Trio Mel-40

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Trio Mel-40

Post by Joust on Mon May 29, 2017 3:18 pm

i acquired a nice Trio MEL-40
i have the schematics and managed to get the amps working. the sound great.
Now i have to tackle the radio receivers.
Wondering if anyone here may have an alignment procedure for this beasty?
It would be much appreciated.

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Re: Trio Mel-40

Post by Joust on Tue May 30, 2017 9:12 am

ok not much love here so far.

my thoughts are this:
i could simply inject 455khz into the AM IF and get it mostly aligned. it can't be too far off unless i have to change some of the smaller caps in that section.
i'm intimidated by the FM section though. there are 5 transformers between the input and the discriminator and that is not including the front end.
Can i get away with just injecting 107Mhz in that IF and tuning the best i can?
I'd really rather not mess around blindly without the proper procedure.

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Re: Trio Mel-40

Post by Paulieb880G on Wed May 31, 2017 11:32 am

What is a "Trio Mel-40"?  Do you have a schematic you could share?  What problem(s) are you having?  There are alignment procedures you need to follow sometimes specific to the radio.  You need a schematic to guide you.  I would not mess with alignment in the FM section without a schematic, proper equipment and experience knowing what you are doing.

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Re: Trio Mel-40

Post by Joust on Wed May 31, 2017 12:45 pm

it is a Kenwood Stereo receiver. Trio bacame Kenwood.
as i understand it, Kenwood kept making it as a KW40


Schematics are all over the net.

forum is not allowing me to put an external link....i'm too new Smile
also can't attach files.

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Re: Trio Mel-40

Post by Joust on Thu Jun 01, 2017 8:52 pm

ok i tested all the tubes in the unit.
there was a 6be6 that was in the middle of the AM IF chain that was weak. i replaced that with a better one. Nothing different. The others are 6au6 and very strong.
the tuners make ZERO sound.
i don't have my RF generator here and will pick that up in a few weeks. so not much i can do at this point.
i was hoping someone might have an alignment procedure for this which i'm told is a typical Kenwood design so any kenwood of this era should be similar.

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Re: Trio Mel-40

Post by John Bartley on Fri Jun 02, 2017 8:43 am

Joust wrote:
the tuners make ZERO sound.

It seems to me that while it is possible that the alignment is so far off that an FM tuner would not send any signal thru', they would have to be wildly off for an AM signal of some sort not to pass. The odds of that are just about zero .... unless .... someone has played with the adjustments just for the heck of it. (not in an attempt to repair)

I would strongly recommend changing nothing in the way of alignment adjustments until you have dome some basic trouble shooting. In other words, wait for your generator to be available, then do a logical trouble shooting process before "tuning up" anything.

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Re: Trio Mel-40

Post by Joust on Fri Jun 02, 2017 8:46 am

Yes that is the plan. Touch nothing until i can inject a 455kz modulated signal into the section just before detector.
My suspicion is silver mica disease, the caps inside the if transformers. But again i won't get in there until i have my generator

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Re: Trio Mel-40

Post by Paulieb880G on Fri Jun 02, 2017 11:05 am

Does the amplifier work, like with a record player? Silver mica disease, as I understand it, should not kill the entire radio on both bands. Again, as I understand it, silver mica disease lets B+ get to the grid of a tube, causing a crashing sound, like lightning. You might have the condition on one band, but the odds of having it in both bands causing the radio to be dead are not very good. I'm just a rookie, but that scenario seems far fetched to me.

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Re: Trio Mel-40

Post by Joust on Fri Jun 02, 2017 11:10 am

yep. changed a couple caps and amps work great. very quiet and sound wonderful.

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Re: Trio Mel-40

Post by Paulieb880G on Fri Jun 02, 2017 11:18 am

Is there a function switch that could be wonky? Seems like the problem is ahead of the amplifier, then?

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Re: Trio Mel-40

Post by Joust on Fri Jun 02, 2017 11:25 am

yes there is but it seems to work. i can switch from tap to mag inputs so it is working there at least.
this thing has a stange setup where fm is through the left channel amp and am is through the right.
it is odd that there is ZERO noise from the receivers though so that might be it.
i can manage that sort of troubleshooting fine. i have the schematic and that is sufficient.

its after i get tuners output to the amps that i need this above requested alignment procedure. won't touch IF transformers before i get to this stage.

observational note: there is metal slugs in those transformers and the goop they put to hold them in place is disturbed. so chances are, someone was in there mucking about with them.

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Re: Trio Mel-40

Post by Paulieb880G on Sat Jun 03, 2017 2:31 am

Is it possible that this receiver is an early FM stereo model? Maybe from about 1960 or so? I have heard of a Pioneer receiver that worked like you describe. It had two separate tuners and dials. AM worked out of one channel and FM out of the other. It had an input for a multiplex adapter which would make the channels work like one would normally expect. Is it possible that your receiver is like that? Is there both an FM and an FM stereo position on the function switch?

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Re: Trio Mel-40

Post by Joust on Sat Jun 03, 2017 11:41 am

if you plug "trio mel-40" into google you can see lots of hits on this thing.
the schematic is freely available in the user manual that shows up in a lot of those hits.

i believe that this has an option for FM stereo but mine does not have that.

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Re: Trio Mel-40

Post by CaptainClock on Fri Jul 14, 2017 7:36 pm

It sounds like if you have AM coming out of one channel and FM out of another then you have the early "FM Stereo" where the AM Band fed the "Stereo" signal for FM Stereo that was pre-FM Multiplex FM Stereo, which like Paulie said would of beem from 1959-1961 as 1962 was the first year for stereo receivers to have built-in FM Multiplex Stereo, which I actually have a 1962 Sears/Silvertone Table Model Stereo Reciver that has built in FM Multiplex FM Stereo and it works like a charm and was pretty easy to repair, the only thing on my stereo that doesn't work is the AM Band and that's because when I was repairing the unit the chassis took a tumble off my work bench and broke the AM Antenna loopstick and haven't been able to find a new one at all, so I just use it for the line-level phono input and the FM band.

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Re: Trio Mel-40

Post by Bill Cahill on Fri Jul 14, 2017 9:00 pm

Ouch. Sounds like you have a project there...

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