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Edited November 12, 201510 yr by JoaMat

Which one is that again? If it was me that suggested that, then I know which one...

It has to do with the (lack of) stability with a base-biased transistor (emitter current isn't temperature stable). It would be even better to use a different design that isn't so dependent on transistor parameters (I.e. Beta) (collector-feedback perhaps?)

I think what happened with the original is that higher case temperatures than we see in the DIY version further inflated the gain of the transistor (this is a bit of a stretch, admittedly) which made the circuit work more consistently.

I think the result would be more stability, but I guess I am the few people that sees this part of the circuit as not being robust - likely because I seem to have the most problems.

Thanks for your response.

Edited November 11, 201510 yr by JoaMat

The darlington pairs of q32, q33 and q34, q35/q36 servo have emitter degeneration which dictates the gain and more or less stabilizes it with regard to temperature and base current. FJPF2145 has much lower beta compared to the original 2sc3675 but it's still adequate in this situation. I think the choice of heatsinking is mainly from deciding how much heat you're comfortable with. On the original DIY T2, Q35 and Q36 are heatsinked. It wouldn't hurt to heatsink Q32, too. Q33 Q34 don't need them.

Thanks a lot.

Edited November 11, 201510 yr by JoaMat

On the original DIY T2, Q35 and Q36 are heatsinked.

 

I missed that you wrote original DIY T2.

Edited November 11, 201510 yr by JoaMat

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Edited November 11, 201510 yr by JoaMat

i went back to the pictures to make sure

 

all of the parts on heatsinks in the original are on the

common heatsink bar in the diy-T2

 

there are 2sc3675's with no heatsinks in the original, and

they are that way on the diy-T2

After reading Walt Jung’s article Audio Current Regulator I think there are reasons to believe that the original output tube CCS has better performance than the 10M90S CCS. According to the same article one can believe that cascoded 10M90S CCS is better than not cascoded.

 

Edited November 12, 201510 yr by JoaMat

Don't know if a 10M90S cascoded with itself is better than a single 10M90S, but a 10M90S upper device cascoded with a DN2540 lower device measures about 1000 fold higher impedance compared with the 10M90S alone - > 160 megohms vs about 170 kilohms.  Whether that makes an audible difference in the T2, I don't know.  My wild ass guess is it makes more of a difference in a lower current design than in the T2, where the standing output current is already overkill.  Beyond a certain point, overkill just means the rubble bounces higher (always wanted to use that line  ).

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Edited November 11, 201510 yr by JoaMat

Hi folks. Been awhile... deepak stoked the hunger for finally gathering some of the parts for the original boards that I have. I missed the boat with some parts that were being sold in the classifieds unfortunately, but I'm looking to buy parts from a guy who posted on head-fi.

 

I understand there's no way to guarantee the parts are genuine based on a picture... but was wondering if anyone would be willing to comment if these look genuine.

 

the guy says they were purchased from singapore in 2005

 

 

Those look like the real deal.

Thanks I'll reply to your PM as well!

suggest you buy the transistor tester meter on ebay, cheap and the best

way to test them before you stuff them in the boards and then find out they

are not real.

Will do, thanks for the advice. Is there any mention of what to look for in buying a meter in the thread or in other diy threads?  

 

Btw thanks for the pics you PM'd me early last year Haven't seen them until this week. I'm glad that it's living up to a decent purpose.

tester is duoyi dy294 iirc

yep that is the one.

thanks guys

what are your plans for the case?

icarium has one of my cases

I have 2 cases, 2 sets of original boards. Originally I planned on trading a kit to a builder to get mine built. 

 

It sounds like I should look to acquiring group buy boards or if you guys ever produce new boards please reach out

 

Also talking to GeorgeP it sounds like besides transistors there are resistors and capacitors that are becoming hard to score too :/ 

No capacitors or resistor issues that I'm aware of.  These are generic parts so there are always subs. 

Thanks Spritzer. Any advice on 2SA1486 or is bdent the spot? I'm probably going to hit the 200 quantity price break.

I've pretty much cleared out all the Japanese sellers at this point but you don't need that many.  Use KSA1156's in the front end so you just need a handful per amp.