Hi everyone ,
question might be silly
Vero is from http://dirtboxlayouts.blogspot.com and its verified
I think something is off with my build.
Pots working and do a change except the gain pot which just cuts volume when turned clockwise, doesnt seem to reduce amount of gain.
Note that i used a 220kA pot for gain instead of 250kA
and 22kB instead of 25kB for tone
I cannot bias Q1 & Q5 Drain @4,5v
can someone provide a guide on how to bias the transistors as i'm not sure if i did it right?
Measuring 2n56457 drains and
Q1 i cant get it over 4.25v
Q2 @ 4.5v
Q3 @ 4.5v
Q4 @ 4.5v and trimpot seems to affect the gate of Q5
Q5 @ 9 (?)
(https://i.postimg.cc/4HQJHN1c/Crazy-Tubes-Starlight.png) (https://postimg.cc/4HQJHN1c)
(https://i.postimg.cc/Z08YMVhq/starlight-schematic.jpg) (https://postimg.cc/Z08YMVhq)
(https://i.postimg.cc/7GM3h0jn/323302709-495716589344134-5795229377594153667-n.jpg) (https://postimg.cc/7GM3h0jn)
(https://i.postimg.cc/xq5GSGv0/324656407-850775992660508-1969627119085365875-n.jpg) (https://postimg.cc/xq5GSGv0)
Q5 is OK..
(it's a Source follower..- No DRain resistor hence no voltage drop..)
Q1 is also OK but if you like to go up to 4.5V, lower 20k Drain reistor value..
(https://i.postimg.cc/V6f1byt4/star-bigcap.jpg)
please advise the what value cap markings you have fitted here.
Nice spot there, my gluteal/Anatidian friend. If that's as large a cap (in value) as it visually appears to be (in size), that would certainly have the effect OP describes...
It indeed looks like a 1μF box cap,,
(instead of 1nF..)
Quote from: duck_arse on January 21, 2023, 09:59:12 AM
(https://i.postimg.cc/V6f1byt4/star-bigcap.jpg)
please advise the what value cap markings you have fitted here.
It seems like 1uf but its 1nf.
(https://i.postimg.cc/cgF3txqD/325596532-1537160216791043-2875859473464592172-n.jpg) (https://postimg.cc/cgF3txqD)
Not relevant to your issue but there is a discrepancy between schematic & layout concering reverese polarity protection diode..
Quote from: antonis on January 21, 2023, 05:40:29 PM
Not relevant to your issue but there is a discrepancy between schematic & layout concering reverese polarity protection diode..
Diode is reversed?
Quote from: harrisxr650 on January 21, 2023, 05:50:38 PM
Diode is reversed?
Not exactly..
In layout is set in series with +9V where in schematic in set between +9V & GND..
(both should work fine with the former suffering from a diode forward voltage drop..)
Quote from: harrisxr650 on January 21, 2023, 05:23:02 PM
It seems like 1uf but its 1nf.
(https://i.postimg.cc/cgF3txqD/325596532-1537160216791043-2875859473464592172-n.jpg) (https://postimg.cc/cgF3txqD)
I have lost all faith in WIMA caps, now. I'm almost tempted to go and look at datasheets to see what series it "fits".
the more I think about that cap, the more I think it is not of WIMA manuf, not unless they lost all their engineering specs and moved to a backyard in chynah. I've never seen a fat wima like that, not a red/black print one, not a 1000pF/100V unit one.
but I suppose if it measures 1nF, it doesn't really matter.
and that I should stop thinking about it.
Quote from: duck_arse on January 23, 2023, 08:02:22 AM
the more I think about that cap, the more I think it is not of WIMA manuf, not unless they lost all their engineering specs and moved to a backyard in chynah. I've never seen a fat wima like that, not a red/black print one, not a 1000pF/100V unit one.
but I suppose if it measures 1nF, it doesn't really matter.
and that I should stop thinking about it.
Its definitely 1nf. but what you say about manuf troubles me, its supposed to be a 100pf/100v FKS2 cap.
Quote.... it[']s supposed to be a 100pf/100v FKS2 cap.
1000pF or 100pF? also, no, Sir! from the FKS2 datasheet -
QuoteMarking:
Colour: Red. Marking: Silver.
1000pF is range minimum. dims should be - 2.5W 6.H 7.2L
FKP2 would be red body black markings. that 1000pF would be 4.5mm wide.
FKS3 would be red body black markings, range minimum is 1000pF. dims should be - 3W 8.5H 10L
I wouldn't worry too much about those JFET drain voltages. Anything 3v to 6v is good.
Q5 must have 9v on the drain, it is wired to it. It is a source-follower/buffer and it's the source voltage that tells you how it's biased.
The Gain pot is misnamed IMHO. It is a volume control for the preamp output. I would call it Drive. It doesn't change the gain of the circuit amplification stages. If clockwise reduces volume have you got the wires to lugs 1 & 3 swapped over?
Quote from: duck_arse on February 04, 2023, 07:41:34 AM
Quote.... it[']s supposed to be a 100pf/100v FKS2 cap.
1000pF or 100pF? also, no, Sir! from the FKS2 datasheet -
QuoteMarking:
Colour: Red. Marking: Silver.
1000pF is range minimum. dims should be - 2.5W 6.H 7.2L
FKP2 would be red body black markings. that 1000pF would be 4.5mm wide.
FKS3 would be red body black markings, range minimum is 1000pF. dims should be - 3W 8.5H 10L
sorry for the late reply, its 1000pf for sure,
i check all components with dmm before soldering, but since you mention it i de-solder it and check it again.
whats not sure is if its a wima or not :D