JoaMat

Happy Birthday Søren!

Me too think FedEx is nice. If I put a Mouser order at 18:00 Swedish time I usually get a knock on my door at 12:00 second day after – 42 hours from Texas to remote Sweden. 🙂

Took some time but eventually I got a CD sent to me. Thanks for post!

Now completed mini T2 with the new boards version .23. Squeezed in film caps with 0.8 mm leads on right channel with 0.76 mm hole diameter, elevated and soldered both sides (see below). Both channels worked right away. Only issues I’ve found with those new boards are mentioned in posts above.

Warning! 0.1u/1kV film cap pads on right channel have 80-30 pads meaning hole diameter is 0.030 in or 0.76 mm. This is to tight for most film caps that have lead diameter of 0.8mm. There are some Panasonic, Cornell Dubilier, Nichicon and Vishay caps with 0.6 mm leads and 15 mms lead spacing. Do not drill the holes for the film caps. The through hole plating is needed as it ties ground planes together and also needed for -460V to be fed to none tube side of the board. Left board have 90-40 pads – 40th or 1.0 mm. This mistake is done by me and the blame is entirely on me. I’m sorry.

While working with latest mini T2 (version .23) boards today I discovered that op amps on left channel have wrong (old) values. The op amp on none tube side, close to VOL168A, should be OPA197. Op amp on the other side should be LF356. Silkscreen right channel seems to be correct.

The Guardian today ”Miles Davis, Newport 1955: the day of a sensational comeback” Now half through (at Qobuz/Tidal; a few tracks unavailable) ...long night …only half of bottle left…

Boards arrived. Thank you, Michael.

Newly released on Qobuz and TIDAL.

Happy Birthday!

Happy Birthday!

Shouldn't R1 be between Q1_source and -Vout?

Happy Birthday, Kerry!

A week without offset servo and most of the time jumpers for balance servo have been removed. Today amplifier started out with offsets up to -40V. After half of an hour offsets between 0V and -10V and unbalance 5V and 10V. I think this is acceptable.

Attacking crowded smd boards with test probes are indeed risky business. My heart rate increases when I just think of it and sometimes my hands shake so it’s not possible…

Newly released.

Think I like trimmers. Instead of servos – miniature stepper motor driven trimmers controlled by Arduino?

BDent has made a fortune out of me due to them stories.

To find out I removed Q10 (also removed vol618) and replaced it with 1K trimmer (just put it in Q10 position) to control the offset. With balance trimmer (jumper removed) and offset trimmer I’ve no problem to manage the amplifier, but this is just after a day. Maybe I tell more later.

I haven’t removed “current limiter” resistor – here I use 15R/3W – just removed the 2n3904 transistor. I’m only used to 4 separate heater windings so I can’t tell about running all big tubes as you do. Mini T2 has big tubes heaters tied to roughly -400 V via R53-56 voltage divider, so you actually connect left and right channel’s dividing points with your single filament transformer. My brain is to slow to figure out what, if any, implications that might have. Perhaps someone out there can enlighten us. But never use same heater windings for big and small tubes. Small tubes don’t like heaters to be tied to -400 V and besides their heaters are tied to ground via 47R resistors.

Thanks, good to know what components that are at risk. I’m using a KGSShv style PSU and I’ve a small inventory of FQPF8N80C, 30V Zener and 15R power resistors and so far that has been enough. Also omitted current limiter since it hasn’t protected me. One other question, @jose. Do you have four separate 6.3 VAC for the tube heaters?

Great, quick recovery. What parts in GRHV needed to be replaced?

I’m sorry for your misfortune. Did it happen direct after you power up the amplifier for the first time?