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Old 21st November 2012, 07:46 AM   #31
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I would like to avoid pcbs and kits if possible. learning is very less with these. dont mind veroboard though, its a good platform to do p2p.
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Old 21st November 2012, 08:43 AM   #32
tinitus is offline tinitus  Europe
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6V6 line preamp

?
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Old 21st November 2012, 09:07 AM   #33
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why would you avoid pcb..you must learn everything. newbie should start in pcb making like starting project in school...I made a McIntosh C22CE with just scrap in workbench and I find it awesome.
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Old 21st November 2012, 10:18 AM   #34
tinitus is offline tinitus  Europe
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Quote:
Originally Posted by Ricdelros View Post
..... newbie should start in pcb making like starting project in school...
pcb
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Old 21st November 2012, 11:45 AM   #35
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Quote:
Originally Posted by Bob Richards View Post
I used an EF86 (the JJ version) in the front end of a guitar amp I built, and it has a voltage gain of about 240, which was more than I wanted. The good news is that a resistive attenuator at it's output might cut noise from the tube more than the noise it ads.
hence the triode connection - let me find the original schematic:

Quote:
Figure 3 shows the EF86 in triode connection. When this is done, the resulting triode is among the lowest-distortion electronic amplifying devices ever made. Typical second-harmonic distortion with 10v RMS output is on the order of 0.05%. This result is achieved without any negative feedback, so this circuit is an excellent choice for high-end audio design. The voltage gain will be about 25 in this connection, making it suitable for line stages
The E80F preamp

circuit was revisited here for an alternative cathode resistor:
http://www.klausmobile.narod.ru/testerfiles/6j32p.htm

Last edited by kstagger; 21st November 2012 at 11:47 AM.
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Old 28th November 2012, 04:15 PM   #36
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I liked what i read about ACF-2, thinking of using ECC88s for that. Good choice for a tube newbie build? Will be doing a p2p for that. Any better designs for my needs from a sq perspective? dont need gain.
would like to use a tube rectifier for that. Will try to get chokes, if not, caps it will have to be. Any good existing power supply designs for that here. What tubes will be suitable for the rectifier for this build.
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Old 6th December 2012, 12:26 PM   #37
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I tried using the psud2, but got stuck at a few points. Sorry guys, quite a few newbie and idiotic questions here.

1. How do I know my current requirements. The ecc88 has a max plate current of 25ma. Is 25*4=100ma good enough. sounds a little too much to me. What should I aim for.

2. What voltage transformer do I need. the tubes need 200v as per the document. The recommended trafo is 120-0-120v. would that do for me. 120v and 240v trafos are easier to get. other values I might have to custom order. If a custom trafo will give me better results, I am all for it.

3. What tube to use. I can get 6x4, 6x5gt, ez80, ez81 (maybe), py88. I can also get gz34, 5u4g, 5y3 but these might be more expensive. Do I need two fw rectifier tubes for a ct trafo.

4. If I want to use a choke, whats a good value to start with.

5. In psud2, what am I looking for. I did create a clcrcrcrc supply for playing around, but which current or voltage fields in the graphs should i look at to determine if my design is any good or not. There are quite a few, one per component. Is V(I1) and I(I1) enugh). What should be my load.

6. For heater, I can get 5,6,7,8,9... volt trafos locally easily. I could also get a 6.3v trafo also from an online vendor. Is ac better or dc better for this app. How many amps do I need for this, is 5A good enough. would 3A do.

7. Whats the significance of trafo resistance in psud2. is that specified to calculate current and hence power of the trafo.

8. The resistance for the caps - is that the esr. Even after i get the caps, i might not know the value for this.
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Old 6th December 2012, 01:34 PM   #38
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Here's the image for the psud2. I am also getting a couple of errors.
A current sink has pulled the voltage below zero for more then 5 mains cycles at time 0.100
The rectifier IRFM of 0.25a has been exceeded with a value of 0.25a at time 0.58

Click the image to open in full size.
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Old 6th December 2012, 04:19 PM   #39
DF96 is offline DF96  England
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Quote:
Originally Posted by doors666
I tried using the psud2, but got stuck at a few points. Sorry guys, quite a few newbie and idiotic questions here.
1. Ask the preamp designer what current it requires - in some cases it may be marked on the circuit diagram.
2. 120-0-120 will give you about 160V DC if very lightly loaded, and maybe 120-140V when loaded more heavily. This is a bit low, but some circuits may be modified to cope.
3. Depends on current draw. No point in using a big fat hungry rectifier if a smaller one will do the job just as well. Do you have a separate 5V winding? If not, some rectifiers are off limits anyway.
4. 5H or 10H.
5. PSUD2 is a tool. Like any tool you need to know what you are doing. You should certainly be interested in the voltage at the PSU output, and the RMS current through the transformer.
6. Octal rectifiers typically need 5V at 2A from a separate winding with good insulation, as the heater is connected to the cathode. Preamp valves typically take 0.3A or 0.6A at 6.3V. For a line stage AC heating should be fine if you learn how to do proper heater wiring. DC heating can actually be harder to get right for a newbie.
7. Transformer resistance has two main effects: it heats the transformer, it drops the voltage.
8. Don't worry too much about ESR at this stage. It is a detail.
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Old 8th December 2012, 03:09 AM   #40
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Thanx a lot DF96, I really appreciate your help.

Quote:
Originally Posted by DF96 View Post
1. Ask the preamp designer what current it requires - in some cases it may be marked on the circuit diagram.
The design is aikido ACF-2 using ecc88, the doc is here. The current is not listed anywhere. If I go by the table at the end of the doc, dividing B+ by Rp gives me values higher than max plate current, that cant possibly be right.
Can I use 25ma per triode * 4 = 100ma. add some margin - 150ma as the current requirements here. Or is it too much of an overkill.
Quote:
2. 120-0-120 will give you about 160V DC if very lightly loaded, and maybe 120-140V when loaded more heavily. This is a bit low, but some circuits may be modified to cope.
Yeah, and that probably is with ss rectifier. With tubes and chokes, that probably will drop further. The document though mentions B+ as 100, 150, 200, 250 and 300v (in the table at the bottom of the doc), so I still might be good.
Quote:
3. Depends on current draw. No point in using a big fat hungry rectifier if a smaller one will do the job just as well. Do you have a separate 5V winding? If not, some rectifiers are off limits anyway.
Got it. that means all tubes starting with 5 are out. EZ81 looks like a decent choice, can give about 150ma.
Quote:
4. 5H or 10H.
What about the current and resistance. I guess the current limits should be well clear of the target current right, so something like 200ma might do in this case. The dcr should be as low as possible to avoid heating and voltage drop. what would be a good value or upper limit for this.
Quote:
6. Octal rectifiers typically need 5V at 2A from a separate winding with good insulation, as the heater is connected to the cathode. Preamp valves typically take 0.3A or 0.6A at 6.3V. For a line stage AC heating should be fine if you learn how to do proper heater wiring. DC heating can actually be harder to get right for a newbie.
Ok, will use ac heating. Is there an impact if I use 6V instead of 6.3v.
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