Building my 5F2A Chassis - progress report

[tubeswell]

Working it up from scratch out of 0.7mm Aluminium

Got the chassis punches today (4 assorted size old-school punches for $80NZ, talk about skint Trev! - ah-well they'll come in handy for the next project aye)

Anyhow took me 2 solid days just to get this far. Now I'm starting to become obsessed. ;-)

I have yet to put the endcaps on. (I'll measure them up as I go, cause I'm doing the bending by hand on a bench top using a bit of nailed-down 4x2 to help the folding, so its a manual labour of love). The top and bottom rear edges are double-folded for extra rigidity (note the claw-hammer marks). The chassis measures 38cm long by 7.5 cw deep by 10cm high.

I think I'll get an engraved dashboard made up to cover the top panel if the thing sounds any good. I've got those cream-coloured chicken-head knobs - what goes good with that and tweed?

[tubeswell]

Finished Chassis end-caps

Ready for the installation of all the stuff that's been waiting stashed in the cupboard.

[Casey4s]

Looks like you're off to a great start with your amp project.

Good luck...

[tubeswell]

My 5F2A Cabinet

Here's what i did with a bit of 3/4" pinus radiata and some 3/4" plywood this avo. Took me about 6 hours (including buying the timber). Pretty crude - needs tidying up a bit. But the basics are there.

I'll cover it with some tweed and put a bit of wicker or something over the baffle. The baffle is floating with rear-mouting battens on both sides (instead of front mounting top and bottom) - something different for a change :-)

[tubeswell]

Cabinet construction finished (bar tweeding)

Here's what I did this morning - (back panels and more sanding)

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5F2A Chassis wiring (start)

Trannies attached to the back - custom-made by Howick Transmormers - good on you Basil ;-)

And inside -Starting with the power input

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Little bit more

Installed the tube sockets and wired the heater circuit and the Pilot light this evening.

Also started connecting the OT taps, (two taps - 4 Ohms and 8 Ohms, with a switch (see underside view of chassis in box)

Put the chassis in the cab for fit. Tight fit but methinks it works - so far so good.

fingers crossed - touch wood ;-)

[Paul P]

You're really moving along. Great pictures, keep 'em coming.

I'm a bit jealous of all that beautiful sunshine and greenery you've got
down there...

Paul P

[tubeswell]

Never mind the trees and sunshine...

I've got serious indoor stuff goin' on... (he he)

Anyhow here's the pics of the heater wiring from yesterday, and tonight's effort (namely output and input socket wiring)

The output section has two sockets for the 4 Ohm and 8 Ohm OT taps, with a switch between them that 'intuitively' lets the operator select which socket to use. The setup is wired so that the 4 Ohm Tap can be used with both output sockets running an 8 Ohm speaker in each socket, or just one 4 Ohm speaker in the 4 Ohm socket. Or it can be switched to just run one 8 Ohm speaker from the 8 Ohm socket. :-)

The input sockets are soldered together (the input of No.1 is soldered directly to the switch of No.2) so that the sockets are in 'reverse order' with No.1 on the left and No.2 on the right. This made sense to me cos I was the one who had to solder it all together from the rear of the chassis - OK?. The 68k 'grid' resistors (emphasis added becuz they ain't mounted at the pin of V1a) are off the input lug of each socket connected to a shielded cable going to the grid of v1a.

The shield is going to the ground lug of No.1 socket, along with a wire to a whole bunch of pre-amp ground wires on a terminal post setup (which ain't connected to the preamp yet). So everything in the pre-amp (including the pre-amp 'filter' cap) will be grounded at the No.1 socket. I plan to put the first and second filter cap grounds to the other ground in the amp (with all the power supply and Heater CT and HT CT grounds in one spot) at the other end of the chassis, so the amp will only have two grounding points. Is that right, or is that right? (all criticism appreciated BTW)

[tubeswell]

Vol and Tone knobs in

This evening's work.

I had to put three mica caps in parallel to get near enough to the 500pF value for the tone control. (390, 47 and 56)

The wiper from the vol to grid pin 7 of the 2nd gain stage is shielded with the shield grounded at the vol pot ground lug.

The topside panel is starting to look prettier (Omigosh!)

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Topside Panel

Here's that top view of the whole thing at the mo'. The extra little hole between the Vol and Tone knobs is for the presence (NFB) switch.

What to do about the state of the chassis face plate?.... Hmmmm... I was thinking of some kind of formica engraved thingy - mid-dark tan coloured with white engraving maybe??? How would that look with tweed fabric? I guess ya can't beat tweed.

Or should I just stain the pine and laquer it? (The whole thing has a hand-made look to it after all).

I was thinking maybe coloured Hessian for the grill cover.

This is not a good time for indecision.

[black_labb]

I was thinking maybe coloured Hessian for the grill cover.

This is not a good time for indecision.

i dont know if your interested, but ive been looking at these materials from the hardware stores around that is used for shade cloths here in australia, which i think would make great protection for the speaker and look good too (comes in a few neutral colours) ive been climbing around on many of the shade cloth's before with other people on the same one, so they should stand any abuse you throw at them. just something you may want to consider, assuming you have them in nz as well.

[tubeswell]

Shade cloth grills

Great suggestion black_labb, I'll look into it.

Cheers

[tubeswell]

Ready for testing

Okay today I wired the turret board and installed it.

Then I hooked everything together. (See pics) The crazy wiring job (comments welcomed) is due partly to inclusion of NFB cutout switch, which adds a couple more wires to the party, and the fact that I have stuck a largish sized first filter cap in which wouldn't fit on the turrent board I had, so I had to mount it on a cable tie stand beside the turret board. On the plus side, there is plenty of room next door to add another 20uF cap of the same dimensions in parallel to the first cap if I want to.

I just need wire up a speaker cable and plug the speaker in. Yikes!!!

The trannys were custom made and there isn't any manufacturers booklet I can turn to, so I guess I better test the voltages first.

[tubeswell]

Cosmetics

Okay I haven't tested yet coz I got a wee bit carried away this evening.

I found some old retro corduroy somewhere and it somehow just 'suits' the speaker baffle hole for now.

Can you get Beam-Blockers shaped like Tweety Bird?

So now I just got to settle on something to cover/finish it with. (and get a carry handle

I found a 2nd-hand Goodmans 15W something for $40NZ. Its rated at 16 Ohms, but only measures at 11.3 on my meter, so I guess it won't be too bad running it off the 8 Ohm tap for now until I find a nice 8 Ohmer.