Getting a head of myself - Marshall 2204 JCM800 inspired build

[kuDo]

Well, I am pleased to say that all drilling went well. The same goes for the use of the hole punch, that I never had used before. All the big holes turned out beautiful and are perfect for the tube sockets I ordered earlier.

All parts are now attached to the chassis except for the potentiometer on the front (as is visible in the attached pictures). Those I will do later on in the prosses.

I think that the next step will be wiring up all the heater supplies.

[kuDo]

Creeping ahead slowly.

Today I have been adding the heater wiring for the 3 x 12ax7 tubes, 1 x 12au7 and 2 x el34 power tubes.
I must say that it was a lot harder then I thought. I always see those nice neatly twisted wirings on the forum, but I now have an idea of how much effort it must have taken.

If have tried to respect al the “rules” that exists concerning this task. Keep the wires tightly twisted, as close to the tube sockets as possible. Keep the wires tucked away in the chassis corners . Supply the various stages in the right order. Heavy consumers first and the most sensitive last. To name just a few.

It didn’t become computer graphics super straight, but I am pleased with how it turned out te be.

I think I deserved a beer now

[romberg]

Looks nice! Those filament wires are never fun to deal with. To cancel hum, they don't really need to be twisted. The hum cancelling happens as long as the wires are parallel. Twisting them is just a nice way to achieve that . Some amps (trainwrecks for example) just use a very loose twist (few turns).

Since it is many orders of magnitue less fun to fix fillament wiring after other wiring is done than it was in the first place, I like to wire up the PT next. If you wire in the mains IEC, fuse, power switch and pilot light you can test out the whole fillament string now while it is easy to fix if something is not right. I simply use some wire nuts to cap off the high voltage windings. Then temprarily ground the HT center tap and fillament center tap (if it has one).

Then you can power up the circuit (use a light bulb limiter just in case) and see if the pilot comes on and you get fillament voltage at the tube sockets. If that looks good you can even plug in some tubes and watch them glow. Then you can be pretty sure the fillament string wont have to be fixed later one .

Mike

[kuDo]

Looks nice! Those filament wires are never fun to deal with. To cancel hum, they don't really need to be twisted. The hum cancelling happens as long as the wires are parallel. Twisting them is just a nice way to achieve that . Some amps (trainwrecks for example) just use a very loose twist (few turns).

Since it is many orders of magnitue less fun to fix fillament wiring after other wiring is done than it was in the first place, I like to wire up the PT next. If you wire in the mains IEC, fuse, power switch and pilot light you can test out the whole fillament string now while it is easy to fix if something is not right. I simply use some wire nuts to cap off the high voltage windings. Then temprarily ground the HT center tap and fillament center tap (if it has one).

Then you can power up the circuit (use a light bulb limiter just in case) and see if the pilot comes on and you get fillament voltage at the tube sockets. If that looks good you can even plug in some tubes and watch them glow. Then you can be pretty sure the fillament string wont have to be fixed later one .

Mike

Hello Mike,

Thanks so much for the advice! Today I did wire in the mains IEC, power switch, fuse and pilot light just like you said.

Can I power up a power transformer while the secondary isn’t completely wired up yet? Does the primary not need to see some resistance there? Or is that only necessary on the output transformer?

Greetings,
Douwe

[romberg]

Today I did wire in the mains IEC, power switch, fuse and pilot light just like you said.

Can I power up a power transformer while the secondary isn’t completely wired up yet? Does the primary not need to see some resistance there? Or is that only necessary on the output transformer?

No need to have a load on the high voltage secondary. You will have a load on the low voltage secondary (the filament winding is a secondary winding). The high voltage windings need to be insulated so they don't short or electrocute anyone . So, I cap them with wire nuts.

When I do this the IEC earth ground is allready wired to the chassis. So, I do temporarily connect the hight voltage center tap do the chassis. This may not be necessary and it could probably be capped. I just like to keep the other high voltage windings with an earth reference while doing this. You could use a transformer bolt or something to ground it.

Then you can test out the primary wiring and filament wiring. Just do treat it like a first start and use a current limiter and make sure the high voltage windings are insulated.

Mike

P.S. Yes the load *is* important on the output transormer. There the secondary side (the speaker output) must be connected to a load. Here we are talking about the power transformer.

[kuDo]

I’ll make sure to take these pointers into consideration! Thanks again Mike!

[kuDo]

...light it up!

The first test was successful!

Well, that’s not entirely true. I made two mistakes, and one of them saved my wallet.

So I wired up the heater supplies, but managed to do it with the 345 volts winding. Oops! Super dumb!

But the thing that saved me, was my second mistake. I had put the pilot light in series in the primary loop instead of parallel over it.
As it turned out to be, my pilot light became a voltage devider with the primary coil of the PT. so the biggest part of the 240 Volts was on the lightbulp en just a small portion on the primary. That meant that on the secondary winding of the high tention coil, there was only 50 Volts and I was so happy I didn’t burn this winding.

Bottom line is that I should pay better attention to my drawings, and not listen to a podcast of some sorts while doing something important. I can’t do two things at ones.

Furthermore I was so excited to see the results of months of preparation. So I proceeded while not having a current limiter lightbulp and a variac in place.

So, slow and steady wins the race.

In the end I figured out what I had done wrong and corrected my mistakes.
This all resulted in a beautiful picture.
Hope you enjoy!

[romberg]

So I wired up the heater supplies, but managed to do it with the 345 volts winding. Oops! Super dumb!

But the thing that saved me, was my second mistake. I had put the pilot light in series in the primary loop instead of parallel over it.
As it turned out to be, my pilot light became a voltage devider with the primary coil of the PT. so the biggest part of the 240 Volts was on the lightbulp en just a small portion on the primary.

Looks like you ended up using a light bulb current limiter by accident! This is exactly what one is suppose to do. A filament in series with the AC mains hot lead which will light up (and increase it's internal resistance) when large amounts of current are pulled through it.

I'm glad it worked out in the end! Looks cool and it is always nice to have this little reward after a long time planning a build.

Mike

P.S. Did your pilot light survive the experience? Or did it give it's life up for the PT?

[ChopSauce]

Congrats! We all enjoy happy endings ...
(I suppose)

Nice pic, by the way ...

[kuDo]

Looks like you ended up using a light bulb current limiter by accident! This is exactly what one is suppose to do. A filament in series with the AC mains hot lead which will light up (and increase it's internal resistance) when large amounts of current are pulled through it.

I'm glad it worked out in the end! Looks cool and it is always nice to have this little reward after a long time planning a build.

Mike

P.S. Did your pilot light survive the experience? Or did it give it's life up for the PT?

Hi Mike,

It was a bizarre coincidence, but it great non the less

The pilot light was rated 260 volts and was suppose to be wired in such a way that it normally receives 240 Volts of main Voltage. So it was no problem and it survived the incident.

(The brave little pilot light would have given his everything for the greater good )

[kuDo]

Congrats! We all enjoy happy endings ...
(I suppose)

Nice pic, by the way ...

Merci beaucoup ChopSauce,

I know I always enjoy those

There is something magic about those glowing filaments.

[Reeltarded]

I have to say you are the most fortunate and also that your work looks excellent!

[kuDo]

I have to say you are the most fortunate and also that your work looks excellent!

Thanks a lot, Reeltarded.

I have to say I did some pretty poor soldering today in my power supply section.
It’s partly because I chose to use real fat copper wire as jumpers and rails. Everytime when I have to solder something to one of the turrets that has one of those rails connected, it’s really difficult to get enough heat in the turret to let the solder flow.
Maybe I am not using the right soldering iron, I don’t know.

There is definitely something to learn there.
Today I discovered that the capacitors I had planned for the power supply won’t fit on the board height wise.
So I had to come up with an alternative plan. Luckily, I had a little room left for them next to the psu board. Not the prettiest solution in the world, but it works.

I had this amp al planned out, but ones you start building there are all sorts of things that I didn’t anticipate. I wanted my first amp to be perfect, but that ship has sailed I am affraid. Next time There are already a couple of things I would do differently.

It’s the journey that counts

[Reeltarded]

if everything is tnned well the flow should be pretty easy and instantaneous-ish

[kuDo]

Ones it flows everything is oke.

I put tin on the twisted wire. Bend the wire around the turret. Hold the iron against the turret en the tinned wire apply a little solder to let the heat transfer. Then I push the solder against the wire and the turret, but it does start to flow. As if my iron does work, but I know it does.

Normaly I solder at 360 degrees Celcius. But when it doesn’t work I sometimes go as high as 400 degrees. So weird.