Does anyone know if Lil Knight were active last week? I was buying a set of KGSSHV boards and the communication was great. My payment went through on July 5th, and I have not heard back from Tran since that. I know that Tran is no scammer whatsoever and I have no problem waiting, but It's quite frustrating to be left in the dark.

I wounld not worry about it. He can go quite for a while sometimes and then he comes back with replies. I think he has school exams too.

Lil Knight is a gentleman. I dealt with him quite bit when I helped him distribute boards in the US. Give him some time.

now i need to stock .01uf 1kv wimas

cheap ceramic discs. Not wimas.

Tran just PMed me. The boards are on their way. I guess I should train myself to be more patient.

correct, and you will need 2 of them and they have to be 1kv rated reed relays.

Anything else sparks pretty nasty.

Any chance you could suggest one? Thank you.

something like this

http://www.mouser.com/ProductDetail/MEDER-electronic/SIL12-1A72-71D/?qs=6LkQJpCWFTifeu4Ctb4tFgDRzs7G8uTK

would work on a 12 volt power supply line with a delay.

Stax uses reed relays? I'm surprised. I certainly would not attempt this.

stax definitely did not use reed relays. since i don't have one open at the moment i

can't pick the exact part they used. But they also used lower voltages too, so

if you were to use the stax relay at 450 vac, it might not behave so nice.

I use those sealed reed relays at work up to and including about 15kv.

(well different models, but the same thing) switching AC and switching DC.

work great.

The Stax amps use just a standard relay but the AC voltages are far lower. I'll check out the part number when I do final checks on this SRM-007tII I have here.

I’m going to do some experimenting with the bias current. My 400mm 3U Modushop heatsinks are running cold with the A1968’s . I assume the only change out is the 1.2k resistors for the current source? I don’t want to go too nuts, just enough for some get some heat happening. How to do I go about working this out?

Please do report your results, John. I'll be very interested in seeing if how high you can crank her and if you can hear a difference.

Please do report your results, John. I'll be very interested in seeing if how high you can crank her and if you can hear a difference.

I shall, I don’t want to push her sky high, just enough to justify these big sinks.

I’m going to do some experimenting with the bias current. My 400mm 3U Modushop heatsinks are running cold with the A1968’s . I assume the only change out is the 1.2k resistors for the current source? I don’t want to go too nuts, just enough for some get some heat happening. How to do I go about working this out?

Well for starters I’m not using 1.2k resistors, I’m using 500R for the A1968 current source, I really should pay attention.

In regards to increasing current I assume the 500R’s are to be replaced? Just after a little knowledge on how to derive mA values.

Its the output stage current you want to bump up. You can bump up the 3rd stage a bit, but no reason

to go crazy on that one.

To change the current in the fourth stage you have to increase the voltage reference, i.e. the led.

or decrease the emitter resistors.

Thanks Kevin and Birgir, I really appreciate your help with this.

I've been digging around here and in the Headwize forums.

I can't find a formula for the final output in the fourth stage.

If a 2.1V LED yields ~ 4 x 5.5ma for 20 watts. How do I for example equate a 3.8V LED?

I just don't want to crap shoot this...

John

2.1v - vbe junction (.7) /180 ohms == 7ma.

But the led's actually are more like 1.7 volts due to

the drive current.

So its about 5.5ma.

You can change to a higher voltage led, but the red led's thermally

match the output transistors.

So you want to cut the 180 ohm resistors to something like 150 or 120 ohms.

Thats absolutely solid. Invaluable info, thanks Kevin.

Edited August 23, 201213 yr by johnwmclean

So,

150 Ohms should give 6.60mA, and,

120 Ohms should give 8.25mA. Hopefully.

100 Ohms = 6.9mA

82 Ohms = 12.07mA

68 Ohms = 14.56mA

56 Ohms = 17.68mA

47 Ohms = 21.06mA

Edited August 23, 201213 yr by wink

IIRC the BH and BHSE run at about 18mA. I've got the same sinks and I wonder if we'll be able to approach (or pass) that.

temperature rise for a 12" length is about 25C for 20W

if anyone is looking for 2SA1968 transistors, these visually appear to be authentic parts at a good price: http://www.ebay.com/itm/5pcs-2SA1968LS-Original-New-Sanyo-PNP-Dynamic-Focus-Transistors-A1968LS-/110935720719?pt=LH_DefaultDomain_0&hash=item19d448c30f#ht_3700wt_1398

I have never bought from ebay for fear of counterfeits. I am tempted though....

Do a search in the T2 thread for "Dalbani". Buyer beware!

If they honor their 14 day return policy, one could dust off the trusty transistor tester and check for Vbr.

VCEO should test at 900V minimum if they are the real deal. If not, return them FAST!

Edited August 23, 201213 yr by livewire