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 Post subject: Lead dress check
PostPosted: Tue Aug 06, 2019 11:50 pm 
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Location: Auckland New Zealand
Hi all,
my Plexi build is coming along nicely, but I have a couple of nagging doubts about lead dress.
I'm a bit concerned that the wiring run for the V5/V6 cathodes is a bit long and that some of the parallel wires may be too close together.

(click below for full size pic)
Image

Any feedback or suggestions welcomed.

Cheers,
Dougal


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 Post subject: Re: Lead dress check
PostPosted: Wed Aug 07, 2019 1:44 am 
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Joined: Sat Dec 04, 2010 3:42 pm
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Location: Qualicum Beach, BC
Hi Dougal

It looks pretty good so far. Nice and neat.

You might want to run the cathode wire from the output tubes to the board from the other tube to shorten it up. That's how it's shown in the layout drawing.

Also, the grid wires at pins 2 and 7 of V3 are running parallel and pretty close to the high voltage anode wires at pins 1 and 6. It's best not to do that. You should try to separate them more. Remember you have three dimensions to work in. All the wires don't have to be close to the chassis.

The heater wires should be, though, as you have done.

The wires to the pots look good.


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 Post subject: Re: Lead dress check
PostPosted: Wed Aug 07, 2019 8:43 am 
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Holy Ghost
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Always, the shorter the lead the better and cross leads at 90 degrees if yu can.
Build looks very good. I will probably be fine as is.

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 Post subject: Re: Lead dress check
PostPosted: Thu Aug 08, 2019 2:59 am 
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:thumbsup:
Thank you gents. I'm re-routing some of the wires today.


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 Post subject: Re: Lead dress check
PostPosted: Fri Aug 16, 2019 8:07 pm 
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Now finished, tested, and all works as anticipated.
Apart from the expected resistor hiss it's very quiet, so a big thank you mitch m and coco for the advice.

Now on to installing the VRM and I'm also thinking about cascading one of the channels into the other (as per various threads here and elsewhere).

Voltage readings below. Some are 15-20% under spec but it sounds freaking awesome, so not sure if I need to be concerned.
It's wired for 240V.

Image


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 Post subject: Re: Lead dress check
PostPosted: Fri Aug 16, 2019 9:13 pm 
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Glad to hear the amp is working and sounding awesome. Your B+ voltage at the rectifier and the heater voltages are pretty close to the expected values, so I wouldn't worry about the others. The main thing is the amp works and sounds good.

Vacuum tubes can vary quite a bit from one to another so the voltages specified are just average values. Also the line voltage might vary throughout the day which will affect the DC voltages in the amp.

And if you are installing a VRM, that will really affect the DC voltages if you turn it down.


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 Post subject: Re: Lead dress check
PostPosted: Sat Aug 17, 2019 12:08 am 
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Thanks Mitch.
Here's the finished cheesecake image

Image

Will post some more pics when it's all done.


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 Post subject: Re: Lead dress check
PostPosted: Sat Aug 17, 2019 3:27 pm 
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Congrats. It looks great. The voltage may be a bit lower due to 1.5% lower mains. Dont sweat it.
Take your time installing the VRM. Play your amp first so you get a good idea what it can do.

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 Post subject: Re: Lead dress check
PostPosted: Sun Aug 18, 2019 3:19 am 
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coco wrote:
Congrats. It looks great. The voltage may be a bit lower due to 1.5% lower mains. Dont sweat it.
Take your time installing the VRM. Play your amp first so you get a good idea what it can do.


Thanks. I spent a good 2-3 hours invoking my inner Malcolm Young when I first got it up and running!
I got the VRM installed today but haven't yet rewired the V1 grids with the blocking caps etc.
Should I go ahead and do this anyway or is it possible it won't be needed?


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 Post subject: Re: Lead dress check
PostPosted: Sun Aug 18, 2019 11:26 am 
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How much they are required depends on how low you go in power. At some point, the triodes will leak DC to the pots and you will hear scratching when you turn them. That's when you need to install the blocking caps and move the 1M resistors.

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