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Old 15th December 2009, 08:50 PM   #21
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I'm just looking at those twin diodes in the CCS reference; Temp drift ? An LED works wonders here. Comments '?
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Old 15th December 2009, 11:31 PM   #22
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Hi TM,

thanks for the links, I will read them through.
As for the PSU I think Eli put it quite well and the voltage is not that exact thing, 450-475 is a healthy and realistic range.

Rich,

I agree with you about the CCS, I had already thought about redesigning it and a LED will be a good choice, they are also low noise.
I'm not too worried about temp.co, it will probably be quite stable when everythng have warmed up and settled.

Cheers Michael
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Old 16th December 2009, 12:50 AM   #23
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I read in later posts that the CCS in the schematic did not work properly. I'm interested in the Supertex mosfets for this use. I wonder in these K&K modules would just "drop in". I'm afraid I know little about modern sand.....

K & K Audio - Lundahl Transformers, audio DIY kits and more

Last edited by TubeMack; 16th December 2009 at 01:05 AM.
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Old 16th December 2009, 03:26 AM   #24
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TM, what post was that about the CCS didn't work so well.. I just made a quick calculation on it and at 6 mA the voltage at the Cathode can't get below 3,5 Volt from above Ground as the CCS stops to work as such if going below.. if I recall my memory correct as it was for a little while I did the calc..

yes those ready made CCS from K&K are ready to drop in and the minimum voltage over them was 4 Volts so they will be able to go even below Ground voltage if they are tied to the -6.3 V rails as in the zafir1981s schematic.

I just wonder what would other think of a second CCS on the KT88 pair or is that overkill?

Cheers Michael

Last edited by Ultima Thule; 16th December 2009 at 03:29 AM.
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Old 16th December 2009, 04:14 AM   #25
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I think it was the link labeled "Amp layout". As to CCS on the output stage, i've heard bad bad things!

Anyone game to sketch out a PS schematic for this project. Something basic like the last one Eli proposed. I'm studing the Morgan VA book, but don't think anyone here would want a amp using any PS I could design. A BOM also needs to be formulated. I'm not sure of resistor wattage ratings, and capacitor types / brands. I want to use higher grade parts, but skip the $200 capacitors. I have an assortment of Dale metal film resistors to start! UT, perhaps you have some thoughts?

Last edited by TubeMack; 16th December 2009 at 04:25 AM.
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Old 16th December 2009, 07:41 PM   #26
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Ok I found the dwelling about the CCS, well as I see it it was just some minor concerns, but would you still feel safer with a ready made CCS module K&K?
It's just 2 legs you have to solder in I think so one can't fail too much on that one.

btw I wasnt too correct when mentioning about the drive stages cathode voltage over the CCS, there's plenty of headroom as the cathode voltage will be maybe 100 Volts up or maybe little bit more, but no worries the current needed from CCS is so small so the power development isn't any gross.

Choice of Cs and Rs, for caps I would go with red WIMA MKP (Polypropylene), that's a sure bet and these are transparent and stable and doesn't add much of its self to the sonic, eg. "invisible".
http://www.wima.com/EN/WIMA_MKP_4.pdf
Resistors I'm not really sure of yet which brand and what type, but one type for sure have to stand outside is the carbon comp resistor, actually they are even dangerous if they start to burn they will flame pretty well, and couple of other reasons too not worth to mention.
Final values and wattage has to be calculated, I am about to start dig in my head into the toob-cook-books so it will take some time before I can calculate anything, tubes aren't that much different from any other type of gain devices like BJTs and mosfets.

The PSU will depend on the final amp drawing, eg when the working points for all tubes are defined and all voltage/current/resistor values are calculated, then we can look at the PSU as from what I have seen is used for tube amps are the sc. "voltage regulation" is pretty crude.
So if we do the ol' toob-way it means burning up power in a series resistor to reach the correct voltage fall and that is dependent on the quiescent current, plate resistors and so on as far as I understand it for now, so that's why it's not that straight forward and, well.. for those who are little bit more engineering mind oriented who like to calculate and estimate and source the "perfect" cap or res is also part of DIY and that is very time consuming so things can some times go a bit slowly and better to not expect to much of the time schedule.

As far as I see it for now the main priorities are:
1. calculating the new working points for a lower B+ voltage (~460V) and eventually new working points for input/drive stage.
2. find a OPT

Regarding the OPT I'm still pondering over the role of DC resistance on the primary side, which I think will have some role of the quiescent current through the KT88s, will check that closer.
btw the KT88 can be bought already now that's for sure, have you found any source where to buy a quad matched set and any brand preference?
If not I found some guy on eBay selling quad matched set of the brand Electro Harmonix and that's what I'm going for, the cryo treated hypo NOS for US$ ++X00 will I leave fore somebody else.
Ok time for break..

Cheers Michael

Last edited by Ultima Thule; 16th December 2009 at 08:04 PM.
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Old 16th December 2009, 08:21 PM   #27
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Hey guys,
I'm currently building a KT88 PP Ultralinear amp, too.
Although it's gonna be on a different circuit style, I had to look for OPTs too and finaly settled with someone, who is registered in this forum and impressed me with his detailed and dedicated answers in past OPT threads.
I'm talking of Bud Purvine of O/Netics (hpurvine at gmail dot com). I tend to appreciate people who take the time to help others without marketing themselves. And so, although I have to pay a lot of shipping costs from the US to Europe, I ordered OPTs from him. I'd advise you to at least consider him, the contact is very nice, fast and informative.

I can't say much about WIMA in tube amps, but in all the many applications I used them in, they always performed without any problems, so I'd recommend and use them any time. The MKP10 is said to even be a very nice coupling cap, although not the very best. But certainly a very good value for the money.

As for the tubes, I researched very carefuly on that matter and it seems that Reflector makes the best in-production KT88, which means Electro Harmonix or Gold Lion. I am going to buy EH, since JAC says that internals and measured data suggests that they are pretty much the same thing and EH is much less costy...

Last edited by Herr Grau; 16th December 2009 at 08:24 PM.
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Old 16th December 2009, 09:38 PM   #28
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It's KT 88's alround.
This is my build i'm starting Patrick Turner design 85 watts with a heap of class A. I don't have the iron but do have the components. I'm using mullard AU7 phillips EL84's and either EH or the genelex reissue. Building them on dual mono chassis.
The PSU and protection circuit will be built on 2.4MM PCB all other circuit hard wired maybe using some Keystone turret strips on the 3 mm ge material.
How much space should i allow around the KT88's?
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Old 17th December 2009, 12:40 AM   #29
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Guys,

Here's the deal with the 12AT7 LTP: 200 to 220 V. on the plate and IB = 3 mA. sounds GOOD.

You can buy the cascode CCS from K/K or you can use what we did in "El Cheapo" and save a few coins. Check Jim McShane's site out. AAMOF, you may be able to get away with the 10M45S IC.

Don't be fooled by appearances. The "reissue" GEC tube IS better than the EH tube. However, the EH tube is an excellent value.

It's likely that a single negative supply can take care of both O/P bias and the LTP tail. A good CCS will "eat" many Volts, if necessary.
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Old 17th December 2009, 07:03 AM   #30
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Quote:
Originally Posted by Eli Duttman View Post
Guys,

Don't be fooled by appearances. The "reissue" GEC tube IS better than the EH tube. However, the EH tube is an excellent value.
AH- ha, Whats the "betterness" about the reissues. pse elaborate ?

richy
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