ODS 124 - revisited for the 21C

[Stephen1966]

Hi Stephen, I had some busy days, but have been working on a full layout for the #60 in Visio. Much like the one by dreric in the other thread. It will fit the tube town chassis that is a bit smaller than the original Dumble one. The PSU board is smaller than original and the power transformer and power tubes are a bit closer to the preamp side.

I managed to straighten the picture that shows the whole preamp. That way I could overlay all eyelets on the picture in Visio and get a fairly accurate layout, with also more accurate spacing for the preamp tubes. By doing this it became obvious to me that the reverb transformer and a can cap are placed between V3 and V4.

Looking closer at the original amp, it also became obvious that there has probably been a lot of tweaking of the original amp. Hence resistors with long leads crossing other components, flux build up on the board at the 1.2meg resistor, a white wire going to one of the preamp tube plates while all others are blue, holes that have been filled and much more. Quite interesting to see.

Hopefully, I’ll have more time to post some work in progress this evening and read you new posts and comment on them. Stay tuned.

I'm all ears! So you went with the Marshall style chassis... What is the original (26"?) Anyway, this 590mm chassis should do the trick. The big unknown for me at the moment is the position of the transformers, particularly the OT in relation to the PI. I really don't want these anywhere near each other if possible so some fiddling is going to be required. This is the next step, to position the transformers and using the headphone trick to minimise the 60Hz hum. PT in relation to the OT and the choke. Once I've determined those positions, I can plan my own layout with a bit more certainty. I think the preamp tubes can be set closer, away from the OT.

It's great if you can complete the work on the 060. Dreric's layout seemed close but it needed a lot of work to finish the job. The photos are very instructive though and I would concur, the amp shows signs of being worked and reworked over time. That white wire (with a black stripe) is just one example - did you notice the hole underneath it that it should have passed through? Once the amp was assembled though, it would have been too much trouble to disassemble the board for the sake of that one wire, so something went on there after the fact... I would keep the resistors on the long leads but you might easily pop in an extra eyelet for each and run jumper cables underneath. What I will be changing is the location of the reverb driver's cathode resistor and cap to the board. I'm not sure if that was some kind of afterthought but they seem to head off to different ground points and that might be a variable we don't need (or want) to consider. One thing with mine that I am going to have to be careful about is the lead dress, this seems fairly critical in these amps and it will be interesting to see how you handle it in the layout.

Next question, will we soon see a rootz 060 build thread? If so, are you going to go with a relatively straightforward clone? Or will you be modding it to suit your own tastes. Either way, it would be a fascinating project.

If you could look at my power board layout, I've had to change a couple of the cap values but I liked that simulation the most because it was a fairly linear stepping down of the voltages, all it seems within range of the 124's original power board. The other sims seemed to offer higher high voltages and lower lows while the midrange voltages came out about the same. I haven't ordered the extra caps yet so there's no problem if I need to revise them.

Speaking of the location of the can cap - between V3 and V4 sounds about right - but also in that area, the reverb transformer and jacks for the tank. The order appears to be cap-jacks-tfmr from left to right in the gutshot. It'd make sense on the top of the chassis that way, I think. I don't think there would be room to place the transformer inside the chassis like in Dustin's Custom Fifty. Even at 26" that would seem too tight.

Anyhow, I look forward to your feedback...

Stephen

[rootz]

Yes, I noticed that hole under the white wire with the black stripe too! A lot of tweaking indeed in this amp.

I wouldn't bother too much about transformer placement. I think you can get it mostly like on the regular ODS amps, the power transformer is clearly visible in my layout and placement is per standard ODS. Reverb transformer is visible too and is in the same place as the one in the #60, as is the can cap.

I'd keep the cathode resistor and cap for the driver in place. It just looks cool and that is my best argument. The ground point of the PS cap for the driver seems to be on the PSU board. Of course you could place it between the stand offs of the middle board on the left side. More logical. I'm not too worried about the different ground points. Not ideal, but at least HAD was fine with it. Reverb transformer grounds through the chassis too; non-isolated rca-jacks. Lead dress important? OT secondary grounding? Through the chassis... The real #60 looks like a rats nest in some places to me, but the clean and od preamp is pretty much done like a regular ODS. For hum I would be concerned about reverb pan placement with respect to the PT. Laydown transformers and reverb pans seem to be a hit and miss in tight head shells when it comes to hum. All my amps use stand up transformers and noise/hum in the reverb from coupling with the reverb tank inductors is not an issue.

A #60 thread? Maybe. It would need to be a very good clone for me to start a thread about it, like in material for a sticky. I'm still a long way from that. There are lot's of thing to figure out. The power supply looks different from what I can see in the pictures, definitely a subject that requires its own or more posts. Some actual measurements of parts inside the #60 would help too. Now I'm just guessing that the boards are 2.8125" high. I could also be 2 3/4". The first seems to add up the best, if I assume the preamp sockets are Belton. Better pictures would certainly help, those scans are good, but I'd like to see more.

Now time for some pictures to drool at. Will look into your PSU designs later, but I'd say that anything that gives you 195V on the clean preamp plates and 200V on the OD should get you started.

[Stephen1966]

... Some actual measurements of parts inside the #60 would help too. Now I'm just guessing that the boards are 2.8125" high. I could also be 2 3/4". The first seems to add up the best, if I assume the preamp sockets are Belton. Better pictures would certainly help, those scans are good, but I'd like to see more.
...

If you have your photos fairly well corrected for perspective you have probably discovered that you can use known component measurements to construct a scale ruler, the larger components - perspective being equal - would give you the best measurements/lowest margin of error. The Belton noval and octal socket diameters (yeah, they look like Belton) are reliable measures, the centres between the retaining bolts, but the dimensions of something like PT pan would be better. Pots could be used also and the relays. String it all together, find your standard deviation, and go with that. The 060 thread appears at least ten years old and Chris Barnett was a reclusive figure even then. That said, if anyone's got more photos, oooh

The last known location of the amp as far as I can tell was at Hillshire Recording Studios in Illinois. I'm not a historian so I'm not sure, but they may still have the amp and more photos. I understand the owner (Bruce) was trying to sell it at one stage though...

This is from Rob Livesey's site https://thesubjectmatter.com/dumblearchive.html

Hello Rob,

I had to register a new account in my wife's name because this site says my email address does not match my user name, and I find no webmaster or site contact to straighten this out, as on other sites.I have a couple of significant Dumbles for sale. Jackson Browne's Skyline modified ODR #0060 (in Bonnie Raiit's purple suede combo cab), and el34 "Bluesmaster" Skyline #0204. The ODR was purchased from Browne by Greg Bayles at Maken' Music, then went to me in 1995. Greg ordered #0204, and sold it to me when it came in, 1997-98. It has never left my studio. I also have a Marshall model 1973 18w 2 X 12 from Brauer/Maken' set up and signed with three consecutive service dates, and signed H.A. Dumble on the chassis. Bayles and Brauer state that Eric Johnston used this one extensively on his first two solo albums in LA, out of the studio rental.I have full provenance on all three, from manufacture on the Dumbles, and emails from Dumble on the amps.I don't believe we have spoken, but I am aware of your reputation in the area, and thought you might like to know about the amps. There are a number of artists and producers very interested, if you think anyone else might want to take a look, please let me know.Contact me for info and photos at thevintageidiot@charter.net , or call below, thanks.Best regards,Bruce IlligHillshire Recording StudioRichmond Il(815) 678 2482

Will you take the red pill, or the blue pill?



Stephen

[Stephen1966]

Hi rootz, did you use Chris Barnett's notes at the head of the 060 thread? I find them quite difficult to follow - his power supply notes are perfunctory to say the least. I'm obsessed with power supplies, I know I can't quite visualise your power scheme yet so I will be interested to see how you plot it out.

I've got say, it's looking great but is it fair to say this isn't a note for note Dumble? I'm totally cool with that, a working amplifier in this style of construction can never reproduce all the elements that make the original sound the way it does. It's just a question of tolerances to me, how far am I willing to deviate from the original...? Answer, as far as I need to. I think we are on the same page here. Good luck finding 20/20uF multisection can caps though. I don't know if you could connect up a 10uF quad core to run in a pair, of parallel pairs.

[rootz]

That is what I tried: correcting for perspective, getting rid of the barrel distortion in the photo's, using parts of the amp that lie in the same distance from the film/sensor. I assume the angle of view stays the same through the photo's and distance to the subject stays roughly the same. But however you do this, there is always some guesstimating to some extend. Using the biggest parts helps keeping the error margin at a lower point.

What I would like to know the exact sizes of some of the largest components. What is the exact mounting bolt distance on the PT, assuming it is a Schumacher 022657? Are the smaller CF resistors Draloric LCA 0309 or 0411? What is the exact size of the IRC RN65D cathode resistors? Are the old Belton preamp tube sockets the same size as the current VT9 sockets? Is the old bias pot (Fender/CTS?) 23.75mm like the current ones?
So in short: I'd like to know as many exact component sizes for parts either on the phenolic boards of directly on the chassis. If I get the board size right, I can nail the exact component placement.

Red pill definitely.

Here's what I can see from the power supply from the wide picture I created of the amp. Caps for power tube plates and screens on separate board. The cap for the reverb driver must be there too, because of the 47k resistor coming from the screens node.
From the screens node there is another resistor of 1k2 on the PSU board along the 20uF cap. That goes with an orange wire to a tag board with that big brown resistor (1k8 or 18k?) and the PI plate resistors. So far rather straight forward. But then? From the tagboard where the orange wire comes in, the is a red wire attached. I disappears under the board, but where does it go?

I'll make a drawing of the PSU parts I can spot. This way we can both have a good look at it. Anyways, it does not look as in the schematics I have seen. Or are these schematics confirmed on the PSU part of things?

Multisection can caps 20uF here https://www.amplifiedparts.com/products ... v-202020-f Now I would be perfectly fine with 16uF JJ caps too. Or you recycle old caps with new innards, which I did multiple times on old radios to preserve looks and be able to use the old mounting holes.

I think component wise we can get very close to the original amp. The pictures are fairly good for that. It more and more looks to me like a 3rd gen amp updated to skyliner 4th gen, but still low plate design. Added ratio pot on the back, added presence control You can actually see how the 470k reverb input resistors are wired on the right side of the middle board. You can see tiny parts of connecting wire sticking out the eyelets on the top side. Also it does not matter to a great extend if the boards are 2 3/4" or 2.8125". The difference is only 2.2% in size!

[rootz]

So that last post was meant for the afternoon, but I had to leave for some groceries and other stuff. I didn't want to throw away my thought process though. And that process has gotten me a bit further, or at least I hope so.

I think all the schematics had it mostly wrong when it comes to the power section. Where is the 15k 1watt Piher/Beyschlag resistor in the schematics? I don't see a 10k resistor in the PSU in the amp like in the schematics too. I do see two 1k resistors on the front can cap.

So time for some more research. The cap between the preamp tubes has just one resistor and two nodes. The orange wire goes to the reverb recovery triodes. So the red wire has to go to the PS, otherwise you'd not have any voltage on the caps at all, right. Red wire has to be between cap between preamp tubes and 15k resistor. If you swap the red wires (the only other possibility I see, you'd have the recovery triodes at the PI node without a cap and one node of the can cap on the pot side not attached to any tube stage. That is just not logical and also I haven't seen such filter before in any other Dumble. The way I see the PSU now lines up with the wire colours I can see and makes sense. the Mixer and pre-driver triodes will be on a separate string coming from the PI node. This will give a lot more voltage to play with and thus make for stages with more clean headroom than the rest of the preamp. IMHO that is exactly what you want with a mixer: preamp clips before the mixer.

Anyway, here's what it looks like with a bit of pencil and paper.

[rootz]

The proof of the pudding is in the simming

Do these predicted voltages line up with the notes we have and what we can expect in an ODS type amp? I think they do! Please note I subbed the reverb driver for a 12aX7, not an at. Why? Because I wonderen if Dumble used a 47k resistor in the PSU for the driver because he used a tube with less current draw. He could also be aiming at a lower driver voltage, but there is no easy way to tell what was the logic. With an at, you'll get around 300V on the plates, with a ax around 370V. The latter is more what I'd expect, but to be honest I don't know exactly.

The 10k to the pre driver and mixer (B+6) is also a guess. I can't see the value in pictures, because it is hidden under a large ceramic cap that seems to be between the reverb driver primary and ground. 22k would give you around 250V on the plates of the pre driver and mixer triode. As I mentioned before, to me that makes sense.

Also visible in the sim: the predicted frequency response with the reverb in and completely out of the circuit. Pretty darn close if you ask me.

[Stephen1966]

That is what I tried: correcting for perspective, getting rid of the barrel distortion in the photo's, using parts of the amp that lie in the same distance from the film/sensor. I assume the angle of view stays the same through the photo's and distance to the subject stays roughly the same. But however you do this, there is always some guesstimating to some extend. Using the biggest parts helps keeping the error margin at a lower point.

What I would like to know the exact sizes of some of the largest components. What is the exact mounting bolt distance on the PT, assuming it is a Schumacher 022657? Are the smaller CF resistors Draloric LCA 0309 or 0411? What is the exact size of the IRC RN65D cathode resistors? Are the old Belton preamp tube sockets the same size as the current VT9 sockets? Is the old bias pot (Fender/CTS?) 23.75mm like the current ones?
So in short: I'd like to know as many exact component sizes for parts either on the phenolic boards of directly on the chassis. If I get the board size right, I can nail the exact component placement.

Red pill definitely.

Here's what I can see from the power supply from the wide picture I created of the amp. Caps for power tube plates and screens on separate board. The cap for the reverb driver must be there too, because of the 47k resistor coming from the screens node.
From the screens node there is another resistor of 1k2 on the PSU board along the 20uF cap. That goes with an orange wire to a tag board with that big brown resistor (1k8 or 18k?) and the PI plate resistors. So far rather straight forward. But then? From the tagboard where the orange wire comes in, the is a red wire attached. I disappears under the board, but where does it go?

I'll make a drawing of the PSU parts I can spot. This way we can both have a good look at it. Anyways, it does not look as in the schematics I have seen. Or are these schematics confirmed on the PSU part of things?

Multisection can caps 20uF here https://www.amplifiedparts.com/products ... v-202020-f Now I would be perfectly fine with 16uF JJ caps too. Or you recycle old caps with new innards, which I did multiple times on old radios to preserve looks and be able to use the old mounting holes.

I think component wise we can get very close to the original amp. The pictures are fairly good for that. It more and more looks to me like a 3rd gen amp updated to skyliner 4th gen, but still low plate design. Added ratio pot on the back, added presence control You can actually see how the 470k reverb input resistors are wired on the right side of the middle board. You can see tiny parts of connecting wire sticking out the eyelets on the top side. Also it does not matter to a great extend if the boards are 2 3/4" or 2.8125". The difference is only 2.2% in size!

Capacitors first... thanks for the link. What I actually went for was a 10/10/10/10uF capacitor for the OD and Clean channels https://www.banzaimusic.com/ce-mfg.-10x10x10x10uf.html However, you should sit down before you see how much they cost. I was looking at the photos of the 124 and for the B+4 node used a 10/10uF multisection cap wired in parallel. Also, of note, the cap used an insulating wafer, I guess to mitigate any problems of hum.

ODS_124020.jpg

I don't have anything like your level of experience with these things but I've heard it said that it's better to go with a same or larger size cap if an original value can't be found. The one problem I saw with the larger choice is the inrush current as well as a longer charging time but 50% larger (~32uF) seems on the safe side. I just figured these 10uF caps would be better. Smaller? You're right, I guess, 16uF is not such a large difference and they're about a tenth of the cost! Anyway, in for a penny, in for a pound...

I've been looking at the photos of the 060 and the sketch of the PS you made and I thought I would give it a shot. I think Aaron's schematic is debatable because I don't see the values he marked. The photos are also not very revealing and Chris's notes leave quite a lot to be desired. But photos first...

I believe the 10k resistor marked in Aaron's schematic - I'm calling it R5 for the sake of convenience - is not a 10k, but i don't see an 18k either! The colours in the photos are quite bad but it just so happens I have some 6PS caps so I took the photos and adjusted the colours to match the cap in my hand. Because of colour shift across the depth of field, caps in the foreground can match, but caps in the background are saturated and vice versa when I filter for the background. So, hitting on a compromise and pooling the band colours of the resistor across the foreground and background values I arrived at RED/GRN/RED/BR, which gave me a value of 2.5k 1% but there are other possibilities: 3.5k, 35k. The latter would be a huge voltage drop so it's unlikely. From there, I get lost and I can't decide if C6 is part of the cap at the front, or the cap at the back. I'm not decided as you will see from my notes - they are surely wrong, there won't be two power nodes to single tubes! - however, I've left the notes as is because you may see other possibilities in them. The best guess is that the red wire coming off R5, leads to the cap at the back creating a branch in the nodes which confirms what you sketched... just about broke me as a man to get this far, but if we accept that as the most likely route it is likely that you have the subsequent nodes correct. The expectation of the voltages with small value resistors for the RVB/OD/CL all make sense. When Dustin built his amp following Aaron's specs he reported "Built following Aaron's schematic to the letter - In stock form I didn't much care for the clean tone, but the OD tone was cool. Something makes me think this amp is still not 100% documented out - maybe needs some small value changes. Other than that, the reverb is heavenly!" That suggest to me the voltages started to go adrift after the main PS board and that the reverb got a good voltage range, the OD and the Clean took a hit though. I don't know what 'cool' means it could mean subdued it could mean "different" it could just mean really nice. Either or any way you look at it, I think you are on the right track. Your later simulation looks promising.

Anyway, here are the photos adjusted to show that pesky resistor R5

P1010007- adjusted.jpg

Scan0001 (16) colour balanced.jpg

I'll attach my notes in an edit to follow...

As promised, the sketches...

060 PS sketch.pdf

[rootz]

Just some quick notes: I think I have the PS correct in my latest schematic. That gives 300V on the latest node for the clean triodes and roughly 130V on the anode of the first triode (remember 180k anode resistor and 1k cathode resistor).

I was wrong on 18k, it should have been 15k. That is perfectly visible: the big Beyschlag/Piher resistor on the tag board next to the can cap on the potentiometer side of the chassis. Compare it to pictures of 15k piher resistors in google and you’ll find it looks very close, like I did (at least I think you will) .The orange is indeed a bit in the brown side.

You could sub the triple 20uF can cap for a JJ 40-20-20-20 and just not use the 40u side. I mean, why not? The other cap can be dual 32u or 16u. 32 will give a bit more filtering on the PI.

[rootz]

Stephen, I now see I swapped two PSU nodes in my schematic. B+5 should be B+6 and vice versa. Biggest question to you (and others): can you confirm my PSU schematic based on the pics?

I do have some pics of #60 in which I might see the actual values of the can caps. Will have a look today.

[Stephen1966]

Just some quick notes: I think I have the PS correct in my latest schematic. That gives 300V on the latest node for the clean triodes and roughly 130V on the anode of the first triode (remember 180k anode resistor and 1k cathode resistor).

I was wrong on 18k, it should have been 15k. That is perfectly visible: the big Beyschlag/Piher resistor on the tag board next to the can cap on the potentiometer side of the chassis. Compare it to pictures of 15k piher resistors in google and you’ll find it looks very close, like I did (at least I think you will) .The orange is indeed a bit in the brown side.

You could sub the triple 20uF can cap for a JJ 40-20-20-20 and just not use the 40u side. I mean, why not? The other cap can be dual 32u or 16u. 32 will give a bit more filtering on the PI.

Here's the picture I found of the 15k Piher resistors...

s-l1600.jpg

You could be right.

I will be playing with your schematic and looking at the pictures again today... remember though, I'm building the 124, I would need to bring the voltages in line with the low plate 100k/1.5k design.

... And please, if you have any more photos, please share them, I haven't seen any of the top of the chassis...

[rootz]

I remember! And the voltages will be in line. Both clean triodes draw almost as much current as a ‘normal’ clean preamp. And even if it were slightly different, you could adjust to taste very easy.

[Stephen1966]

I remember! And the voltages will be in line. Both clean triodes draw almost as much current as a ‘normal’ clean preamp. And even if it were slightly different, you could adjust to taste very easy.

Apologies, I could have framed that better, certainly not implying you weren't mindful. I need coffee

[rootz]

No need to apologise Stephen, I shouldn’t sprinkle with exclamation marks.

Added some pictures, but values of the can caps not visible. Maybe verify them by size?

[Stephen1966]

Oooh!