Left channel    510R: 10.178V,  6k2: 11.428V

Right channel  510R: 10,147V,  6k2: 11.395V

Edited November 11, 201510 yr by JoaMat

new board is exactly the same size as the original board. 11.95 x 16 inches

and fits the original case i made and all the pots are in the same place.

The test points are in the same place.  A couple of led's have moved slightly

and a whole bunch of led's in the batterys are removed.

 

not the slightly shrunk board for lil-knight case which was 11.95 x 15.65 inches

thru the miracle of cut and paste, this version is almost complete, just need to

do the heatsinks in the middle.

 

joamat's amp board is 9.35 x 12.02 inches

Edited October 20, 201411 yr by kevin gilmore

It’s more than a year since I used lsk389. Tested them for a while than back to tubes, not sure I will go back to them again. So I can’t help there. But I do have some measurements for you.

Left channel 510R: 10.178V, 6k2: 11.428V

Right channel 510R: 10,147V, 6k2: 11.395V

I can get measurements from two modified amps if you wish. Those above come from KGT2 genuine.

Wow good job. You are nearly identical to the design: 19.96mA assuming your 510 resistor is exact. If everything measures good (offset and balance) I would say you are perfect. If not, adjust the 6.2k (up to remove positive offset) resistor and I bet you can get within mV or so.

Thanks for info, that's good to know.

It might be better to put the trimmer on the larger resistor. I have found 6.2K with 1K in series to work well. I can even get many of the tubes working that others couldn't with this setup, for example Amperex 6DJ8. I think in the original T2 transistors these two transistors were selected to have certain properties which are now lost to time (maybe... See more on this below)

Using the third resistor has allowed me to get offset and balance in the mV range. The mystery I haven't solved is why others didn't need this and are still claiming 0 offset and 0 bias. Seems that transistors would have to be chosen exactly the same way as Stax did for this to happen. Regardless, evidence is there for example with Kerry's experience of setting things at 6.55V and everything zeroing out.

Would it be possible to get a survey of your voltages across the 6.2K and 510R resistors? This will give the gain of the transistors. It would be useful (for me) to compare this to your original T2 as well. If the gain is as low as the datasheet suggests, I can't see them working in my T2 which means perhaps I have some other marginal component that is causing "problems" I haven't found. Again, just don't see a way for this circuit to be as well behaved as it is for people.

 

Marc, is your board the original one that Kevin organized or the group buy that Tran did (not the more recent failed group buy) (or your own board but made from the original version)? From what I could tell, there were a few fixes that were incorporated in the Tran group buy that made it more stable out of the gate. Haven't tried Amperex 6dj8 but do recall someone saying it sent some of their transistors to an early grave (I recall they were bugle boys) - I have only used JAN Philips 6dj8 from the 80s and some german-made siemens from the 50s or 60s, all without issue.

I have the very first version.

all these board files updated with latest parts, changed batteries,mini heatsink etc

 

 

joamat board files

 

http://gilmore.chem.northwestern.edu/t2shrinkedv10.zip

http://gilmore.chem.northwestern.edu/t2250.zip

http://gilmore.chem.northwestern.edu/t2hv2.zip

 

slightly shrunk board for lil-knight chassis

http://gilmore.chem.northwestern.edu/t2shrink2.zip

 

original board

http://gilmore.chem.northwestern.edu/staxt2nc3fdh7.zip

_{Does anybody have a rough idea regarding the price difference between the KG T2 and the latest JoaMat iteration with less parts & cheaper, easy to source sand? (sans chassis)}

Edited October 22, 201411 yr by livewire

I think that depends on volume discounts.

Well yes, of course!

I'd be down for a full kit, I was definitely toying with the idea of finding parts for the original version

/

Edited November 11, 201510 yr by JoaMat

so basically you saved head-case thousands of dollars, truly a boss among bosses

there will be a kgsshv version of joamats power supply layout.

 

my original T2 power supply had about 1.5 mv of noise, the kgsshv

power supply is about 3 microvolts of noise.

I will then modify it for Megatron duty... 

I did one rough estimate a while ago. Buy a1486/c3675/c3381 from bdent cost 540 USD - replace those with parts for modified T2 from Mouser cost you75 USD.

 

Buying from bdent is maybe more expensive than ebay, but risk for fakes is considerable lower. 

 

Thanks for the informed reply, boss!

 

Amen to that!!! I've never had a problem buying anything from them - other than them draining my wallet.

I did one rough estimate a while ago. Buy a1486/c3675/c3381 from bdent cost 540 USD - replace those with parts for modified T2 from Mouser cost you75 USD.

 

Buying from bdent is maybe more expensive than ebay, but risk for fakes is considerable lower.

Bdent is obviously the safest, but there are other good sources for 3675 ($1-2) and 3381 ($1-2). Still more than the newer stuff from mouser, but not a lot more when you consider the overall cost of the t2.

/

Edited November 11, 201510 yr by JoaMat

I think that seller on diyaudio stopped selling 3381s in moderate quantites because the T2 ruined his christmas

Yup! I bought a butt-load of those from him at that time.

I just forgot I have a bag of 3675s that I bought for like 1.50 a pop... Thought they were fake, I need that transistor tester I guess

Did anybody hear from Tran about the T2 cases?

 

I'm guessing our money is long gone at this point...

/

Edited November 11, 201510 yr by JoaMat

Either a good meter directly (use AC scale on finest setting) or a way to accurately amplify the AC component of the signal (and block DC)

measuring that is very tough.  Need a screen room, a very heavily filtered mains supply and

expensive meters designed for this kind of thing. Mine is a keithley ac microvolt meter.

 

And you have to block the DC first. Film caps work for this.

Edited October 31, 201411 yr by kevin gilmore