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 Post subject: Tube Pre amp
Unread postPosted: Thu Jan 17, 2008 7:27 am 
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Hiho i got a small problem :) im building atm an tube pre amp from an guitar magazine it sounds good but some parts there are wrong!

1. I got only 8V on my tube Heating and PCF .P stands for 9 Volts... but im using there an 2200 uF cap and i should use 1000uF do you think this is the problem? but on DC voltage caps arent workin like a resistor
2. i have only 16 Volts not 48V... i think the diodes got killed maybe i was heating them to long up :(
3. what values at R2/C2 should i change to get more dirty distortion? i could add some other values and handle it like the booster there


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 Post subject: Re: Tube Pre amp
Unread postPosted: Thu Jan 17, 2008 11:11 am 
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Hi

I don't really know about this particular amp but measure everything and use Ohm's law for calculating to see everything is right in the theory, and if it doesn't match reality, then something is not connected as the schematic OR a component is broken and then you gotta search for that component.

For the boost caps, you could calculate how the filters will work.... or just experiment with different values.

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 Post subject: Re: Tube Pre amp
Unread postPosted: Thu Jan 17, 2008 11:15 am 
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Small edit! whats goin on? i measured (BEFORE) the resistor 9,2 Volts and after the Resistor (R10) 8Volts I could add an lower resistor dont you think?to burn just like 0,2-0,3 Volts away then it will be 9Volts but im not sure... I dont want burn the heater away :twisted: i will measure now the voltages after plug'n in the power and then some minutes later maybe it stabilize then I wanna know the difference! I will post later!


EDIT: okay i got the values now! if I plug in Voltage is 7,9 after 1-2 Minutes its 8,15V what should I do now? Change resistor eh :d ?

Nah forget it all! I will start now from 0 and build an stabilated power supply I will use an 7809! first I will build an good bridge rect. because i get with the 1 doide an buzz.. then I will use 1N4148 Diodes to get like 14-15Volts because an 7809 needs 3 Volts difference so minium would be 12 but ill do better 14-15... Or I will use an small 12V traffo for about 4€ to do the heating supply...
Pushing up power with diodes? or use an other traffo???

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 Post subject: Re: Tube Pre amp
Unread postPosted: Thu Jan 17, 2008 2:32 pm 
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Edit# okay found the bug i forgot one wire to gnd now it works but its 42 Volts... not 48.! but it sounded much better with 16 Volts now its just fuzzing and no energy in it it sounds really like a fuzz without highs just mid and bass hm but on 16V was everything okay. Nice overd. but now its just destroying really hard hmm maybe its because the heating power is to low... it goes down from 8,1V to 7,8 volts... after the change hmm well what could this be?

Or i change R11 fo a pot. so I can change the Plate voltage dunno if thats possible but would be great... because it sucks with 42 Volts. I dont know normal is it that: -> then higher the Voltage it sounds warmer as like a tube but if I go higher here im just adding very bad distortion. hm

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 Post subject: Re: Tube Pre amp
Unread postPosted: Thu Jan 17, 2008 7:38 pm 
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hmm... ok. Do you have any reference voltages from people who have built this before?

And for the heaters: why do you need 9V to them anyway? standard is 6.3V. But if you would like that anyway I would bet for the diode/regulator (7809) setup, so you get DC the most of the way, to eliminate AC hum. That's what I'm going to do in my 15 watter. Just make sure the 7809 can handle some amperes (depending on how many 12AX7's you're using)

I don't know why its not stable, I have only seen stable heater voltages in my amp. Maybe it's your transformer?

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 Post subject: Re: Tube Pre amp
Unread postPosted: Fri Jan 18, 2008 2:06 am 
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No honk :) if you look on the shematic! its an PCF 802 and they need 9Volts :) hehe yeah. the 7809 got an TO-220 so you can heat it up for about 2A and i need just 300mA because its just an overd. with 1 tube :)

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 Post subject: Re: Tube Pre amp
Unread postPosted: Mon Jan 21, 2008 3:01 pm 
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Hm I tryed much things last day but nothing changed to make it better its sounds actually as like as a Fuzz... not very great for an tube cruncher...
http://www.supload.com/listen?s=KYCFIEBDJ2WF
here is the soundfile... first clean then a "little bit gain..." and then everything on MAX

and i changed the 1 MOhms on PIN 3 (Pentode) (Screen grid) to 4-5 MOhms... i hoped that the distortion gets lower now because i reduce then the voltage there!! but its just making it more fuzzy!

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 Post subject: Re: Tube Pre amp
Unread postPosted: Mon Jan 21, 2008 4:41 pm 
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Wow :shock: It's really crazy schematic.
R2- 1k8-3k5 take into hear, R5-470k, in cathode PCF802 from clean channel take the resistor 1k8-2k5 and in parallel capacitor 16uF/16V . C2- try 1uF to 25uF. 25uF would sound more like fender. C3, about 1n-22nF, C4 try to kick out, or experimenting with 10p-220p . More Fender sound :-) C4a this same as C4 . Cathode PCF802-take 1k8 with 25uF/16V.
You can also try with taking capacitors in parallel with P2. IMHO something from 10nF to 220nF will be good.
Enjoy!
P.S. Give some photos ;-)
P.S.S.If you want me to i can draw a scheme which is in my opinion proper?


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 Post subject: Re: Tube Pre amp
Unread postPosted: Mon Jan 21, 2008 9:34 pm 
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You might also try lowering the value of R3 then R6 in half, if that show any improvements then go even lower in value.

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 Post subject: Re: Tube Pre amp
Unread postPosted: Tue Jan 22, 2008 9:48 am 
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Lotnik wrote:
Wow :shock: It's really crazy schematic.
R2- 1k8-3k5 take into hear, R5-470k, in cathode PCF802 from clean channel take the resistor 1k8-2k5 and in parallel capacitor 16uF/16V . C2- try 1uF to 25uF. 25uF would sound more like fender. C3, about 1n-22nF, C4 try to kick out, or experimenting with 10p-220p . More Fender sound :-) C4a this same as C4 . Cathode PCF802-take 1k8 with 25uF/16V.
You can also try with taking capacitors in parallel with P2. IMHO something from 10nF to 220nF will be good.
Enjoy!
P.S. Give some photos ;-)
P.S.S.If you want me to i can draw a scheme which is in my opinion proper?


Wow thx !!! Yes sure would be nice if you could do that!!!!! Btw. im using the Pentode first... (the first shematic)

Quote:
P.S.S.If you want me to i can draw a scheme which is in my opinion proper?


That would be very nice!!! Man, you know im now angry because i tested much mods and nothing sounds very well.. So im asking around now... I just wanna use this as a Cruncher... and as you can hear it sounds like nothing... here are the photos ! srry its just my bad cam! but I think you can see the most important things!

Ps: The heating Voltage is to low... Im measuring about 7,9 Volts.. Should be 9! because the PCF (P) stands for 300mA

here you are:


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 Post subject: Re: Tube Pre amp
Unread postPosted: Tue Jan 22, 2008 4:20 pm 
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We've got some problem... :-(
Firstly: You're looking for a crunch and using 48V. It isn't a good idea. Some big firms (like Mesa, Marshall and Hiwatt) have tested low-voltage tube amps, which are cheaper but not good. If you really want to use 48V, try to find ECC88. It's a good tube to low-voltage application.
Secondly: Do you have only one PCF802? I've thought about your amp, but I've continent that you have two tubes... Maybe ECC83 or 6N2P? Or any other duo-triodes?
IMHO it's impossible to have a crunch on one PCF802. BTW,do you know that it is the tube from TV?
My advice:
-Try to find power trafo with ~150-300V AC
-Write what kind of tube you have.
-If you have two PCF802, I have some schematic for you
Kacper
P.S. Did you change your last amp? Did you do it in a way I and RMS have shown you?


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 Post subject: Re: Tube Pre amp
Unread postPosted: Tue Jan 22, 2008 7:32 pm 
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Its a nice testing platform though; but it may also do you some good to put it in a metal case for shielding.

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 Post subject: Re: Tube Pre amp
Unread postPosted: Wed Jan 23, 2008 2:55 am 
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I have some ECC82 (would be better) becuz of lower distortion!
and PCFs costs me about 4,50€ it isnt he world! But it sounds really crappy lol... But like I sayd I got the shematic from a guitar magazine im sure that I did everything right! on the shematic... So maybe I will use this project now for testing stuff... or giive me an better suggestion what I can do better! :) would be nice if you could draw a small shematic for me!

Greets from Germany

PS yeah firstly the Tubes were used in TV's


Bye have to RUN!!!! to shool now :D

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 Post subject: Re: Tube Pre amp
Unread postPosted: Wed Jan 23, 2008 2:21 pm 
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ECC82, that's right. I going to drawing something for you today.
Quote:
But it sounds really crappy lol... But like I sayd I got the shematic from a guitar magazine im sure that I did everything right! on the shematic...

I told you: THINK!!
You can not coping amps if you don't understand it. This schematic is bad, really bad. Look on polarization triode. There is not cathode resistor or bias :-| :!: . I don't know in English name but in Polish it's "polaryzacja prądem wybiegu". It can be using some special amp (microphone or HF), because grind is about -0.3V.
Kacper
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 Post subject: Re: Tube Pre amp
Unread postPosted: Wed Jan 23, 2008 2:52 pm 
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Yeah! well... Youre right but im starting to learn now :P soon im going to buy a book with like 300 Pages only Tube-Guitar-Stuff I have to order it I think I will get it in like 1 Week

Yeah youre right ! Maybe thats one reason why its buzzing really much and why it sounds crappy! You know if youre setting your: for example EL34 amp BIAS to low or to high it sounds crap too :) so maybe thats one reason! But I dont like the PCF802 anyway... this tube wasnt made to give a great Guitar sound... It was used in TV's like you sayd! I got some nice ECC82 from JJ at home! would be great if you could draw me a (BASIC) "cruncher" I think I can change then the (TONE) values by my own in to what I want! but a nice Fender pre would be nice! I think my Telecaster will like it! :)
But the best would be if you could mark the values for Fender BLUE and for Marshall RED then I can pick the one which sounds better!

PS. Yeah but I picked my bike this morning too... :) I realized that I was a bit late :) then I looked on my Watch and sayd: F*#k lol 10 mins too late x)

PPS: ale ja wiem oco ci hodci :D (srry I think its wrong :P)

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