Hahaha Tomz, in which part of the country? 
Yes, of course they are available. And I think your basetown has them too as it exports drivers to big companies, and produces many fake components too You just need to hang around with the right people
Well, I guess transistor is transistor, and ccs is ccs. They must be easily switchable with other MOSFETs.
Yes, of course they are available. And I think your basetown has them too as it exports drivers to big companies, and produces many fake components too You just need to hang around with the right people Well, I guess transistor is transistor, and ccs is ccs. They must be easily switchable with other MOSFETs.
you'll need depletion mode MOSFETS for that circuit. See Gary Pimm's pages for designing with enhancement mode devices. A BJT ccs will not do the same thing if implemented like the Bottlehead C4S. That one also requires 3 terminals, the third on the MOSFET one is the low impedance mu follower output, and is optional...you can connect right to the plate.
cheers,
Douglas
cheers,
Douglas
So, what must i change if i use 12au7 tube.What value of the Rp&Rc resistor should i change. Can i substitute the mosfet with another type of MOSFET?
Last night, as a beginner project, i build this very simple preamp.It's based on "dave dove" recommended link (SJS electroacoustic's site).Would u mind to check this out?
regards
---------
TomZ
Attachments
Hi dave_dive thx for your suggestion.I try to rebuild this PCB using my favourite PCB software (eagle) and i have rewiring the path of stop grid resistor.I will upload the PCB picture again.Should i have regulated DC for heater or using AC?I still don't know the different between using AC/DC for heater.What about the sound?
Mr.Dave_Dove, i used CRC filter,what is the minimum value for PSU's capacitor value?100uF?50uF?
I do some simulation for CRC filter in PSU buildeng using Duncan Amp's sofware, but i don't know the best capacitor value for the 12au7 preamp.Does it need high capacitance?
regards
---------
TomZ
hi tomZ
i used AC heating with this linestage
never had any problems
as long as you twist heater wire tightly and keep it out of the way of the signal stuff as much as possible
i am not very technical
i used whatever capacitors i had
someone will be able to tell you better
i used LCLC
20H>470uf>20H>470uf
it was quiet enough for me
try get someone else to check your pcb
i never use them and don't know a good one from a bad one
good luck
dave dove
i used AC heating with this linestage
never had any problems
as long as you twist heater wire tightly and keep it out of the way of the signal stuff as much as possible
i am not very technical
i used whatever capacitors i had
someone will be able to tell you better
i used LCLC
20H>470uf>20H>470uf
it was quiet enough for me
try get someone else to check your pcb
i never use them and don't know a good one from a bad one
good luck
dave dove
how's it going thomgun?
sorry i was in a rush last post
you have not too far to go now.....
your HT voltage is way too high
you only want 280V
in psud
if you change the transformer to 240V
(i believe you are using back to back transformers)
change load section (R2) to constant current
than set that to 10mA which will be close enough
you'll see you have too much voltage
in your case
the best way to reduce that is with second RC filter
try less resistance than the first RC stage
till you get 260-280V
3*22uf caps should be fine
or you could try 220uf but watch how long the line takes to rise
the longer this takes the slower you amp will sound
there will be a good compromise
let me know how it goes...
dave dove
sorry i was in a rush last post
you have not too far to go now.....
your HT voltage is way too high
you only want 280V
in psud
if you change the transformer to 240V
(i believe you are using back to back transformers)
change load section (R2) to constant current
than set that to 10mA which will be close enough
you'll see you have too much voltage
in your case
the best way to reduce that is with second RC filter
try less resistance than the first RC stage
till you get 260-280V
3*22uf caps should be fine
or you could try 220uf but watch how long the line takes to rise
the longer this takes the slower you amp will sound
there will be a good compromise
let me know how it goes...
dave dove
Hi Dave_dove thx for your concern in my thread.Actually, i still get stuck on PSU.I don't know what is a minimal value for this 12au7 preamp. Is it 100uF+220uF?Or 22uF is sufficient for this preamp?
Is 12au7 like high capasitance?
Yes,of course i use back to back transformator.My mains supply is 220v.
Mr.Dave_dove, i will use a bleeder resistor for the safety.How a bout if i use a "load" in psud as a bleeder resistor?So,a load resistor=bleeder resistor?
Need your suggest to build this PSU
I got many option to build this PSU:
1.Using CRC filter
2.Using some MOSFET(IRF 840)/Transistor(Tip 50) as a stabilizer.
I want to build a fast PSU with a very small ripple.But i still get no idea, of course with a bleeder resistor.
Please need your assistance.
regards
----------
TomZ
Ok,Mr. Dave dove.
It will use 2 level CRC filter. It will take a time to rebuild my PCB layout, because my computer is re-format and all of my eagle layout are gone
Still don't know how to recover my files from formating harddrive Could u help me in pm?
Mr.Dave_dove, what about the bleeder resistor?I think a bleeder resistor should be draw about 1mA to drain the capacitor and bleeder resistor will act like a"load"in psud, is it right?
regards
---------
TomZ
It will use 2 level CRC filter. It will take a time to rebuild my PCB layout, because my computer is re-format and all of my eagle layout are gone
Still don't know how to recover my files from formating harddrive
Could u help me in pm?Mr.Dave_dove, what about the bleeder resistor?I think a bleeder resistor should be draw about 1mA to drain the capacitor and bleeder resistor will act like a"load"in psud, is it right?
regards
---------
TomZ
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