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Post by thetragichero on Mar 11, 2022 9:06:11 GMT -5
so i picked up a silvertone stereo tube reel-to-reel player for all of ten bucks because all it did was hum loudly when plugged in (obviously had power supply issues). my plan was to repair it and flip for a small profit, but there were no schematics available and the guts were about as densely packed as the solid state organs i pick up (how in the 'ell did folks ever service those?!) so plan b: got the mechanical stuff and build a blues amp inspired by some 50s designs (tweed fender, series string aa5 amps but with an isolation transformer, with a dash of 60s supro thunderbolt tone control). I'll post the schematic from my laptop no clue where the before photos are but here is everything stripped with the tube sockets and transformers fitted. board is laid out and drilled so I'll work on staking eyelets and populating today  my goal with this is to keep the overall look of the reel-to-reel player because i feel like that would be a nice quirky thing |
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Post by thetragichero on Mar 11, 2022 9:59:56 GMT -5
 V1 6SJ7 V2, V3 12AX7 V4, V5 25L6 V6 25Z6GT |
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Post by thetragichero on Mar 11, 2022 10:19:16 GMT -5
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Post by ashcatlt on Mar 11, 2022 16:20:16 GMT -5
If you don’t use that tape setup as a some form of effect, I’m going to cry.
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Post by thetragichero on Mar 11, 2022 22:05:43 GMT -5
nah just for looks. I'd rather grab a solid state reel-to-reel for that, which would no doubt be less hectic inside (i do have a sweet magic eye tube to figure out a use for) took the sheet of welding steel that the tubes are attached to off to paint it as bare steel will end up rusting most of the board is populated, just waiting on a few parts to come in next week  |
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Post by newey on Mar 12, 2022 0:17:13 GMT -5
If you don’t use that tape setup as a some form of effect, I’m going to cry. Onboard analog tape delay?? |
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Post by thetragichero on Mar 12, 2022 19:03:48 GMT -5
wired the series heaters as far as i could until the 90 ohm 25w dropping resistor gets here  also got as much of the power supply as i can done until the rectifier tube gets here and i install the power cord (which will be one of the last things i do since it feeds through the cabinet and it's easier to work on the chassis without the cabinet)  so parts I'm waiting on: rectifier, power resistor, 3n3 cap for tone stack (i thought i had a 2n2 cap in either 400v film or ceramic but apparently i do not or just need to look harder). i left the cathode resistor/cap from the 12ax7 stage and D power node off of the board so those went on a terminal strip |
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Post by JohnH on Mar 12, 2022 22:48:25 GMT -5
If you don’t use that tape setup as a some form of effect, I’m going to cry. Onboard analog tape delay?? Any chance it has separate record and playback heads? Ive got an old open-reel Akai 4000 from about 1975, and it was great for recording into head 1 and picking up the signal from head 2 for delay effects and sound on sound. |
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Post by newey on Mar 12, 2022 23:04:50 GMT -5
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Post by gckelloch on Mar 13, 2022 0:17:15 GMT -5
What about driving the playback head with the record head and some low and high filtering for a Neve style overdrive channel?
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Post by reTrEaD on Mar 13, 2022 8:23:05 GMT -5
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Post by reTrEaD on Mar 13, 2022 8:33:33 GMT -5
1 - I absolutely HATE series heaters but when trying to use tubes you already have, you're pretty much stuck with that.
2 - I prefer self-bias to fixed bias for the cathodyne, but in either case, definitely stick a grid stopper in there.
3 - I suspect you'll find the values chosen for your Big Muff tone control will give you a slight mid-scoop (which is nice) but it's at least an octave below what I think is optimum.
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Post by b4nj0 on Mar 13, 2022 9:17:31 GMT -5
I see your "Tapestry" and I raise you "The Würm".
でつ e&oe ...
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Post by thetragichero on Mar 13, 2022 15:30:44 GMT -5
I'm thinking "baliset" or "gurney"
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Post by newey on Mar 13, 2022 18:29:08 GMT -5
Yeah, I'd say stick with the Dune-themed naming, it has served you well . . .  |
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Post by thetragichero on Mar 13, 2022 18:35:36 GMT -5
got about as much done as i can until my remaining parts get here: wired input jacks, B+ up to the D node, etc. i really want a red led (and don't have a yellow one that would give me the 2.4v i want on trem cathode) so i did a red led in series with a silicon diode. should work  |
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Post by thetragichero on Mar 14, 2022 18:10:11 GMT -5
last few parts arrived in my po box today so i have finished populating the board, fixed some routing errors on the back of the board (and realized i left out a whole node on the power rail. i did confirm that the tweed vibrolux (i think) had two gain stages and the cathodyne on the same node so it *might've* been okay but... I'd rather take care of it now than have to chase down gremlins/lift the board after installed). started wiring up the pots so i can install the board. stopping early for the night.  might not get much done tomorrow as I'd like to unpack the shipping container into a storage unit with some semblance of organization (my reverb shop has been in vacation mode for two months while packing and moving). can finally do this as this week is warm enough to get rid of the snow |
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Post by reTrEaD on Mar 15, 2022 14:22:34 GMT -5
i did confirm that the tweed vibrolux (i think) had two gain stages and the cathodyne on the same node so it *might've* been okay but... I'd rather take care of it now than have to chase down gremlins/lift the board after installed). Yes, the tweed Vibrolux (and Harvard) only had three PS nodes. Plates fed through the OT from the first node (reservoir cap), screen grids from the second node (and no series resistors on the screens ... yikes!), and everything else - cathodyne, tremolo, and two stages of preamp fed from the third node. While it's possible to get away with something like this, it's not a particularly good idea. Especially when using a voltage doubler which is notorious for poor voltage stability under load and relatively high ripple. Although the Delon circuit is often cited as being "full-wave", my opinion is this is undeserved. Only one of the two stacked reservoir caps is being charged on the positive half-cycle and the other cap is being charged on the negative half-cycle. Decoupling the preamp stages will pay huge benefits. Also, I noticed your schematic scribble indicates a 10k resistor feeding the second node. Seems way too large to me. |
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Post by thetragichero on Mar 16, 2022 8:03:01 GMT -5
Also, I noticed your schematic scribble indicates a 10k resistor feeding the second node. Seems way too large to me. even though the screens are being fed from from the 'center' of the voltage doubler so there's considerably less current draw on the main power rail? from what i've read, the rub on these 25L6 power tubes (besides the obvious of having a non-6.3v filament) is that the plate voltage can be relatively high (as far as series string ac/dc amps go, at least) as long as the screens are strictly held below 120v, hence taking it off the main power rail figure the 10k gives me better ripple rejection and if it's too big, it's easier to parallel other values to figure out what works better. not so easy to test which larger resistance value is needed |
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Post by reTrEaD on Mar 16, 2022 11:52:14 GMT -5
Also, I noticed your schematic scribble indicates a 10k resistor feeding the second node. Seems way too large to me. even though the screens are being fed from from the 'center' of the voltage doubler so there's considerably less current draw on the main power rail? Admittedly, I hadn't taken that into account. But I still think it's too large, just not way too large. 10k will give provide a 10v drop per mA of current. Typically I calculate for 1mA per stage, although it looks like you're running a bit leaner than that. Still, you don't have nearly the supply voltage you'd have with a Fender (in excess of 400v). There, the function of series resistance two-fold. To knock the voltage down to something more reasonable like 300v or so, and also to aid in filtering. Your supply voltage is sorta low to begin with. |
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Post by thetragichero on Mar 17, 2022 7:41:20 GMT -5
didn't get much done yesterday on this, although corrected more board errors, figured out what i was doing on the tremolo, and got my power tube grid resistors in (i did get everything into my storage unit and organized so a big win)  |
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Post by thetragichero on Mar 17, 2022 20:28:27 GMT -5
okay i think it's ready to plug into light bulb limiter and then check bias before wiring up the speakers, printing waterslide decals to label controls, and throwing it all together. tomorrow though, knocked off early today   undecided whether or not I'll add a footswitch for the tremolo... unsure where it would go |
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Post by thetragichero on Mar 19, 2022 7:31:41 GMT -5
as an update: i neglected to wire the filaments for the rectifier tube (explains why i wasn't getting any dc), and then wired them in parallel to the rest of the string instead of in series, so i am waiting on a replacement rectifier from two separate ebay sellers (let's see who wins)
guess this gives me time to figure out some waterslide decals to relabel the control plate
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Post by reTrEaD on Mar 19, 2022 12:15:15 GMT -5
then wired them in parallel to the rest of the string instead of in series A Homer moment, eh? |
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Post by thetragichero on Mar 19, 2022 16:13:25 GMT -5
first it was "why am i reading a negative volt on the b+ rail?" followed by "why am i reading zero volts dc and the rectifier is glowing brightly?" then "ohhhh.... 🧐"
i ordered two so if they both work I'll have one to use up some more of these 25l6 (i think i paid ten bucks shipped for six of em). maybe to use in my small stereo single ended idea... i like that the ampeg echo twin runs the reverb off one of the output transformer secondaries so I'm gonna do a riff off that
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Post by thetragichero on Mar 26, 2022 16:35:52 GMT -5
one of the replacement rectifiers came today so i got this all plugged in and it worked (besides the trem) and sounded pretty decent for what it is. then it got really quiet. voltages seem to be about the same although the heater voltages are lower than they should be. not going to troubleshoot right now as I'd get too frustrated
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Post by reTrEaD on Mar 27, 2022 7:35:03 GMT -5
then it got really quiet.  |
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Post by thetragichero on Apr 9, 2022 12:28:03 GMT -5
hopefully just my first update for the day: put in the other rectifier tube i received and it works! seller of the other rectifier said the one he sent me was questionable and i guess that's why. probably too late to try to get a refund but that's okay
there was a pretty substantial hum that got louder when the volume pot was turned up. dawned on me that with a metal envelope tube the shield ought to be grounded (i cheated and connected to the cathode because it's right on the socket and tests with a clip lead showed similar amount of hum reduction. still have high frequency noise when the tone control is turned up but I'm guessing that's because the chassis is face up in a shop with all led lighting
tone tweaks were next on my list. added a 1nf bright cap and changed the second stage cathode bypass cap from 10uf to 220nf because there was too much low end for these little 6" alnico speakers to handle. 2k7 and 220nf puts the corner frequency right at 268hz, G string 5th fret. made neck humbucker have a little more life and have a much more pleasing tone cranked
now i need to tackle the trem because it's currently not working
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Post by thetragichero on Apr 10, 2022 18:38:53 GMT -5
verdict is that the B+ is just too low (152vdc on that particular node. output tubes are running at 198vdc) to get my wiggler wiggling, so might have to investigate either other tubes or using a power mosfet
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