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Old 4th March 2008, 12:09 PM   #11
zigo3 is offline zigo3  Italy
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Quote:
Originally posted by Lorne
In the power supply module of my Melos GK-1 there was a transistor mounted in a similar heat sink. If you think it is worthwhile pulling the cover and so on, I'll look and see what it is. I believe that I replaced it when I rebuilt the PS.
hello Lorne
if it's not a disturb for you, everything is well accepted and know what is mounted on your pre could be interesting. Even if i suppose your transistors could be similar to those of Sha Gold, low current transistors.

Quote:
Originally posted by Lorne
Another thing Melos under-engineered the heat management in my pre-amp. Could it be true of your amp as well? I vastly increased the size of some heat sinks in accordance with some advice I received from a professional. Perhaps heat was the cause of your transistor failure in the first place. The transistor in question was finally mounted vertically on a massive, finned aluminum sink.
Thankyou so much, this is a very good suggestion. I will follow it by sure.
Please, what heatsink size did you mount on yours? Did you substituted all the original heatsinks?

Thanks in advance
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Old 4th March 2008, 05:13 PM   #12
Lorne is offline Lorne  Japan
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Hi Zigo3: Sure thing! Give me a bit of time. It is a bit more involved than the stock hood. I put a whole new cover on the power supply module (it's separate on the GK-1). On top of the hood, there is a large 12 VDC computer fan.

I have drawings and notes to remind me what heat sinks were replaced and so on. I have no idea as to how similar or not this unit is to yours. But, there are two transformers. And this power supply gets hot. In the summer, it gets very hot. The transformers give off a lot of heat. When I rebuilt the module, the big cement resistors had scorched the board. Some parts showed signs of bad heat stress. One transistor in a sink like yours had discolored the board in the immediate area. There was nothing wrong with the unit. As far as I know, it was performing as designed. But I rebuilt the module to save the amp from disaster in the future.

To tell you the truth, I am going to rebuild it again using (a) point to point wiring (b) a bigger chassis (c) a fully ventilated cage. It's the only pre-amp I know of that will help heat a room in winter!

I replaced most of the parts including the transistors and regulators. Some small glass encased diodes I was not able to identify. I had to put them back in the circuit.

I hope that my English is not too difficult for you. I can easily understand yours

I'll be back with news Lorne
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Old 5th March 2008, 02:25 PM   #13
Lorne is offline Lorne  Japan
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Hi Zigo,

Look at the first attachment. The device of interest is 'A'. I believe that I replaced this. It is the same as the stock/original. Written on it is 'Mospec 2N3055 XO 96'. I thought that I had enlarged the heat sink. But when I look at my notes, I see that I didn't.

Now look at 'B'. The original was a TO package like 'A'. The replacement is an SC-65 package a D1092.

The original heatsink for 'B' was about the same area/volume as 'A'.

Now go to the next attachment (in the next post after this one) and compare the replacement heatsink with the one used by 'A'. There is a massive difference.

My reference manual says that both of these devices (A & B) are used in television circuits. It is interesting because some or all of the tubes used in the GK-1 are also types that were commonly used in television.

Now, find 'C'. 'C' indicates devices used in a regulation section. Originally these were free standing and had no sink wafer. I fixed a single copper fin to them.

I had not looked at the board for some time. I can see that the diodes I replaced have stayed in good condition no sign of charring or stress. But, I made a mistake. I put the large cement R's too close to the surface of the board. You can see where the board has been burned. And worse two large capacitors seem to have been boiled. And this happened even after a large fan was put on top of the hood. I am going to have to completely rebuild and change this PS circuit before I use the pre-amp again.

I do not have any idea if this helps you with your Melos model. I hope it does. It is a shame that no documents exist for Melos gear Lorne
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Old 5th March 2008, 02:30 PM   #14
Lorne is offline Lorne  Japan
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Here is another view.
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File Type: jpg gk-1-2.jpg (80.9 KB, 100 views)
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Old 5th March 2008, 02:30 PM   #15
Lorne is offline Lorne  Japan
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Here is another view.
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File Type: jpg gk-1-2.jpg (80.9 KB, 96 views)
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Old 6th March 2008, 01:37 PM   #16
zigo3 is offline zigo3  Italy
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Quote:
Originally posted by Lorne
Hi Zigo3: Sure thing! Give me a bit of time. It is a bit more involved than the stock hood. I put a whole new cover on the power supply module (it's separate on the GK-1). On top of the hood, there is a large 12 VDC computer fan.

I have drawings and notes to remind me what heat sinks were replaced and so on. I have no idea as to how similar or not this unit is to yours. But, there are two transformers. And this power supply gets hot. In the summer, it gets very hot. The transformers give off a lot of heat. When I rebuilt the module, the big cement resistors had scorched the board. Some parts showed signs of bad heat stress. One transistor in a sink like yours had discolored the board in the immediate area. There was nothing wrong with the unit. As far as I know, it was performing as designed. But I rebuilt the module to save the amp from disaster in the future.

To tell you the truth, I am going to rebuild it again using (a) point to point wiring (b) a bigger chassis (c) a fully ventilated cage. It's the only pre-amp I know of that will help heat a room in winter!

I replaced most of the parts including the transistors and regulators. Some small glass encased diodes I was not able to identify. I had to put them back in the circuit.

I hope that my English is not too difficult for you. I can easily understand yours

I'll be back with news Lorne
Hello Lorne

you are absolutely right, my Melos powamp suffered a lot because heat too: there are pcb areas who are brown, instead of green, because heat. In particular around those big white resistors that I suppose are similar to yours.
About schematics I found only a preamp service manual: if this can help you tell me I will send you by email.


Quote:
Originally posted by Lorne
Hi Zigo,

Look at the first attachment. The device of interest is 'A'. I believe that I replaced this. It is the same as the stock/original. Written on it is 'Mospec 2N3055 XO 96'. I thought that I had enlarged the heat sink. But when I look at my notes, I see that I didn't.

Now look at 'B'. The original was a TO package like 'A'. The replacement is an SC-65 package a D1092.

The original heatsink for 'B' was about the same area/volume as 'A'.

Now go to the next attachment (in the next post after this one) and compare the replacement heatsink with the one used by 'A'. There is a massive difference.

My reference manual says that both of these devices (A & B) are used in television circuits. It is interesting because some or all of the tubes used in the GK-1 are also types that were commonly used in television.

Now, find 'C'. 'C' indicates devices used in a regulation section. Originally these were free standing and had no sink wafer. I fixed a single copper fin to them.

I had not looked at the board for some time. I can see that the diodes I replaced have stayed in good condition no sign of charring or stress. But, I made a mistake. I put the large cement R's too close to the surface of the board. You can see where the board has been burned. And worse two large capacitors seem to have been boiled. And this happened even after a large fan was put on top of the hood. I am going to have to completely rebuild and change this PS circuit before I use the pre-amp again.

I do not have any idea if this helps you with your Melos model. I hope it does. It is a shame that no documents exist for Melos gear Lorne
Thankyou so much Lorne! Your suggestions are very interesting, in particular about those television transistors. On my 200+ are mounted some television tubes too.
Those A and B transistors are high or low current?

And your heatsink ideas are very interesting too. great idea to mount a computer fan too. I think I will follow your "street" to try to cool better mine too, once it will perform without problems (I hope ).

All these Melos products, if are right, perform very well, but it's unbelievable that they was mounted in a so fragile way and that there was only ONE place, in USA, where the schematics was disposables to repair them correctly. I can understand that business is business and restauration is a part of business, but there are limits...
At the end a good after-buy service produce more business: next time I will try a power amp firstly I will see how many time they are protected by the guarantee, then if the schematics are availables.

Your english is perfect for me
Thanks again

zigo

p.s.
great drivers you have in your avatar, I have a pair of HPD315 mounted on Devon cabinets.
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Old 6th March 2008, 05:48 PM   #17
Lorne is offline Lorne  Japan
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PM sent to you Zigo. Thanks.

None of following is reliable information. It is only what I have scraped off the net as reported by members of the audio community over the last eight years or so. I cannot verify as to it's unalloyed accuracy.

As for the Melos documents schematics and so on: as far as I know, the entire archives of the Melos company were sold at auctioned or were intended to be sold. This happened after Melos declared bankruptcy. The appointed receivers had possession of the archive. Unless I have gone crazy, I actually remember seeing the notice. I believe that I even asked myself if for a couple of thousand dollars I should try to buy the stuff myself. I've asked around. No one knows who if anyone got the documents. No one that I have heard from, anyway. And no one knows where the documents are. Well ... perhaps someone does, but not anyone that you and I know, for sure.

And furthermore, the word went around that the service company that set itself up to repair and restore Melos products was doing so from memory. That is, they were relying on staff who had worked at Melos to remember stuff.

In my opinion, there is more Melos stuff out there than meets the eye. A lot of it must have failed and faded by now. And it makes sense that if you own the documents for an orphaned family of products, you would keep them secure. You would capitalize on their unique importance. They would put a service company in a unique position. So the mystery gets more intense, because no one to my knowledge is using the archive if in fact it still exists.
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