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  #1  
Old 12th August 2006, 07:56 PM
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Default Newby first build amp 832.

Hi-i thought i would give a few thoughts on my first amp build.

the 832 project has gathered pace (only just) and now the base and baseplates have been joined and bits have been bolted/soldered on.

i seem to have been a bit careless with my reading of resistor colour codes as a couple have ended up in the wrong places,so now i write down the value and work out the colours then test with a DMM to make sure.

i dropped one of the 832 valves and it fell on the top pins,breaking the glass.good job i got 3 from the seller !

boy am i glad i listened to the advice about not trying a transmitter amp as a first project !!! i am learning as i go along and i link to a picture of the underneath as it is now.

if you see anything odd let me know please.





Philip
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Old 12th August 2006, 08:15 PM
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Default Re: Newby first build amp 832.

so far so good eh! - Keep us posted.

Andrew
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  #3  
Old 12th August 2006, 09:49 PM
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Default Re: Newby first build amp 832.

Looks lovely.

PS that is a transmitter valve used in ship to shore radios on trawlers to this day. That is why they are prevelant and cheap. Yes they damage very easily because of the top two pins if they hit the ground they invariably go gassy (milky, completely U/S).

pps, valve still make the most clear to hear transmitions, it's just that because so many hams use non voice comms. like rtty that they can get away with the apauling quality of solid state transmitting equipment.
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Old 12th August 2006, 10:57 PM
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Default Re: Newby first build amp 832.

Nice piece of work Phillip.

Keep us posted on how it goes.

Steve.
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Old 14th August 2006, 11:33 PM
Single end Single end is offline
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Default Re: Newby first build amp 832.

Hello Pre65,
I like the workmanship it looks nicely build.
Since you are asking, I would like to comment on 1 matter though.
I noticed your ground wires run per chanel from the input chasis to the output chasis. What this does is to create an earthloop. You could view that as a single winding of a coil. This is not guaranteed to create problems but if the conditions are correct it will give you a popping sound that is called "motorboating" .it sounds actually more like a WW2 V1 missile. I had it once in a home build RIAA amp, and I could not get rid of it unless running in mono :-(

In any case If you get this, you might want to rethink your earth wiring design, and go for a "star configuration" This is where you choose a single earth point, and run all the ground wires (1 only per reference, so if 2 cinch connectors are mounted on the same metal bracket, connect only 1 chanel to ground) to this 1 point.

let us know how the amp wil sound.
Hope you will not have the problems mentioned.
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  #6  
Old 14th August 2006, 11:51 PM
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Default Re: Newby first build amp 832.

Hi Single end-i did wonder about that.

what i will do (have done) is to snip a bit out of the earth bar at the input end.

thanks for taking the trouble to tell me.

im off to the Lake district for a few days on Weds,hope to climb Scafell Pike if the weathers OK so the amp will have to wait for now.

Philip
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  #7  
Old 15th August 2006, 08:19 AM
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Default Re: Newby first build amp 832.

Yes the obligatory diy earthing method has been star ground for two decades. Make a loop of wire about 1cm diameter, put it beside the input connections and return every earth individually to that ring.

Sukuma has another way it also works well. Time to introduce you to Direct Heating. Look on Google.
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Old 15th August 2006, 09:38 AM
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Default Re: Newby first build amp 832.

Yes,, but, star earthing isn't the only way, in fact I may suggest its a simple way of not having to think too hard about the earth loops. I actually like using the buss earthing that this amp has used, as long as connections are not just applied where its convienient, it can allow isolation of the small signal parts of a circuit from the large signal parts. I have used it on my Wad phono, the LCR phono and the 211 output stage. The only thing I regret about the way I built the LCR, was I didn't use a silver buss bar as MJ suggests.

You could argue that star earthing is just an attempt to produce buss earthing with zero spacing between the earth points, and as its never zero, then random order star earthing will always be a compromise.

So there :-)
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  #9  
Old 15th August 2006, 09:41 AM
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Default Re: Newby first build amp 832.

Yes, and star ground looks but uggly, and Sukuma actually claims it isn't the best method, and I have tried his method and I like it.
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  #10  
Old 15th August 2006, 12:31 PM
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Default Re: Newby first build amp 832.

Quote:
Originally Posted by NickG
Yes,, but, star earthing isn't the only way, in fact I may suggest its a simple way of not having to think too hard about the earth loops. I actually like using the buss earthing that this amp has used, as long as connections are not just applied where its convienient, it can allow isolation of the small signal parts of a circuit from the large signal parts. I have used it on my Wad phono, the LCR phono and the 211 output stage. The only thing I regret about the way I built the LCR, was I didn't use a silver buss bar as MJ suggests.

You could argue that star earthing is just an attempt to produce buss earthing with zero spacing between the earth points, and as its never zero, then random order star earthing will always be a compromise.

So there :-)
The importand thing is that you do not allow too much vlotage differences in your ground wiring. If you go for the buss config, use a thick wire or a copper strip
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