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]

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]

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]

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

[tubeswell]

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

And inside -Starting with the power input

[tubeswell]

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]

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]

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!)

[tubeswell]

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]

Great suggestion black_labb, I'll look into it.

Cheers

[tubeswell]

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]

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. :cool:

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.

[tubeswell]

Well I tested the voltages from the HT winding (318.5VAC) to ground from each side) and the heater winding (6VAC) this morning, before inserting the Toshiba 5Y3GT (NOS) I bought and testing the Plate to ground (439VDC) and screen to ground (432VDC) without load. Then I plugged in the New Sensor "Tung-Sol" 6V6GT and a sovtek 12AX7 (I'll try some other pre-amp tubes this afternoon for sound check) and fired up the heaters with the standby switch off - and yup all the filaments appeared to be glowing (touch wood).

So I flipped the Standby on and got a wee hum (but not unexpected - I've got a second 20uF Sprague Atom arriving in a few days, so I'll biff that in and see how it goes), and a lovely quiet hiss as I turned up the vol, which altered in pitch as I fiddled with the tone control (still haven't plugged me Strat in yet - I'm drooling for this afternoon when my wife goes out).

When I flipped the Presence (NFB) switch on, there was this horridibel screeching, which turned out to be the primaries from the OT being back-to-front, so I swapped them around and now she's all good. I'll do the bench-burn later this avo to see if she smokes anywhere, but for the 2 or 3 mins I had it on before, I couldn't see anything ominous.

All up about $473NZ for all materials, and that's allowing for more than a bit of leftover Aluminium sheetmetal for my next few builds and another baffle boards worth of 3/4" ply.

Since I had a ball making it, I don't count my sweat and toil as anything negative or costly, (infact it was actually free entertainment). So I figure that's better value than paying $499NZ for a new, teency, diode-rectified Champion 600 that doesn't even have a tone control or a presence switch or a fancy-pancy dual/single speaker output system.

I gots ta finish the cab with something retro and get an engraved dashboard for the control panel (to cover the chassis faceplate).

I definitely recommend building one of these as a first build to anyone contemplating it.

[tubeswell]

Well the bench test didn't turn up any further problems at this stage and I test drove it a couple of times this afternoon with my Strat.

Dare I say It sounds surprizingly hum free, although there is a tiny little bit of hum (quite liveable) when the vol is maxed out, but its almost nothing. Maybe another 20uF in the first fliter cap will reduce that.

Got a fab range of sounds. The vol dial goes from nice'n'fendery clean at one end to nice'n' dirty at the other end, and the tone dial goes from nice and round at one end to nice and bright at the other end. Definitely like the NFB switch - this adds a whole nother dimension. All in all its quite bluesy, jazzy, rocky little piece.

I'm definitely going to have to build something else now. I'm hooked.

[Paul P]

Glad to see a happy ending to this story. Must have been a bit tense when
you fired the thing up for the first time.

Thanks for sharing your journey with us. So what'll it be next time 'round ?

Paul P

[Casey4s]

Well the bench test didn't turn up any further problems at this stage and I test drove it a couple of times this afternoon with my Strat.

Dare I say It sounds surprizingly hum free, although there is a tiny little bit of hum (quite liveable) when the vol is maxed out, but its almost nothing. Maybe another 20uF in the first fliter cap will reduce that.

Got a fab range of sounds. The vol dial goes from nice'n'fendery clean at one end to nice'n' dirty at the other end, and the tone dial goes from nice and round at one end to nice and bright at the other end. Definitely like the NFB switch - this adds a whole nother dimension. All in all its quite bluesy, jazzy, rocky little piece.

I'm definitely going to have to build something else now. I'm hooked.

Good for you sir, seems like you did a great job on this build, thanks for sharing your progress with everyone.

Now you have discovered the real danger of building your first amp, cronic addiction. :)

Looking forward to your next project.

[tubeswell]

So what'll it be next time 'round ?

Paul P

Dunno - a tweed deluxe maybe.

[tubeswell]

Casey4s - That is some piece of art! You must be a master craftsman! What sort of reverb pan did you use? (or did you make one?)

[Casey4s]

Casey4s - That is some piece of art! You must be a master craftsman! What sort of reverb pan did you use? (or did you make one?)

Thanks for the nice comments, but no I am not a master anything LOL, Just a hobby level builder. Building a complete amp, as you discovered, is more than just one discipline, from woodworking and metal work to electronics, it takes me a while from start to finish but I really have a lot of fun.

I don't remember the model number, but the reverb pan is a stock accutronics Fender replacement unit I got from AES. http://www.tubesandmore.com/

[tubeswell]

Got a bit carried away with a bit of cheap brown Hessian today ($5.99NZ/metre).

So I thought its a bit better than the bare plywood baffle. Whaddaya reckon?

[Casey4s]

Got a bit carried away with a bit of cheap brown Hessian today ($5.99NZ/metre).

So I thought its a bit better than the bare plywood baffle. Whaddaya reckon?

Looks like you did a good job with the grille cloth but it is hard to tell much about the cloth itself in the photo.

What do you plan to do with the rest of the cabinet? Stain it or Tolex or....?

[scole]

now you just have to learn how to do finger joints.

http://www.flickr.com/photos/10451485@N02/sets/72157601675424588/

[Casey4s]

now you just have to learn how to do finger joints.

http://www.flickr.com/photos/10451485@N02/sets/72157601675424588/

Nice looking Champ Sir, you seem to be an expierienced woodworker too.

[tubeswell]

now you just have to learn how to do finger joints.

http://www.flickr.com/photos/10451485@N02/sets/72157601675424588/

Yep that's the scary next phase. I don't have the proper equipment. If I have to do them by hand, it'll take me years and probably waste heaps of pine.

But I must say, that a nice champ Scole. What're all those knobs for? (Vol. Tone and ?? (and the little switch mounted in the wood?)

[tubeswell]

Looks like you did a good job with the grille cloth but it is hard to tell much about the cloth itself in the photo.

What do you plan to do with the rest of the cabinet? Stain it or Tolex or....?

Hessian is basically sack-cloth, made from quite stringy thread with quite a loose weave, so there's plenty of holes for it to breathe. This stuff has been dyed a tan colour. I glued and tacked it over the back of the baffle. I might get back in there with a wall staple-gun today.

I don't know yet whether to tolex the rest or stain it or varnish it, or do a suit job. I found some cheap tweedy plaidy fabric which would look good with the hessian, but its not your traditional diagonal tweed, and its not brown, its more like little black and off-white and grey squares.

On the other hand, the woodgrain's got a nice natural theme going for it. The cab's got little screw-holes on the sides, (which could be a varnish feature?? ha ha).

I was thinking of getting a tan-coloured formica dashboard made up for the instrument panel, - the sort with fine routing-engraving in a white or cream colour that tells you elegantly that it is a Tubeswell Tweed and what all the fiddly bits are. - More on that later.

[Casey4s]

Hessian is basically sack-cloth, made from quite stringy thread with quite a loose weave, so there's plenty of holes for it to breathe. This stuff has been dyed a tan colour. I glued and tacked it over the back of the baffle. I might get back in there with a wall staple-gun today.

I don't know yet whether to tolex the rest or stain it or varnish it, or do a suit job. I found some cheap tweedy plaidy fabric which would look good with the hessian, but its not your traditional diagonal tweed, and its not brown, its more like little black and off-white and grey squares.

On the other hand, the woodgrain's got a nice natural theme going for it. The cab's got little screw-holes on the sides, (which could be a varnish feature?? ha ha).

I was thinking of getting a tan-coloured formica dashboard made up for the instrument panel, - the sort with fine routing-engraving in a white or cream colour that tells you elegantly that it is a Tubeswell Tweed and what all the fiddly bits are. - More on that later.

On several of my builds (5F1/F2, 5E3, 5F6A Ampeg SB12) I used a piece of brushed brass stock and had a local engraver cut the lettering in for me, it's not really expensive and has a nice look to it. Usually engravers have that brass stuff in the shop. ( I provided my own)

Here is the faceplate from my 5F6A Variation to give you an Idea of how it might lool.

http://i238.photobucket.com/albums/ff243/Casey4s/DIY%205F6A%20Bassman%204%20Valve/4b48.jpg?t=1202017319

http://i238.photobucket.com/albums/ff243/Casey4s/DIY%205F6A%20Bassman%204%20Valve/24f5.jpg?t=1202017238

[tubeswell]

Very nice Casey4s - thanks. How do you make sure they get everything (holes etc) lined up with your chassis?

[Casey4s]

Very nice Casey4s - thanks. How do you make sure they get everything (holes etc) lined up with your chassis?

I drew a 1:1 layout with what I wanted where. I also predrilled all the holes to fit and made the little "divits" for the numbers on the 5F6A in advance so it was a lot easier for the engraver to get it right the first time.

In my case I actually drilled the pilot holes through the chassis and the faceplate blank at the same time for perfect alignment.

BUT, if you get the cut to size engraving stock from the engraver, you can pull the contols out, place the stock on the panel and trace the hole locations onto the faceplate stock from the inside, then drill them out and get it engraved. Your engraver can make the marks for the numbers as either dots or dashes.

There are some photos of making the faceplate and chassis set-up at this link: (CH-11 to CH-17)
http://s238.photobucket.com/albums/ff243/Casey4s/Basic%20DIY%20Chassis%20Set-up/?start=all


EDIT: CH-9 shows the layout sheet I gave the engraver.

[tubeswell]

Tackled this today after much preliminary anxiety. Still didn't quite mange to get the fabric lined up straight, but I'm going to let it be.

The top and sides is a single piece.

Excuse the back shot, the glue wasn't quite dry on the bottom bit when I took the pic.

The fabric is a Gingham Tweed (of some nameless colour) that sort of goes with the Hessian grille. Now for a handle (and maybe a brown formica dashboard) (and possibly some square metal corners) - and this saga is nearly complete.

[Paul P]

Hey tubeswell, have you had time to get to know your amp a bit more ?
What do you think of it sonically ? I know you were happy initially, I'm
wondering if you have a bit more to say about the tone and whether or
not you intend to tinker with it.

Paul P

[tubeswell]

yeah I have taken it to a couple of practices now and played on it a bit for the last couple of weeks (has it been that long?). I have noticed that with the NFB switched out, it really comes alive and this lifts the low gain input. But on the high gain input, with the NFB switch cut, there is a faint but noticeable intermittent mid-to-high-end electronic buzzing noise when I have been thrashing the amp, but it gradually stops after I have stopped playing it for a while. It sounds similar to a ground buzz, but I don't think I can be, because the intermittentness doesn't seem to be related to whether I touch the strings or chassis or not, and it also stops immediately if I kick the NFB loop in. So I'm guessing that maybe its something to do with the power supply reservoir. So I was wondering maybe I should add a second Sprague Atom 20uF in parallel with the first filter cap (the tweed narrowpanel princeton had two 16uF in parallel for the first filtering stage).

Also at present while its very nice on low vols, it breaks up quickly when cranked and loses a bit of high end definition, I thought that maybe also lowering the 2nd and 3rd filter caps from 22uF that I have presently got in there to 10uF each (which is closer to the orignal 8uF value - and is also what MWJB suggested for tone) would do the trick. I did an A-B comparison side by with the new Champion 600 yesterday, and the Champion can't touch my thingamy for subtlety, although the Champion was obviously less bassy, it also had brighter mids (if my ears weren't deceiving me). So I'm guessing that has something to do with what MWJB was talking about.

Although the 10uF 450V caps I have are quite piddly in size compared to the Sprague Atoms, I don't think that should matter, especially if I have two of those big 20UF caps in parallel for the first filter stage.

I was also toying with the idea of maybe putting a lower value resistor in at the first supply resistor, say 4k7 instead of the 11k I have in there, in order to get a bit more headroom and chime. I've got plenty of leeway in the screen and plate voltages at present (55 volts difference at idle).

Having a look in the back of the chassis again, I also see possibilities with improving the lead dress, particularly where I have the blue wire going from the coupling cap to the output tube grid (see pic), as this is crossing the turret board right next to the two 22uF filter caps and also crosses the other 2 or 3 inch length of blue wire I have going from the NFB switch to the cathode of v1B. (This part of the disconnected NFB loop remains 'active' in as far as it is still attached to the cathode of the 2nd preamp gain stage when the switch is disconnected, and may be acting as some sort of antenna coupling between the aforementioned pre-amp plate to output-grid coupling wire and the cathode of v1B. - How's that for a hair-brained hyothesis?)

Anyway I thought I could move the aforementioned plate to output grid coupling wire to be located behind the turret board, thereby reducing that potential RF coupling source.

After that I'll do one tweek at a time, starting with the 20uF cap.

Another thought I had was that in completely disconnecting the NFB, that the 2 or 3 inches of little blue wire that remains connected to the cathode of v1B (that I was just talking about) could be acting as some sort of RF antenna without the NFB signal going through it.

Therefore another possibility I thought of instead, is that it might pay that instead of making the NFB loop switch completely disconnect, I could make the 'off' position of a DPDT switch connect back to the top of the OT secondary via a 1M or 2M2 resistor (i.e. the DPDT switch would switch the NFB loop between a 22k stock resistor and (say) a 2M2 resistor). I wonder in theory whether this would effectively provide 'infinite' resistance thereby mimicking the disconnect function of the current NFB switch setup, but without leaving any little RF antennas lying around. Is that too bone-headed or might it just work?

I also liked the (Holland made) NOS Philips 12AX7 I recently acquired in there. Its very sweet.

[Paul P]

Great report. I bet having your amp working gives you a much better
understanding of what all the different parts are doing (or might be doing).

But on the high gain input, with the NFB switch cut, there is a faint but noticeable intermittent mid-to-high-end electronic buzzing noise when I have been thrashing the amp, but it gradually stops after I have stopped playing it for a while.

This must be some sort of distortion, just the thing that the NFB is there to
cancel out. Could the fact that it happens under heavy playing and goes
away after having stopped playing be some heat-related thing ? It sounds
like a resistor (or a tube ?) is heating up too much when you're playing
hard and then it gets a chance to cool down when you stop.

Why would you play through both low and high inputs ? Isn't one better
suited to guitar than the other ?

Paul P

[tubeswell]

Thanks for the feedback and suggestons Paul P.

Yep the intermittent buzzing could be related to dissipating some sort of energy I guess. I have a 2W 11k (2 x 22k 1W in parallel) resistor at the first supply (from plate to screen) node. If I try a 4k7 5W in there, I guess it might:

a) reduce the resistance load (and thence and heat dissipation) on that first resistor, but also it would do something to the tone by bringing the screen and plate voltages closer (I don't quite know what to expect in that regard)

b) give more headroom and chime

On the Hi/Lo input question, the Hi Gain input is definitely brighter, but when I play my strat through it, it can be too bright in some applications - I can get nice muted jazzy tones through the Lo Gain input, and the combination of the tone control and the NFB cutout switch makes the amp very versatile in this regard. The 1MA tone control pot works very well with the mica caps. (I used 'Alpha' brand pots)

[tubeswell]

Well I added another 20uF to the first filter stage today (bringing it to 40uF).

The voltages all went up about 8V.

So I am getting about 364 on the Plate and 303 on the screen. Ran it for 15 or so mins, taking readings and didn't see any smoke yet. (Will update my report in this regard on the New Sensor Tung Sol 6V6GT in the Tubes forum).

I also twiddled a bit with the lead dress by re-routing the coupling wire between the pre-amp and the output stage so that it no longer crosses over the filter caps or the NFB switch wires.

Have yet to road test it with these refinements.

[tubeswell]

I put a strap handle on it a couple of days ago so its alot easier to carry around (Duhhh!)

$40NZ for a Fender strap handle! (Pushes the price of the amp over $500)

[Paul P]

Nice !

$40NZ for a Fender strap handle! (Pushes the price of the amp over $500)

Who said you could save money building your own :). My wife told me
today, with maybe a touch of exasperation in her voice, that I was getting
close to 3000$ with my amp. This does include quite a bit for shipping
charges, an extra part or two, and a lot of extra wire, but still. Quality
parts aren't cheap. It better sound good !

And I still need grill cloth...

So how's the tone of your amp coming along ?

Paul P

[tubeswell]

By and large I like what I'm hearing.

At this point I don't know if I did needed the extra 20uF in the first filter stage to be honest. It seems to make some difference when I cut the NFB loop. Otherwise I don't think it takes out much in the way of hum. The hum was pretty low to begin with. It does lift the Plate voltage about 8V. I'm thinking that maybe the amp loses a bit of it champiness with a plate voltage of 364

The way the cab is built, the amp is very bassy on the neck pickups. I haven't tried putting in the 10uF filter caps in the other positions yet. I have conflicting stories about whether they will make any difference in tone or not. I might try putting the switch in at the first cathode bypass cap to see if that takes any bass out. I don't want to have to change the coupling caps yet.

I wish I had a spare $3k to spend on building amps

[Paul P]

I wish I had a spare $3k to spend on building amps

So do I. I initially thought 500-1000$. At one point, somewhere in the
middle of it all, I began to realize that the thing was going to cost a
fortune. I also realized that I was pretty much past any point of no return
so I just said to myself ah, to hell with it, and plowed on. What's sort of
kept some sense in the picture is that it would have cost me about as
much to buy an equivalent amp (though I don't think one exists).

The way the cab is built, the amp is very bassy on the neck pickups.

Have you tried moving your amp up off the floor ? That'll reduce bass for
sure.

Paul P

[tubeswell]

Well after a couple of weeks jammin' and taking it to the regular band night practices, I saw another opportunity for improvement. Last night at band practice there were a few comments about the "ear-piercing highs" from the other guitarist who was standing next to his own amp 10-20 feet away across the room, and would I please tilt it back to face the ceiling mate! (Sure thing mate, but I was nervous about the angle it was left dangling at...) Well I never had taken that into account because I was always standing near the amp when i was playing it before!

So today in my spare time I made a beam blocker out of 3/4" ply and a bit of aluminium. Ist one was 120mm (or 4.8") diameter. I tried that out for a while and decided it cut slightly too much from the top, so I put a smaller one in 85mm (3.25") diam. The beam blocker appears to stop the dreaded ear piercing high freq intensity beam manifesting itself across the room and looks kind of retro. You can just see the disc and the aluminium mounting bracket through the grille cloth if you squint.

Following a hint a while back from MWJB, I also put 10uF caps in the 2nd and 3rd filter cap positions. I am happy to report that the 10uF caps have (to my ears) indeed reduced the bassiness slightly. Fancy that! Thing sounds a bit lighter and brighter in the mids.

I also adjusted the internal wiring a bit and re-soldered what appeared to be one or two dirtier joints, to improve the lead dress a bit more and limit potential coupling sources and re-tensioned the socket pins to limit other potential noises. It sounds pretty good now

[Paul P]

Just a thought on the treble response. Your speaker may not be the best
match for your amp. It looks like it's seen better days, is that a repaired
tear in the cone that you can see in the picture ? You must have another
amp lying around, can you try playing your amp through its speaker, or
vice versa ?

Paul P

[tubeswell]

I've noticed a phasey warble (like a phaser effect unit would produce) at high volumes that is quite apparent on certain notes esp when I hve the guitar vol knocked back a bit to clean up the signal. I'm not sure whether its more pronounced when the amp warms up.

Trying to find reading about this to see whether its related to higher than expected B+ and Plate voltage.

When I soldered in the 2nd 20uF filter cap I put the leads onto the first filter cap right at the point where the lead comes off the cap. I wonder whether I over-heated something in the soldering?, or whether perhaps the phasey sound was always there and I hadn't noticed before, and it might possibly be something to do with a defective coupling cap maybe? (I'm using old-style NOS 400V mustard caps).

[tubeswell]

On second thoughts, after re-evaluating it a bit and fiddling around tonight, I have decided the phasey warble is normal for when the amp is cranked with the guitar vol nearly cut, and that it is probably just the pre-amp harmonic distortion showing through. So I am coming to terms with it.

[fernando]

I don't know yet whether to tolex the rest or stain it or varnish it, or do a suit job. ...

On the other hand, the woodgrain's got a nice natural theme going for it. The cab's got little screw-holes on the sides, (which could be a varnish feature?? ha ha).

I think the wood grain is great. I'd varnish it
(oops, too late, sorry)

[tubeswell]

Thanks Fernando.

Maybe I'll do that with the next one (But I am kind of getting hooked on gingham tweed - zany retro).

[slowfingers]

This is starting to get exciting:)
slow