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Thread: Two stroke amp diy build

  1. #1
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    Two stroke amp diy build

    Hi all I am preparing to build the two stroke tube amp that is featured in dave hunters guitar amp handbook and rather than buy the kit I am going to source all the parts myself as this will be part of the enjoyment for me and i already have some of what I need i have studied the schematics and read through the comprehensive build notes over a hundred times and everything makes sense in my head apart from one thing :-

    In the parts list the electrolytic capacitors all have the voltage ratings i.e 25uf / 50v
    But the signal caps do NOT have a voltage rating included? The caps are as follows
    0.022uf
    0.0047uf
    500pf
    Does this mean that I assume 630v rating or would this be overkill
    Sorry if this is a dumb question but I just want to be sure !!

    Hope someone can help

    Scott

  2. #2
    "Thermionic Apocalypse" -JT nickb's Avatar
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    It would have helped to post the schematic. I would say that ONLY the electrolytics that are in parallel with the cathode resistors are 25V. Every film cap is likely 630V. Power supply electrolytics will be 450 or 500V
    Last edited by nickb; 07-28-2017 at 10:42 PM.
    Experience is something you get, just after you really needed it.

  3. #3
    Supporting Member eschertron's Avatar
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    most film caps are rated 600 or 630VAC. common enough to find. Good luck!
    Quote Originally Posted by Steve Conner View Post
    If it still won't get loud enough, it's probably broken.

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    Thanks guys that's what I thought but just wanted to make sure

  5. #5
    "Thermionic Apocalypse" -JT nickb's Avatar
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    This will help
    2ss.jpg
    2ss.pngI also found this to which I have annotated with voltage ratings:

    2s2.jpg

    If a cap has a bigger rating than required, that's OK.
    Last edited by nickb; 07-28-2017 at 10:50 PM.
    J M Fahey, sgelectric and The Dude like this.
    Experience is something you get, just after you really needed it.

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    Thanks Nick if you fancy lending a bit more advice what would you recommend on the following question :-
    I have an engineer friend that can make me my chassis out of whatever i want which leads me to my next dilemma steel or aluminium ? Also I was thinking of having it made bigger than the Princeton size in the book just to make it less cramped inside and easier to work on, is this a bad idea?

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    I forgot to say that I am not making a combo, I am making a separate head unit as I have a selection of vintage celestion drivers that I am going to make some cabs with I have the following :-
    Celestion g12m 25watt 16ohm x2
    Celestion g12h 30watt 8 ohm x1
    Eminence big cat 100watt 16ohm x1

    This means I'm going to have to source an ot with 8 and 16 ohm outputs not sure if the eminence driver will be any good with this amp or not being 100watt but I suppose I'll find out in due course !!

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    Senior Member Enzo's Avatar
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    100 watt speaker? Let me ask you, if you have a step ladder rated at 300 pounds, would it be OK for a 90 pound woman to climb it? If you have a 10 ga power cord, it is OK to plug a little 50 watt table lamp into it?

    100 watts is a limit, not a requirement.

    Just my opinion, but I prefer steel chassis. They tend to be stronger, less likely to bend under transformer weight, or the inevitable argument with gravity.
    Justin Thomas likes this.
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    Thanks enzo I feel a bit stupid now!!

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    "Thermionic Apocalypse" -JT nickb's Avatar
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    Enzo is not wrong. Steel is strong, cheap and heavy. OTOH aluminium is softer, lighter and easier to machine. If you think there is any chance that you'll need to add holes to the chassis at a later date then I'd go for aluminium, especially if your tool selection is limited. You can use screw U channel or right angled sections under heavy items to give extra strength as required.
    Experience is something you get, just after you really needed it.

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    Quote Originally Posted by Enzo View Post
    100 watt speaker? Let me ask you, if you have a step ladder rated at 300 pounds, would it be OK for a 90 pound woman to climb it? If you have a 10 ga power cord, it is OK to plug a little 50 watt table lamp into it?

    100 watts is a limit, not a requirement.

    Just my opinion, but I prefer steel chassis. They tend to be stronger, less likely to bend under transformer weight, or the inevitable argument with gravity.
    I had some friends who in the beginning tried to tell me that you needed watts on a speaker paired up with watts on the amp. Later on I came to understand Enzo's wit. They were trying to run things balls out on the edge of destruction because that's where they thought the tone was. The tone comes from the soul. Put any great guitarist on a cheap setup and they still have tone. Mind you the people who used to tell me that really only just regurgitated what was on the net they had no real understanding of things. Kinda of like audiophools.
    nosaj
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    I have heard much about "speaker distortion." In my various travels, I have also heard much speaker distortion. I don't like it. At the power you're talking, I don't think it'll be an issue...

    Justin
    "When receiving a shock I emit a strange loud high pitched girlish squeak." - Alex R -
    "Sort of like not checking for toilet paper before taking a dump. ." - Chuck H -
    "All I ever managed to do with that amp was... kill small rodents within a 50 yard radius of my practice building." - Tone Meister -

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    Old Timer J M Fahey's Avatar
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    Quote Originally Posted by nickb View Post
    This will help
    Click image for larger version. 

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    Hi Nick, this one you found is missing a CT in the PT, also as drawn seems to require 2 separate tube rectifiers, which I doubt is the case
    The one you annotated is perfect, of course.
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    Juan Manuel Fahey

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    "Thermionic Apocalypse" -JT nickb's Avatar
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    Quote Originally Posted by J M Fahey View Post
    Hi Nick, this one you found is missing a CT in the PT, also as drawn seems to require 2 separate tube rectifiers, which I doubt is the case
    The one you annotated is perfect, of course.
    Well spotted. I just did a search for the relevant schematic and I didn't even look at it and neither did the author by the look of things. I expect we'll see a thread soon asking to explain this new rectifier configuration...
    g1 likes this.
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    Supporting Member eschertron's Avatar
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    Quote Originally Posted by nosaj View Post
    I had some friends who in the beginning tried to tell me that you needed watts on a speaker paired up with watts on the amp. Later on I came to understand Enzo's wit. They were trying to run things balls out on the edge of destruction because that's where they thought the tone was. The tone comes from the soul. Put any great guitarist on a cheap setup and they still have tone. Mind you the people who used to tell me that really only just regurgitated what was on the net they had no real understanding of things. Kinda of like audiophools.
    nosaj
    Quote Originally Posted by Justin Thomas View Post
    I have heard much about "speaker distortion." In my various travels, I have also heard much speaker distortion. I don't like it. At the power you're talking, I don't think it'll be an issue...

    Justin
    Not to derail the thread, but...
    Near the beginning of my relationship with tube amp design, I too read many posts/blogs/what-have-you about the need for for guitar amp speakers to be pushed to their limits. Something about the voice coil leaving the magnetic field and producing a characteristic speaker distortion. In the last 5 or so years, I have failed to find much more about it, and practically no discussion about matching speaker to amp power on MEF. Which is surprising, since we have a world-class speaker builder who regularly contributes here.

    In absence of reliable witness, then, I'd have to say that Enzo's observation is most likely the rule.
    Quote Originally Posted by Steve Conner View Post
    If it still won't get loud enough, it's probably broken.

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