Leaderboard

I wanted to find out the currents “produced” by Q1 and Q2. Since I don’t have the courage to stick my nose or test pins in a live amplifier I made this test board today. Measurement on the test board indicates voltage cross emitter resistors at R1, R3 and R9 close to 1.10 V. If we actually have 1.10 V than current through small tubes are 2.6 mA and not 3mA that I mentioned in previous post. The Q1 current sources give 3.8 mA each source. I’m considering changing R1 and R3 to 270R and R9 to 180R. Now days I check for the polarity of the LED TLMS1100 by using DMM in diode testing mode. Positive pin on anode and the other on cathode you get a red light. But be careful the LED will easily pop away and it’s not sure you ever will find it again.

R9 is 255R on silk screen on the boards now sent out by Michael. For some time I have run the amplifier with 200 ohms which increases current through the small tubes a bit. I haven’t made any measurements on the amplifier to verify currents but 200 ohms will give something like 3 mA through tubes (T2 has 5 mA). I do think the change improves the amplifier a bit. As I want voltage at base Q8 and Q9 to be 20 volts above -HV, same as the real DIY T2, I’ve today increased R13 and R14 from 200K to 330K. I don’t get +20 volts but it’s closer to it now. R9 on latest schematic is 200 and I think it should be so. R13/14 are 200K on schematic. To follow the DIY T2 you may increase it to 330K. But maybe it doesn’t matter which you choose. Any thoughts out there?

Lucky to have found a localish shop that carries this at decent price!

Silver is very affectionate on her own terms, but Dunhill nee' Mittens is such an amazingly docile cat that I feel bad that that he doesn't belong to some big family. This is him settling down next to me after I danced with him to Stevie Wonder for about half an hour. He was purring the whole time.

Breakfast. Healthy part Fun Part Local Part (Joanne) Location / View / lighting conditions part

Rushed away to my local supplier and arrived just in time before they closed for the day. Got 0805 180R and 270R. At home they turned out to be 0603 but I managed to get them in place. On the test board I get exactly what I expected and I assume that that’s the case with the amplifier as well. Measured 18.5 V above -HV at bases of Q8 and Q9 with R13/14 @ 330K. I think Susumu RG is a good choice. ToshibaTTC004B is interesting – thanks INU. The smd transistors are also Toshiba.

A few points regarding the boards Michael have had made on my gerbers. They are basically the same as my kitchen made boards I made five months ago. The small tube footprint has no hole for the center pin. So far I’ve cut away the center pin on the small tube socket after checking the pin holders to be not to tight nor to loose. One time I got tube sockets where the tubes fell out when turning upside down. So either you have to cut pin or drill a hole. Be aware that upper tube has a trace between the grids that might be to close to center pin. Right board 270K resistor has a 0805 pad (intention was 1206). It’s possible to solder a 1206 resistor on the 0805 pad. If +220V you get about 130 V cross the resistor so Vishay CRCW0805 is OK here. But with +250 V you get close to CRCW0805’s limit of 150 V. Some of component values on silk screen are poorly place and almost unreadable. The blame is entirely on me, I’m very sorry. There are four octagons on bottom side. One at each big tube socket center hole and one each side of small tubes filaments connections. Here I have standoffs. A few comments on updated layouts. Small tube footprint with center hole. 270K resistor pad corrected - now 1206. Silk screen remade. Pleas notify me if there is any left that needs additional attention. Now “value” of connections on both sides (except heaters). No terminal blocks on my boards. Top right. Updated 2019-02-27. Bottom right. Updated 2019-02-27. Top left . Updated 2019-02-27. Bottom left. Updated 2019-02-27. I call above version .2. My kitchen made and Michaels are version .1. Regarding this amplifier - there is nothing I've invented. I just have picked up different things and tried to put them together. As: Opto servo (the only offset servo you need) by Kevin. 01N100D/TL1021 current source by Kerry. Schematic of Stax T2 provided by Kevin, Et. al. Schematic of Stax T8000 provided by Kevin and Birgir. Etc. etc. Thanks for all knowledge, information and inspiration from you DIYers and Head-Case members. Please look for errors or other issues.

I dug some stuff out of boxes, tonight. Can you tell which company has an inferiority complex?

I was expecting it to actually be around $500, but you'd be shocked with a replacement OEM gator strap can cost from a dealer.

Finally got down to assemble this thing, followed Spritzer's suggestion of the M3. Nice making use of the old Noble pot (once doing service in a modified PAS3 in the eighties) and the psu mistakenly bought - 15 bucks - for the Dynalo. Doesn't sound bad at all.

OK – Connected an unmodified T2 PSU. Raised voltages to +250 and +/-500V. Top 6922 anode voltage sits at 227V and grid at 78V. So far it works. Will run this for a while and check for darkening spots on the boards.

An imposing site that is...

Goldfrapp – Black Cherry This album never gets old for me – listened to it three times in a row (trying to sort out battery issues on my portable CD player)

Literally tons of snow everywhere in Tahoe. Tomorrow or Tuesday should be ideal on the slopes, assuming forecasts are correct and it stops falling.

Snow is really good in the Sierra Nevada's this year. Debated heading up to Tahoe for snowboarding but the lines are fuct on Sundays(64 inches in the last 3 days). Desert trails on the other side of the valley have 2 to 4 inches depending on where you are, so lots of fun in the x3.

RIP Mark Hollis. [emoji3525]