Dumble ODS 102 Mistakes and Recovery

[desertmouth90]

After talking to you guys on this forum, I have come to the conclusion you are all the most useful and nicest people to do with amps.

Since my last post I have resolved quite alot of choices, not least what transformers I am going to use. (I am going to use Modulusamplification PT & OT).

I have arisen from my bed today and decided I want to get this amp as perfect as I can get. I have aquired an old Oscilloscope that will help me orientate the Orange Drops. I have decided I will remove the PCB then re orientate the Orange drops to the correct orientation, then it would be easier to get the ground circiuts perfectly inline.

Also I think that the Ground Bus bar for the pots extends too far out. So I am tempted to reduce the over hang of this. Also the pots stick out quite far, do you think I should leave them or stick a nut and washer behind to space them in slightly?

Let me know what you think and also if any of you guys learnt anything building this amp model?

Thanks
Clive

[Stephen1966]

After talking to you guys on this forum, I have come to the conclusion you are all the most useful and nicest people to do with amps.

Since my last post I have resolved quite alot of choices, not least what transformers I am going to use. (I am going to use Modulusamplification PT & OT).

I have arisen from my bed today and decided I want to get this amp as perfect as I can get. I have aquired an old Oscilloscope that will help me orientate the Orange Drops. I have decided I will remove the PCB then re orientate the Orange drops to the correct orientation, then it would be easier to get the ground circiuts perfectly inline.

Also I think that the Ground Bus bar for the pots extends too far out. So I am tempted to reduce the over hang of this. Also the pots stick out quite far, do you think I should leave them or stick a nut and washer behind to space them in slightly?

Let me know what you think and also if any of you guys learnt anything building this amp model?

Thanks
Clive

Hi Clive, Welcome.

Congratulations you haven't just built an amp but are now starting to see ways it can be improved and so you're rebuilding. The scope is a good purchase and good for a lot of things other than cap orientation and if you pair it up with a signal generator, it will allow you to do a whole host of tests across your circuit.

Generally speaking then, what type of hookup wire did you use, stranded or solid core? If it is solid core it is a lot easier to press into shape. Some should lie flat against the chassis, some should run perpendicular to other wires and some (like the filament wires) should fly over their surroundings. Some should run parallel with other wires and some should be kept apart. Solid core allows us manage the capacitive and inductive coupling, exploiting its effects in some instances, negating it in others. I'm sorry you probably think this all sounds a bit vague and nondescript. and you'd be right. It isn't the end of the world if you used stranded cable but my experience with it is that unless you are very lucky, it always contributes to a noisier sound floor - and I'm not that lucky! So, when breaking down the elements of circuits as complicated as these, it gets easier to see and deal with individual cases. I suggest a lot of reading of past builds and study of photos of lead dress that people have posted. You will soon get an idea of what to look for and how to get it yourself. The FAQ section has some good articles about grounding for instance.

If you concentrate on your own amp it will help us greatly if we can see a lot more pictures, go close up on the preamp and power amp sections and focus on the tube sockets and pots, jacks and switches. There can be a lot to unpack there so photos will be instrumental in figuring it all out.

No description yet of how it sounds. Have you had any transformers in there yet and if so, how does it sound? Was there anything about that that stands out as remarkable - good or bad? Recordings are also very useful but are difficult to do well and describing it can be even harder - more info is always better though so don't get hung up on the quality of recordings.

A good idea to tidy up your bus bar. Look around at similar builds, you will see it is normally directly placed over the back plane of the pots.

The pots are protruding at the front not necessarily because there's anything odd about them, they look normal but you don't have fascia panels and so you have an extra length of thread around the bushing to deal with. If you aren't going to put fascia plates on the front or back then an extra nut and a single lock washer on the back is going to allow you to adjust the depth for a tight and firm electrical contact which contributes to shielding the pots through the grounding of the chassis. It doesn't seem your chassis has been powder coated or anything, but if it has I would recommend taking it down to bare metal where the lock washer makes contact on the inside.

My advice. A lot of the guys here know a lot of stuff. You will discover as I and everyone else here did, that many of your questions have probably already been addressed so do your research and look for already published answers in the forum first, but you don't need to be afraid to ask if you get stumped. Treat it as a given that if you ask nondescript questions you are likely to get nondescript answers, if you get a reply at all.

[desertmouth90]

Morning, sorry for the late reply.

Im already seeing the benefits of the scope purchase, the next I am going to upgrade my Digital Multi Meter to a Fluke 101 of sorts.

I used stranded mostly for this build, but for the heaters I did use Single core. For my next build though i have alot of Solid Core wire rated at 600v I intend to use. Given the tight nature of this Dumble ODS build I have had to remain with stranded wire as it got rather chaotic. I used Modulusamps Shielded wire, which I didnt rate at all, so I may replace that at some point too as it had two cores, when I only needed one.

Yes the purchase of the transformers has proved difficult as I didnt know what spec transformers I needed but I have since found that a firm in the UK sell Dumble Spec tranformers. Unfortunately due to my governments decision to leave the EU I have found it difficult to order from european countries so Tube Towns Dumble specific transformers would be too much hassle.

I have attached a bigger photo dump.See the Shielded cable at the pot and how messy that is.

I havent yet powered this up but when I do I will be sure to post on here and drop you a message to inform you of it. and I will post sound recordings.

I thought about using a bus bar like this to aid maintenance. but it does get in the way slightly.

Thanks for the reply btw its been a great journey and I already know what im going to build next! My friends who have seen this build hold me in such high regard as though im a professional. But I know im knowhere near and need to improve for the next build.

Clive

[Stephen1966]

Hi Clive, no worries. Many of us have busy lives so a response can sometimes take days, it's normal. We don't take it as a Sign of anything! Also, you don't need to worry about posting messages to us when you add updates to your thread. When anyone places a comment in your thread they are automatically subscribed to it. You don't need to do anything except post new content.

A fluke! Wow, you must be made of money Perhaps you've seen the EEV blog on YouTube which went into why many digital multimeters at half the price are just as good. For one Fluke you could probably get two very good no-name meters and two meters are going to be much more useful to you practically speaking than a single one with a high quality of metrology. But Fluke are heirloom quality instruments. If you can afford them - why not?

I wouldn't discount Tube Town Dumble transformers - they actually use grain oriented M6 laminations and are very good. I'm using them in my 183 (Delta) amp. I think what matters is that TT are actually very good on supply and delivery and I'm not sure you would be looking to pay any extra import costs above VAT and ordinary shipping. Maybe try ordering something smaller and lighter and non-critical from them and see how it goes. These no-name transformers I suspect are made by Inmadout but good luck contacting their English office. Their transformers are. Very. Good.

The thing to do now is to get it up and running, I'm sure the Modulus transformers will sound great. Your ears will tell you if there is anything else wrong or needs further investigation.

[ijedouglas]

Hey Clive,

Congratulations on your build! There is not much more I can add than the fantastic advice Stephen has given. One thing I did notice is the orange drops you have appear to be the 716P series. If so, you may want to swap them out for the 6PS series. This is what Mr. Dumble used in this amp and will get you closer if that is what you are trying to accomplish.

[desertmouth90]

Haha I like planning for a lifetime! its what I do for a job (Architecture).

Yeah I think see it as an investment. I have one DMM but the capacitor test isnt sensitive enough and it does do Milivolts.

Would the 716P and 6PS make much of a difference? I just checked my stash of Orange Drops and they are all 715Ps apart from two 503l 6Ps!

Might test it and see.

On the Transformer front, I did ring Modulus and they said their transformer does work with a Dumble Type amp and they supply a retrofit plate for the chassis (also from modulus). I am however going to inquire to see if they can make a transformer exactly the same spec as the TT one. I will email them tomorrow (or tonight as I may not be able to switch off without doing it before bed!).

https://modulusamplification.com/100w-p ... 3413-p.asp
https://www.tubetown.net/ttstore/en/tt- ... ormer.html

[Stephen1966]

Haha I like planning for a lifetime! its what I do for a job (Architecture).

Yeah I think see it as an investment. I have one DMM but the capacitor test isnt sensitive enough and it does do Milivolts.

Would the 716P and 6PS make much of a difference? I just checked my stash of Orange Drops and they are all 715Ps apart from two 503l 6Ps!

Might test it and see.

On the Transformer front, I did ring Modulus and they said their transformer does work with a Dumble Type amp and they supply a retrofit plate for the chassis (also from modulus). I am however going to inquire to see if they can make a transformer exactly the same spec as the TT one. I will email them tomorrow (or tonight as I may not be able to switch off without doing it before bed!).

https://modulusamplification.com/100w-p ... 3413-p.asp
https://www.tubetown.net/ttstore/en/tt- ... ormer.html

An LCR bridge meter comes in handy for the accurate measurement of capacitors - in circuit as well. Several of us around here use this, the DE-5000. Cheap and plenty accurate enough. Something your DMM probably won't do is test the caps at 100Hz or 120Hz - typical datasheet values and particularly useful for measuring the actual values for caps in the power section. It's very easy to get carried away with all the fancy equipment though and you can spend a fortune on stuff you may ever only use once. Before tooling up anything I ask myself if I really really need it. In guitar amps, you will find that you don't need all the really pricey high-end gear to do the jobs well. The best instruments you can invest in are on the sides of your head and free.

Would the 716P and 6PS make much of a difference?

That's a good question. You have to try it yourself. I hear a difference, and you might hear one too, but not everyone does.

The JCM800 PT should be fine. The components in your bias circuit should be rated for the extra (100V) voltage. And, if you want to run your relays off the PT, they should all be the 12V non-latching type. The TT also has a tap I use to drive my relays without switching noise though I'm not sure if you will get it with the Modulus PT. Many traditional build 102s have a separate relay transformer. They are cheap and can usually be fitted in a standard chassis with little difficulty. Post schematics if you want more detailed feedback. Take a look at Tony's layout for the 102 for the original transformer specs.

https://ampgarage.com/forum/viewtopic.php?t=12707

The Mojotone transformers have some useful specs and these are made by Heyboer

https://www.mojotone.com/Showman-Twin-R ... er-125P34A
https://www.mojotone.com/Showman-Twin-R ... er-125A29A

A company that I know does wind custom transformers based in England is Primary Windings, a company endorsed by Merlin Blencowe, the Valve Wizard. And looking at the specs for several of their builds, they use high quality grain oriented steel. I'm considering them for a future project but I haven't commissioned anything from them yet.
https://primarywindings.com/our-policies/

[desertmouth90]

I have spoken to the main man at Modulus and he can build a custom OT and PT to the exact spec. He said however the idea by using M6 laminations is to reduce the size of the PT which im not too bothered about.

I have sent the schematic for the 12v tap so its a win win. I wanted to keep the main parts fairly local to avoid customs issues.

Hopefully post some stuff up soon on it!

Clive

[Stephen1966]

I have spoken to the main man at Modulus and he can build a custom OT and PT to the exact spec. He said however the idea by using M6 laminations is to reduce the size of the PT which im not too bothered about.

I have sent the schematic for the 12v tap so its a win win. I wanted to keep the main parts fairly local to avoid customs issues.

Hopefully post some stuff up soon on it!

Clive

Great! I agree, the size isn't the main point though https://edcorusa.com/pages/m-6-steel-lamination

Looking forward to your updates. Good luck!