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!
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
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
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
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
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
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
..... 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;
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!
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
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...
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
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