Another MoFo

What people are working on at the moment
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pre65
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#151 Re: Another MoFo

Post by pre65 »

steve s wrote: Fri Jul 03, 2020 12:11 pm You crack on Phil.. I'm enjoying your thread,
Thanks Steve, I hope we are all learning something (however small) from each other. :)

As I know that prototype A will work, I've made a start on prototype B. That way there are less bits cluttering up my workspace.

In all my monoblock builds so far, constructing the second one has always been a chore, but, so far, I've not felt that yet.

The hoover is to hand, so I can clean up my mess as I go. MDF dust and shavings don't go down well with Jean. :lol:
Life is what happens to you while you're busy making other plans. John Lennon

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Paul Barker
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#152 Re: Another MoFo

Post by Paul Barker »

I’m learning to build a valve amp instead
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pre65
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#153 Re: Another MoFo

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Paul Barker wrote: Fri Jul 03, 2020 3:49 pm I’m learning to build a valve amp instead
I've got the 833a with a James D A2 buffer to do next, then perhaps rejuvenate my 811 amp.

So I've not given upon valves. :lol:
Life is what happens to you while you're busy making other plans. John Lennon

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#154 Re: Another MoFo

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Too right! You’re baptised in valves!
"Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe." – Albert Einstein
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#155 Re: Another MoFo

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pre65 wrote: Fri Jul 03, 2020 4:11 pm
Paul Barker wrote: Fri Jul 03, 2020 3:49 pm I’m learning to build a valve amp instead
I've got the 833a with a James D A2 buffer to do next, then perhaps rejuvenate my 811 amp.

So I've not given upon valves. :lol:
Few, a new post not about heat sinks!
"Two things are infinite, the universe and human stupidity, and I am not yet completely sure about the universe." – Albert Einstein
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pre65
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#156 Re: Another MoFo

Post by pre65 »

I've been pottering about with MoFo today.

Prototype unit 1 (henceforth known as unit A) is complete, apart from the stud that holds down the mosfet.

Just need to insert the stud, grease the insulating washer, fit mosfet and top hat and secure with nut. Then need to solder the three mosfet leads. Tighten everything up, do a double check on the wiring, then it should be ready for test and initial bias adjustment.

As the M3 material won't be here till Monday I can do more on unit B tomorrow.
Life is what happens to you while you're busy making other plans. John Lennon

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Nick
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#157 Re: Another MoFo

Post by Nick »

Out of interest what insulating washer are you using?
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pre65
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#158 Re: Another MoFo

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Nick wrote: Sat Jul 04, 2020 9:48 pm Out of interest what insulating washer are you using?
I'm very glad you asked that question Nick. :oops:

I sort of realised that a TO-247 was a different size to a TO-220 but I'd not realised the insulating washers were different. Bugger. I'll order some tonight, but probably won't get them till Weds/Thurs, still-never mind eh.

Mia Culpa.

EDIT. Some on Ebay are sold individually and cost more than the mosfet did, but that's probably the "free" postage.

Do I need anything special ?
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#159 Re: Another MoFo

Post by Nick »

Its not easy finding insulators. I use these, sticky side to the device making sure all the metal parts are covered. No grease.

https://www.rapidonline.com/bergquist-h ... 3p-38-0402
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#160 Re: Another MoFo

Post by pre65 »

Thanks Nick, If I'd been really desperate I could have driven to Colchester and collected some. As it is, I ordered some silicon ones on Ebay last night and paid £1 extra for first class post.Might be here Tuesday.

I did find some TO-3 ones in the spares box which could be cut to size, but I'd end up with 1 tiny hole in the material and I didn't want to risk it.
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pre65
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#161 Re: Another MoFo

Post by pre65 »

There was one detail on unit A that bugged me a bit, and I didn't really want to perpetuate it on unit B, so I've stripped unit A back to do some modifications.

I have the time. :)
Life is what happens to you while you're busy making other plans. John Lennon

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#162 Re: Another MoFo

Post by pre65 »

If the prototype units pass muster, I'm going to have to make each monoblock a two box unit.

This is because the weight of the prototype is really too much to lift up, and put down. They are a gnats under 20KG.

So, I'd need to put the heatsink, choke (microwave oven transformer), circuit board and one (extra ?) PSU cap in a box of their own.

The boxes I already have would house the power supply and could cut down (height wise) if necessary, but I don't have to decide that just yet. I would like the top box (PSU is bottom box) to be more stylish, but without being gaudy, so clearly some thought is necessary. Initial leanings involve dark blue acrylic sheet in some form, and I hope the heatsink can be fixed (rather than the original hinged idea) and the bias adjustment pot accessible from underneath, with the top box turned on its side.



*
Life is what happens to you while you're busy making other plans. John Lennon

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#163 Re: Another MoFo

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pre65 wrote: Mon Jul 06, 2020 2:30 pm If the prototype units pass muster, I'm going to have to make each monoblock a two box unit.

This is because the weight of the prototype is really too much to lift up, and put down. They are a gnats under 20KG.

I went to see an Osteopath Tuesday evening for a consultation. She was not too impressed with my weightlifting. :lol:
Life is what happens to you while you're busy making other plans. John Lennon

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pre65
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#164 Re: Another MoFo

Post by pre65 »

WAHEY !!!!!!

First one (actually unit B) works. I've got it rigged up with a crap (and expendable) speaker and an old portable CD player.

I've set the bias voltage to 4.5v initially (about 2 1/4 amps) and will see how things progress as it heats up.
Life is what happens to you while you're busy making other plans. John Lennon

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#165 Re: Another MoFo

Post by pre65 »

It's still going after an hour. I've adjusted the bias to 5.1V = 2.5A

The heatsink is warm, but not hot.

The choke (MOT) is mildly warm.

The bridge rectifier is warm.

Everything else is at room temperature. (21.4 C)

I'll leave it a bit longer, then get back to finishing the other one.

I've ordered 2 sets (of 4) hardwood legs to make a couple of small tables to place them on, not sure about the table tops yet.
Life is what happens to you while you're busy making other plans. John Lennon

G-Popz THE easy listening connoisseur. (Philip)
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