Amp kit rebuild (edit - with fancy wood shell)

WezV

About 12 years ago i was looking to learn a bit more about amps and got a kit.  This was before the days of ampmaker so I had to import  from a company called STF electronics.   The website is long gone

It was a 5w champ style with added tone control and master volume.   

I built it, it worked  well and sounded nice.  but my build was quite messy, potentially dangerous and a little noisy so as soon as kids came along it got put away and forgotten about.

I found  it today, and i am much better at wiring neatly these days so time to rebuild it 

Thankfully i still have the instructions from the kit


paints peeling off in big chunks and surplus PT wires just taped up



and now for something really scary - a proper rats nest of wires... not sure why these never got trimmed back???





That's the starting point.  Its now dismantled ready for a much neater rebuild.   The wiring on the board is actually okay and the soldering is fine so i think it should go back together well


those pics above are an embarrassment, but it will be nice  to see it put back together properly.  and I plan on making a proper case for it - i think something fancy in solid wood will be nice 

Adam_MD

Looking forward to updates on this Wez I'm planning on having a go at an 18watt Marshall as soon as ampmaker gets his 18w kit back in stock.

paulnb57

Following with interest, I built a little Ampmaker a while back, neater than that though!

WezV

paulnb57 said:

Following with interest, I built a little Ampmaker a while back, neater than that though!

I don’t mind admitting not everything I have ever done has been perfect. 

I seem to remember rushing this with the intention of tidying up once I knew it worked... but once it worked I just never got around to it.  Until now.

anyway, its all dismantled now.  I put some primer on the chassis front yesterday and sprayed a coat of gold top gold this morning


The board:


The transformers

The circuit 

4114Effects

Bypass that first 1.5k Cathode resistor with a 22uf Capacitor and see how much more alive the amp becomes.

WezV

4114Effects said:

Bypass that first 1.5k Cathode resistor with a 22uf Capacitor and see how much more alive the amp becomes.

You guessed my first question- any simple improvements I can make to this circuit?

i guess noise levels will be improved just by improving the neatness of the wiring

also, what’s the best way to deal with the mass of unused wires on the PT?  Is cutting them short and heat shrinking the ends enough?

4114Effects

WezV said:

4114Effects said:

Bypass that first 1.5k Cathode resistor with a 22uf Capacitor and see how much more alive the amp becomes.

You guessed my first question- any simple improvements I can make to this circuit?

i guess noise levels will be improved just by improving the neatness of the wiring

also, what’s the best way to deal with the mass of unused wires on the PT?  Is cutting them short and heat shrinking the ends enough?

Try that one first. 

Also a switch to change the negative feedback (22k resistor from the PT secondary) is usually worthwhile. Use the switch to either change it to a higher value or remove it completely. 

Heat shrinking is OK, or alternatively you can run them through the hole into the chassis and terminate them in a suitable terminal block that's mounted to the chassis - nice and neat then. 

WezV

cool, thanks for that.  First step will be to enlarge the chassis holes so i can get all the wires through easily, then i will mount a terminal block directly underneath for all those spare wires.  that will be half the rats nest gone

normula1

Bundle the excess wires neatly and use a couple of cable ties to stop them flapping about inside the chassis.

WezV

The plan is to remove almost all excess wire for neatness this time

normula1

4114Effects said:

Also a switch to change the negative feedback (22k resistor from the PT secondary) is usually worthwhile. Use the switch to either change it to a higher value or remove it completely. 

I've just had a trawl through my schematics library and one of the mods suggested was to add a 100k pot in series with the 22k to give more control over the negative feedback so not a million miles from @4114Effects' suggestion.

You can also have a play with different (or even remove) the 6v6 bias resistor bypass capacitor(s). 50uF seems to be quite common.

WezV

going back together



and rewired all the PT  section.  All spare wires have been cut short, heat shrinked and held out the way in the block.



i plugged it in at this stage with the tubes in.  The purple jewel light works and the valves are glowing

Its ready for the board to go back in

RiftAmps

4114Effects said:

Bypass that first 1.5k Cathode resistor with a 22uf Capacitor and see how much more alive the amp becomes.

Noooo don’t do that! Ruins the touch response of the amp. Probably my least favourite ‘mod’ on a 5F1

If you are going to do it, have it on a SPST switch for a ‘boost’ mode

ICBM

RiftAmps said:

4114Effects said:

Bypass that first 1.5k Cathode resistor with a 22uf Capacitor and see how much more alive the amp becomes.

Noooo don’t do that! Ruins the touch response of the amp. Probably my least favourite ‘mod’ on a 5F1

If you are going to do it, have it on a SPST switch for a ‘boost’ mode

Interestingly my original '59 5F1 had it as stock. I know a lot don't.

That amp had very little touch response too - although I think a lot of that is down to the speaker, since it was *much* better through a 4-ohm-wired Marshall 4x12" . Basically the 8" makes it almost totally a one-sound amp whatever you put through it.

4114Effects

RiftAmps said:

4114Effects said:

Bypass that first 1.5k Cathode resistor with a 22uf Capacitor and see how much more alive the amp becomes.

Noooo don’t do that! Ruins the touch response of the amp. Probably my least favourite ‘mod’ on a 5F1

If you are going to do it, have it on a SPST switch for a ‘boost’ mode

Interesting. I almost always prefer it. The extra gain makes it more sensitive to guitar volume changes. Each to their own :-) 

WezV

I am going to leave it stock for now, but may add a switch for it later

this thread will move onto the cab build shortly.  I fancy something in solid wood.  I have some lightly flamed olive ash on the way that will work well although I may mix it up with some walnut.  I just picked up a dovetail jig and like the idea of contrasting woods in visible dovetails

Chalky

4114Effects said:

RiftAmps said:

4114Effects said:

Bypass that first 1.5k Cathode resistor with a 22uf Capacitor and see how much more alive the amp becomes.

Noooo don’t do that! Ruins the touch response of the amp. Probably my least favourite ‘mod’ on a 5F1

If you are going to do it, have it on a SPST switch for a ‘boost’ mode

Interesting. I almost always prefer it. The extra gain makes it more sensitive to guitar volume changes. Each to their own :-) 

I'm with @RiftAmps on this one, but having a switch that adds the cap and cuts the negative feedback loop at the same time is going to give the amp two quite different settings.

WezV

Its all back together an looking a lot neater - think i could improve  on this if i did another with fresh wire - but this will do



I plugged it in to test and it worked, but was really dull.  I spent a minute or two fiddling with the controls to see if they helped.  They didn't

Then i realised the i was playing the guitar  on the neck pickup with the tone all the way down.   duh.




It sounds great and all the controls work as they should so I am not going to mess around with the circuit just yet, althoug a switch that gives two voicings is pretty tempting 

Lets move onto the box.   My main considerations at this point are size and ventilation...I assume i don;t want to make it too small

WezV

oh, and noise.   It used to be a noisy amp.   Its now pretty quiet, certainly a lot quieter than my selmer

Nomad

It's been a while since I read much on wiring in valve amps, but the following sounds familiar with regard to keeping noise down...

Maintain the twist in heater wires for as long as possible, run them close to the chassis, and don't span one of the wires across the valve base (come in from each side).

Avoid having signal and HT wires running alongside the heater wires - cross over those at 90°.

At the bottom valve, the heater wires to the left look like they could have a bit more twist, and it looks like there are signal or HT wires running alongside for some of the way. If you try raising them, or routing them differently, you might be able to reduce the noise further. Easy enough to check the effect by moving them around while the amp is on (with the aid of a couple of bits of stick or the like, if you want to keep your fingers clear).

WezV

tbh its quiet enough that i won;t worry about it now