12au7 Bassman Micro build

ping-ping-clicka

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View attachment 1054668 That'll be the front, my jigsaw wandered roughing the wooden trim but the palm router should save it (hope so as the oak's now 10mm thick from 20mm and I hope to avoid having to thin another plank :/ )

I've emailed my mate the faceplate drawing I've drilled to, red circles for cuts and black for engraving, most likely in black laminate with white writing as he doesn't sound keen on stainless steel :/ failing that a friend of a friend has a diode laser at home he doesn't know how to use so I've been invited to try and set it up for him, if I took a fire extinguisher with me it can't be that hard can it? :p

NFB, sounds good :) so when I read up on it, it seems there's a bit of uncertainty on the resistor's values, reading suggests a value between 2.6k to 6k for the 'Marshall' NFB resistor and the 15k one for the Bassman so I'll have to find a 2.6k one, and at the back there'll be an on/on switch for the bypass cap, 220uf and 2.2uf, I'm going to use a 100k pot for the mid as there's no room for a tone stack cut switch :p

I'm enjoying this :)

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A little further on, I’ve the circuit board to cut to length next and PT to position and drill for, then I want to stretch a diylc file to the board size to mark the turret holes from then adjusting to put a couple of new turrets in too (and a bus Lane 😝)
very pretty.
 

Kev-wilson

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I feel quite posh at this moment in time :) even though I didn't manage to remove all my border marks, this is two old workmates 'collaborating', 80 miles apart who served mechanical engineering apprenticeships, machining and fitting out sewage control machinery in the early 80's :p so for a 'luddite' like me it's fascinating seeing technology at work!

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Myriad pro's a nuisance font as the outline has lost a few lines but my mate reckons he can add them back in.
 

Kev-wilson

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Is the photo I was sent, and I like that 😀 all apart from it being 5/16” short 😩

It was an offcut I’m told so will have to wait for him to get some the right size, or reshape my front panel to suit.
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Edit, so my chassis turned out at 305mm, I'd aimed at 300mm (12") so error had crep' in :p and his plate is 296mm, I can make it work but will have to make the oak front piece again.

I've dropped a ball hook drilling v1, I'd marked a centre line but it's near a tape joint so I've mistaken the joint for the pencil line :/ not a problem but a reminder I need to replace a broken fluro fitting :p

Turret board next :)
 

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Kev-wilson

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Due to busy-ness I've not had chance to work on this but the faceplate arrived today and I think it's pretty decent, I need to make a front piece for the cab with the hole in the middle about a 1/16 a side shorter to house it neatly, but I've a cunning plan for using a palm router to so, as my jigsaw mounted upside down on the router table wobbles around like it drinks spirits...

I'm making hard work of the circuit board which is the 'to do' job, I was going to do a little 'point to point' wiring for my v1 cathode bypass cap & nfb switches but I'd probably be better turret mounting the cap/resistors once I'm happy how I've drawn them in.

The drawing shows a 15k nfb resistor, I plan to be able to switch a 2.7k one from a toggle switch but having recently struggled to grasp parallel resistor networks don't know/can't grasp whether if by sharing a terminal the resistors become in parallel as if so I need to do some more reading :) I've seen those values used so am happy enough, but like everything involved here would like to know more. :)
 

Kev-wilson

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My first turret board 😝 the 2 previous ones were perforated, a bit short of space but I can manage the soldering I think, turrets need peening over with my special tool 😀(small hammer, stake and a centre punch)
I’ve been short of spare time the last few weeks but can move forward now, tho I was nervous drilling to my marking as there’s a couple of extra turrets.
 

willholt92

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Just found your thread, absolutely love it great work. I really must pull my finger out and get back on my JTM micro, it's stalled for a couple years now. House renovations, kitchen builds have taken priority ( and a parts caster haha)
Nice to see another in the UK building one.

One thing that I have done on mine which you might consider for the tone stack defeat switch, I bought a switched 1 meg SPST pot the type usually used in Tweed champs for the on/off and volume.
I used this for the bass pot, want to take the tone stack out, turn the bass all the way down and off. Saves a micro switch and extra hole.
You will need some extra room behind the pot for the switch on the back mind you depnding how tight your chassis is, looking at it I'm guessing pretty tight.
 

Kev-wilson

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Just found your thread, absolutely love it great work. I really must pull my finger out and get back on my JTM micro, it's stalled for a couple years now. House renovations, kitchen builds have taken priority ( and a parts caster haha)
Nice to see another in the UK building one.

One thing that I have done on mine which you might consider for the tone stack defeat switch, I bought a switched 1 meg SPST pot the type usually used in Tweed champs for the on/off and volume.
I used this for the bass pot, want to take the tone stack out, turn the bass all the way down and off. Saves a micro switch and extra hole.
You will need some extra room behind the pot for the switch on the back mind you depnding how tight your chassis is, looking at it I'm guessing pretty tight.
Cheers, my amp/cab building started at the end of my house renovation so I had one to match the floor, it started out as making a speaker cab and a head to suit a Night train clone which was far too loud so I had a crack at a Deluxe Micro :)

I had planned a lift switch, didn't think of a switched pot so was going to go down the lines of RobRobs suggestion "An excellent alternative to the Raw Switch is just using a 100KA pot for the Mid tone control instead of the standard 25KL pot. The 100KA (yes, audio taper) pot will allow you to gradually roll on more preamp gain and mid freqs instead of having the all or nothing of a raw switch." as it sounded the simplest.
 

Kev-wilson

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‘Lazy Sunday afternoon’ 🙂 with the switchable nfb resistors.
It’s going to be interesting building this 😬 as there’s more going on than in the Deluxe’s. There’s a pre amp bus Lane running down the top(2nd cap is the start) and I’ll likely run wires underneath as it worked for me on the other 2.

Question, Rob mentions wiring the 6.3 pair to the rectifier and running to the pilot light and other filaments from there, I have 2 lovely hole pairs on the pilot light, is there any reason I can’t wire from there to the rectifier and the other 4 valves?
 
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Kev-wilson

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Just the 2 caps for the V1 switchable cathode bypass to solder, Mr Fender would be shaking his head at the layout but there's continuity where it needs to be so I'm getting there, the top last resistor pair is supposed to be for the switchable nfb but I've confused myself on the switching and omitted a wire in my little drawing.

I know it looks messy but I'm quite pleased with myself :p
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Kev-wilson

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yikes 😬 debating whether to pull a nighter or not, better a fresh start tomorrow tho I need to do some Christmas shopping.
Not being good at schematics I lean on layout drawings, the brown wire from the tail resistor to the nfb resistor was unseen till yesterday so I’ve been confused how to switch the nfb but they can join at pin 3 of the presence pot.
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Kev-wilson

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A question on these layouts
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The bottom is the lar mar & ef80s the top is the 3 pin pot, I’ve no schematic to work from so don’t understand the wire routing fully.

Hard to word the question properly but the yellow wire I’m pointing at connects to the right hand grid stopper one way and the left the other, Is that correct?
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I still need to do my Christmas shopping 😝
 

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Kev-wilson

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I don't think the wire color is intended to be meaningful here, if that answers your question.
Thank you :)

I'm working from right to left so haven't got to that pair yet :p, I soldered the 100k resistor on the input jack, looked at it and thought huh, and looked twice as not only had I not used a 1 meg one I'd used the tail as the jumper to the jack switch so it'd never have worked anyway. 🤔🥱

Duh, I can see the end in sight and I'm losing my concentration, best go and do the Christmas shopping I think and a bag of Lavazza coffee for tonight...
 

King Fan

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Ah, Christmastime in England -- wild boars hanging in the market, chestnuts roasting over a coal grate, the red-hot poker sizzling in the rum drink.... My holiday thought; don't rush through Christmas or amp building. Both will be over all too soon, and for both you want to do it just right and take it all in.

But have a lovely holiday whatever you do. :)
 

Kev-wilson

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Ah, Christmastime in England -- wild boars hanging in the market, chestnuts roasting over a coal grate, the red-hot poker sizzling in the rum drink.... My holiday thought; don't rush through Christmas or amp building. Both will be over all too soon, and for both you want to do it just right and take it all in.

But have a lovely holiday whatever you do. :)
:) smiling at your Christmas thoughts there as it's persisting down outside :)

My youngest kid's 16 and her older siblings late 20's & early 30's so santa is a bank transfer :/, dinner's at the eldests and I live alone, my mate's coming round later for jam night but he'll have to be a soloist :p

I've had the youngest staying since the weekend which has put me back with the amp, or I've worked slowly but this evening should see me either playing it, or troubleshooting and swearing at it, I've still got the front panels to make but have a laser diode machine to try as I've got my hands on a bargain and it should cut the wood, when I learn how to use it over the holidays...
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Kev-wilson

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I didn’t manage to finish it yesterday but got up early to write cards/wrap presents so my time was my own 😝 so time to test as it’s finished.
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If you want to snigger, I’ve just spent 15 minutes with it upside down looking for high dc voltage on a meter and see none, I even tried my old dmm.

In a few minutes I shall put the rectifier valve in this time and try again 😂
 

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