Wonderland/JM100 build

[norburybrook]

the 1x 12 Larry Carlton, Sealed, ported Dumble cab. I had one already but sold it with my BLuesmaster. They're amazing cabs with a powerful amp, you get the air blast/punch of a 4x12 in a small package.

I have a Dumble style oval backed 2x12 with G12 -65 already and a marshall 4x10 and a 1x12 thiele cab.

I think I've decided on Cream for a change.

Marcus

[telentubes]

I built the 1X12 oval back for an EV12L that you are talking about. Fantastic cab.
I'm going to make my 50 watt JM Sig as a combo, leaning towards aged tweed covering. Cool to watch our different interpretations of this amp unfold.
Do you like the Thiele?

[norburybrook]

slow progress I'm afraid. Still on tour and writing the Music for a film in between.

drilled out the chassis the other day when I had an hour to spare so it's starting to take shape


Marcus

[Matt J]

slow progress I'm afraid. Still on tour and writing the Music for a film in between.

drilled out the chassis the other day when I had an hour to spare so it's starting to take shape


Marcus

That chassis looks fantastic!
- Matt J.

[norburybrook]

started to put some bits and pieces together and realise I've ordered 220R instead of 220K bleed resistors for the power board......bugger....

I've got some Vishay 2w metal film 270k.....would they be up to the task? they have a working voltage of 500V.

Marcus

[pompeiisneaks]

I get (500 / 270000) * 500 = .93 watts, so you've got double what max diss should be, so yes.

~Phil

[norburybrook]

I get (500 / 270000) * 500 = .93 watts, so you've got double what max diss should be, so yes.

~Phil

thanks Phil. It begs the question though; why do people use such huge resistors then on the power boards if you're looking at less than 1w max diss? I mean 2w would give you 100% safety margin. Would that formula work for the entire dropping string?

next to my over spec'd 500V 220uF F&T's these resistors look so tiny

Ok, onwards and upwards, lets see what I've forgotten when I start again tomorrow


Marcus

[pompeiisneaks]

I get (500 / 270000) * 500 = .93 watts, so you've got double what max diss should be, so yes.

~Phil

thanks Phil. It begs the question though; why do people use such huge resistors then on the power boards if you're looking at less than 1w max diss? I mean 2w would give you 100% safety margin. Would that formula work for the entire dropping string?

next to my over spec'd 500w 220uF F&T's these resistors look so tiny

Ok, onwards and upwards, lets see what I've forgotten when I start again tomorrow


Marcus

it's just ohms law, V=IR. You know voltage and resistance, so I=V/R. That gives you amps. Then multiply by voltage again for power in ways. P=VI easily repeatable. Then over engineer by at least 50% or more fir spikes and our safety. Realize that as resistance goes smaller, for the same voltages, wattage and current go up.

Sent from my LG-V521 using Tapatalk

[JazzGuitarGimp]

There is a quicker way to get there: P = E^2 / R
Take the voltage (E) present across the resistor (R), square it, then divide by the resistance. So for example, 400V across 200K would be 400 x 400 / 200,000 or 160,000 / 200,000 = 0.8 watts.

Another useful power formula is, if you know the current flowing through a resistance: P = I^2 x R
Using the same example above, 400V across 200K, the current (I) is 0.002A, so 0.002 x 0.002 = 0.000,004 x 200,000 = 0.8 watts.

Power Formulae:
P = I x E
P = E^2 / R
P = I^2 x R

[norburybrook]

thanks guys, I can see that 2w is plenty in this scenario.

I've managed to get in a day of soldering today and made some progress. Look at the size of those 220uF 500w caps!!!! a bit OTT and ridiculously expensive but they were an ordering mistake.

quick question; what do I do with the black lead on the reverb transformer? is it a Ground in this build?


cheers

marcus

[martin manning]

what do I do with the black lead on the reverb transformer? is it a Ground?

It is indeed. Check the layout, but I would ground that with the reverb recovery stage.

[norburybrook]

there's no mention of it on the layout, I had a quick look at the original Peavey schematic and it's a ground there so presumed it would be here too.

The two grounds from the reverb phono jacks are grounded at the pre amp ground so I'll ground it there.


Marcus

[xtian]

Look at the size of those 220uF 500V caps!!!! a bit OTT and ridiculously expensive but they were an ordering mistake.

Wow! Where did you find those?

[amplifiednation]

Ground the reverb transformer with the preamp grounds. I solder it to the reverb jacks which are isolated...then run a wire to the input jack ground point.

[norburybrook]

fitted my transformers today. they're BIG!!

looking at my bias circuit; I don't have a 3k3 resistor, if I use a 2.7k instead what should my Bias pot resistor value be changed to from the 27k?

and; On the layout I cant see where the other choke wire goes. One is going to the standby with the OT HV , the other isn't marked. Should it go to the + end of the first 20uF cap where the B+ voltage goes to the 6L6's?

Marcus