I calculated I would need a ~6R resistor to drop the volts enough (-6V). I had some 5w 6r8 resistors and tried one out. It did drop 6V (yayy, my maths worked) but it also got very hot and is now brown!! So its not a sustainable solution.
In any case the other transformers are on the way to me.....
Also got my russian K40Y and K42Y caps and some 6N2P- EV today, so once its back running (fingers crossed) then I can try them vs. the panasonic ones....
Fran
In any case the other transformers are on the way to me.....
Also got my russian K40Y and K42Y caps and some 6N2P- EV today, so once its back running (fingers crossed) then I can try them vs. the panasonic ones....
Fran
Well, I got the new transformer today and hooked it up. Unfortunately, when I was testing it on the bench, I shorted the HV supply and managed to let out some smoke from the HV shunt 
The current set resistor blew (47R). Replaced that and it all powered back up OK.... but.... there is a difference. When I turn off the power, the 3 LEDs now go out immediately. Before they would take some time to dim down. Also, now I have a nasty buzz when I hook it up to the stereo.
The circuit I followed is this one: quanghao SSHV also here:
So in that sch, R1 blew, and I also replaced C1, the cap at the LEDs. I've checked most of the resistors and they all seem OK. The circuit still regulates, heatsink still gets warm as before and voltage slowly climbs as heatsink gets hotter until it settles.
Any ideas?
*******************************
Now that the heater voltages are correct, there is almost no microphony on the valves - worth remembering for future builds.
Fran
The current set resistor blew (47R). Replaced that and it all powered back up OK.... but.... there is a difference. When I turn off the power, the 3 LEDs now go out immediately. Before they would take some time to dim down. Also, now I have a nasty buzz when I hook it up to the stereo.
The circuit I followed is this one: quanghao SSHV also here:
So in that sch, R1 blew, and I also replaced C1, the cap at the LEDs. I've checked most of the resistors and they all seem OK. The circuit still regulates, heatsink still gets warm as before and voltage slowly climbs as heatsink gets hotter until it settles.
Any ideas?
*******************************
Now that the heater voltages are correct, there is almost no microphony on the valves - worth remembering for future builds.
Fran
Ah, I'm afraid nothing much to report tonight. I've made a bit of a balls of the shunt. I replaced Q1 - but when I powered it back up I got no regulation at all. So I ended up replacing the MJE350 and the SK170 with no joy. I think at this stage I might just start from scratch and rebuild the whole thing. I still need to check the diodes too.....
Fran
Fran
I wonder if someone would double check me here. I'm confused about the pin out of the mje350...
See here: the first one is from the mouser datasheet for the part I bought:
http://www.diyaudio.com/forums/attachment.php?attachmentid=222014&stc=1&d=1304811857
The second is from the SSHV DVB-projekt wiki page:
http://www.diyaudio.com/forums/attachment.php?attachmentid=222015&stc=1&d=1304811917
So, looking at the front of the MJE350, plastic facing you, metal piece to the back, legs are numbered 1-3 L to R and you have E, C, B.... correct?
Fran
See here: the first one is from the mouser datasheet for the part I bought:
http://www.diyaudio.com/forums/attachment.php?attachmentid=222014&stc=1&d=1304811857
The second is from the SSHV DVB-projekt wiki page:
http://www.diyaudio.com/forums/attachment.php?attachmentid=222015&stc=1&d=1304811917
So, looking at the front of the MJE350, plastic facing you, metal piece to the back, legs are numbered 1-3 L to R and you have E, C, B.... correct?
Fran
Attachments
So I got the shunt rebuilt today and have it working OK again. FWIW, I rebuilt it using your the schematic linked back in this thread (i.e. the Salas one, not the Quanghao one).
But....I still have hum at an unacceptable level. I'm pretty much convinced that this is PS related because when I turn off the PS the hum dies instantly even though the phonostage stays playing for a while (lifting the earth makes no difference). I've checked the diodes on the HT - all check out ok. Looking back at the PS, I dropped the filtering on the first CRC to 100R (from 470). I wonder if thats coming back to bite me now.
Anyway I need to think a but more about this now and decide where to go next.
Fran
Fran
But....I still have hum at an unacceptable level. I'm pretty much convinced that this is PS related because when I turn off the PS the hum dies instantly even though the phonostage stays playing for a while (lifting the earth makes no difference). I've checked the diodes on the HT - all check out ok. Looking back at the PS, I dropped the filtering on the first CRC to 100R (from 470). I wonder if thats coming back to bite me now.
Anyway I need to think a but more about this now and decide where to go next.
Fran
Fran
You need a scope. Hum from the regulated rail is a bit unlikely. That would be buzz if there was a PSU problem. You know, 100Hz and multiples ''zzzz''. If it is deep like ''vooomm'' its some ground loop between stages and PSU. You use bus bar grounding right? Is it all well with that? PSU ground should attach at the end of the bar towards stronger stages.
*There is some good advice on star or bar grounding in that article http://www.aikenamps.com/StarGround.html
*There is some good advice on star or bar grounding in that article http://www.aikenamps.com/StarGround.html
Tiny bit of buzzzzzzz when its turned right up. Huuuummm though is the main issue.
Oh look!!!! I'm not under any illusions - I'm quite sure its my build!!
I will look again tomorrow night and see what I can do. Ground is a piece of 2.5mm copper running down along under the 4 valves - various grounding points connect to the bar as appropriate. PSU ground connects at the end nearest the upper tier valves, this is also where input and output grounds connect (separate wire to each transformer/rca jack).
Now that I think about it though, while the upper tier heaters are referenced to 1/2B+, the lower ones are not referenced to ground at all. That needs fixing I think.
Need to go back over grounding in particular now.
Fran
Oh look!!!! I'm not under any illusions - I'm quite sure its my build!!
I will look again tomorrow night and see what I can do. Ground is a piece of 2.5mm copper running down along under the 4 valves - various grounding points connect to the bar as appropriate. PSU ground connects at the end nearest the upper tier valves, this is also where input and output grounds connect (separate wire to each transformer/rca jack).
Now that I think about it though, while the upper tier heaters are referenced to 1/2B+, the lower ones are not referenced to ground at all. That needs fixing I think.
Need to go back over grounding in particular now.
Fran
Read that link I added above. Talks bar if you will scroll down enough. ''A properly implemented buss ground can be every bit as quiet as a star ground, and is usually neater looking. By the same token, an improperly implemented buss ground can be a humming, oscillating nightmare''. On a bar we ground at the input side to chassis only, and we go from lighter to heavier currents in a row on it ending at PSU. Something must be mixing there most likely.
Salas - a big thank you for the ideas and the link above. I rearranged all the grounds and the hum is much much less now. It is now inaudible at normal listening levels. However, I think I can get it quieter (now that I know that I'm on the right track), maybe I might try a star ground.
the fix was as you suggested - simply moving the ground attachment points along the bus so that the input end was at one end of the bus and the output stuff, PS at the other.
I think complete separation into a couple of stars might be even better. However.... now I get to listen for a few nights first!!
Fran
the fix was as you suggested - simply moving the ground attachment points along the bus so that the input end was at one end of the bus and the output stuff, PS at the other.
I think complete separation into a couple of stars might be even better. However.... now I get to listen for a few nights first!!
Fran
Actually its better than that - it's quieter than I said -I found i left the tt ground wire disconnected. Now that it's on, the itch is very quiet. Happy days!
Sound is very sweet, little more clarity than the pass ono clone so that's very good indeed. I still have only the panasonic pp caps for coupling so no doubt adding the ky42 should bring another jump.
For now though I want to monitor heatsink temps and voltages, plus see if I can add back in the wiring for mm input.
As I said back up..... happy days!
Fran
Sound is very sweet, little more clarity than the pass ono clone so that's very good indeed. I still have only the panasonic pp caps for coupling so no doubt adding the ky42 should bring another jump.
For now though I want to monitor heatsink temps and voltages, plus see if I can add back in the wiring for mm input.
As I said back up..... happy days!
Fran