Hey Everyone!
I've been reading up on here, asking questions, and slowly acquiring parts to build a Dumble Small Special. If you are one of the members who answered some of my questions, thank you very much! I appreciate it! I wanted to take my time putting this together. I didn't want to just jump into it. A little patience can go a long way.
Well, lately I've finally had everything together to start putting it together, so I thought I would go ahead and create a separate thread for it. It's been an interesting undertaking. This is the first time I've drilled my own chassis. I picked one up off of Reverb that had the PT hole and IEC knockout already cut, from there I've used various drill bits and a step bit to cut the rest. A little rough, but a deburring tool certainly helped. I'm still trying to scrub out some scratches. There will not be a faceplate. Since this is just for myself, I'll write in the front and rear text with a marker and cover it with a thin layer of metal-friendly lacquer. I'm currently building the head cab out of a cabinet drawer, similar to how I made one for a Trainwreck Express several years ago.
Right now I've just been test fitting components and making sure all electrical components are as close to the values listed in the schematic as possible.
A little more info on the amp:
- 50 watts compared to the original's 100w via two 6L6GCs
- It uses a "Tubes down" configuration compared to the original.
- Single input, no FET.
- Some of the power supply and rectifying has been changed to match that closer to a 2nd/3rd gen model.
- PT: Classictone 40-18004, OT: Classictone: 40-18001, Choke: Classictone 40-18003.
- Wire: NTE WHS22 for the signal paths and grounds, NTE WHS18 for the heaters, NTE WH618 for the B+ and plates since it is rated for 600v.
- Alpha pots, 1 Meg A for the Vol and Level, 500k A for the Treb. and Bass.
- Bright, Deep, and Rock/Jazz switch are from the 2nd/3rd gen layout.
I'll be posting pictures as I work on it. Feel free to point out any errors or suggestions!
My Small Special Build
Moderators: pompeiisneaks, Colossal
My Small Special Build
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Re: My Small Special Build
I test fitted some parts on the rectifier and bias board this evening. I've noticed that some rec. boards use .1uf ceramic caps in parallel with the diodes. I've placed this out here as the attached images show, and on the bias rectifier section as well as the B+. I've also seen, and I think Watts Tube Audio offers a kit for this, that their rect. board also include 470k resistors in parallel with the diodes and caps. Anyone willing to offer any thoughts on this? I some 1 and 2 watt 470ks in stock, but I'm worried they may drop the B+ too much.
If the board looks a little odd, it is because I haven't soldered anything in place yet, this is just test fitting. Also, several of the connecting wires will be running beneath the board.
Thanks!
- Matt J.
If the board looks a little odd, it is because I haven't soldered anything in place yet, this is just test fitting. Also, several of the connecting wires will be running beneath the board.
Thanks!
- Matt J.
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telentubes
- Posts: 894
- Joined: Mon May 24, 2010 11:29 pm
- Location: Bellingham, WA.
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Re: My Small Special Build
My understanding is that the 470K resistors protect against a mismatch in the diodes, and the ceramic caps protect against voltage spikes when turning the amp on and off. I have used .01uf ceramic caps rated at 1000V. Not the .1uf caps you mentioned.
I just built this for the JM Signature I have underway.
I just built this for the JM Signature I have underway.
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Re: My Small Special Build
Thanks for the info Telentubes, and great looking build!
I'm going to pull out the components and refit them to make the bias board look a little cleaner. I misplaced my drill template before drilling the boards (still haven't found it), so I had to do some of it with grid lines and by eye. The diode/cap/resistor solder points are separated from each other so that, in case of an issue, it would be easier to work on each one separately. Connecting wires are underneath the boards.
- Matt J.
I'm going to pull out the components and refit them to make the bias board look a little cleaner. I misplaced my drill template before drilling the boards (still haven't found it), so I had to do some of it with grid lines and by eye. The diode/cap/resistor solder points are separated from each other so that, in case of an issue, it would be easier to work on each one separately. Connecting wires are underneath the boards.
- Matt J.
Re: My Small Special Build
Thanks again for your input, guys!
I managed to get a little more work done on it over the weekend. I would have done more, but the South Carolina Guitar Show was in town and I don't like to miss out on seeing a bunch of odd, rare, and neat stuff.
I remade the bias board, did some further test fitting, and soldered some components in place. I also started putting together the power supply board and main circuit board. After testing all the components to make sure they were correct and some further test fitting, I soldered some of the connections and added the lead wires that go to the tubes. The components are pretty straightforward: 6PS coupling and tone caps, carbon film signal resistors, Dale RN65 for the plates and cathodes, and metal oxides for the B+ dropping string. I went with F&T for the large electrolytics, Sprague Atoms have just become too pricey.
The solder points did not bind as cleanly as I had hoped. I light sanded the eyelets and cleaned them before hand to make sure any grease or other coating materials were removed, but there were some patchy spots and left over and some solder rosin had to be cleaned up. Also, I don't think I'll be using solid black circuit board material in the future because it picks up your finger prints and scratches too easily!
I finished drilling the chassis, engraving some labels with a pin drill, and labeling the front and back with a Sharpie. I sprayed a thin layer of satin metal enamel over this to protect it. I've started placing the hardware in. I'm basically working from the outsides and bottom of the chassis inward to large parts don't get in the way of my soldering iron when the time comes. Transformers and heater wires will probably be the last things put in.
I did drill the power, standby, and indicator light mounting holes a little too big, so I'm using large washers and lock washers to make sure they fit now. I still need to pick one for the indicator light tomorrow at the hardware store.
Next up I'll be wiring the control pots and switches.
- Matt J.
I managed to get a little more work done on it over the weekend. I would have done more, but the South Carolina Guitar Show was in town and I don't like to miss out on seeing a bunch of odd, rare, and neat stuff.
I remade the bias board, did some further test fitting, and soldered some components in place. I also started putting together the power supply board and main circuit board. After testing all the components to make sure they were correct and some further test fitting, I soldered some of the connections and added the lead wires that go to the tubes. The components are pretty straightforward: 6PS coupling and tone caps, carbon film signal resistors, Dale RN65 for the plates and cathodes, and metal oxides for the B+ dropping string. I went with F&T for the large electrolytics, Sprague Atoms have just become too pricey.
The solder points did not bind as cleanly as I had hoped. I light sanded the eyelets and cleaned them before hand to make sure any grease or other coating materials were removed, but there were some patchy spots and left over and some solder rosin had to be cleaned up. Also, I don't think I'll be using solid black circuit board material in the future because it picks up your finger prints and scratches too easily!
I finished drilling the chassis, engraving some labels with a pin drill, and labeling the front and back with a Sharpie. I sprayed a thin layer of satin metal enamel over this to protect it. I've started placing the hardware in. I'm basically working from the outsides and bottom of the chassis inward to large parts don't get in the way of my soldering iron when the time comes. Transformers and heater wires will probably be the last things put in.
I did drill the power, standby, and indicator light mounting holes a little too big, so I'm using large washers and lock washers to make sure they fit now. I still need to pick one for the indicator light tomorrow at the hardware store.
Next up I'll be wiring the control pots and switches.
- Matt J.
Re: My Small Special Build
Some pics.
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Re: My Small Special Build
More:
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telentubes
- Posts: 894
- Joined: Mon May 24, 2010 11:29 pm
- Location: Bellingham, WA.
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Re: My Small Special Build
Looking good. The Small Special is a wonderful amp. You're gonna love it.
Re: My Small Special Build
Always fun to see amps going together and you're doing great.
Mark
Mark
Re: My Small Special Build
Thanks guy!
I figure posting up pictures on here as I go along was the least I could do considering how much information I have learned from endless hours of reading on here! They may help some other builder working on their own in the future.
- Matt J.
I figure posting up pictures on here as I go along was the least I could do considering how much information I have learned from endless hours of reading on here! They may help some other builder working on their own in the future.
- Matt J.
Re: My Small Special Build
Got a little more done this evening. Didn't get a chance to take pictures though. I'll try to grab some tomorrow. My PC desktop finally died on me after 8 years of faithful service, so I've just purchased a new HP and have been busy getting it setup.
I worked on measuring out some of the lead wire lengths and trying to decide the best way to run them to avoid any hums or oscillations.
I've also started putting together a light-bulb current limiter from the instructions found on here. I'll finish it tomorrow and give it a test run with my 5F1 Champ. I actually made one several years ago that worked really well. Sadly, in process of moving stuff around and putting things in storage I misplaced it and still cannot find it!
I have decided to omit the effects loop. As I thought over it, I really don't use any effects that would need to go there, and there is the possibility of having to construct a Dumblelator to make sure any effects used there do not cause a drastic signal loss. Plus, it will save a little more wire from having to run around the amp and possibly causing noise. I'll just stick with using any FX in front of the amp. I am going to cover up the holes for the effects jacks with some shielding tape.
Looking ahead, I was measuring out the output transformer primary and secondary leads. I am worried I might wire the OT primaries up out of phase. Any advise on how to unsure the correct lead goes to the correct 6L6GC?
Hope everyone's builds are going well!
- Matt J.
I worked on measuring out some of the lead wire lengths and trying to decide the best way to run them to avoid any hums or oscillations.
I've also started putting together a light-bulb current limiter from the instructions found on here. I'll finish it tomorrow and give it a test run with my 5F1 Champ. I actually made one several years ago that worked really well. Sadly, in process of moving stuff around and putting things in storage I misplaced it and still cannot find it!
I have decided to omit the effects loop. As I thought over it, I really don't use any effects that would need to go there, and there is the possibility of having to construct a Dumblelator to make sure any effects used there do not cause a drastic signal loss. Plus, it will save a little more wire from having to run around the amp and possibly causing noise. I'll just stick with using any FX in front of the amp. I am going to cover up the holes for the effects jacks with some shielding tape.
Looking ahead, I was measuring out the output transformer primary and secondary leads. I am worried I might wire the OT primaries up out of phase. Any advise on how to unsure the correct lead goes to the correct 6L6GC?
Hope everyone's builds are going well!
- Matt J.
Re: My Small Special Build
Managed to get a little more done today....
- Finished wiring out the circuit board, I'll trim the leads when I'm fitting it into the chassis.
- Installed the bias board, I'll take it out momentarily to properly install the PT secondaries and bias feed.
- Wired up the control pots and switches. I need to go tomorrow to pick up a .005 uf cap that needs to go on the bass pot. (Unless someone else has a different cap value recommendation for that part.)
- Wired up the bias probes, output jacks and impedance switch, artificial center tap resistors, plus the screen and grid resistors to the output tube sockets.
I'm considering partially wiring up the PT tomorrow to a certain point (just before the standby switch) and giving it a test with my current limiter. I want to make sure the bias board is working properly. Would this be an advisable test?
- Matt J.
- Finished wiring out the circuit board, I'll trim the leads when I'm fitting it into the chassis.
- Installed the bias board, I'll take it out momentarily to properly install the PT secondaries and bias feed.
- Wired up the control pots and switches. I need to go tomorrow to pick up a .005 uf cap that needs to go on the bass pot. (Unless someone else has a different cap value recommendation for that part.)
- Wired up the bias probes, output jacks and impedance switch, artificial center tap resistors, plus the screen and grid resistors to the output tube sockets.
I'm considering partially wiring up the PT tomorrow to a certain point (just before the standby switch) and giving it a test with my current limiter. I want to make sure the bias board is working properly. Would this be an advisable test?
- Matt J.
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Re: My Small Special Build
Some more, also attached is the layout for the control wiring, though it does not include the level control and accent switch.
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telentubes
- Posts: 894
- Joined: Mon May 24, 2010 11:29 pm
- Location: Bellingham, WA.
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Re: My Small Special Build
Looking good
Re: My Small Special Build
Update:
Tested the PT yesterday evening. I wired it up to check the secondaries and bias feed. The lead and neutral tabs of the IEC receptacle needed to be switched, but after that every thing worked fine and the current limiter dimmed properly. Today I'm going to try to pick up the .005uf bass pot capacitor and finish wiring up the controls and the preamp board. From there I want to trim and tidy up some of the wiring then get ready for a full power up and test.
- Matt J.
Tested the PT yesterday evening. I wired it up to check the secondaries and bias feed. The lead and neutral tabs of the IEC receptacle needed to be switched, but after that every thing worked fine and the current limiter dimmed properly. Today I'm going to try to pick up the .005uf bass pot capacitor and finish wiring up the controls and the preamp board. From there I want to trim and tidy up some of the wiring then get ready for a full power up and test.
- Matt J.