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Post by thetragichero on Aug 15, 2019 21:42:25 GMT -5
this was the main amp that came out of the Hammond tore everything out, hit it with the wire wheel and some chrome polish, added new 50/50 can caps and moved the inductor that was on the reverb (at first thought it was a driver transformer but with only two leads and a glance at the schematic, it's a 14H 125mA 400V inductor/choke. 5h choke i had purchased years ago for a superlead-ish build stays on the shelf (at some point i'd like to make a combo similar to the plexi 6v6) have to stop for the night, hopefully the parts I've left off the past several orders will arrive Saturday so that i can get back to it. I'm excited to see how the 65 year old reverb tank is gonna sound (12dw7 should make a perfect driver and recovery tube) as far as the tubes that came with it, they're mostly mullard (made in great Britain) save for two ameperex (made in Holland) for the preamp tubes. el84s appear to be telefunken (made in Germany). only usa tubes are the 12bh7 (wanted to use as the reverb driver but then I'd need another triode for recovery. I've seen some 'lunchbox' type amps using these) and the 5u4 rectifier tube. not a bad haul!
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Post by thetragichero on Aug 20, 2019 0:40:27 GMT -5
getting there. mouser order came on with wrong parts (that's what i get for ordering on a Friday), so I'll get the rest of my components tomorrow. point tho point is all new to me so I'm taking it slowly and trying to think 3 moves ahead before touching anything with the iron. I'm enjoying myself
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Post by reTrEaD on Aug 20, 2019 10:12:36 GMT -5
point tho point is all new to me so I'm taking it slowly and trying to think 3 moves ahead before touching anything with the iron. Paper and pencil should be your best friends right now.
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Post by thetragichero on Aug 20, 2019 17:10:20 GMT -5
thankfully with the terminal strips after soldering the components to the tube sockets/pots i just wrap the other end around the terminal lug but hold off soldering until they're all there. good thing since i almost had the preamp ground bus soldered to the lug that's screwed to the chassis instead of JUST the input jack sleeve. the internet seems to agree that that may cause hum
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Post by thetragichero on Aug 21, 2019 10:22:18 GMT -5
everything from the input jack to where the reverb signal is joined to the preamp before the phase inverter (save for the HT wiring... will get that in after i figure out where the PI terminal strip is going) is done. preamp ground bus now correctly had one point of contact with the chassis (input jack). i measured before drilling the chassis holes. going to have the old man cut a face and rear plates into aluminum on the cnc machine. will also ask his advice (as a former wood shop teacher) on best/easiest head case construction methods
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Post by thetragichero on Aug 22, 2019 0:40:31 GMT -5
wired up the PI and B+ nodes to PI, preamp, and reverb what's left: master volume control, cathode resistor and bypass cap fur the power tubes, wiring up mains to switch, fuse, and pt primary
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Post by thetragichero on Aug 23, 2019 0:54:58 GMT -5
temporary placement of fuse holder and output jack but it is ready to test tomorrow. going through the super slow process i found on aiken amps page (or somewhere similar) making use lightbulb limiter and lots and lots of measurement before ever playing through it gonna be difficult because i am am impatient fella, but just like good process is to start up an amp after any changes on a current limiter (even if it's like just one cap I've changed) I'd rather do it right than let out any magic smoke
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Post by thetragichero on Sept 8, 2019 18:43:17 GMT -5
so this was my testing rig for my Hammond ao-43 18 watt amp conversion (that way i could install tubes and take voltage readings) sounded GREAT except only the upper end of the tone controls (baxandall) produced sound, and not all that i expected. thought maybe a solder joint until i took some readings of the pots at their extremes. treble pot tested fine while bass pot was less than 200k (on a 1meg pot). trace back to where it connects to the last gain stage. 100k to ground on one end, 100k to the cathode on the other. no wonder the pots were kinda scratchy! I'm sure the EEs here have solved the riddle i had to confirm with an orange amp schematic from the 70s that.... maybe i should include a coupling cap from the cathode! heating up the iron but now that i think about it I'm convinced this is why it's not working i shall report back
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Post by thetragichero on Sept 8, 2019 19:17:13 GMT -5
it's amazing what happens when you block the dc going to the pots... bass control is wired backwards but that's just moving two resistors
the hard part (for me) is next: constructing a box, covering in tolex. have to make some vector graphics for the old man to cut the face/rear plates out of aluminum on the cnc machine
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Post by thetragichero on Sept 8, 2019 20:59:17 GMT -5
quick video in low power mode (22k resistor between rectifier tube and first filter cap... was intended as a standby switch a la merlinb but i didn't have a higher value 2w resistor it's for bedroom playing) attemped to record full volume but it just distorted the camera input... two el84s is LOUD through my kustom 2x15
once it's all done i will post proper videos in sound samples section
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Post by thetragichero on Oct 1, 2019 16:21:59 GMT -5
started my 2x12 build. pine sides, (mostly) poplar bracing, plywood baffle and back. attempting to construct the sides/bracing with no nails or screws, just dowels and glue
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Post by sumgai on Oct 1, 2019 22:37:05 GMT -5
..... attempting to construct the sides/bracing with no nails or screws, just dowels and glue You better have more than a few good clamps, and I'd strongly suggest that you use glue with long set and cure times. The reasons cab builders use screws are twofold:
a) It helps to keep things lined up correctly and sealed tightly; and b) Once the box is screwed together, it can be set aside to let the glue cure without fear of something going 'bump' in the night. To assure the same results with clamps requires one to ignore his wallet as it shrieks with agony upon investing in the necessary number of clamps. Moreover, when the box is sitting on the bench waiting for the clue to cure, the clamps tend to reach out and snag your clothing as you pass within three feet of the things. Ask me how I know.
True story: I once had a friend who built bird houses, usually a dozen at a time. He owned over 300 wood working clamps of various sizes. His motto: You can never have too many clamps!
HTH
sumgai
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Post by thetragichero on Oct 2, 2019 0:15:48 GMT -5
for awhile every time i was at home depot i purchased a pair of clamps i need another 4 right angle jobbers (didn't occur to me that a box is 3 dimensional so it has 8 and not 4 corners to clamp lol)
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Post by thetragichero on Oct 3, 2019 17:52:30 GMT -5
woodworking bdsm/starting to look like a box
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Post by thetragichero on Jan 21, 2021 0:46:48 GMT -5
above posts were pruned from the "what're you working on today?" thread in the coffee shop subforum. i left the schematic and discussion re baxandall/james tone stack in that thread as that is good general info that spurned a conversation about tone stacks and referenced some published material here's the schematic [/url] when i built this i just used a wire wheel to take the chassis down to bare shiny steel without painting or adding control labels... guess what happens to bare steel in humid florida? rust. at some point i will remove controls so that i can get rid of the rust, finish, and label the chassis. in the meantime i've picked up a number of hammond organs so i'll be completing version 2 before version 1...
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Post by thetragichero on Jan 21, 2021 1:49:40 GMT -5
okay so we'll try this again, this time painting and labeling the chassis FIRST that first preamp tube is nice and close to the input jack but kills a lot of chassis space. have some adapter plates coming that should hopefully allow me to move it to the hole left by the big can cap. the alpha dual gang master volume pot doesn't help an already cramped chassis, so for this one i ordered a piece of tag board that would fit. need to add some terminal strips for the filter caps for the power tube plates and screens but then i can get this all wired up, make a head box, and then FINALLY get some tolex on the speaker cab whenever i do version 3/the deluxe version, I'm going with a pentode (6au6) for the first preamp stage
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Post by thetragichero on Feb 11, 2021 3:25:11 GMT -5
we've reached the pile of spaghetti stage, with all of the tube sockets wired and just needing to connect to the board
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Post by thetragichero on Feb 13, 2021 4:47:58 GMT -5
almost done, just need to wire the pi coupling caps to the master volume and a big power resistor from the screen supply to the preamp board
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rones09
Rookie Solder Flinger
Posts: 2
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Post by rones09 on Feb 13, 2021 14:21:36 GMT -5
Wow, killer work!
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Post by thetragichero on Feb 14, 2021 1:23:10 GMT -5
knocking off early for the night since i actually have to wake up to an alarm, but this is done. still have to do some tests before plugging in and letting 'er rip
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Post by thetragichero on Feb 16, 2021 19:05:20 GMT -5
amp sounds good, very loud. tone controls and reverb don't work, swapping tubes didn't help (and shooting the reverb send to receive didn't produce an appreciable volume boost when turning up reverb knob) so there's some troubleshooting that will need to happen. nature of the beast
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Post by unreg on Jul 21, 2021 17:34:51 GMT -5
amp sounds good, very loud. tone controls and reverb don't work, swapping tubes didn't help (and shooting the reverb send to receive didn't produce an appreciable volume boost when turning up reverb knob) so there's some troubleshooting that will need to happen. nature of the beast How does troubleshooting work? Well, maybe I learned a bit while exploring my analog echo pedal. You measure continuity with multimeter and try to find bad solder connections? Troubleshooting on NES game is just using the debugger, setting breakpoints, and observing data as the “game” goes through its paces. Lacking a debugger makes your troubleshooting more tedious? But maybe it’s more fun too? God bless your efforts sir! It’s super amazing already! 👍😀
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Post by thetragichero on Jul 21, 2021 19:58:33 GMT -5
inject signal into various spots and see where it stops. i haven't picked this up since. have to be in the right headspace to troubleshoot, otherwise i become quickly frustrated
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Post by unreg on Jul 22, 2021 1:43:33 GMT -5
I can imagine it being frustrating injecting a guitar’s signal. But you didn’t say “guitar’s signal”. I was imagining you playing a note and then transitioning over to the amp to read whatever troubleshooting info from multimeter(?)… that would get tiresome fast, for me at least. 🙂 So, I was going to suggest using a metronome as your signal input; that or running an 3.5mm audio cable from your computer’s audio-out port and playing a short guitar sound file on temporary-endless repeat. You know, so the back and forth frustration would be absent. 👍
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Post by newey on Jul 22, 2021 5:28:30 GMT -5
He's talking an electrical signal, not a guitar signal.
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Post by thetragichero on Jul 22, 2021 21:26:11 GMT -5
1khz sine wave (okay so my scope only does a square wave, works well enough) with the amp on a dummy load (and even then you can still hear the annoying EEEEEEEEEEEEEEEEEEEEEEEEEE) scope probe (in ac-coupling mod because i care about signal getting through not dc) to see where it stops. that's where to look, most likely for a miswired component (or wrong component value) same way i'll test pedal builds/repairs for working before actually plugging in good way to confirm the controls work too as they should guitar and speaker are only used for tone testing
sure cold solder joints can happen, but one of the reasons i started working on amps in the first place is that a local place couldn't figure out why the preamp i dropped off intermittently so he just hit every solder joint and deemed it okay (i later discovered one of the power cord leads had been snipped so it would work fine when the cord was dangling but not when coiled neatly). most likely the issue in a new build is human error
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Post by reTrEaD on Jul 22, 2021 21:43:21 GMT -5
have to be in the right headspace to troubleshoot, otherwise i become quickly frustrated I can relate ... tone controls and reverb don't work Sometimes assessing what doesn't work can point you in the right direction. If both the bass and treble controls don't work properly, I'd start by focusing on the ground connections. Do the bottom end of the 100k resistor connected to the CCW lug of the Bass pot and the bottom end of the 2.2 cap connected to the CCW lug of the Treble pot share the same path to ground? If that path is broken, the tone controls won't do much.
Not saying that's for sure the problem, but I'd look into that first.
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Post by unreg on Jul 23, 2021 8:27:26 GMT -5
1khz sine wave (okay so my scope only does a square wave, works well enough) with the amp on a dummy load (and even then you can still hear the annoying EEEEEEEEEEEEEEEEEEEEEEEEEE) scope probe (in ac-coupling mod because i care about signal getting through not dc) to see where it stops. that's where to look, most likely for a miswired component (or wrong component value) same way i'll test pedal builds/repairs for working before actually plugging in good way to confirm the controls work too as they should guitar and speaker are only used for tone testing sure cold solder joints can happen, but one of the reasons i started working on amps in the first place is that a local place couldn't figure out why the preamp i dropped off intermittently so he just hit every solder joint and deemed it okay (i later discovered one of the power cord leads had been snipped so it would work fine when the cord was dangling but not when coiled neatly). most likely the issue in a new build is human error Sounds really cool! You use a 1khz square wave from your probe, in ac-coupling mode, and see where that electrical signal stops. I used to become frustrated during troubleshooting too. I was frustrated with myself for creating the errors and bc I thought time was being wasted. However, after praying, God taught me that troubleshooting is just part of the game building process; none if us are perfect; errors will definitely be made. Troubleshooting transitioned into an interesting, fun, and necessary process for me! In my head, I’m the only one who can effectively troubleshoot our game bc I wrote the code and so have ideas about its intended purpose. (Though, I’m sure others could troubleshoot our game much better than me bc they have vastly more troubleshooting/game-creation experience; that doesn’t matter bc I’m following God’s will for my life; He always has the BEST plan in store! 😃 That makes me relaxed and content; quite an inverse from my prior troubleshooting frustration. And I’m learning too! 😀) Yes, I agree, solving problems is extremely fun! Congrats on that snipped power cord lead find thetragichero! 👍😀
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Post by thetragichero on Jun 7, 2022 13:11:15 GMT -5
didn't even need to probe to see why the tone controls weren't working. the tag where the cap and resistor to ground from my tone controls and the grid resistor going into the reverb send meet was neither soldered nor had a jumper to the preamp ground. have to pick up a reverb tank from storage to test the reverb out but in the meantime i cooled down the bias to 100% with a 180r cathode resistor
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Post by thetragichero on Jun 7, 2022 17:06:57 GMT -5
aaaaand the reverb didn't work because i reversed the plate and cathode leads on the recovery stage. amp works now but I'm tweaking it
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