JoaMat
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Happy Birthday!
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Kerry Design mini GRHV\GRLV and JoaMat mini T2 Group Buy
JoaMat replied to mwl168's topic in Do It Yourself
Shouldn't R1 be between Q1_source and -Vout? -
Happy Birthday, Kerry!
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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.
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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…
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Newly released.
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Think I like trimmers. Instead of servos – miniature stepper motor driven trimmers controlled by Arduino?
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BDent has made a fortune out of me due to them stories.
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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.
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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.
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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?
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Great, quick recovery. What parts in GRHV needed to be replaced?
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I’m sorry for your misfortune. Did it happen direct after you power up the amplifier for the first time?
