/4/2017 at 01:38 by LordKenmore (The Laundry Room)        

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BUT - we've all seen the super short lifespans of so many appliances. I'd want a SS microwave oven to last longer than the two years max. we have gotten out of the Panasonic Inverters.


Yes, we have seen how long things last. Or don't last.


Being cynical, I personally won't expect a new solid state microwave to last a long time. It might be marketed as potentially longer lasting since there is no longer a magnetron tube, of course, but would companies improve overall quality to match the longer potential life? I doubt it. Not in this era. And being fair to makers of microwaves, there is the problem of getting normal people to pay extra for better build quality. Most people want the cheapest price possible at Walmart or Target. Even I am somewhat like that--although for me it's cynicism that "nothing here will last, so might as well get the cheapest choice!"


Post# 930528 , Reply# 9   4/4/2017 at 09:08 by panthera (Rocky Mountains)        
Reliability versus planned obsolescence

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One of the greatest advances in computing was the replacement of vacuum tubes with solid-state switching components.

Not only did things speed up, the reliability also went through the roof.


One of the greatest advances in audio recording came about when sound engineers figured out that those of us with absolute pitch weren't making it up and the manner in which SS clips versus the way tubes clip is relevant to dynamic range...and, in short order SS recordings sounded really good.


I don't quite believe that SS components have indefinite lifespans, there's too much evidence about micro-cracks and silicon atoms wandering, to name but two confirmed limitations.


What excites me about replacing magnetrons - better frequency control (wouldn't be hard), fewer mechanical components, higher efficiency (again, wouldn't be hard).


What worries me: I've had tens of microwaves through the years and never seen a magnetron failure. Every single time one has had to be replaced it was because the SS electronics had failed, usually a logic component. There's no reason to believe the perfectly awful consumer electronics to which we've all become accustomed in household appliances will improve. None.


I look at it this way - once we get past the early 1980s, how often do automotive electronics actually fail? Relatively seldom. Safety related, nearly never. But who amongst us can say the same for electronics in heat, steam, wet, high temperature stress home appliances? 

Post# 930540 , Reply# 10   4/4/2017 at 10:53 by combo52 (Beltsville,Md)        
Magnetron Failures In MWOs

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The number one part we replace on MWOs we service is the MT tube, failed MTs are about 1/2 of all service calls we do today, the rest of the problems are spread between bad fuses, thermal cuts outs, door switch problems and lastly electronic board problems.

Post# 930565 , Reply# 11   4/4/2017 at 13:38 by LordKenmore (The Laundry Room)        

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I look at it this way - once we get past the early 1980s, how often do automotive electronics actually fail? Relatively seldom. Safety related, nearly never. But who amongst us can say the same for electronics in heat, steam, wet, high temperature stress home appliances?


Unfortunately, I think there is more pressure on car companies to engineer the stuff to last better than a microwave. If a car has massive electronics failure at 5 years old, the PR could sink the company. Few people will complacently replace a $20,000+ car that wears out/has really expensive problems prematurely. It's even worse for a car company if it's a safety issue. Even a minor safety issue recall can hit the news heavily.


The problem is...there is no real pressure on appliance makers. If there was some huge safety problem, that might be one thing. But when something wears out earlier than it should, most people just shrug and--at most--say "that's the way things are built these days!" And then they go to Target to buy something of similar quality (or lack of).

Post# 930573 , Reply# 12   4/4/2017 at 13:52 by panthera (Rocky Mountains)        

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Of course there's another aspect to this - since Reagan killed the middle-class rise up the ladder, people not only like having appliances cost the same, year in, year out - they can't afford to pay more for better quality.

Post# 930605 , Reply# 13   4/4/2017 at 16:12 by LordKenmore (The Laundry Room)        

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since Reagan killed the middle-class rise up the ladder, people not only like having appliances cost the same, year in, year out - they can't afford to pay more for better quality.


Quite true.


I know the quandary of can't afford to pay more. It's something I deal with all the time... Which is one reason I like shopping used--it's a way of getting better quality than I can afford with my new dollar. And when I do buy new, and have to buy cheap, I shudder a bit because I know I'm not able to get something lasting.


I'm probably not alone. I remember my mother's mixer breaking, and we went to the store to replace it. My mother decided on the $13 mixer. Thirteen was a fitting number, not just the price, but also the luck we had in the long run with the mixer. But at the time, it was appealing, because it was the cheapest thing in the store at a time when my mother's finances were not their most robust. My grandmother tried to talk my mother out it, and get something better, but cheapest mixer won the contest that day.


That mixer was not very good. It worked, after a fashion, but it was not as good as the mixer it replaced. And it lasted less than two years before it started acting up. The previous mixer had lasted 20 years, and had been more heavily used during at least half those years than the new mixer. would have been better to spend more than $13 on a mixer... I think even my mother recognized that at the time (she'd used the "lasts longer" partly to justify buying more expensive coffee makers). grandmother became very cost conscious herself, given the realities of retirement income in modern America. Towards the end of her life, she bought a new mixer only barely better than our $13 wonder. It probably wasn't $13, but I'm betting it was one of the cheapest mixers in the store.



Post# 930692 , Reply# 14   4/5/2017 at 09:07 by cadman (Cedar Falls, IA)        

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Not to derail things too much, but I've always found it odd that people are willing to buy a new microwave, it goes bad in a few years, they buy another, it lasts a few more years, they buy another and on and on instead of just picking up a vintage Radarange.

Yes, the new ones are more powerful, but I'm willing to dial in an extra minute or two for a machine that will literally last my lifetime.

Post# 930745 , Reply# 15   4/5/2017 at 13:49 by RevvinKevin (Between Mickey Mouse & the Queen Mary (So. Cal.)        
Two year lifespan?

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I guess I must have gotten a good one built on a Wednesday or something, LOL.


I have a Panasonic 1100 watt inverter microwave oven that was new and came with the house I bought 16 years ago.  I've been really lucky **knock on wood** as it gets used daily and the only thing that's happened is the light bulb inside burned out about a year ago. 




Post# 930750 , Reply# 16   4/5/2017 at 13:57 by kb0nes (Burnsville, MN)        

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Kevin, the Panasonic Inverter model I repaired a few years ago is likely the same vintage as yours. That one is still going strong with lots of usage after the inverter repair.

When I finally pull down the KitchenAid convection OTR microwave I have now, I have a hunch that one of those Panasonics will replace it.

No doubt that the old ovens were tanks though, we have a 1984 Whirlpool MW8550XL here at work and you just can't kill it!

Post# 931172 , Reply# 17   4/8/2017 at 00:50 by tolivac (greenville nc)        

RadarRange oven-the machine itself Could last awhile but doubt a lifetime.The magnetron tube will not last your lifetime-and will a replacement be available in the future when the tube fails-if not the Radarrange ends up in the dumpster with the others.

Post# 931178 , Reply# 18   4/8/2017 at 01:29 by GusHerb (Chicago/NWI)        

We have a GE microwave/convection oven from 2004 that works fine to this day. Thing draws a little over 15 amps in microwave mode. I wish it heated more evenly but it has been reliable.
My parents had a 1990 Montgomery Wards convection oven and the circuit board was always failing, I can't begin to think how many times that thing was serviced. My mother loved it and they used the hell out of it though. I think it microwaved pretty evenly too, even despite not having a turntable.

Post# 931224 , Reply# 19   4/8/2017 at 09:26 by panthera (Rocky Mountains)        
Turntables vs. wave strirrers

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That's probably not quite the right word for them, but there are two systems for distributing the radiation more evenly.

You know, while technically correct, 'radiation' just isn't working for me. It always leads to 'ionizing' vs. 'non-ionizing' discussions.

Let's say energy.

Turntables have many advantages - they can result in food being really evenly cooked. They have two disadvantages - the closer you get to center, the less well they work, not working at all in the center. Their second disadvantage is that the are by their very nature limited to a smaller size of container than the cavity can hold.

Wave stirrers, done well, let the entire cavity be used and distribute the energy evenly throughout.

Those ancient Montgomery Ward/JC Penny and Sears ovens had wave stirrers and cooked really evenly. I remember them.


I don't think anyone expects a magnetron to last indefinitely, but at this point in my life, my anecdotal experience with kitchen electronics versus automotive tells me the things are built to fail.


Post# 931247 , Reply# 20   4/8/2017 at 12:08 by GusHerb (Chicago/NWI)        

My complaints regarding the GE not heating evenly, it always heats the top of things up but not the bottom or sides. No matter if I put it on the edge of the turntable or in the center. Even warming up water it does this.

The wave stirrer makes sense why the old Montgomery Ward worked so well, and without a turntable. My grandma had a small one with a turntable and that heated evenly too, about the same age.

If I was gonna replace the GE right now I would only replace it for something that cooks evenly. Does such a thing even exist in modern microwaves?

Hmm, perhaps like the trusty commercial Bunn, one could turn to a commercial microwave?


Post# 931260 , Reply# 21   4/8/2017 at 14:05 by panthera (Rocky Mountains)        
If you don't mind

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The short lifespan, Panasonic inverters cook very evenly. The inverter function doesn't work any better than the timed systems, it's just a gimmick, but the high power and the even cooking are the real deal.

Post# 931285 , Reply# 22   4/8/2017 at 18:45 by earthling177 (Boston, MA)        

"[...] The inverter function doesn't work any better than the timed systems, [...]"

Well, that depends a lot on what you need. The Inverter is not actually a continuous power range like you'd get from say, a rheostat, it seems to produce around 3 "bands" of power, and then it chops like the timed system does. It seems to me, for example, that 10% is achieved by a band that produces 30% power and it's then modulated by chopping it.

The results might be identical for some things (defrosting, for example), but make a big difference for others. I've shown many people how to make bread dough rise in the microwave by using 10% power in intervals of nuke/rest, and you can make the dough double in size in about 10-15 minutes this way with the Inverter, but it seems to fail a lot in other nukers -- some you can fix by putting a cup of water alongside the dough, some you can't.

Then again, not everybody wants to bother doing that and prefer to wait the hour or two it takes to rise naturally.

Post# 931368 , Reply# 23   4/9/2017 at 05:23 by kb0nes (Burnsville, MN)        

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Microwave ovens even back to the earliest units always had a wave stirrer to aid cooking uniformity. The wavelength of a common microwave is about 4-3/4" so there will be a number of nodes and anti-nodes across the cavity hampering uniform cooking. The stirrer helps by adding random reflections to try to even things out.

The pity was that the turntable came and basically replaced the stirrer. Since the turntable was a sales "feature" it was quickly adopted in every model, people wouldn't buy one without a turntable... The manufacturers were quick to junk the stirrer when the turntable was added to keep costs down. The stirrer probably also reduced the cavity volume slightly, another thing that became a sales feature.

I had an old Whirlpool microwave years ago that I used one of those Nordicware Micro-Go-Round turntables in. The combination of the stirrer and rotating food cooked far more uniformly then today's turntable only ovens.

Post# 931378 , Reply# 24   4/9/2017 at 08:18 by panthera (Rocky Mountains)        
Yes! Phil, that's right

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A good wave stirrer and movement mechanism - some now go side to side - produces very even results.

We won't get better ones until we have solid-state emitters capable of staying on frequency - then we can do several different time and frequency and phase variations, eliminating the need for much of the ultra-high voltage and energy losses we now face.

Given my background in IT, I'm the last person to hold onto a technology which can be replaced with a better one. I just have my doubts that the manufacturers will make any attempt to produce products built to last. The earliest consumer microwave ovens still work after 50+ years because they were too expensive not to be 1)built to last and 2)not be fixed when they failed.

Post# 931381 , Reply# 25   4/9/2017 at 08:48 by combo52 (Beltsville,Md)        
Turntables VS Stirrers

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Many good MWOs have both, and in my experience having both is the best way to go.

Post# 931420 , Reply# 26   4/9/2017 at 13:02 by kb0nes (Burnsville, MN)        

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Interesting to know that some microwaves still have both stirrers and turntables. Apparently I'm looking at low cost ovens that are pinching pennies.

I never put any merit into the idea that things are intentionally made to fail. I consider that a form of paranoia. BUT, due to the fact that nobody will pay money for reliability anymore, many modern items are far less well made due to cost concerns. Therefore lots of modern stuff has a shorter lifespan, but I am not convinced it is intentional.

The second thing I seem to notice is how much better technology is often made initially. When a technology is new there tends to be a lot over design and safety margin built in. Then as time proves out the design is simplified largely for cost cutting measures. I'd wager that the early solid state RF power microwaves will have some of this dynamic in play. Time will tell but I find it all interesting.

Post# 931425 , Reply# 27   4/9/2017 at 13:46 by panthera (Rocky Mountains)        
I translated too many white papers and repair manuals

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In Germany to doubt for a second that planned obsolescence is part of company design today.

In fact, I know it is. They really do plan for the things to fail and electronic components are ideal for that.

Post# 931436 , Reply# 28   4/9/2017 at 15:56 by cadman (Cedar Falls, IA)        

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Actually, the way these tubes are run in the Amana's, they only way you're going to kill them is with lots of MW popcorn. There are really three generations of magnetrons used in the entire production run. RR 1/2/3H use the old fashioned electromagnet variety (really a military grade tube). There are lots of RR-2 owners in the club, some used as daily drivers (myself included). The mag won't be the weak point if these ever go.

Starting with the RR-4 you have a more conventional PM design. I've sold a few replacements of this tube, but I suspect this might have more to do with the rise in popularity of the RR and the price drop around '74. These machines are everywhere.

If you really want a life-long Radarange, go for a model 8A/9TA/10 or newer. These would be in the '77/78 timeframe, have the revised cooling design that doesn't rely on a couple foam strips, and uses the same Hitachi mag that's still in use today and can be bought brand new. Not bad for a machine that's 40 years old.

Post# 931449 , Reply# 29   4/9/2017 at 17:49 by GusHerb (Chicago/NWI)        

Your mention of the Micro Go Round just jogged my memory. My grandmas little Montgomery Ward microwave didn't have a turntable it had one of those but it was broken and she just kept it in there anyway. So it must've had a wave stirrer, I know it cooked evenly albeit slower than ours at home.

Post# 931522 , Reply# 30   4/10/2017 at 01:43 by tolivac (greenville nc)        

There is no way I will have faith in an older RR oven that is 40yrs old+The tube is bound to go sooner or later.And---can you still get replacements-often when the magnetron goes-other items can go with it.I can remember the electromagnetic magnetrons-same idea as the old electromagnetic speakers.I used to have a service manual on microwaves-lent it out-never saw it again-was an exclllent book!from Tab Publications.They printed all types of service manuals on various devices.

Post# 931545 , Reply# 31   4/10/2017 at 06:27 by warmsecondrinse (Fort Lee, NJ)        
BRIEF Topic Hijack!

"Absolute pitch" - I'd love to experience that just to know what it's like. It's a brain thing, not an ear thing. I've seen people with almost no usable hearing rip their hearing aids out and/or run out of a room because someone is singing (VERY loudly, obviously) off-key, flat, etc. What's funny is that they can't fathom how people with normal hearing are able to stand it.

"Of course there's another aspect to this - since Reagan killed the middle-class rise up the ladder, [people] can't afford to pay more for better quality."

Thank you! Thank you! Thank you! It's a major pet peeve of mine to hear consumer behavior (or any behavior, really) framed as though preferences, desires, etc. are the only relevant factors.... as if the majority of consumers aren't forced to work within parameters they do not set and cannot change.

I now return you to your regularly scheduled forum discussion:-)


Post# 931563 , Reply# 32   4/10/2017 at 08:56 by panthera (Rocky Mountains)        
Two aspects of hearing don't fade with age/old magnetron

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Transient response and perfect (absolute) pitch.


Jim, you're welcome to my perfect pitch. It's a curse, a congenital disease and a major source of nausea and headaches.


It's why I defend Andrea Bocelli when my non-dilettante music loving friends decry my 'taste' in singers. It's why I was forced to play the violin as a child/teen/student even though I'm horrid at at. Can you imagine the agony of playing in an orchestra filled by people who can't discriminate pitch closer than an octave who are playing fretless instruments?


The stupid discussions about how it's all cultural and tempered scales 'prove' blah, blah, blah.


Pass. Totally, completely, pass. If only I could. In my next life, no freckles, skin and hair colour besides pink and orange and normal hearing. 


As to the lifespan of vacuum tubes - it's all over the place. Just like transistors - we now know that silicium atoms wander out of of place (a lot like Teflon creep or aluminium flow, though the process is, of course, totally different) and that's that for a lot of solid state devices which we once believed were going to last indefinitely.


I'd expect a 40 year old magnetron to be coming to the end of it's life, too - but I know a few real Amana RR that are still running perfectly well from that long ago, so - who knows? The transformer, capacitor, diode and tube are all still available so, worst case, it's all repairable.


For that matter, there's youtube clips on repairing the most typical Panasonic Inverter failures on all three generations, and all the repairs are pretty easy. It's mainly (shocking, I know) discreet components which go. So, maybe I'll think about one again. I sure do miss the 1350 Watts....

Post# 931583 , Reply# 33   4/10/2017 at 10:39 by cadman (Cedar Falls, IA)        

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Tolivac, you might have missed it in my response, but yes, you can still get the '78 and up magnetron brand-new from just about any source- amazon, ebay shops, your local dealer through a WP #, there's millions of them. The only other parts in the power supply on these are a combo filament/power xformer, diode and cap. Diode and cap are also readily available and the xformer has overcurrent protection to fail safe. You've also got two thermal cutouts on these models, and those parts are available, too. Door springs and glass trays are the biggest weakness, and they're easy to replace.

Should anyone have an old RR they'd like to keep running for the next 50 years, do a google search and I'll pop up. At any given time I've got 50+ Radaranges here, some in the collection, some as parts machines and some under repair for others. I also do board-level work on panels for '76-'84 models. As long as I'm around, there'll be parts.

Post# 931741 , Reply# 34   4/10/2017 at 23:47 by MattL (Flushing, MI)        

Speaking of microwaves, talking about repairs jogged my memory.  I'd guess it was mid 70's we bought a Litton microwave - huge thing just barely fir in the 18" between the counter top and the upper cupboards, had to be 26-28" wide.  Had a basic touch panel, nothing special.  Worked for years.  then the panel died.  I was adventurous so I bought the latest model control panel - it was the same dimensions, and replaced the old controller with the then high tech model with lots of extra options.  The guts of the machine were the same, but we did gain some functionality. Lasted a number of years after that to be replaced in the late 80's with an OTR GE unit that survived another 15 years.

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