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Blue Hawaii BJT Build thread


joehpj
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1 hour ago, kevin gilmore said:

really think you should add the t2 current source modified with 2sc4686 and cascade current source to drive the led reference, that still synthesizes the best of everything

...which is what I is using since trying it out ;o)

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I do believe that the T2 current source is the one to aim for. But that’s only for the squirrels and the boys with big pockets filled with c4686. If you want a CCS based on components from Mouser or equivalent then I think 10m90s is good enough for most people, including myself. But we should look for alternatives for 10m90s so in that respect I’m grateful to Kerry’s work.

I’ve had a T2 with c4686 and isolated switching power supplies for a while and I really like that amplifier. Probably the cascaded current source for driving the LED is preferred but I like the isolated things. Maybe I should try current source for driving LED, anyone have a schematic?

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I saw some noise issues in the Spice model for the regulator version as well.  I could mostly control it, but not completely (especially once you go above 20KHz).

Here's another idea I came up with (CSS #2 and #4).  They will also support 1,000V.  You could improve it slightly by adding a DN2540, but I'm not sure it's worth it.  These other two models work almost as well as the battery at 10KHz and only a bit worse at 20KHz.  The second (#2 below) is probably the best bang per parts.  # 4 could be made to be a bit better, but I'm not sure it's worth it.

The results are for the first three only (which includes the battery that Kevin came up with).

Capture1.thumb.JPG.4ef357cf484bfe163499a98d38018c33.JPG

R1 May not be necessary, but it felt good :)   I want to experiment a bit more with it.

Edited by Kerry
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6 hours ago, JoaMat said:

Nice picture. If a1486 had been a kV device the T2 current source would be a better one? Most of the variation of the green curve must be due to the 150k resistors.

Ops! Kevin pointed out the resistors in this post.

On ‎2017‎-‎04‎-‎24 at 1:44 PM, kevin gilmore said:

the closest thing to a perfect current source is a high voltage tube with a cathode resistor, i.e. megatron

T2 current source is actually not really very good because the resistor divider for the pnp current source causes a significant change in current

for example 700v peak to peak on the plate the current varies from 13.3 to 15.8ma

same thing for a cascoded depletion mode is 14.8ma to 14.85ma

a better idea would be to replace the stacked pnp and resistor with a very highly isolated dc to dc converter, something good for 2kv of isolation and you would need 4 of them per amplifier.

Sorry.

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I was wrong about not cascading the MOSFETs.  It really did help.

At this point, spice is showing me the same results as the battery.  It would be nice if someone could check this to confirm.  The models I'm using for the IXTP01N device seem to be optimistic.  Note that J1 only helps if the top MOSFET performs worse. 

So, if the model is right, then you don't need J1 and we're right back to what Kevin was suggesting :) 

Capture2.thumb.JPG.00940f38823f568bedd164eee145d32c.JPG

 

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1 hour ago, Kerry said:

I was wrong about not cascading the MOSFETs.  It really did help.

How would these compare with LDO+IXTP01N. I assume noise will improve a little bit by using using LT3042. I like the simplicity of the LDO and modern parts are easier to source.

Edited by joehpj
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20 hours ago, joehpj said:

How would these compare with LDO+IXTP01N. I assume noise will improve a little bit by using using LT3042. I like the simplicity of the LDO and modern parts are easier to source.

01N100D with LT1021 to the left. Got the idea from Kerry.

wr.thumb.jpg.1a360cb5cede6bb54c0a97f9710cf63f.jpg

LT3042 is a nice piece, but 1021 is a bit bigger and then easier to deal with.

Edited by JoaMat
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No access to Spice right now but I've had great luck with this circuit and a variation using two PNPs and two DMOSs.

LRbqmso.jpg?1

If base current starves the zener, use a Darlington or replace the LND150 with a BSS126 or BSP135,

I think the reason why the DMOS circuit is so good is that it does not have a bias string that runs parallel to the CCS. The way it's cascoded also holds the lower device's Vce or Vds constant rather than holding Vbc constant, as most PNP cascodes do. Using a BJT as the lower device almost always results in more transconductance, and thus higher impedance.

 

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Today I’ve equipped my modified T2 with the 01N100D/LT1021 current source Kerry has simulated, see previous posts. From beginning it had a straight 10M90S set to 10 mA. When JimL came with the cascaded version I removed the two resistors at 10M90S and added a small board with the DN2540 and corresponding resistors(red circle below). Today I made new daughter boards containing LT1021, 1k resistor and 47pF cheremic capacitor (green circle).

DSC00313.thumb.JPG.2e77eded7589a94e2e284280021ef951.JPG

Have listen to this for an hour. It works and I’m satisfied.

Thanks Kerry for coming up with this.

Below solar cell. Only for experimental purpose.

DSC00312small.jpg.9611ca32632d7f6ecd60a62d1e549133.jpg

 

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Excellent!  I'm curious if you were thinking of testing this same current source as a replacement for the battery (2mA to bias the CCS transistors) in the larger T2 as well.  I'm curious how it compares to the batteries.

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It was actually very easy to rebuild the large T2 with the DC/DC converters. Used same daughter board layout as for as for my modified T2, only had to move one hole 50th. I also have plenty of space since I only use one and not three output transistors and I found some nice spots for the daughter boards. One channel has the DC/DC converters and the other the newly made 01N100D/LT1021 boards. Both channels seem to work OK.

Below: Daughter boards with LT1021 and 01N100D on heat sink.DSC00314.thumb.JPG.bf657c27c07a11a515ab792fd91bf17f.JPG

Boards with DC/DC converters and LT3045.DSC00315.thumb.JPG.95b66265862e7a895def7efda0c5d353.JPG

Now it's late, done for today.

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  • 3 weeks later...
11 hours ago, jose said:

What current do I have to measure between R50 pins?


 

If you are referring to the 50 ohm resistors on the EL34 plate CCS, 1VDC measured across the resistor gives you 20mA ( I = V/R, 1/50  = .02) of plate current which I think is conventional. 

I've know builders that run their Blue Hawaii from 18mA up to 25mA. The Blue Hawaii runs HOT, so need to take into account the heatsink size. 

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2 minutes ago, mwl168 said:

If you are referring to the 50 ohm resistors on the EL34 plate CCS, 1VDC measured across the resistor gives you 20mA ( I = V/R, 1/50  = .02) of plate current which I think is conventional. 

I've know builders that run their Blue Hawaii from 18mA up to 25mA. The Blue Hawaii runs HOT, so need to take into account the heatsink size. 

Thanks. Sorry, yes I was thinking about CCS. R50 is between DN2540 and the EL34 plate. If 20mA is a normal set-up, I´ll try this.

Other stupid question. What value is necessary for 150K resistor (on Gate of 8N80C)?  I'm not sure that 1 / 2W is enough

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