DefQon

Stax SR-X circuit For cheap http://www.ebay.com.au/itm/Audio-Valve-Board-PCB-Electrostatic-Headphone-Kopfhorer-Verstarker-Amplifier-DIY-/261876469298?pt=LH_DefaultDomain_77&hash=item3cf90dce32

Ok Ok bad news, tried to do the winding measurements, powered it up and tripped the fuse. So I put in another fuse this time magic smoke start sipping through the El core case, powered off immediately. So the transformer is absolutely dead....what are my options.

Yep, black probe in the chassis ground holder on the amp, transformer is still secured to chassis just unsoldered all secondary taps to test each winding to see the voltage. The relay doesn't even engage possibly due to the completely off power supply.

Ok tested by isolating the secondary leads from the ps board. Trafo gave me completely off measurements. Should be 260 0 260, it gave me 80 50 190. 26 0 26 winding gave me 140 110 140. All on vac. Tried two dmms an itt mx52 and a old fluke gave same results. What are my replacement transformer options with what specs like current rating for the secondary windings etc.

Thats exactly what Iwas thinking its hard to kill a power trafo. I think the trafo is out of phase or something which is burning up the primary windings. Is live(hot) wire straight to switch or fuse holder and then neutral to switch? I think the mains wiring is messed up.

What a shit day has it been for me. So all the parts and everything came and I rebuilt everything on this 12S except the phono boards and the 1/2 watt resistors on the output stage boards, wired everything properly. Trafo is wired up good and proper with the jumper set to 240v. Powered her on and noticed something unusual. Trafo which gets warm to hot-region on IDLE. Output stage boards are hardly putting off heat. Plug in headphones and a source, no sound unless I put it on full blast there is distortion and a miniscule amount of sound coming out. Not good as I knew there was one thing wrong: Trafo fucked. Well so I powered it up, put DMM on VAC and measured the secondary windings to the psu board. Measurements should be 260 - 0 - 260 and 26- 0 - 26vac, so I measured mine. Nope not even fucking close. Measurements read something like 17-0-70 and so forth. What I also noticed is the trafo gives off this weird whooshing noise when the amplifier is on. But the amplifier worked before I pulled it apart and the chassis (after it was cleaned) and the trafo (untouched and foam wrapped in a box) and now everything is soldered together and its not working. I did replace the mains cable. The old cable had a red wire from AC cable to switch, green wire to ground and a black wire to fuse holder (fuse holder then goes to universal jumper for AC primary). Red, Black and green was the color code AC wiring for 80's Australia, after the 90's they changed it to Brown, Blue and Green/Yellow. Red is hot/live wire (brown) and black was neutral to fuse holder (blue) and green/yellow is ground. Any suggestions. And any recommendations on the trafo specs and exactly where can I buy a trafo that is identically rated to the current one in the Stax amp also with multi-tapped primary windings?

Use a DMM.

Payment made for mine.

Ohh that one, yeah heard know about that, I'm still waiting for one of my boards from his last GB run for the KGSSHV (till I bought John's old offboard set) but from what I heard a typhoon hit his town pretty hard and seemingly he was unable to turn up with the stuff. Whether it's true or not it sucks either way as I heard he had half of somebody's T2 order.

12AU7 = 6S4? Spritzer may say its stupid but I find it funny. In reference to tube rollers on H-fi, "Ohh look ma it has same amount of pins lets plug it in and hope for the best."

There was a Chinese T2 GB?

Where does one go with the not so cheap route and obtain a fabricated L plate with TO-3 transistor template holes cut out? Almost a dozen on each side and I think its a painstaking process if I did it with the drill press.

Damage like that could be due to shipping. I`ve had one my old T1S amp tubes shattered and top cover completely knocked in because some post guy took a kick into it. Only got a partial refund from JapanPost though.

Those prices are so cheap. Compared to here.

I remember seeing these pop up for $700-900. Then around the time I joined the prices went $1k+ out of no where. Heck I've even seen these sell for $3k with the AKG speaker adaptor. $1.2-1.5k is about the price range I've seen for them these days. With original box and all.

Ah didn't know only have seen the green ones from Tran's GB. I thought the pcb's were original Stax SRM-T2 ones.

Such a rare sight to see something like this: But overpriced http://buyee.jp/item/yahoo/auction/r126553633

They would be the same except the SRD-6 box has a bias supply for full blown Stax electrostatic models. The SRD-4 don't have bias which suits exactly the SR-80's electret nature as it has a fixed/charged bias. I think the original SR-80 Pro's came with a pro-bias solution box. (Again the Pro was just purely for marketing because it came with a pro-bias capable adaptor and not the standard SRD-4 electret adaptor).

Tell me about it, I've been on a similar journey myself over the past few months, buying few older Parasound, Monarchy Audio and EAD dac's from late 90-early 2000's. Prefer most of them over the new ESS Sabre crap which all sounds like plastic to me. For me PCM63-K's is where the moneys at, maybe occasional AD1851/3, PCM1794 with PMD100 HDCD decoder in some transports are alright. Been trying hard to get my hands on some Vimak's and Fullcrum TT but no dice. Have noticed most of the late 90's DAC's don't have power switches.

Wait Jocko Homo designed the Legato 2? Wtf that's news to me.

I don't think Frankcooter has ever released the schematics to his 845 tube amp. I know the Stax mafia have an 845 tube amp in the works to be released anytime in the not so distant future and few other designs.

So UF4007 can be used to replace all diodes including the funky looking ra-1 types on the ps board?

If you don't want to charged for an arm and a leg do it yourself. Or accutech (yama) in the States.

Thanks for that. Here are some pics I took before disassembly of the amp of what I was referring to (I've changed the 2.2kohm resistor to 22kohm Kiwame's as I want pro-bias through this): What is the purpose of the 100uf 25v cap? Also looking at your old pics few pages back, is one end of the 220kohm resistor connected to one of the empty tabs (essentially GND) and the other end connected to where the 22kohm resistor is, which then another wire is feeding from the 22kohm point to a 5Mohm ballast which is connected to one of the bias pins on the output jack? Where about's should the 1uf 1kv filter cap connect to? Can 10/100nf caps be used as well? So the round and RA-1 diodes sandwiched in between the ceramic film capacitors be replaced to UF4007?

Some internal driver pics. Numark ES-701 (same driver used in the Kmart, Pioneer and Lafayette clones) Odd driver construction. Mine came in original box and manual and looks relatively unused, but takes a while to charge up and distortion instantly kicks in with sub-bass music. Also received a half arsed Stax SR-60 electret (marketed as SR-30 in non Europe regions, so USA, Oceania etc). Got my partial refund from seller months ago, there was almost 0% sound, leaving it to charge a few days didn't work, unit looked to be tampered with. Always wanted to disassemble one of these electret drivers as they are absolutely destroyed when pulled apart: The driver itself taped up ... well not for long... Dust protector (backside) Tape removed: And this is why there is almost no sound output regardless of power and volume, looks to have been stored away in piss poor conditions stretching the electret film. I tried to do a quick repair ML style by reheating the membrane but it was no go, the film seems be stretched as per spec by a special machine jig when Audio Technica made these electrets for Stax. They are currently in the process of being turned into full blown ESL headphones. The spacer and bias connection is proving to be a problem at the moment as the yellow tape was the thing holding the driver together. Anyway here's one for Spritzer, not sure what circuit design I got outbid on the last second: http://buyee.jp/item/yahoo/auction/k182173704 I purchased the other Stax tube amp from the same seller he was selling a month before. http://buyee.jp/item/yahoo/auction/d163346459 This is the amp I was asking about converting the bias from the claimed 470vdc to full or near 580v pro-bias in the KGST normal bias thread in the diy section. There is a switch to change from normal to pro-bias, but as mentioned some compression and distortion if volume pushed too high with pro-bias headphones. It sounds pretty sweet though. There are 2 260vac taps and 1 350vac tap on the secondary winding of the trafo. Here are some internal pics of the circuit (bit messy but the amp is smaller then the SRA-3S and about same size as my SRD-7 SB MK2's: