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Old 12th May 2012, 04:58 AM   #11
tinitus is offline tinitus  Europe
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Quote:
Originally Posted by evanc View Post
I had trouble with the heater voltage. after the regulator drop I was a little below 6 volts.
its adjustable

R24, from where Im looking
bigger resistor = higher voltage
if too big(high), you can adjust it down with a paralel resistor

I think the tolerance would be +/-0.3V
so it shouldnt be below 6V
that is, if your meter measures correct
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Old 12th May 2012, 05:21 AM   #12
evanc is offline evanc  United States
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It's r 19 and 20 that set the heater voltage. I can't remember why, but according to the build guide you need at least 7vac to get 6.3vdc for the heaters. Running just below 6 volts seemed OK, but the tubes only lasted a couple of years. When it was time for new ones I went for the 8cg7s.
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Old 12th May 2012, 05:43 AM   #13
tinitus is offline tinitus  Europe
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Quote:
Originally Posted by evanc View Post
....... according to the build guide you need at least 7vac to get 6.3vdc for the heaters.
at very low voltage you are a bit low on 'free' voltage to waste, thus AC slightly higher than the regulated DC

at high voltage it might be the opposite way round, giving too much DC voltage for the reg to handle

regulator spec sheet should tell this
but hey, Im no expert
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Old 12th May 2012, 06:54 AM   #14
tinitus is offline tinitus  Europe
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ok, went back to study again

you get a 2V voltage drop on the 4x rectifer full-wave bridge setup
the 2V drop remains the same for all voltages
thus a very large percentage at very low voltage

the other alternative configuration, with a center tapped trafo and 2 rectifers, have lower 1V voltage drop

hope this was a bit more clever
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Old 12th May 2012, 07:12 AM   #15
tinitus is offline tinitus  Europe
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well, there are a few annoying things with the manual

on-board heater supply smoothing cap numbers on schematic shown in manual appears not to match the numbers used on actual kit/print board

manual is obviously a kind of one-for-all, with small changes
its ok tho, but could confuse a bit
and there is not a proper schematic of the complete onboard supply
I find that very annoying

but nothings ever perfect I guess
probably still a far better manual than you would find elsewhere

I would aim more directly at a totally 'general' manual
and then supply all the actual individual specific kit info added in loose paper form

well, I will be still and shut up, for now
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Old 12th May 2012, 12:04 PM   #16
evanc is offline evanc  United States
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yes, there were some discrepancies between the manual and the board I got. The tough part was the kit. Some of the parts were numbered to the manual and some to the board. I used the schematic and got stuff in the right place. The thing I never got right was the heater voltage.
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Old 12th May 2012, 10:42 PM   #17
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Quote:
Originally Posted by mattmcl View Post
Migkiller, does that wood top board get too hot? I've got a killer piece of figured maple but was thinking I'd need to make that top plate metal.

Not at all, I drilled holes on the bottom. I think i paid 20 bucks shipped for the case.
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Old 13th May 2012, 02:25 AM   #18
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Originally Posted by evanc View Post
yes, there were some discrepancies between the manual and the board I got. The tough part was the kit. Some of the parts were numbered to the manual and some to the board. I used the schematic and got stuff in the right place. The thing I never got right was the heater voltage.

you'll have to take in consideration a couple of things.

one, Tom is having board manufacturing issues, he's swapped boards makers a few times after the manual is printed.

and second, when Tom prototyped these designs, he used a motorcycle battery as the heater supply. the little bit of under voltage is OK, its the ground referencing that has to be tweaked for the tube type used.
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Old 13th May 2012, 01:59 PM   #19
Einric is offline Einric  United States
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I set the regulated voltage to 12.6V and used the jumpers to set the 6.3V to the heaters.
This way at some point in the future I could change to a 12*** series tube and only have to switch jumpers.
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Old 15th May 2012, 03:56 PM   #20
mattmcl is offline mattmcl  United States
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Heh... I'm obviously out of practice and made my first mistake- didn't remember that diodes are polarized. The manual talks about orientating caps and resistors but doesn't mention diodes. So anyone else reading this, remember to align the cathode end of the diode as marked on the board.
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