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    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Valve pre-amp maintenance and purchase

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#162
choky, 27mA per tube.

here is the schema of what i used before to peg the voltage of the driver tubes (around 10mA @) to 255V.

i'm sure you can suggest improvements. 🙂
 

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#164
poobah said:
Relax...

The power supply is probably the easiest thing to do...

It should be the first thing you design... partially... very roughly. And then it should be the Last thing you design... in a very detailed way.

Hope I'm making sense.

:xeye:
Click to expand...

Ok - I wont worry about it 😀

arnoldc said:
mark, the 12B4 linestage adaptation of mark g. is a very easy build, half simpler than foreplay. i am actually building one, the prototype will have a simple power supply, while the ultimate version will use fdegrove's 300V regulated psu.
Click to expand...

If it is easier than foreplay then I'll go for it!

choky said:
I don't wanna to step on anybodys toes here,especially on fdegrove's ,but series reg is long time ago not my cup of tea;
what I like,and use ,is any sort of shunt reg.

gass tube only,gass tube with resistor in parallel,gass tube as voltage ref with additionall shunt element,whatever...

in strictly line amp psu purpose,usually is plain one gass tube /per channel or even for both channels -hard to beat overkill,especially when combined with at least one choke in preceding stage(s)
Click to expand...

Hmm Choky - I didnt get any of that!! 😕 I think I am getting in over my head!

Is this the "mark g." amp referred to?
http://www.diyaudio.com/forums/showthread.php?s=&threadid=68267&highlight=


P.S - arnold - email sent 😀
 
#166
Right - reading through Mark G's post - a few questions..

The CCS mod might raise the PSR a good bit
Click to expand...
What does this mean?

This line stage has just about zero Power Supply Rejection and requires the very cleanest power you can give to it.
Click to expand...
This worries me - our grid supply is very dirty - horrible in fact, I can hear it in my speakers when someone in another room turns on/off a light etc. I'm worried about hum also.. Any ideas/suggestions? I'm thinking for this reason the foreplay might suit me better, unless there is a cheap and simple to build ultra clean supply out there!

How do LED's improve the sound?!

The schematic looks shockingly simple!

Are NOS JAN 12B4 the best choice?

How much to build?
 
#167
Commited said:


This worries me - our grid supply is very dirty - horrible in fact, I can hear it in my speakers when someone in another room turns on/off a light etc. I'm worried about hum also.. Any ideas/suggestions? I'm thinking for this reason the foreplay might suit me better, unless there is a cheap and simple to build ultra clean supply out there!

How do LED's improve the sound?!

The schematic looks shockingly simple!

Are NOS JAN 12B4 the best choice?

How much to build?
Click to expand...


do not worry about grid supply-any decent mains filter will do adequate job.
anyway-if you are in trouble-you are in trouble with any preamp,regarding mains pollution

12B4 stage can be made with shockingly good PS,still cheap(?!) or non-complicated

simple?
all good things are simple,but not simpler than needed (choky reinventing boiled water here)

regarding JAN 12B4,that you'll choose-where,how much etc.
 
#168
#171
Commited said:
Any hints for mains filters? They cost a fortune!

Is this a good 12B4 schematic?
http://www.diyaudio.com/forums/attachment.php?s=&postid=771329&stamp=1132532298

I will have a slightly different requirement for a PSU then the americans, as We run 230V here, and I'm getting confused with all of the power supplies on those pages! It is vital that I get little to no hum.

This looks good:
http://www.diyaudio.com/forums/attachment.php?s=&postid=786078&stamp=1134167752

Is 12B4A the same as 12B4?
Click to expand...


fortune?!!

are you in DIY or not?
if not-then go to first fifi salon and buy most expensive piece of crap preamp ,and use it:clown: :devilr:

search for my posts in "power supply" board (sub forum) and you will find at least one thread with some usefull info

this 12B4 schmtc looks good,but I can say that Mark's look promising ;
anyway-start with plain resistor in cathode and later you can try CCS

this PS supply schmtc looks exactly what I'll do,except that I must put on paper currents through VR tubes etc

like I say-before-choose which variant you will make,then say something about available xformers and chokes ,and then we will make few PSU proposals
 
#172
choky said:



fortune?!!

are you in DIY or not?
if not-then go to first fifi salon and buy most expensive piece of crap preamp ,and use it:clown: :devilr:

search for my posts in "power supply" board (sub forum) and you will find at least one thread with some usefull info

this 12B4 schmtc looks good,but I can say that Mark's look promising ;
anyway-start with plain resistor in cathode and later you can try CCS

this PS supply schmtc looks exactly what I'll do,except that I must put on paper currents through VR tubes etc

like I say-before-choose which variant you will make,then say something about available xformers and chokes ,and then we will make few PSU proposals
Click to expand...
Of course I am willing to make one 🙂 (it is what I originally meant - hints on how to make one because they cost a fortune to buy 🙂 )

I will search for it 🙂

The schematic I posted is Marks schematic is it not?

Back to one of my previous questions - What is CSS?

Sorry if I'm missing something, but before last week I'd never really looked into tubes before!
 
#173
CCS - constant current source. could be tubes or SS, that provides constant current (duh! how can i explain it), maybe you should read of gary pimms CCS, but that will make you off track, so as choky said forget CCS first and use a cathode resistor.

PSRR - power supply rejection ratio, the ability of the circuit to reject power supply noise (geez, i hope no tomatoes are coming my way 😀)
 
#174
Commited said:

Of course I am willing to make one 🙂 (it is what I originally meant - hints on how to make one because they cost a fortune to buy 🙂 )

I will search for it 🙂

The schematic I posted is Marks schematic is it not?

Back to one of my previous questions - What is CSS?

Sorry if I'm missing something, but before last week I'd never really looked into tubes before!
Click to expand...


first to throw few tomatoes ...:devilr:

huh-I'm little lost in these 12B4 threads-just go and do your homework with "this schmtc is from...)
last iteration of Mark's preamp is with CCS in cathode-in fact plain LM317 heavily bypassed with caps
start from end of thread ,and go backward,then you'll see what goes first

you can always go (if not already,and if I'm not boring with that) clicking at my www button and see what sort of PS I have for my WOT preamp;amount of current through stage is pretty same as for 12B4

what xformer and choke you can have fro free,or cheap?
 
#176
Punch this number into DigiKey:

CCM1613-ND

This will keep out the "nasties out" of your amp and "the nicies" in your pocket.

😉

Now these won't take care of line sags and all... that's poor wiring... sometimes all the way back to the generator.

🙁
 
#177
Commited said:
Just had a look at mains filters:

This looks good:
http://www.diyaudio.com/forums/attachment.php?s=&postid=780350&stamp=1133492948

4 x 50V 10000uF caps @ €30 ish dollars incl postage
4x 1000v 35a rectifiers @ $19 incl postage

Total of about $50. That's not bad at all! To buy in Ireland it would be $90.

Opinions?
Click to expand...


oh boy............😀
just build that bloody preamp first!

there are way cheaper variants,you choose one from our Eastern friend,and he made that from leftover parts.....

ya know nutin' about Eastern approach to audio and related stuff?

they will pay 10 times more for parts,just for piece of mind,not for better functionality
btw-I admire that:clown:
 
#178
poobah said:
Punch this number into DigiKey:

CCM1613-ND

This will keep out the "nasties out" of your amp and "the nicies" in your pocket.

😉

Now these won't take care of line sags and all... that's poor wiring... sometimes all the way back to the generator.

🙁
Click to expand...

Thanks for the link, but with delivery and everything, it'd end up being more expensive than the DIY design 🙁 Living in Europe is a pain.

Is there anything interesting on ebay?

Something like this:
http://cgi.ebay.ie/RFI-R-F-I-Mains-...5855481827QQcategoryZ4673QQrdZ1QQcmdZViewItem
 
#179
choky said:

what xformer and choke you can have fro free,or cheap?
Click to expand...
As far as I know, absolutely none.. Certainly none lying around - I have an old VCR here I could butcher, but that is about it! Otherwise I am starting out with nothing!


choky said:

oh boy............😀
just build that bloody preamp first!

there are way cheaper variants,you choose one from our Eastern friend,and he made that from leftover parts.....

ya know nutin' about Eastern approach to audio and related stuff?

they will pay 10 times more for parts,just for piece of mind,not for better functionality
btw-I admire that:clown:
Click to expand...
:bigeyes: I'd like to have a mains filter anyway, so might as well build one now - It looks easier than the pre-amp 😀 Or does "Oh boy..." mean it's a bad filter design?

Re the parts - that is the cheapest i have found that is accessible to me - Ireland is the most expensive country in the world to post to, it seems.

I want to build the pre-amp - I understand the basic circuitry, it's just the power supply I have no idea about and I'm starting from scratch!
 
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