GeorgeP
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Posts posted by GeorgeP
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On 7/15/2023 at 11:38 PM, jokerman777 said:
Should signal ground meet chassis/earth ground in the PSU box?
I found that the center stand-off pad near the output terminals on the PSU board is connected to PSU board circuit ground and mounting a standoff there will make the chassis gnd to signal gnd connection, otherwise the two grounds will be separated in both boxes.
I found Kevin's old post in this thread mentioning "everything floats" so should I leave out this stand-off?
Kevin commented on how to ground the amp, at the end of this post. The picture doesn’t work any longer but there was a short wire going from the terminal block ground to the board stand-off hole. Make sure to remove some anodizing from the chassis so there is continuity among all the pieces, that particular standoff and the IEC. The chassis ground from the amp section would then go directly to the IEC ground tab.
On 7/15/2023 at 11:38 PM, jokerman777 said: -
3 hours ago, demonkuro said:
HI！My exploded T2 is back to life.
Today I finally connected the PSU to AMP after replacing all the damaged parts. Following the instructions in the forum, I set the R42 (22K) at 6.55V using RV2 (10K) and then set the battery at 740V (+190V/-547V) using RV1 (2K). When I was ready for success, I found that it was not so simple. The output R- to GND was -91V, R+ to GND was 0.05V, L+/L- to GND was -28.6V, and the BIAS (574V from PSU) was only 384V after 5M resistance.
I tweaked RV2 (10K) and RV1 (2K) to get a near-zero DC output, but I couldn't get a 740V battery at the same time and made the DC output zero.
Do I need anything else? Or are some parts damaged again? I checked, but nothing seemed to be found.
Try getting your 190v closer to 200v if possible. And then readjust after 30min or or as the value will change until the temps stabilize. If your offsets are still problematic then adjust as required (30ish volts or lower is good) but it might suggest an issue somewhere.
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56 minutes ago, Mach3 said:
Ok found out the reason why fuse blown. primary and secondary winding was wired incorrectly to the terminal block.
Grey and brown mixed around.
I need to replace the transformer, did a continuality test on P1 and it failed.
I tried to contact [email protected] at Toroidal Engineering Co.
But GeorgeP inform me it looks like he's close door since COVID.
Anyone got a spare one for sell?
@Kerry do you mind sharing what specs you're using with your transformer. Alternative route I get toroidy custom make one base on the correct current specs below. They made a custom one for my KGSSHV.
Kevin mention that the total of the primary winding should be 90watts, so would 0.5 amp each for P1 and P2 be enough.
P1 = 120V, (unsure of current rating)
P2 = 120V, (unsure of current rating)
S1 = 15V - 0 - 15V, 1 amp (Kevin provided these rating)
S2 = 6.3V, 5 amps (Kevin provided these rating)
S3 = 6.3V, 5 amps (Kevin provided these rating)
S4 = 6.3V, 2 amps (Kevin provided these rating)
S5 = 6.3V, 2 amps (Kevin provided these rating)
As discussed in PM, all three toroids are miswired. Someone has tinkered with the PSU and re-wired the toroids incorrectly. This amp was built in 2016 with Houlden's transformers, which are what I have in my T2. Toroidy may be the cheapest option for you given you are in Australia. Alternatively Primrose/Sumr can supply the required transformer. Hopefully your only issue the transformer.
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3 hours ago, kevin gilmore said:
DO NOT ROLL TUBES on a T2.
Definitely do not roll fake siemens tubes as they cause the amp to blow up many expensive parts.
1000%. I have seen people do this with unfortunate results. Even what some consider to be drop in replacements for the el34, like kt77, should not be used.
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6 minutes ago, Craig Sawyers said:
For a transistor mounted on a heatsink there 6 possible lead orderings, 3!. For a small signal transistor that you can insert either way round, that reduces to 3 effective orderings. 3!/2.
I'll get my coat...
It’s even easier for the ones not mounted on the heatsink. 😉
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1 hour ago, Reima said:
I got them from littlediode_components.
The 2sa1486 from little diode are 100% fake. They are pretty scummy.
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3 hours ago, Reima said:
I see that my link to the photo does not work unless you have an account at imgbb.
Is there a better place to store photos?
Where did you buy them? Most 2sa1486 being sold at the moment are fakes.
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2 hours ago, starcat said:
Phew, soldered some 50x LEDs... Checked the C3675 and A1468 for breakdown voltage. Will use the ones with the highest in the batteries.
Are there any fakes of the C3381 and K246 and is there any special procedure for testing those?
I mounted only 4 of the total 8 standoffs as the ones close to the front panel are in the way of the Stax connectors and the ones in the back are exactly where the Amphenol connectors are. 4 of them should be fine I think.
If the 2sc3381 and 2sk246 are the ones you got from me, then they are real. That said, I have seen fake 2sc3381.
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39 minutes ago, starcat said:
Hi Kerry, can't the 1156 be used as a 1486 substitute everywhere unless mounted on a heatsink?
Need to check, might be that Q1, Q2, Q3, Q28 & Q29 is "everywhere" not on a heatsink 🙂
use 1156 on the heatsinks, 1486 (if you have them) everywhere else.
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Oof! So something has also gone in the psu *and* some resistors in the amp sparked (to ground or just blew?)? Sounds like you have a bit of work to do, obviously fix the psu first.
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Ooof - then it sounds like you have some work ahead of you...
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So you only have one properly working side then?
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Sounds like current limiting in the power supply if only one side is powered up at a time and it powers up normally - 30r resistor to 25r or 20r will fix that. What happened though to cause you to start replacing parts in the amp section first - there may be something else afoot?
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47 minutes ago, Laowei said:
Something lost in the translation to Chinglish? ?
I don't think so. He actually has a picture of a train and a picture of a bicycle side-by-side, and then goes on to state that they are not the same thing. I found that illustration particularly compelling. Though I think he might have had the arrows from the amplifiers pointing the wrong way...
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Only thing I learned from Fang's latest post is that a bicycle is not a train...
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1 hour ago, phixphi said:
The tubes are Justins standard Mullards. They have only 5h on them so still very fresh. The measurings were same -27V
Russian Mullards? Maybe you messed up the balance/offset process.
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53 minutes ago, phixphi said:
Wink, i checked bias after some 45mins of warmup and it was 27V off.
Fuses-yes I know,mine will be inserted by a virgin at full moon
More seriously, I had a positive effect changing to ussr silver military fuses at less resolving 717, so i expect some change here too.
Sounds like your tubes are the issue. If your tubes are within spec, you probably shouldn't have had to rebias at all. What were they measuring at before you rebiased?
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Well one thing in the earshock guy's favour is that Hifiman wasn't able to get him to be one of their shills - that's got to be worth something.
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But smoke and mirrors work wonderfully on their audience.
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6 minutes ago, spritzer said:
It's on Head-fi so I don't care
It is just a link to a tutorial on caps : https://www.electronics-tutorials.ws/capacitor/cap_7.html (so you can better edumacate yourself, of course...), and the following Pf calculation:
MOSFET C1=65 Pf
Transistor C2=6 Pf
Ctotal=C1*C2/(C1+C2)
Ctotal=5.49 Pf-
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The Board error is an easy fix - a missing trace if I recall. There are some posts on it in this thread. I seem to recall G600 had this issue.
Why not post some pics of the sand (2sk216, 2sj79, 2sc3675 and 2sa1486) - sometimes it is easy to tell from a visual.
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13 minutes ago, mwl168 said:
Or you can build the relay-based, full-balanced, true ladder attenuator that Kevin designed and there was a board-run for it a few months ago so there may still be PCBs available for it.
Have a couple of these I've been meaning to get to. Wish I got in on the parts group buy as I just can't get motivated now.
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yeah but the rk50 is all gold-like and purdy lookn.
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1 minute ago, swampsong said:
....
Still though if this guy ripped some users off and is now selling those on head-fi maybe i should ask him about it? he has been very forthcoming... i liked to see what his response it... its weird and i think other users at headfi should know... he sold a few more sets after me and is asking for others to do a board run with too...
First, it would be hard to prove (and to what end, now, 4 years later). Second, you would not have known, so you shouldn't have any guilt on your part.
I corresponded with him back in 2015 about the Lil Knight T2 boards he was selling and he indicated that "Last time I heard from him was 8-9 months. At that time, he was in hospital, probably in a coma. He was a big help to me back then, not sure what happening until now." Maybe it is true. If so, prior to going into a coma Lil Knight gave this guy all his partially completed amp builds, audio parts, T2 boards and chassis parts to sell on Head-fi...
More seriously, I had a positive effect changing to ussr silver military fuses at less resolving 717, so i expect some change here too.
The ultimate DIY? A Stax SRM-T2!
in Do It Yourself
Posted
Yup, that’s it.