What 50w Dumble Should I Build?

[PicknStrum]

Hey all,

First time poster here and I gotta say, I love all the threads, layouts, soundclips, etc, that you guys have laid out here. I just want to say thank you!

I'm looking to build my first dumble amp and didn't necessarily want to go 100 watts. I'm wondering what 50 watters you'd recommend I start with? I want something that can get close to the quintessential "dumble" sound, however, I understand that there are tons of variations and there may not be such a thing as quintessential. The reason for going 50 watts is really just volume and a somewhat simpler circuit.

A bit of background, I'm not completely new to building amps (but new enough). I've got a 5E3 Tweed Deluxe and an AA1164 Princeton Reverb under my belt. There are definitely some things that I haven't been exposed to in a Dumble build, however. Things like the FET relay board and the DIN switch. I've been looking at the 50 Watt ODS 2nd generation and 3rd generation layouts. I'm thinking maybe one of those would be up my alley. Let me know what you guys think. I'm going to be scouring the threads and stuff to see if there are any other options or if there is a 50 watter that has some supplemental info such as parts lists, etc.

Thanks!

Tommy

[ijedouglas]

Hey Tommy,

I don't have near the level of experience as some of the other members here but it definitely helps having a well documented and tested layout and schematic from my own experience. #0124 is a great start. There is a ton of information and a lot of build threads to follow. Regarding 50W vs 100W...there is really little difference between the 2 with regard to volume. Build complexity is the same (maybe easier if you are building from a 100W layout/schematic) but there is definitely something "more" in a 100W. I would highly recommend building the 100W with a 50/100W switch.
Good luck in your quest!

[PicknStrum]

Hey Tommy,

I don't have near the level of experience as some of the other members here but it definitely helps having a well documented and tested layout and schematic from my own experience. #0124 is a great start. There is a ton of information and a lot of build threads to follow. Regarding 50W vs 100W...there is really little difference between the 2 with regard to volume. Build complexity is the same (maybe easier if you are building from a 100W layout/schematic) but there is definitely something "more" in a 100W. I would highly recommend building the 100W with a 50/100W switch.
Good luck in your quest!

Done! Just needed someone to talk me into it. I'll go for #0124 - I keep seeing that amp come up when I search DIY Dumble Builds. The only thing I'd need a reference for is a 50/100W switch. Any threads or layouts you can send my way for that specific mod?

[norburybrook]

Hey Tommy,

I don't have near the level of experience as some of the other members here but it definitely helps having a well documented and tested layout and schematic from my own experience. #0124 is a great start. There is a ton of information and a lot of build threads to follow. Regarding 50W vs 100W...there is really little difference between the 2 with regard to volume. Build complexity is the same (maybe easier if you are building from a 100W layout/schematic) but there is definitely something "more" in a 100W. I would highly recommend building the 100W with a 50/100W switch.
Good luck in your quest!

Done! Just needed someone to talk me into it. I'll go for #0124 - I keep seeing that amp come up when I search DIY Dumble Builds. The only thing I'd need a reference for is a 50/100W switch. Any threads or layouts you can send my way for that specific mod?

the 124 low plate classic in the files section has a 50/100 switch on the layout.

M

[PicknStrum]

Got it! I see it in the "A Collection of #124 Information" thread also. I found a BOM in that thread too. A couple of quick things to clear up if you guys could for me:

I'm going to build based on the first #124 layout in the #124 Collection thread, which I believe the BOM in that thread is based on.

1) Is this layout different than the low plate version? Think I'm going to stick with the Collection Thread layout b/c there is so much info there. EDIT: I see this written on the layout: "Originally low plate - upgraded to skyliner" - so that answers that.

2) In my other builds, I've omitted the ground switch - I don't completely understand how to use them and don't want 400v going through me. I assume I'd just omit the ground switch and death cap to go directly to mains switch? Can anyone confirm?

3) For my own reference, is that slide switch between standby and speaker jacks in the layout the actual 50/100w switch?

4) Edit: Also, anyone know where to get boards for this specific amp? I'm mainly concerned about the small relay circuit boards shown in blue on the layout.

Thanks again!

There will be more questions later but I think I 'll actually start a build thread. For now, I'm going to start collecting parts and reviewing more threads.

[ijedouglas]

Got it! I see it in the "A Collection of #124 Information" thread also. I found a BOM in that thread too. A couple of quick things to clear up if you guys could for me:

I'm going to build based on the first #124 layout in the #124 Collection thread, which I believe the BOM in that thread is based on.

1) Is this layout different than the low plate version? Think I'm going to stick with the Collection Thread layout b/c there is so much info there. EDIT: I see this written on the layout: "Originally low plate - upgraded to skyliner" - so that answers that.

2) In my other builds, I've omitted the ground switch - I don't completely understand how to use them and don't want 400v going through me. I assume I'd just omit the ground switch and death cap to go directly to mains switch? Can anyone confirm?

3) For my own reference, is that slide switch between standby and speaker jacks in the layout the actual 50/100w switch?

Thanks again!

There will be more questions later but I think I 'll actually start a build thread. For now, I'm going to start collecting parts and reviewing more threads.

2) You can leave out the ground switch and death cap. Neither are needed
3) Yes

[pompeiisneaks]

Got it! I see it in the "A Collection of #124 Information" thread also. I found a BOM in that thread too. A couple of quick things to clear up if you guys could for me:

I'm going to build based on the first #124 layout in the #124 Collection thread, which I believe the BOM in that thread is based on.

1) Is this layout different than the low plate version? Think I'm going to stick with the Collection Thread layout b/c there is so much info there. EDIT: I see this written on the layout: "Originally low plate - upgraded to skyliner" - so that answers that.

2) In my other builds, I've omitted the ground switch - I don't completely understand how to use them and don't want 400v going through me. I assume I'd just omit the ground switch and death cap to go directly to mains switch? Can anyone confirm?

3) For my own reference, is that slide switch between standby and speaker jacks in the layout the actual 50/100w switch?

4) Edit: Also, anyone know where to get boards for this specific amp? I'm mainly concerned about the small relay circuit boards shown in blue on the layout.

Thanks again!

There will be more questions later but I think I 'll actually start a build thread. For now, I'm going to start collecting parts and reviewing more threads.

1. The #124 is a low plate amp. That term just means the anode resistors in them had the typical 100k anode 1.5k cathode. In some of his amps dumble uses what is referred to as 'high plate' topology which utilizes preamp anode/cathodes in combinations of 220k/3.3k 150k/2.2k etc or something along those lines that just means the bias and load line of the tube is done differently.

2. Ground switches were a relic of when you didn't know which side of the power plugs (which also had no earth protection) were neutral and which were hot. You'd get bad hum if they were opposite of how your switch was wired, so you'd pop it over... this was very dangerous and is no longer needed with a well done safety earth. (doesn't mean some places don't do a mix up of hot/neutral but it's gotten a lot better)

3. The slide switch is indeed the 50/100k. It is a super smart way to do it. It leaves the two tubes connected in circuit but puts a 10k resistor in their path to ground basically putting them in idle and unable to conduct any real current, and in shutoff. This way no other tweaks are needed and the amp is basically just running in identical state, with bias fine, etc and the tubes still act like they're 'live' but won't pass signal.

4. I had to build mine from scratch. I don't know if anyone is currently building them. You can print off the layout, cut out the boards and tape them to some FR4/Garolite and drill the holes to match, then get some turrets/eyelets (I prefer eyelets) and swage them into place yourself... up to you.

~Phil

[PicknStrum]

Ah thanks guys! Appreciate all the help I've gotten already.

I'm going to start sourcing some stuff and hopefully there will be a build thread to follow. This guy is definitely going to push me but I'm excited for the challenge.

I may ask some circuit questions along the way as well - I try to understand what the circuit is doing as I'm building it. Super excited!

[martin manning]

3. The slide switch is indeed the 50/100k. It is a super smart way to do it. It leaves the two tubes connected in circuit but puts a 10k resistor in their path to ground basically putting them in idle and unable to conduct any real current, and in shutoff. This way no other tweaks are needed and the amp is basically just running in identical state, with bias fine, etc and the tubes still act like they're 'live' but won't pass signal.

When switched to 50W, the speaker load should be doubled, i.e. move the impedance selector down one click. Voltages will go up a bit due to the reduced current draw, and the NFB will be reduced.

[pompeiisneaks]

3. The slide switch is indeed the 50/100k. It is a super smart way to do it. It leaves the two tubes connected in circuit but puts a 10k resistor in their path to ground basically putting them in idle and unable to conduct any real current, and in shutoff. This way no other tweaks are needed and the amp is basically just running in identical state, with bias fine, etc and the tubes still act like they're 'live' but won't pass signal.

When switched to 50W, the speaker load should be doubled, i.e. move the impedance selector down one click. Voltages will go up a bit due to the reduced current draw, and the NFB will be reduced.

I thought when using the 50W switch the impedance reflected doesn't change because the tubes are still in circuit and in theory 'working' but not transmitting any signal... Is that not the case? Why not? I get that when a tube is pulled, it is not present and not electrically 'active' in the circuit, whereas the 10k resistors to ground allow it to still operate, but not pass signal?

Or is it effectively identical just quicker than pulling the tubes?

~Phil

[norburybrook]

3. The slide switch is indeed the 50/100k. It is a super smart way to do it. It leaves the two tubes connected in circuit but puts a 10k resistor in their path to ground basically putting them in idle and unable to conduct any real current, and in shutoff. This way no other tweaks are needed and the amp is basically just running in identical state, with bias fine, etc and the tubes still act like they're 'live' but won't pass signal.

When switched to 50W, the speaker load should be doubled, i.e. move the impedance selector down one click. Voltages will go up a bit due to the reduced current draw, and the NFB will be reduced.

Yes, this is important.

So if you're using an 8 ohm speaker, if you switch to half power then set your impedance selector to 4 ohms


M

[martin manning]

I thought when using the 50W switch the impedance reflected doesn't change because the tubes are still in circuit and in theory 'working' but not transmitting any signal... Is that not the case? Why not? I get that when a tube is pulled, it is not present and not electrically 'active' in the circuit, whereas the 10k resistors to ground allow it to still operate, but not pass signal?

Or is it effectively identical just quicker than pulling the tubes?

Pretty much like pulling the tubes. Switching in the 10k cathode resistors biases them into cut-off, with only a few mA flowing. Enough to make the LED's glow.

[PicknStrum]

Will do - if cutting to half-power, cut the ohms as well.

I'm an 8ohm speaker kind of guy anyway so I'll plan on changing the amp impedance to 4 as recommended.

Any other tips are appreciated. I have some e-mails out to different companies / people to start sourcing some stuff. I think for this build, I'm going to go for a pre-drilled chassis. I've done the chassis bending and drilling thing before and I'm not great at it. I was able to find some premade boards through Ceriatone as well - I can get them unloaded for $45 so I'll probably end up going that route for price and convenience. The boards are pretty much the same (as far as I can tell) as I'd need for the #0124. The one thing I saw for sure is the filter cap board is a bit different but I can definitely make that work. Also waiting to hear from another source on what parts he has available, if any.

[ijedouglas]

Take your time, pay careful attention to lead dress and have fun!

Here are threads which outline a good approach (although I prefer to mount the transformers at the latest, just before the preamp board):
http://ampgarage.com/forum/viewtopic.php?t=4657 (take a look at Brandon's(Funkalicousgroove) post, I use this) and
https://ampgarage.com/forum/viewtopic.php?t=30369

[dreric]

Welcome and good luck on your build.

To save you time....................

Go to Taylor at Amplified Nation for chassis and boards, he usually has them for sale in the "For Sale" section.

Ceritone has a mixed reputation on the page. Some guys don't like him some of us don't really care. He uses cheap electrolytics.

There is also a vendor who sells a complete PCB that can be used for 3 different models.

There are other vendors who sell similar products.

Don't worry about the 50/100 switch, you'll never use it.

Magnetic Components has the best transformer prices.

All of the parts lists will be out of date.

Between Mouser and Antique Electronic Supply (6PS caps) you'll find all the parts you need.

Decide on a chassis, pre-made or DIY but get it or make it before you build the amp. It's hard to to after the chassis weights 30 pounds.

Create a build log as you build, take and post lots of photos. This creates interest in your build and more people will follow the thread. This way when trouble come up you'll have more eye on your project.

Most of all have fun!

Eric