My 5 F1 kit build

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5F1 BUILD PART 1

So my kit did arrive after a very long time. I think it would have been faster to order from overseas, and split the opinions about quality whichever way anybody feels like. Included in the box was a very shiny steel chassis, two transformers with lots of wires and no labels or tags or anything, some wire, Chinese valves, a turret board, and a bag of whatevers. Looks like capacitors and stuff. No instructions. No diagrams. No nothing. Looking at it, a very basic bare bones “you will have to supply a lot of items and thought and genius to get this to work” kit. Ah well. I would have at least expected a power chord…
Steel chassis, no thanks, but it seems there are as many “Yes” as “No” votes between steel and aluminium out there. At least it is sturdy, heavy, and, well, too shiny. And barely big enough to house the bits supposed to make up an amp. I suspect that the kit is aimed to those fortunates who actually knows what is what, and can immediately tell a power transformer from an output transfomer, a diode from a pentode, and such minor things. Output transformers being talked about by my very unhelpful valve amp expert friends as pure magic vodoo. This one looks like any cheap transformer to me. I expected something, well, output transformer-ish?
Decision time – does this lot go to the trash bin, do I make up a better (?) chassis, do I try to assemble the kit, must I beg the supplier for assembly information, which is widely available on the internet, but the internet did not take my money for this kit. I do not like the layout of the F51 amp, valves hanging upside down next to the speaker magnet doen not make any sense to me, and I understand valves tend to get warm, and hanging upside down all that heat rises up into the valve socket. Now that sounds like a good idea? And there is no good ventilation in this design at all. Oh, only 5 Watt, so what. Hmm, life of already suspect components so what.
I do have this very shiny laser cut steel chassis, might as well see if I can adapt it for use in this project before I decide to order abigger aluminium chassis. I do have an aluminium chassis blank here, but it is only about 40 mm high, which will require extra material on the front and back, unless I separate the face panel from the chassis, not a problem if you have 2 mm aluminium plate. I do not.
More to follow.

guitarboy2828

Well, I think it goes without saying, if you're going to throw it away, throw it my way ?

BUT, you should definitely put it all together. At the moment, it'll cost you nothing extra to put the chasis together. Assuming you have a soldering iron and some solder. Outside of that, I'm pretty sure you don't need anything of your own.

As for a layout or schematic, i'd just pull one from the web. This looks like it'll do!

Personally, i'd build it stock and standard. THEN, once it's done and its working, I'd start adding in some mods to make it truly epic. A tone knob, a 1w/5w selector switch, etc.

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Guitarboy2828, I shall proceed with a more-or-less standard build. With space for later expansions. The Mojotone cuircuit you show has stuff on it not included with this kit, or shown on the (Weber) diagram supplied earlier by Karel. But all of it is discussed in detail on the internet, anyway. Pro this, Con that.

You mention a 5W / 1W selector switch, but I am at a loss of how to accomplish this without a mess. Your ideas on how to do this easily? Internet seems to imply a dropping resistor after the diode, before the first big cap, but this apparently deadens "tone". Karel says I can play with the screen grid voltage by altering the screen grid resistor, I ordered a 22K fat pot for this purpose as well. But, other sources naysay this idea due to the increased voltage difference between the grid and the HT side... Not that I have the faintest idea about how these things are supposed to work. I only know that valve amps work well in Hi-Fi, and with guitars they tend to amplify stuff never heard on cheap transistor amps, thereby messing up years of perfecting (hidden) bad technique.

My initial mods will include a new faceplate with space and holes for future expansions (like a bright switch, tone pots x 2, decent On/Off toggle, maybe a Standby toggle (not required due to diode valve rectification.. ? Bah. Cannot hurt.)

Mods to the circuit will be the Screen grid pot, added to the 10K resistor. It seems that any mods to this circuit usually results in less "tone". And then some swear they improved matters by re-designing extensively. Maybe we are spoilt with too many knobs on our more modern amps. ( I think less is more. That may be why I enjoy the Ibanez TSA15H. Which insists on rejecting my "new" Strat-alike. Too much Strat brightness and sharp, twangy tone. )

Mods to the existing chassis will be lots of ventilation holes, and shifting the output transformer to the side on an angle plate, to allow space to fit the valves on "top", implying the chassis will not hang vertically as per Champ, but sit "flat" as per normal amp head, with the friendly glow of tubes on top of the chassis, faceplate front. Improving heat dissipation too. This will be the least invasive process and leave the chassis almost standard if I ever feel like going the traditional route. The chassis will also receive two bolt-on aluminium angles on the sides for mounting in the proposed head cabinet, with the standard mounting holes in the existing faceplate used for stand-off pillars to attach the new, improved faceplate. Which leaves extra space for me to try and solder all the wires. Thus no
messing up the rather shiny, neat standard face.

Speaker? 10 Inch speaker lying in box, waiting for wood.

This is going to be fun. I hope.

guitarboy2828

I honestly have no idea how I'd do a 1w/5w switch. All I know is I bought one of these (already made champs) and I think Matta had done a mod on it, it had the switch. Can't confirm nor deny if it deadened tone as I never heard it before. The one on the 1w was definitely not as bright as the 5w. But it was still usable, especially at home (I usually cranked it to 10 and it broke up nicely without killing my ears).

I really really missed having a tone knob on the champ I had. I found it was rather dull and I would've liked to have added a little more treble via a knob when I wanted it.

Jonathandj

I have just completed the exact same amp with the same parts, used a Jensen 25W 4ohm alnico speaker, made the cabinet from Oregon pine - end result is an awesome sounding little amp. Sound is vintage pure. some humming was reduced by re-soldering bad joints. Chinese valves are very good quality.

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Jonathandj, sounds as if I can rely on help from your side when things get muddy.

My plan is to use soft pine shelving (already waiting in garage) for the cabinet, no covering. I have punched new valve socket holes, still trying to see how they expect everything to go into that chassis. Now I need to relocate the output transformer.

The valves supplied are
12AX7B
6P6P - this valve is dark on the inside, as if it has a half-finished coating, ??
5AR4
One looks like SOVTEK. I verified heater filament pins on all three (to do the socket mounting holes) and shall try to internet the specs. I have drilled extra vent holes in the 12AX aluminium screen tube, and will now proceed to drilling vent holes in the chassis where required, taking shields between components into consideration.

I see a lot of wiring variations in the power supply side, where some diagrams connect the center tap to the rectifier filament, and taking that out as ground. ?? Others use the center tap out as ground. All these variations on the theme does not help me much. I would really have expected Karel to include a manual. For this kit.

Jonathandj

No drilling required. Everything fits perfectly onto and into the chassis and the four holes for attaching the chassis to the cabinet are already there too.. The pre-amp valve IS dark but that is normal. All the valves get really hot which is also normal. The biggest confusion I had was sorting out the 2 x transformer wires but I can send you the correct destination for each one. Also, every 5f1 drawing/wiring diagram on the net is subtlety different as there are a mix of original and improved versions, but again it can be figure out. The Mars kit is the newer version with mains grounding - not through a capacitor like the original. Also you will find 2 little black and white diodes which protect the input transformer in the event of a valve failure. There is great set of videos (1 to 6 I think) on u tube showing the cabinet build and you see the correct chassis construction clearly too. The finished success depends very much on good soldering, assuming the wires are in the right place. Do not switch power to the output amp without a speaker connected!! It will be damaged.

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More progress. Or less, maybe. I decided to save the original chassis, it is a bit small for everything to fit with comfort. I had on hand a chassis blank, wider, and I cut a piece longer than the 5F1 bit, the "faceplate" part is a bit shallow, but things will fit. I managed to cut holes. I received this from someone ages ago, I now realise the person was trying to tell me he does not like me, the aluminium is butter soft. At that stage I was under the impression it is a reject, handed to me to get me off his case about helping me with valve amps, but no. A reject yes. Malice, yes. No way to drill and de-burr without hassles. One simply cannot use a rotating cutter to de-burr the holes. It just raises another burr. Pen knife to the rescue. So the holes are all but neat. There is much to be said for "aircraft grade aluminium", I have in all my years never worked with stuff this bad.

Ok, so the chassis is done, apart from sanding off the tool marks and so on. The tubes will sit on top, there will be space to work on wires to and from the turret board, and the components are spaced further apart than standard. The new chassis has an abundance of holes for future switches and knobs.

I started on the electrics, but am running into problems. It looks as if I might have to end this project build report here, but will give feedback on that soon, I hope.

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Started building again, after forcing some work-space on my desk. I received a replacement power transformer in January, but only now started to look at it. It tests out fine, no smoke or explosions, no shorts. High Volts here, Low Volts there, in accordance to the supplied lead ID's this transformer had with it.

Question: Before I work on the chassis some more, apparently I need to orient the power Transformer perpendicular to the output transformer (apart from doing an earphone test...?). Am I correct to interpret the requirement to be that the two be mounted as in the photo?

Hmm, I am used to the Brown-Blue-Green/Yellow thing, and most of the time I can successfully connect a three prong plug without smoke all over, even connect a speaker into the guitar cabinet, but here seem to be a few more wires than that....

OK, on to finishing the chassis.

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My measurements show the best orientation for the transformers, to minimize signal from the power transformer in the output transformer secondary, to be as follows.

0.6 mV on the ouput lead. Ah yes, the different output leads give different signal strengths, as expected from 4 ohm vs 8 ohm outputs. Now I understand why all the pictures of this type of amp show the power transformer with a bell-side up, plates lying down, and why these small amps used to run 4 ohm speakers. Some work ahead to mount the transformer like this, and keep the leads out of the way. From a noise point of view, I would prefer the output transformer to sit as pictured, to minimise the run of those leads above the chassis.

Interesting how fast the induction in the output transformer declines with distance from the power transformer. I find the most induction with the transformers oriented as in the picture in the previous post. It is clear that "perpendicular" has more than one orientation. Should really not have flunked that Classical Electrodynamics course when I wuzz a wee ladd.

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I see a lot of other amps with the transformers oriented as in the first of the two options above, all claiming low noise.

Input from you amp guys please?

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More progress – The power transformer has now been converted to “lay down”. Most of the hardware has been installed onto the chassis, still need to source a tone pot. Face plate from galvanised sheet. Still debating making a cover for the power transformer.

All the spaghetti inside.

The pre-amp valve socket’s mounting tabs are very soft, so I managed to use the mounting screws as chassis punches and removed most of the tabs’ material. The picture shows the new assembly with a washer (no space for same was available on the original tab) sitting skew. Will have to replace the socket.

OK, so maybe I can start on the turret board now?

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More, slow progress.

I made up a “socket clamp” to save the pre-amp socket with the sheared mounting ears, as such:

I decided it does not suit this build. Quite. Looks rough anyway. Suited to a later, home-made old vintage project, maybe. I managed to obtain a new socket from ToneTubes, and suitably modified the ears to accept modified washers for load spreading.

Much better!

Now to start on sorting out all those small bits which goes onto the turret board.

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Looking at the simple, clean beauty of the chassis as is, I decided to do what I tried to convince my self is not required. But it is. As I see it, this chassis will spend a lot of time upside down, while I try to destroy stuff on the “inside”. As such, it will lie on the power transformer, and the exposed wires will be in harm’s way. So, I sighed, dragged out scissors and thin cardstock, and proceeded to make a cover to protect the wires.

Not as good as a real bell, but it will do. Need a transformer that was wired to be installed this way.

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The wiring procedure has started - chaos in progress…

Heater wires done, I hope. Whole lotta (masochistic) Fun.

Rectifier socket all wired up. I hope.

The kit-supplied pilot light is crap. Other words come to mind, but this being a friendly family forum… The cheap plastic housing’s threads strip in the supplied nut, and the solder tabs are not DIY friendly, no way that I can easily attach two wires to each tab (Two? Yes, the tightly twisted 6.3 V leads from the power transformer, and then back again to the heaters.) Various plans to ease my way failed. I stripped my nut, and am now using a normal chest freezer indicator lamp. Sitting right next to the ON-OFF thingie, less wiring all round.

Still using the original lamp fitting, with dollops of loctite on it, in the hope that it will never loosen to more than a slight rattle fit in future. Long-term solution is a custom-turned fitting, maybe brass? Hmm. Maybe short term too. Yes, yes, the right way to do things.

warrenpridgeon

Now I want to add "build an amp" to my list of things to build, which already includes "build an electric guitar".
Looking good!

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I tried to do the input jack wiring. What a mess. This was not fun at all. Had to re-do a few times, and I am not happy with what I achieved. Too many wires in too little space. The design does not make sense to me, but what do I know. If you need two different input signal strengths, why not wire up two inputs separately, with different resistors?

Fitted in chassis, with wires trial-fitted in position:

What a struggle. No thanks. Some medicinal ethanol to calm my nerves, thank you!

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Perfecting my Masochistic tendencies: I just had to re-do the input sockets again. I goolged a bit, thought about this system, decided, what the heck, it is a bad idea, even if some people find it an elegant solution, but let’s try to get it neat (er). Just the right thing to do, eh?

It looks slightly better, I am sure one can clean it up some more. That poor 1M resistor has been on, off, bent, straightened, on, off, poor thing. Better stop now, I do not have a spare, and soon the legs will fatigue off. But this does not solve my idea of a star ground here, I shall have to take that off the turret board pin.

My measurements show that the input resistance does vary, 1Meg plus for high input, or 68 K for low input. With both jacks plugged, they are both over 1 Meg. As I understand it is supposed to work. ?

Also found some grounding ideas (Rob Robinette) for separating the pre and power circuit ground busses. Sort of. Will incorporate that as well.

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“Help! I need somebody! Help! Not just anybody. Help!...” Apparently these amps were popular back when this song made the charts. Probably inspired by a reluctant (Ch)amp.

Positive proof of the Principle of Entropy. Or, rather, Chaos begets Chaos. It has been whispered behind closed doors that there are people who enjoy this stuff. Not likely. Some wild stories about whole factories building stuff like this. Hmm. Unconfirmed rumours of rugged individuals who manages to, or tries to, scratch out a meager living building , fixing, working on these. Sure. I did not realise making a living from viable means is so difficult that people need to resort to this. Torture.

Not there yet, by a long shot. It gets worse by the wire. I think I have most of the turret board wires and components placed, some more wires to go to the sockets here and there, and I have altered the ground bus scheme. If it makes any difference. That big white block is the 470 Ohm resistor, why it needs to be that size, well? I have installed the 22 microFarad capacitor parallel to the 1.5 K resistor from the input jack – Pre-Amp ground (to apparently increase amp output). Note, that 1.5K resistor’s leads are too short to span the turret board anyway. More scope for dry joints. Invest in a bigger resistor.
The ground circuit will include two separate chassis (well, more, in fact, the input sockets earth too) ground points, at the power transformer for the high voltage center tap and the power amp side of things, which mixes with the pre-amp side of things through a yellow capacitor anyway, but the pre-amp side of things will ground to the chassis far away from all else, on the input socket side of things. They also act as extra earth points for this side of the circuit.

Speaking of which, I have re-measured the input resistance (“impedance”) across the input jacks, not across the earth and the lead to the valve (on the turret board side of things). According to Rob Robinette’s explanation of how this is supposed to be an elegant idea, it checks out perfectly to what he says. Still, ? If I need to plug two guitars, surely, there need only be a toggle switch adding/removing a resistor/capacitor from the one input, label this switch “High / Low”. I have seen that somewhere.
Grumble: No black wire for earth wiring in kit. Only thick wires supplied, where some thinner gauge would have helped where more than two thingabies plug into a turret pin. More colour codes would help too, to trace out the circuit’s, well, circuit.

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On to installing the 240V feed, via fuse and switch and so on. Fuse before switch, for safety.

Opened the covering to extract a piece of “LIVE”, and twisted the rest back into the cover, with some heat shrink and a layer of black tape to keep it all together.

The switch, pilot light. The “NEUTRAL” all soldered together, might be a good idea to use plugs here too, for easy disconnection and removal. Three layers of heat shrink over the joint. The 240 V cable is clamped to the chassis at the screw at the bottom centre of the picture. A simple loop clamp, should keep it safe from any tugs.

I separated the center tap earth and the transformer earth. Star washers onto chassis. Nyloc’s to help avoid vibration loosening.

The 240 V earth is installed at a third point, on a transformer mounting bolt too. Hiding away in this picture:

With this formality behind me, the next step is to install that turret board and try connect the wires. Seems like every time I touch this project it sprouts more wires…. I have read/seen better wiring on the internet, but most use thinner wires, as well as open (tinned?) wires for the earth runs, wrapped around the turrets. Hmm. Next time, definitely. This one is a concept evaluation for me, and I had to go with what was supplied. A “better” turret board layout can be done as well, to ease wiring the turret board (refer to Hoffman Amps).