My first build: 18w TMB

[guitardude57]

How is it coming along?

Most folks wire up the board before installing onto chassis. Easier to get it wired out of the chassis. All leads to pots and tubes are done before installing.

It is a good idea to mount the transformers first, before anything else too.
Getting larger wires in first helps the wiring jungle to be more manageable.

If you look at Metropolis Amps website, they have a Marshall build guide that is quite nice for beginners. Also has a section on biasing, and a little troubleshooting.
They also give a clue how long wires off the board should be, so you have little to no waste cutting them to their destination.

Here is their build guide for a jtm 45 that would be a good read for you.

http://www.metroamp.com/downloads/JTM_45_KIT_V2.1.pdf

I wouldn't worry about jacketing all the component leads on the board.
Added work, not necessary.

Since everything has it's place, there is not much chance of anything shorting together.

There are times when you have a tight spaced lead crossover, where it is a good idea to do this to prevent a short to ground or another component flying nearby.

Good luck, and help is on this fine forum when you need it.

[labb]

I would suggest that you go over to Paul Ruby's site and read through his "initial start up" guide. Can save you a lot of heart ache. I think it is www.paulrubyamps.com also a simple current limiter consisting of a light bulb wired in series with the incoming power is a very hand device to have. If you really want to learn about what makes a tube amp tick, there are several good articles out there. AX84 has a pretty good one..You are correct in that you can not learn what makes a tube amp by building one from a pre-designed kit which is mostly just color by the numbers..All of the component selection has been done for you, the lay out is proven so you don't have to worry much about lead dressing, etc. Good luck with you amp. I think that you will find that the 18 watt Marshall really sounds good..Also, don't get discouraged if you have some problems on initial start up..Most do.

[Structo]

I would find a piece of sheet metal and make an adapter to fit your power transformer.
THe wood there just looks terrible.

Cut the sheet metal so you can mount it on the farthest outside bolt holes there then cut the proper sized opening and drill for the transformer bolt holes.

The rest looks very good for a beginner.

Another tip is when you are soldering to the tube pins, be sure to have some old junk tubes in the sockets beforehand.
This will prevent solder from flowing down into the pin. If that happens you will have difficulty installing the tubes later on.
I had that happen one time and it was very hard to get it so the tube could plug in.

Oh, and putting the tubing on the component leads will not shield anything.
It won't hurt anything either but is unnecessary.

[Dano]

Structo said

Another tip is when you are soldering to the tube pins, be sure to have some old junk tubes in the sockets beforehand.
This will prevent solder from flowing down into the pin. If that happens you will have difficulty installing the tubes later on.
I had that happen one time and it was very hard to get it so the tube could plug in.

+1

I had this happen on my Rocket build while soldering the heater wires on one of the power tube sockets. What a total pain since I discovered it when putting tubes in it before initial start up. I did manage to get it cleaned out using twisted braided copper ribbon and a few strategic curse words. One of these days I'll replace that socket since it got a bit ugly, but it does work at least. Live and learn

[Mono243]

Thanks for the tips guys, they are all going in the memory bank
Yeah I agree, the wood look really bad, but I wanted to get building and try it out as soon as possible! I will sort out something in sheet metal in due course, but for not, it'll hold.

I think you are right about the tubing on the turretboard, if was more effort than it was worth

[Phil_S]

Ok, just a couple of other things you might want to tuck away for the next time.

Regarding wood -- wood is conductive because of the moisture content, so be careful where you use it.

Regarding how you are wrapping wire on turrets and some other places make a C shaped bend around the turret and don't close it up. I see places where you have closed the loop and wrapped the wire back on itself. If you ever need to service it, with what you did, you'll have no choice but to snip. With a C bend, desoldering is possible and the C bend should be adequate to make the required solid physical connection. If you really have trouble, wrap around the turret, but don't twist back on the wire itself.

Good job for a first timer. There is lots to learn, both electronics knowledge and to build hand/eye skills.

[Mono243]

Thanks

I have three questions that I can't seem to answer for myself:

1. I sent a 0v and 6.3v tap to pins 4 and 5 of the rectifier tube respectively, as indicated in the Ceriatone 18w TMB layout, whereas the Trinity layout which I had been following said it should be 3.5v to each of these pins... Should I change the wiring or are these the same thing effectively??

2. I cannot understand the wiring of the top row of lugs on the OT. They are, from left to right, An1 CT An2. In the Ceriatone layout, two of these are meant to go to pin 7 of the power tubes and one also to the can-cap.... but which is which?

3. There is also a lug marked CT between the two 3.15v lugs and between the two 290v lugs. I have understood this to be 0v and wired it as such, is this correct?

Any help appreciated

[CapnCrunch]

Thanks


3. There is also a lug marked CT between the two 3.15v lugs and between the two 290v lugs. I have understood this to be 0v and wired it as such, is this correct?

Any help appreciated

CT typically stands for center tap and typically goes to a chassis ground. Some Fender layouts send the high voltage CT to the ground end of a power supply cap, but it's the same difference, it goes to ground. If when you say "0v" you mean you routed your CT's to ground then you are good. This is true of the center tap for both your heaters and high voltage secondary.

Have you run this stuff by the folks over at the 18Watt forum? I can understand why you would want to post here at the Amp Garage, the friendliest, most knowledgable, and helpful forum I have run into. However, you may also want to try the 18Watt forum, this circuit is their bailiwick.

[Mono243]

Yep, I just went over there. I know it's a crappy thing to do online but I have asked in both places, really don't want to kill myself over something as sillly as bad PT wiring

[RevD]

One other little tidbit that I bet nearly every builder has done before.. Make sure and leave the leads going from your OT to your power tubes long enough where you can reverse them (from one tube to the other) if need be. You have a 50% chance of getting this right and you'll need to reverse them because of the squeal you'll get if they are not going to the right tube. If it squeals thats the first thing I do is reverse the leads, and usually unless its a really high gain amp it will correct things. If not, then its a whole other troubleshooting session, usually lead dress or wires that need to be moved to get the circuit to settle down. Just thought I'd mention it, to often people cut the OT wires to the tube the exact length and then they're wrong and they have to splice wire on to reverse them.
As mentioned sleeves over the components, not worth the trouble and its not a source of noise unless another wire is crossing over it and to close to something sensitive, but this has already been mentioned. Overall looks good (and on the transformer deal with the wood which I agree doesn't look good, even some fender washers (its what they're called, large diameter washers with a small hole in the middle) in each corner would hold that thing in better and look nicer although a complete bracket would be the ultimate solution.l Good work.

Regards,

RD

[Richie]

I wouldn't worry about jacketing all the component leads on the board.
Added work, not necessary.

Probably not, but in combo amps, componets can vibrate and make buzz noises,that come through the amp on certian notes. In some amps you see they glue caps etc.. to keep this from happening. Sometimes the added dampining of the long leads,can keep the componet from vibrating.

So, nothing wrong with using it, and it does kind of make it look neat. Does take more time.

As for the PT, the 6.3/0 is for the 6 volt 6CA4 recto tube the 3.15 [0-CT] 3.15 is for the heaters.

Quite a few people make 18 watt trannys, so it might be good to look at the one you have, to make sure.And not try to compare it to another.But the info on the 18 watt site should have that in the downloads section.

[Cliff Schecht]

...valve retainers...

HA!

[Mono243]

Is it because that is the only time I refer to them as "valves?"
I'm in the UK! I was calling them "tubes" for your benefit!!

Anyway, I've just finished checking the wiring. Going to do it one more time before I fire her up tomorrow.

Quick question: is it OK to use a 2-Amp Slo-blo fuse with the UK mains voltage of 240v, or should I get a 1-Amp one...?