PCB based Dumbles

[rootz]

Some time ago my attention was matched by 'The Don', an ODS owned by Bonamassa (does he still do?) that has separate PCB's for all preamp tubes. I saw just one other example of an ODS build like that. Ryan and Erwin's beautiful work on a PCB based #002 gave the last spark I needed to do some tinkering on the subject, but now concerning ODS's.

Long story short: I've drawn a couple of PCB's based on the pictures I have from the Don and the other PCB based ODS and made a Visio layout with it. The fourth board in de Visio layout houses 2 double triodes for the reverb. It can be left out, it's actually an add on.

It would be nice if someone has somewhat accurate dimensions of the boards. I made estimations based on relative sizes of components and thus had to cut some corners for accuracy. Maybe there is already a layout of these boards? I don't know. I had some good fun (yes, I really have fun tinkering with this) and some welcome relaxation after a busy week.

Any interest in working on some fab ready boards? Should be doable with a bit of help.

[rootz]

And some pictures of an original.

[Mr. dB]

The photos are the "Hoyt Axton" amp, right?

[talbany]

The photos are the "Hoyt Axton" amp, right?

Yep! Thats the Hoyt Axton Amp I believe Joe's is a Silver face chassis and am not aware of any real detailed shots of his amp. (If someone has some ) I guess for the sake of doing the boards PCB style am not sure it matters much which amp it drawn from
Nice Rootz,
The Don #80

Don.jpg

Don.jpg

Tony

[erwin_ve]

Nice work Rootz!
What did you use for creating the pcb?

Erwin

[rootz]

The pcb’s were done in a slightly older version of Cassidy Eagle. In the new versions of this software there are board size limitations, unless you pay for an unrestricted version. I, as a hobbyist, can’t justify the expenses for a pro version.

What do you use Erwin? Kicad?

[rootz]

The Hoyt Axton amp uses a Taiko RKT-5 relay. I can’t find much info about that one. It seems to be replaced by an NTE relay with the same pinout as an Omron g5v-2. What I don’t get is that the 220k resistor before the trigger control seems to be connected to the normally open side of the relay (at least it would be on an G5V-2), while it should be on a common pin. So, can anyone confirm that on the Taiko relay the comm pins are on the outside/opposite side of the coil pins?

By the way the Don Alvarez amp has at least two mods I can spot. The accent switch is replaced by a presence control (while leaving the trimmer in place) and the seems to be a ceramic cap over the PI plates. There also seem to be eyelets around the holes for the tube sockets. In the Axton there are two holes in those spots for a bent piece of wire to connect to the sockets.

Let me see if I can straighten the images from the Axton in Photoshop to take some better measurements of the boards.

FWIW, both amps look pretty standard low plate classic to me, much like a 124 in pcb version. The only obvious difference I can see is the accent switch with a preset trimmer. That has been noticed before iirc.

[rootz]

Okay, so I looked in the Hoyt Axton Dumble a bit more. There has been a topic about this amp some 2 years ago I think, but can't seem to find it.

Here are the biggest differences I see when comparing to ODS amps in the files section:
- Obvious PCB versions, etched boards;
- Boards seem to have been made for 3rd gen circuitry. See the missing resistor next to the coupling cap of the second overdrive stage. That same coupling cap seems to be quite small to for the drilled holes, suggesting there should be a larger cap there;
- Different feedback network. 3k3 feedback resistor, 270r resistor to ground. Probably a 1uF tantalum presence cap. 500r 15mm Piher presence trimmer, preset. Accent switch. Something as a crossover between a 3rd gen and 4th gen;
- Overdrive relay wiring is done 3rd gen style if I'm not mistaken. OD entrance does not get shorted to ground when on clean;
- 100k 15mm Piher OD entrance trimmer (trigger);
- Deep switch instead of a mid switch;
- Latest resistor in the psu dropper string is 2k7, not the usual 2k2;
- Parallel 100uF 350 mains filter caps;
- As far as I can see no 22meg resistors on the PAB relay;
- All grid stoppers wired directly to the preamp tube sockets;
- OD relay is a Taiko RKT-5;
- Resistors look to me like a mix of Dales for the plates, Dralorics/Q-lines for signal path and PSU and some Pihers in the v1b feedback network. Some IRC's (RN65C?) on the cathodes of V1. Can't see what's on the screens of the output tubes. All coupling caps Sprague 6PS, couldn't spot a 715P. Small output coupling cap from V1b, something like 10n or 22n, certainly not 47n. All ceramics apart from the one on the deep switch look like X5F Ceramites to me, can't read the value of the snubbers on V2. Bright switch is 150p.

There seem to be differences concerning the chassis too. It looks to be 7" instead of 8" deep, hence it looks more crammed than usual.

If I did my work correctly, the board should all be 2.5" in height with differing widths. This corresponds with standard 0.6" lead spacing for resistors, 15mm for the Piher pots. This would mean the holes for the tube sockets in the boards are something like 23/32". Measuring from pictures is not entirely accurate, but I did what's possible to be as accurate as I can be.

I made a new layout in Visio, some new boards in Eagle. Some people make a puzzle on their Sunday, or go for a walk. I did my bit of brain training and hopefully someone finds it helpful

PS. layout is not totally accurate: no FET, different rectifier/bias board, etc, etc.

[didit]

Hello --

I'm impressed and fully pleased.

PS. layout is not totally accurate: no FET, different rectifier/bias board, etc, etc.

When that Axton amp first came through all the photos were diligently captured with my general goal to base from it some new designs. I suggest you're on the track but be bold. Use modern radial electrolytic. Integrate around a later "precision" power, then put 'em where the loads are when that make sense like on that reverb board.

KiCad is a something of a transition to learn, but that Eagle particularly has flown off, with the gang at Autocad. Making sharing both the effort and the results are harder.

Best .. Ian

[talbany]

Rootz
I believe the technical description of this amp would be considered a "Transition Generation" sort of in between a 3rd and 4th generation with the classic stack, Sesame Street logo,and 220k trigger (OD) entrance 50W however wired like a 2nd/3rd generation (no gnd on relay)
Parts are more consistent with a 4th generation, more than likely built on the early 80's like the Axton amp (81) probably built not far apart but don't know for sure. IMO and given the parts Dumble used and you describe are the "Grail era" Dumbles and would bet these sound fantastic!!..If I were to get one and had the dough it would be either a transition or 4th gen classic (IRC Q-Lines,X5F and Dale RN's).Let me know if you have any questions and Nice work!!

BTW.The snubber across the PI plates is a new one.Have not seen that before could be there were some oscillations going on at high volumes and was installed during the testing phase. The Don Amp.

Tony

[erwin_ve]

The pcb’s were done in a slightly older version of Cassidy Eagle. In the new versions of this software there are board size limitations, unless you pay for an unrestricted version. I, as a hobbyist, can’t justify the expenses for a pro version.

What do you use Erwin? Kicad?

Looks great and obviously you can work fast with Eagle.
Kicad is impressive for sure and for complex schematic/pcb design it's a wonderful tool. I found creating a small/simple pcb in KICAD overcomplicated and switched to Sprint Layout for that reason.

Erwin

[rootz]

I need to be schooled on both Kicad and Sprint. I currently only use Eagle, but as Tony says it is for the Autocad boys only nowadays and pretty expensive to use as a consumer. Free version allows only 100x80 mm I think. Fine for small layouts.

Now, who here gives online training or social distanced training in Kicad or Sprint?

[Aurora]

Google Kicad tutorial.... there are several levels of tutorials online..

[rccolgan]

Oh man... This is nuts, @rootz! Some people make a puzzle on Sundays, but I'm pretty sure you just reversed engineered a spacecraft and painted a Mona Lisa (or Don?) on the same day. Lol. This is incredible

[dorrisant]

Beautiful work rootz!! Can you post the Visio file?