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Thread: Looking for Supro Thunderbolt 6420 Build info

  1. #141
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    so, the repurposed Deluxe Amp AB763 eyelet board was so ugly, parts all crooked, that I fished around and found the link to DIYLayoutCreator on Doug Hoffman's Amp site. A lot easier to use than I thought, even a banana like me picked it up. Took a few rounds, but I got a board layout nice and straight, triple checked the measurements, all parts will fit. Sent it off to Hoffman to make a turret board for me. (Shoulda done this with the first attempt build, since the resistors these days just don't span the old board widths, had I known. Same with the JTM45 but REALLY should have known by then).

    This is the image spit out by DIYLayoutCreator.

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    More stuff. Mix of parts and symbols, will make 2 versions
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    Last edited by mikepukmel; 08-04-2019 at 04:31 AM.
    The only good solid state amp is a dead solid state amp. Unless it sounds really good, then its OK.

  2. #142
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    DIY Layout Creator is pretty good and very easy to use. A few things not possible to do, like bend leads on parts; rotate tube sockets, but the workarounds are good enough. At least, better than my horrible hand drawings.

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    The only good solid state amp is a dead solid state amp. Unless it sounds really good, then its OK.

  3. #143
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    need re-engineering or leave well enough alone? -- grid stops on input jacks

    Im assuming the 2 47k resistors on the input jacks are functioning as "grid stops". The grid leak is on the other side of the 0.005 cap.

    Is it better to
    - to leave well enough alone,
    - move the grid stop to pin2 of V1
    - leave everything as is but add a grid stop on pin2 of v1.


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    For the other end of the amp, someone recommended to move the output tube grid stops right to pin 1-5 like Fender did, so I'll do that.

    Thanks, and happy SUnday. Hope its cooler and less humid wherever you are.

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  4. #144
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    Quote Originally Posted by mikepukmel View Post
    Im assuming the 2 47k resistors on the input jacks are functioning as "grid stops". The grid leak is on the other side of the 0.005 cap.

    Is it better to
    - to leave well enough alone,
    - move the grid stop to pin2 of V1
    - leave everything as is but add a grid stop on pin2 of v1.
    The 47K's there are combined grid stops & mixers. BUT a grid stop located at that remoteness isn't doing much as a grid stop. Even worse, on the other side of the DC blocking cap .005. On this schematic, neither input has a shorting bar to ground, so the 47K's act as mixers only and the 2nd input is not attenuated 6 dB as in the Fender style input circuit.

    In fact that .005 cap isn't really necessary circuit wise - the triode has a cathode resistor, so its grid will tend to stay at 0 volts anyway as long as there's a grid leak R. However the .005 does act as a filter for very low frequencies, and that has something to do with the tone of the amp.

    A couple refinements: A/ As on Fenders, a signal entered at the #1 input passes thru both (typically) 68K resistors, so the effective value is really 34K. On your amp, 23.5K. So you would be justified in using a 22K, close enough. and... 2: The grid leak resistor in the schemo is 270K. If you want to sound brighter, not loading your guitar pickup as much (assuming you will plug your guitar into the amp without intervening effects/preamps/buffers) you could increase that to the Fender standard of 1M, or even more.

    Another mild mannered mod, if you choose to go with one input, you could use the hole for the 2nd input to mount a "brown tone" pot, where you could vary the value of that grid leak/pickup load resistor. Or just forget about the whole thing, and stick with 270K because it's what Supro used. Gotta try to get that Page tone, y'know! Nothing wrong with that.

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    Last edited by Leo_Gnardo; 08-04-2019 at 05:59 PM.
    Enjoy. Every. Sandwich.

  5. #145
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    I think the primary purpose of the two 47k resistors is to avoid mutual downloading when 2 instruments are connected. A second effect is that they constitute a low pass filter together with the input (Miller) capacitance of around 100pF, resulting in a HF roll-off above audio frequencies - a typical grid stopper effect. This is slightly mitigated by the 270k grid leak resistor but not influenced by the 0.005 coupling cap as this can be considered an AC short at high frequencies.

    Mounting a grid stopper directly to the grid pin only makes a differency in the MHz range. Reason is that any wire length between grid stopper and grid inserts some tiny series inductance which may (in rare cases) give rise to MHz oscillation. If you are afraid of this, just add a 2k to 5k grid stopper at the socket.

    As already mentioned I also recommend to increase the grid leak resistor to 470k or 1M. This might slightly increase noise level, though.

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  6. #146
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    Thanks!!!

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  7. #147
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    THinking about downloading the source code, and seeing what makes DIYLayoutCreator tick. Nire program, would be nice to have discrete parts that you can bend the leads into place, like the cathode cap/resistor; would be nice to have rotatable tube sockets, and maybe a little fancier hookup wire routing.

    Its not a pro layout, but can read it ok!

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    Doesn't yet take into account all your suggestions, working on that tonight: bigger grid leak, some work on the grid stops, fixing the input wiring.

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  8. #148
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    Board is tighter fit than anticipated. By dumb luck, just fits under the input jacks and pilot light. Had to drill out all the holes except switches and IEC. didn't butcher them too badly. Holding off gluing and soldering parts on the board until. Still have to drill for transformers (will be here in a few weeks) and drill a few other screw holes.


    By some stroke of good luck, ended up with a powder coat chassis, liking it better than bare aluminum due to my greasy fingers.

    Thanks for all the tips and pointers to great info.

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  9. #149
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    Quote Originally Posted by tubeswell View Post
    Not quite. In the 'daisy chain' system Merlin describes, all the grounds are daisy-chained together into one ground buss/wire, but only the input stage end of this daisy chain ground wire is attached to the chassis. The output tube end of the ground wire is floating (because it it weren't, you'd end up with a ground loop. Similarly, if you split the daisy chain up into components, and grounded each section separately, you'd be more likely to get ground loop hum, depending on whereabouts the chassis mains ground was situated w.r.t. each of the other signal stage grounds in the split-up ground).

    The idea behind the daisy chain is that the most sensitive pre-amp stages get a ground that is as-close-as-possible to chassis ground potential, and the other higher-current signal ground returns are further away from this, so that the daisy chain acts like one long (albeit low-resistance) voltage divider, and therefore any micro-rises in ground potential along this voltage divider caused by the high-current ground returns, will be smaller nearest to where the chain is connected to the chassis, so that there will be less interference (through filter cap reverse-shunting noise in) to the power supply rail of the most noise-sensitive ground returns in the input end of the pre-amp.

    Hi Tubeswell,
    Getting close to the point of having to decide where the ground wires would go. This board (completely by accident) is laid out so that the daisy chain scheme would be easy to implement except for the ground side of the cathode bias resistor for the output tubes. I could run a wire under the board to a reasonable place in the ground bus.
    Ive never seen an amp wired like that before, e.g. the merlin diagram daisy chain. Is there an danger of ruining something, or would I just get more noise/hum if I didn't do it correctly? If the single ground point came loose, would the amo smoke it self? With more standard commercial grounding schemes, there are lots of chassis tie points so if one came loose, the others would still be there. Damned if I understand what that means.

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  10. #150
    Supporting Member tubeswell's Avatar
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    Quote Originally Posted by mikepukmel View Post
    Hi Tubeswell,
    Getting close to the point of having to decide where the ground wires would go. This board (completely by accident) is laid out so that the daisy chain scheme would be easy to implement except for the ground side of the cathode bias resistor for the output tubes. I could run a wire under the board to a reasonable place in the ground bus.
    Ive never seen an amp wired like that before, e.g. the merlin diagram daisy chain. Is there an danger of ruining something, or would I just get more noise/hum if I didn't do it correctly? If the single ground point came loose, would the amo smoke itself? With more standard commercial grounding schemes, there are lots of chassis tie points so if one came loose, the others would still be there. Damned if I understand what that means.
    Doesn’t matter if you run the output tube cathode ground return to the daisy chain end with its own wire. Just make sure you follow Merlin’s ground layout. The amp won’t smoke itself if the PT second-side ground return gets lifted. Commercial amps with multiple ground returns for the signal path use elevating resistance for all but one return, and only that single return gets a direct chassis connection.

    But you don’t have to follow Merlin’s grounding scheme. It up to you

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  11. #151
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    Awesome, thanks. Have you ever built or rewired an amp with a daisy chain ground scheme like this? For me, fear of a very large unknown.

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  12. #152
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    Yes I have, and it works perfectly if you follow it.

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  13. #153
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    Getting dangerously close to major progress. New 9 pin sockets arrived. I have all the discrete components. I think I have enough wire to do the rough wiring on the board. The output transformer came in. Really cool frankenstein lab looking thing.

    Last thing to figure out is the input jack wiring. I more or less understand the Fender type wiring now Shorting, and uses either one 68k or two in parallel for 34k (high low input). I have Cliff jacks, the same ones I bought for a JTM 45 build. But the Supro schematic does not show low/high and shorting. They *must* short unused inputs, no?

    The Marshall and Fender (not surprisingly) wiring looks exactly the same. 1M grid leak, right on the input jacks, on the opposite side of the grid leak. The supro has the grid leak on the tube side of a small cap. I hope not to change the tone of the thing, but akk, its not 1966 and the components are not 1966 either. IS there something special about the placement and size 0.005uf/270k high pass filter on the input?


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  14. #154
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    Mishmash has grid-to-ground resistor missing. Grid needs a DC ground reference. I would use 1M.

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    Quote Originally Posted by Helmholtz View Post
    Mishmash has grid-to-ground resistor missing. Grid needs a DC ground reference. I would use 1M.
    Thanks Helmholtz. I think I understand. The clip of the input jack wiring was copy/pasted from a JTM45 schematic. It has a 1Meg grid leak but does not have that odd capacitor between the V1 grid and input wiring. The Weatherford schematic (more authentic Supro) has a grid leak where its supposed to be.
    So "grid leak" is a DC thing, so needs to be on the grid side of any capacitor.

    In this case, can I move the 1M grid leak that is on the input jacks, and move it to the place the 270k is on the weatherford schem, will this work? I never quite understood, if the resistor is to function as a "grid leaK' why amp mfr's didn't put the resistor right there at the grid.


    Attachment 54875

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    Last edited by mikepukmel; 08-24-2019 at 06:34 PM.
    The only good solid state amp is a dead solid state amp. Unless it sounds really good, then its OK.

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    In this case, can I move the 1M grid leak that is on the input jacks, and move it to the place the 270k is on the weatherford schem, will this work? I never quite understood, if the resistor is to function as a "grid leaK' why amp mfr's didn't put the resistor right there at the grid.
    It doesn't matters where the grid leak R is physically located, but it needs to be directly connected to the grid to allow for DC current to ground.

    It is not quite clear to me what kind of tonal changes you intend to achieve and what (switching?) input jacks you are going to use.
    I prefer high (1M) input impedance, because this preserves the full tonal spectrum of the PUs. 270k input impedance acts like turning back the guitar's tone controls.
    Now the Weatherford input circuit has a high pass filter formed by the 0.005 (= 5nF) series coupling cap and the 270k grid leak. Its -3dB frequency is around 120Hz, so it cuts some bass. If you replace the 270k by 1M (this is what I would do), the -3dB frequency will be 32Hz. But if you like the 120Hz bass cut, you will need to use something like a 1.2nF coupling cap.

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  17. #157
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    Quote Originally Posted by Helmholtz View Post
    It doesn't matters where the grid leak R is physically located, but it needs to be directly connected to the grid to allow for DC current to ground.

    It is not quite clear to me what kind of tonal changes you intend to achieve and what (switching?) input jacks you are going to use.
    I prefer high (1M) input impedance, because this preserves the full tonal spectrum of the PUs. 270k input impedance acts like turning back the guitar's tone controls.
    Now the Weatherford input circuit has a high pass filter formed by the 0.005 (= 5nF) series coupling cap and the 270k grid leak. Its -3dB frequency is around 120Hz, so it cuts some bass. If you replace the 270k by 1M (this is what I would do), the -3dB frequency will be 32Hz. But if you like the 120Hz bass cut, you will need to use something like a 1.2nF coupling cap.
    Thanks. Well, Ive heard low resolution internet recordings of a few of the original amps, and id like to get as close as possible (which now I understand is sort of a ridiculous statement since the components, tubes and speaker are all new manufacture ) But anyway, close as possible.

    I have switching cliff jacks, same ones used on a JTM 45 type build. Yeah, didn't quite understand that high pass, thanks, so it will be a little more "bassy" just switching out the 270k with 1M. I'll try that then order a 1.2N cap today, and see how that sounds as well.

    The only reason for looking to switching jacks is that won't this amp let a bunch of noise in to through the unused jack wiring, when only one input is used, and the other (unused) jack is not shorting?

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  18. #158
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    Between 32hz and 120hz, that's the bottom 1/3rd of the guitar! So, the original amp would really cut the boomy bass quite a bit, before it even gets into the preamp. Hmmm.

    82 Hz,
    110 Hz,
    147 Hz,
    196 Hz,
    247 Hz,
    330 Hz.

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  19. #159
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    The only reason for looking to switching jacks is that won't this amp let a bunch of noise in to through the unused jack wiring, when only one input is used, and the other (unused) jack is not shorting?
    You don't want the other jack shorting as this would place 2 x 47k across the main input. Leaving the unused input open won't increase noise with the main input. You will have noise if no input is used, though.

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  20. #160
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    82 Hz,
    110 Hz,
    147 Hz,
    196 Hz,
    247 Hz,
    330 Hz.
    That's only open strings. High register fundamentals extend up to 2kHz.

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  21. #161
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    If it was me I'd build the amp as original as possible, then once it works, tweak from there. The originals sound great and don't hum overly much. I've even used one in the studio for bass as it was originally intended and it sounded great, though we did use a 4x10 cabinet instead of the original 1x15. I plan to build my clone PTP as the original did, though it will be awhile until I get to it unfortunately. Would love to see pics and hear your impressions of it once you get yours done.

    Greg

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  22. #162
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    Quote Originally Posted by soundmasterg View Post
    If it was me I'd build the amp as original as possible, then once it works, tweak from there. The originals sound great and don't hum overly much. I've even used one in the studio for bass as it was originally intended and it sounded great, though we did use a 4x10 cabinet instead of the original 1x15. I plan to build my clone PTP as the original did, though it will be awhile until I get to it unfortunately. Would love to see pics and hear your impressions of it once you get yours done.

    Greg
    Thanks for the tip/suggestions Greg, what I have so far, is pretty close. Yeah, for me, its all about the tone! I started looking into ptp on terminal strips, but could not convince myself I could 'debug' it and get all the connections right, so I fiddled with some existing layouts on a board. Tried to mash the components close to the tube side of the board to keep wires short to the preamp and pi.

    Only big item left is the PT, from Heyboer. Can't wait to hear the thing, will post photos, and try to find a way to get sound clips, as soon as its more 'together'.

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    Quote Originally Posted by mikepukmel View Post
    Thanks for the tip/suggestions Greg, what I have so far, is pretty close. Yeah, for me, its all about the tone! I started looking into ptp on terminal strips, but could not convince myself I could 'debug' it and get all the connections right, so I fiddled with some existing layouts on a board. Tried to mash the components close to the tube side of the board to keep wires short to the preamp and pi.

    Only big item left is the PT, from Heyboer. Can't wait to hear the thing, will post photos, and try to find a way to get sound clips, as soon as its more 'together'.
    Looking forward to hearing it and seeing pics!

    You should try a PTP amp at some point. Draw it up on paper first and it will make more sense. Once you've done it, then it is easy to do more. The debugging can sometimes be an issue....I had one I built up out of an old Bogen, and it worked perfectly except once you got past a certain point on the volume control it would squeal. I couldn't find it on a scope, but by poking around with a chopstick I could make the noise come and go if I moved one wire. So I found where it was quiet and zip tied the wire in that spot. 4 years later the amp works flawlessly. Moral is, PTP sometimes takes a little more effort to sort out, but once you have it sorted, it won't change, and it isn't that hard to follow the circuit and troubleshoot it either.

    Greg

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    Greg, thanks, man will do! I think I'll try to find a really simple one to do first shot PTP. As with most stuff, usually more worried than I should be.

    The Heyboer PT arrived this week, paid the invoice! Hell week at my job, so could not do any work. The chassis has the OT sitting on top, and most small holes drilled. Bitch of a thing to do with a hand drill, keeps moving off the punch mark. Only a few holes left to drill for PT and OT, then I can start wiring up. Determined on this amp to get every single hole drilled and double triple checked so I don't have to take the whole thing apart 3 times to drill a new hole .

    I have a basic layout drawn, https://music-electronics-forum.com/...1&d=1565056792 this is about how I envision it would be built. Im not sure I did the ground chain right. and there is a connection not shown from the output tube cathode resistor to the negative side of the diodes. Working on it, will post an update. Thanks everyone for all the suggestions and help.

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  25. #165
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    Quote Originally Posted by mikepukmel View Post
    ... most small holes drilled. Bitch of a thing to do with a hand drill, keeps moving off the punch mark. Only a few holes left to drill for PT and OT, ...
    If you want accuracy sheet metal drilling with a hand drill, you need to make a small guide indent by hammer-punching a guide-indent for the drill bit. A 3 to 4 inch nail makes a handy punch. Lay the part of the sheet metal you want to punch hard against* a flat steel surface/bench (or metal vice) and hold the nail punch so it’s touching the metal right on the mark where you want to drill, and give the nail a single light and quick (but firm) tap with your hammer. This will make a tiny indent sufficient to guide the bit exactly where you want.

    * this is important if you want to keep the sheet metal nice and flat ��

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  26. #166
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    Quote Originally Posted by mikepukmel View Post
    Bitch of a thing to do with a hand drill, keeps moving off the punch mark.
    What tubeswell said. Also, as extra insurance, you can do what a machinist taught me: Start with a bit no bigger than the mark you made. Step up a size or two, redrill. Take several iterations to get to the final size. Not only does this keep the hole centered, but it puts less stress on the material, and the bonus is that all the bits in the set get to share the wear.

    [RANT] I hate to open up my bit set to find that the two (or three) sizes I use most need replacement, while the rest of the set is unused. I feel better at least having used most of the bits in the set before having to shop for new [/RANT]

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  27. #167
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    I learned that lesson^^^^the hard way. As a kid I had few tools and only hand operated drills. Then I got a 3/8 Black and Decker power drill for Xmas. Trying to drill a hole with a 3/8' bit into a center punch spot doesn't work. SO I'd start with a 1/16, then a 1/8, and so on up my drill collection.

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    If you can get your hands on a centre drill such as https://uk.rs-online.com/web/p/centr...-bits/4087938/, you'll find it helps a lot for starting holes. The small-diameter end is very short so it won't flex, which is part of what is causing the wandering. Also the flute at the tip is ground straight as opposed to helical, which will also reduce wandering and will stop it being pulled into the work as happens with brass especially. You can drill a little way onto the larger angled section to provide a good starting point for the next, larger drill. Note that the angled section is 60 degrees to suit lathe centres and so is not appropriate for countersinking flat-head screws which are typically 82 or 90 dergees.


    Another thing that also leads to drilling problems is using the wrong speed. It's true that steel needs to be drilled at slower speed than wood, but for a drill around 1/8" diameter you still want to be up around 2000-2500rpm. This will greatly reduce wandering and breakage as well.

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    Mea culpa. (again). I had a teeny drill bit, the head was just small enough to fit into the punch mark. Must have broke that, because the slightly less than teeny bit I have now doesn't fit the punch mark and wanders. or I could have dropped the teeny bit someplace. The bad thing I go through, is taht I buy a new drill bit, and keep it in the little cardboard with shrink wrap plastic as long as I can. Eventually they fall apart, and the bit ends up in the box I have for smallest bits. But they all look about the same and I have no way to store them. My friends father, an amazing craftsman, years ago I was lucky to just wander through his basement, had a piece of wood, like maple or oak, drilled holes, and stored the bits there, with teh size marked in pen on the wood. If I could go back in time, Id do that. Too late now.

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    The only good solid state amp is a dead solid state amp. Unless it sounds really good, then its OK.

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    The 6420 circuit build is under way. The heyboer PT arrived a while ago. Im using the Weatherford schematic that i understand is very authentic. So I got a few really good photos, gut shots, and for some reason got the idea to match up all the parts in the photo, with the schematic. First, I got a count, and the preamp side is off by 1 part. That is, there is 1 more resistor inside the preamp than on the schematic. Curious, I wrote down all the resistor color codes, in order, went to the web, got the ohm values, going through the photos, putting a resistor code (R1, R2, etc) and seeing if I can find out where the phantom resistor would go in the schematic. Tough part, there are very few photos, and its really hard to see where the connections are on all of those terminal strips.

    I got the angelfire site photos, they're awesome, anyone know where I can get a few more good gut shots of the preamp side? I only know its a 6420, not year, or variation. I think there are many variations, by comments on the web.

    I'll post what I have so far, later tonight. One of you guys will probably point it out in a second.

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    The only good solid state amp is a dead solid state amp. Unless it sounds really good, then its OK.

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    Found the extra resistor, which isn't an extra resistor! The 100k dropping resistor and 4uf filter cap, for the preamp is in the preamp! Tough to reverse engineer which part goes with the schematic, without a working amp that I can look at, since the photos are from one angle.



    Click image for larger version. 

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    The only good solid state amp is a dead solid state amp. Unless it sounds really good, then its OK.

  32. #172
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    Quote Originally Posted by Leo_Gnardo View Post
    The 47K's there are combined grid stops & mixers. BUT a grid stop located at that remoteness isn't doing much as a grid stop. Even worse, on the other side of the DC blocking cap .005. On this schematic, neither input has a shorting bar to ground, so the 47K's act as mixers only and the 2nd input is not attenuated 6 dB as in the Fender style input circuit.

    In fact that .005 cap isn't really necessary circuit wise - the triode has a cathode resistor, so its grid will tend to stay at 0 volts anyway as long as there's a grid leak R. However the .005 does act as a filter for very low frequencies, and that has something to do with the tone of the amp.

    A couple refinements: A/ As on Fenders, a signal entered at the #1 input passes thru both (typically) 68K resistors, so the effective value is really 34K. On your amp, 23.5K. So you would be justified in using a 22K, close enough. and... 2: The grid leak resistor in the schemo is 270K. If you want to sound brighter, not loading your guitar pickup as much (assuming you will plug your guitar into the amp without intervening effects/preamps/buffers) you could increase that to the Fender standard of 1M, or even more.

    Another mild mannered mod, if you choose to go with one input, you could use the hole for the 2nd input to mount a "brown tone" pot, where you could vary the value of that grid leak/pickup load resistor. Or just forget about the whole thing, and stick with 270K because it's what Supro used. Gotta try to get that Page tone, y'know! Nothing wrong with that.
    Thanks again Leo. I haven't had many amps, maybe dozen or so max, and played through a handful of others, mostly junky amps in friends basements. There are some guitar tones I haven't heard from other amps, e.g. typical fender, marshall, ampeg, sunn, vox. Curious if I could get some of those with this amp circuit. I have the parts for a few versions. Stock, and a few mods you guys have suggested. Haven't thought of a speaker yet.

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    The only good solid state amp is a dead solid state amp. Unless it sounds really good, then its OK.

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