I've made a start :) 50w #102

[norburybrook]

Hi guys,

Well after a lot of hesitation and deliberation I finally made a start on my first Dumble type build.

There are going to be lots of questions as I go along, but I'll keep everything in this thread.

Spent today doing basic chassis drilling etc.


Marcus

[sepulchre]

Is this a kit, or did you gather the parts yourself?

Looks like fun to me.

[norburybrook]

It's definitely not a kit it has taken me ages to get the parts together.

I was given the chassis by a friend so I'm having to mod it to take my boards/components etc


Marcus

[sepulchre]

Gathering parts takes a lot of effort & time but you get to pick exactly what you want (OK, that's obvious), that makes it well worth it to me.

I've wanted to build a #124 for a long time, but finding the time, resources and convincing my wife that I really do need yet another amp, well it doesn't look likely. So have fun. I will follow whatever you post with interest.

[norburybrook]

Thanks, it seems quite daunting and the moment as I'm working from about 3 different layouts all with slightly different value components etc.

Also my previous builds have been made using turrets and I'm finding eyelets a complete PIA as you can only solder things when all the wires ,components are in the hole. With a turret you can solder components on a board and then attach wires afterwards.

I think I might have to drill out my relay boards too as the hole for the wire is very very small.


Marcus

[ic-racer]

Also my previous builds have been made using turrets and I'm finding eyelets a complete PIA

Think of it in terms of getting all the wires on the board first, then inserting the board to the chassis with all the wires attached. If you analyze the wiring of originals, it seems as if many of the wires are attached to something at one end prior to being inserted into the chassis. The fee end of wires either go to a socket, pot, jack, ground or to an eyelet that you can solder to from the front of the board.

So, for example your relay boards need eyelets so you can solder wires to them after the boards are already in the chassis. All the original amps were built with a certain logical order.


[img768]http://img.photobucket.com/albums/v670/ ... ile-50.jpg[/img]
[img768]http://img.photobucket.com/albums/v670/ ... ile-51.jpg[/img]

[norburybrook]

Thanks that makes sense.

My boards don't have eyelets so I'm going to haver to solder all the wires on directly before fitting the relay boards.


I presume that's how they're intended to work as that's how they're sold.


On another note I've just opened the bag with the trimmer pots and they're tiny, if I bend out the lugs they'll just go in the eyelets, will this be OK or should I re order some large ones, or possibly put the OD trimmer on a regular pout on the back?



Marcus

[martin manning]

I've used 3/8" square Bourns trimmers with eyelets and they work fine that way.

You could add small (3/32") eyelets or tiny turrets to the relay boards if you have them. Looks like the boards are different (the one pictured has no connections to the N.O.), so you'll have to use the right one in the right place.

[norburybrook]

sorry Martin ,what's the N.O?




here are my two boards? didn't realise they were different.

Marcus

[martin manning]

NO is "normally open," NC is "normally closed."

I'll save you some work here. Those boards are not like Tony's ODS 102 layout, in particular the contact sets are swapped. I think I have it labeled correctly below.

[norburybrook]

Thanks Martin that makes sense now

Another question: why don't Dumbles have an HT fuse, and should I fit one?



Marcus

[martin manning]

I guess HAD didn't think the HT needed fusing, otherwise he'd have done it. If you do, use two, one on each leg of the HT. Don't put it in the HT center tap as that will cause problems in the bias supply if it opens. Personally, I'd leave it out.

[MKB]

The majority of Fenders don't have HT fuses either FWIW. Maybe that's where HAD got the idea to leave it out?

[norburybrook]

I guess HAD didn't think the HT needed fusing, otherwise he'd have done it. If you do, use two, one on each leg of the HT. Don't put it in the HT center tap as that will cause problems in the bias supply if it opens. Personally, I'd leave it out.

Interesting Martin as the ceriatone layout has exactly that, the HT fuse on the center tap which is what I was going to do as my donor chassis has two fuse sockets at the back.

I'm all for simplicity if it's safe so I'll just blank it off.

Marcus

[norburybrook]

on the original talbany 102 layout the capacitor at the top of the pre amp board from the presence control into the phase invertor circuit is show as a 2.2uF orange drop but on other layouts it's shown as an electrolytic, can I use a 2.2uF orange drop 600PS as I don't have an electrolytic to hand?

also can I use a 100k( or 120) instead of a 110k resistor on the 10k P.I trim pot?

Marcus