Lorne said:
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.
Lorne said:
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.