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Guest Farnsbarns

my new amp - It lives!

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Guest Farnsbarns

This is the volume and tone wiring. This is perhaps a little bit too agricultural. I'm going to see how this pans out before considering a proper tone stack.

 

IMG_20130823_162228.jpg

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Guest Farnsbarns

Gotta have a standby switch. In this case it cuts the power to the the entire circuit, leaving only the valve heaters powered.

 

IMG_20130823_234559.jpg

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Guest Farnsbarns

The only thing left now is mains into into power transformer and onwards into the circuit and then the output transformer.

 

Really, given that this is pretty much just a Marshall Plexi this build should only have taken a day or a few evenings. I have had to take it slow and do a small amount each day.

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Guest Farnsbarns

I almost forgot, I also trimmed all the pot shafts and tidied up the front.

 

 

IMG_20130824_000728.jpg

 

Left to right...

 

3 way rotary switch for 2/9/18w switching.

 

Power indicator

 

Power switch

 

Standby

 

Tone

 

Volume

 

Normal and Hot inputs.

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Very nice work you have done there, all that good work will make for a great sounding amp!

 

rct

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Guest Farnsbarns

Well, the electrical stuff is all finished. Here's the power end of the chassis...

 

IMG_20130826_010246.jpg

 

 

From the power socket we go via a fuse and over towards the switches.

 

IMG_20130826_010253.jpg

 

 

The blue and brown wires go to the center lugs on this dual pole switch. From the top pair of lugs the red pair goes over to the input of the power transformer, there's also a light connected across this. The power transformer has 0v, 190v and 275v outputs. Across the 190v and 275v taps the potential difference is 85v which will be approx 2w, the 0v to 190v gives us approx 9w and 0v to 275v gives us 18w. I have connected these taps to a 3 way rotary switch, the output from that switch then goes into the rectifier on the board. The board output goes through a hole (with a gromet) to the output transformer. The return comes back through the hole to the output jacks. There are 8 and 16 ohm outputs....

 

IMG_20130826_010258.jpg

 

 

 

And here's an overall shot of the finished chassis wiring...

 

IMG_20130826_010318.jpg

 

I've done all testing I can for now, all connections, grounds, switches, pots and key components are fine. I need tubes to finish the testing and try it out. I've got the 12ax7s but need the EL84s. I might be able to order some on payday but I'm missing quite a chunk of work this month so it might have to wait. I'm on the lookout for some wood to build a cab for it in the mean time.

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Well, the electrical stuff is all finished. Here's the power end of the chassis...

 

IMG_20130826_010246.jpg

 

 

From the power socket we go via a fuse and over towards the switches.

 

IMG_20130826_010253.jpg

 

 

The blue and brown wires go to the center lugs on this dual pole switch. From the top pair of lugs the red pair goes over to the input of the power transformer, there's also a light connected across this. The power transformer has 0v, 160v and 270v outputs. Across the 160v and 270v taps the potential difference is 110v which will be approx 2w, the 0v to 190v gives us approx 9w and 0v to 270v gives us 18w. I have connected these taps to a 3 way rotary switch, the output from that switch then goes into the rectifier on the board. The board output goes through a hole (with a gromet) to the output transformer. The return comes back through the hole to the output jacks. There are 8 and 16 ohm outputs....

 

IMG_20130826_010258.jpg

 

 

 

And here's an overall shot of the finished chassis wiring...

 

IMG_20130826_010318.jpg

 

I've done all testing I can for now, all connections, grounds, switches, pots and key components are fine. I need tubes to finish the testing and try it out. I've got the 12ax7s but need the EL84s. I might be able to order some on payday but I'm missing quite a chunk of work this month so it might have to wait. I'm on the lookout for some wood to build a cab for it in the mean time.

Well done Farms, your wiring skills are very good, keep up the good work.

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Guest Farnsbarns

Today I ordered two GrooveTube EL84s from hotroxuk.com who were brilliant when I made a recent order of a new set of glass for my Marshall. They weren't the cheapest option at £29 (£32.95 delivered) for a matched pair but are renowned for their power valve overdrive so they suit this amp very well, in theory. Should be making noise by early next week.

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I'm really impressed with the meticulous neatness of your work,you certainly take pains to make everything look tidy.Good on you.

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Pre-update...

 

Got the valves but have a friend on the way over to dump some furniture in my garage for a few weeks. Maybe I'll have time to do the final safety checks and voltage checks and make some noise tonight! If not tonight, then very soon.

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Last night I powered up for the first time, after a lot of tests to ensure it was safe. First power up was without valves, at this point I took a load of measurements with my multimeter, everything was within spec so I inserted the valves (AFTER ENSURING THAT MY 3 LARGE CAPACITORS HAD DISCHARGED). The speaker cab hummed, that was the first good sign. The hum was constant with no oscillation, that's the second good sign. Some more measurements and some calculations and every is OK. Plugged my lester in, cranked it and boom, holy hearing damage, this is loud! Even at 2 watts it's immense, easily able to keep up with a drummer. At 18 watts it moves your internal organs about.

 

I'll make a quick vid soon.

 

Next step, having got the basic essentials working, is adding the line out's but I've had a change of heart, spring reverb and an effects loop are on the cards too.

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an effects loop are on the cards too.

 

Having knocked out my first Mesa-inspired question re valve rectification - here's my second question: series or parallel loop? [tongue]

 

Looks great Farns and I am full of admiration. I wouldn't know where to begin in building something like that (electronics duffer). I'm looking forward to the vid.

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Having knocked out my first Mesa-inspired question re valve rectification - here's my second question: series or parallel loop? [tongue]

 

Looks great Farns and I am full of admiration. I wouldn't know where to begin in building something like that (electronics duffer). I'm looking forward to the vid.

 

Oh I think definitely parallel. These things aren't hard, just find a schematic with the features you want. Scrutinize it until you understand it. Order up the bits and go.

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Are you wearing a lab coat and rubber gloves? You have to tease your hair and take a picture with the deranged Doctor look in your eyes.

 

So cool! Demo demo demo demo !!!

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Plugged my lester in, cranked it and boom, holy hearing damage, this is loud! Even at 2 watts it's immense, easily able to keep up with a drummer. At 18 watts it moves your internal organs about.

 

Yeah the 18 watt is a great Marshall - and plenty loud! Nice build! [thumbup] Looking forward to the vid and seeing how the power scaling works. I have a PPIMV on mine.

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Guest Farnsbarns

very well done sir!

 

how does the wattage selection functionality work? very interesting layout. :)

 

thanks!

Don

 

The power tranny has 0v, 190v and 275v outputs. I take a wire from each to a 3 way switch. At the switch I can select 0v to 190v, 0v to 275v, or 190v to 275v which is a potential difference of 85v which, in theory, gives me 2 watts. In reality all my calculations were based on a 220v mains supply and 0% tolerence on all component values. In reality I found I'm getting 248v at my wall sockets and most of the ccomponents are 5% tolerance and I think I'm getting more like 4/12/24 watts.

 

Edit: just by the way, it s illegal for any more than 242 (220v +/- 10%) volts to be arriving at my wall sockets so I have 6 uninvited, gate crashing volts at my party. I'm not going to say anything because the electric company have some system glitch and we pay £5 per month regardless of how much electricity we use. I'm not turning that stone!

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