JoaMat

Here is my solution for filament transformer… …mounted on bottom case plate, belonged to a now retired Blue Hawaii. I also found a piece of Bergquist Gap Pad for the transformer to rest on. It seems that cathode resistor voltage is much lower for Emission Labs tube than for EL34, so I decreased the negative high voltage from 460 V to 400 V. The lowered voltage called for change of Cathode resistor and trimmer, now 402R resistor and 100R trimmer. A few things had to be removed before component changes.

Now my Emission Labs tubes finally have gotten a dedicated DHT amplifier. Picture is taken in almost complete darkness, so most of the light comes from LEDs and tubes. Current is 27 mA which gives a voltage of 15V cross cathode resistor. Filament transformer is on the bench behind the amplifier - I have to find a more permanent solution I guess…

That looks great! At picture above, are you removing copper with a 2mm end mill?

I do think it will be with direct heated transformer in amp chassis and my original external PSU. The amphenol connectors have no free positions plus it’s 5VAC tor the Emission labs filament. …but if I put one transformer in amp house, I might very well put everything in the same house? Then it will be my first single chassis build.

The milling machine has been busy today. Width is same (to the last decimal) as Kevin’s original DIY T2 board but only half the length. Transformers for 4 direct heated triodes (each). Need a hair cut.

No need for old laptop. It seems as 8.5 works along with new version if they are installed in different maps.

Thanks. So, I better keep my old out of date lap top with 8.5 installed to be able to view gerbers.

I’m trying to open Kevin gerber files in a newer version of Proteus and I get this message “Cannot parse all drill tool information from 'NC Drill Setup' section of the tool information (read-me) file.” and “Failed to successfully parse tool information (read-me) file. Gerber view aborted.”. In Proteus 8.5 gerber viewer works just fine. What might the problem be? Any idea how to solve it are appreciated.

After yesterday’s post I thought the project was completed. But no, not completely… how about the EML direct heated triodes? Tubes with their filament injector adapters and “portable” filament transformer. I had to decrease cathode resistors to approach a good offset. For the moment output current is set to approximately 19 mA, only 2 of 3 2SC4686 in each CCS are in work.

Pertusi - Michele: Live Recital

Here is another picture of my megatron something. Made the fifth board in this small project yesterday, seen at left side. Main reason for this project is that I had Mundorf capacitors just laying in a “good to have bin” and, I also have too many unused 2SC4686 and 2SA1968. You can build a similar amplifier with 4 x KSA1156, 4 x 01N100D and 4 x DN2540. Plus, tubes and a few passive components. The easiest electrostatic tube amplifier I’ve built so far.

A report from JoaMat Kitchen. My idea of a servo as shown in a 3D visualizer a few posts up doesn’t make anything better, unless you like aerobatic inverted high g flights. If you want a nice ride just pull the jumper which disables the servo. Glad I didn’t gave that layout a version number.

Thanks for the suggestion. 🙂 But the amplifier is too good for having my "name". It’s a Gilmore design combined with JimL cascode CCS or T2 CCS. I have tried both, my privilege as a DIY:er.

I’m still working with “Megatron something”. Here is another version. Similar to earlier, but no trimmers. Room for 3W cathode resistors and opto servos (the only servo you need). I built an original Megatron back in 2013, but it’s disassembled long time ago and that was kind of a challenge, top tubes with separated floating filaments. I must say this is a bit easier and sonically it’s all right. I can’t call this Megatron, can I? I’m thinking of Hybritron – a combination of Hybrid (tubes and solid states) and Megatron. Or maybe I just call it my little ampy. Don't want to be sued by Bourns.

Just made a third board (right side) of “Megatron something”. Output CCS are T2 style - 3 x 2sc4686 and 2sa1968. All ten LEDs are on top side of board. I’ve to compensate for the missing tubes. Picture is shoot in weak light, ISO 12800 and 1/6sec.

It really made my life a lot easier when I started to use integrated schematic. But if schematic is wrong, this might happen… Interesting project you have, AlexS.

Roon pointed to this for me. For some info about the recording follow this link.

A right channel is finished now. Here is an aerial picture. Output current sources differ between channels. Left, as said in a few posts earlier, has T2 style CCS while right channel only has 01N100D/DN2540 CCS - a “Carbon style” CCS. The boards are ready for both CCS. The boards have same size and tube positions as mini T2. I run this on +400/-460V PSU, same PSU as I use for mini T2.

Just small plastic jars with garlic sauce, found them in the fridge. Suites me perfect. All the sauce makes me fat...

Here is one of my mini T2. Left channel is changed to this… A Megatron something. Upper EL34 changed to T2 style CCS with 3 x 2SC4686 and 01N100D driving two LEDs. Current 28mA, cathode resistance 1390 ohm (the 500R resistors and a trimmer). The big black capacitors are Mundorf MCap Supreme silver/gold/oil, expensive but they look nice. My kitchen at lunch time.

While waiting for the replacement I today brought forward my home-built headphone which has been stoved away for a year or so. It sounds really good, even better than I remembered. Perhaps it ages as a good wine. Wonder what happens if I put it away in our wine cellar for a couple of more years? Original home-built Faulty Stax

Back in 2011 I bought 50 2SA1486 from www.utsource.net. Price 0.30USD each plus 28USD for FedEx, a few days from China to Sweden. They were green and I haven’t used them at all, but they measure same on DCA75 and DY294 as 2SA1486 from bdent. Anyone tried www.utsource.net ?

My condolences to you and your family, Steve.

I’ve tested two dozen 2SA1486 randomly out of my small supply with same meter as you. I get roughly hFE at 60 - 70 and VBE at 0.60 - 0.65V. If possible, test breakdown voltage. Some of us use transistor tester DY294 for that purpose. Your measurements diverts to much for my taste… even compared to datasheet...