Some newbie questions

[Knars]

Hey everybody! I've been lurking around this forum for a few weeks, and finally decided to start building my own 18 watt.
I am a guitar builder, made a few pedals and extremely simple amps (like the noisy cricket and ruby) So I have a little experience with electronics, but not a lot (mostly following pre-made layouts and schematics).
I'm amazed by the amount of information that can be found in this forum, but honestly, for a newbie it gets to be a little intimidating and hard to follow.

So I got a few questions, sorry if its already been discussed, but I couldn't find the answers.

Maybe the most important is: Which variant of the 18watt should I start with? I want something simple but functional (maybe a super lite?) and based on layouts and schematics that have been proven to work.

Second question is about transformers, I live in south-america and the only source of transformers that I could find are vintage amp repair shops, that actually make their own transformers. So without talking about brands is there any way to know if a transformer is good or not? (maybe resistance, or materials? i really have no idea about transformers)

My last question is less important, but I'm very curious to know what speaker you guys use on your amps and why (I noticed that greenbacks seem to be the most popular choice).

Sorry for the long post, and if I'm repeating questions that have already been asked.
And thanks for all the great info!

[Daviedawg]

Hi Knars. Welcome.

A lot of us started from the same position as you. This is indeed a great place full of info.

My advice on the transformer issue is to find the specs from one of the big suppliers and see if you can find local suppliers for that. You should find that on the Mouser site for example. Also since they ship all over, they may be a cost effective supplier. I can't recall what source they use but they do sell an 18 watt set I think. If not look on the Hammond sites.

Speakers are very much a personal choice which makes it one of the hardest to advise on, being an expensive variable. Greenbacks are indeed popular but not the only good choice. Reading up on this forum will help you to see what choices there are. It is now possible to get good speakers with similar characteristics at better prices. But in the end your location may dictate what you get.

Which version? The Lite iiB is a good choice which has been built a lot and therefore there is a lot of feedback on it. It will give you the true 18 watt tone, which you can modify easily later on if you wish, based on all the info here. The TMB is a variation on the original, is not so straightforward to build as the Lite but is a great amp with a wide range.

Let us know how you progress.

Dd

[colossal]

If you are looking for vintage transformers, try to keep your eye out for Radiospares. They were the supplier for the original Marshall 1974 amps. That would be a rare find, but you never know. You will want a power transformer capable of 290-0-290VAC on the secondary at about 120-150mA, a 6.3-0VAC 2A filament winding for an EZ81 rectifier (only takes about 1A), and a 3.15-0-3.15 filament winding for your preamp and power tubes. The rectified DC voltage should be about 345VDC. The output transformer should be an interleaved 8kΩ plate-to-plate primary and 4/8/16Ω secondaries, M6 steel.

As for which model, I agree with Davie: you can't go wrong with a Lite IIb circuit. An incredibly rich sounding amp. Very touch sensitive and expressive. I am also partial to the Greenback.

[mehfuzhoss]

Hello,

I have an hammond 290paz for lite iib. It has 6.3v 3amp. Can i use this to power all the tubes - ez81 12ax7 and el84s? It doesnt have 3.15v.?

Thanks

[geoff 1965]

hello,
no the 3 amp supply is'nt sufficient for all the tubes,2 el84's & 2 12ax7's will draw just over 2 amps current and adding the ez81 will take it over 3 amps. you'll need to use the 2 amp supply for the ez81 "the yellow and white wires" have a look at the specs added.

290PAZ.pdf

[mehfuzhoss]

Ok. Now for 2 x12ax7, 2 x el84 wiring; i wil wire it so that -
6.3v green wire connects with pin 4 and 5 joined together for each of the tubes
And the greenyellow (center tap) goes to pin 9 of each of the tubes.
Is green yellow 0v?
Am i wiring it correctly?

Thanks.

[geoff 1965]

no the green/yellow and red/yellow are your centre taps and are grounded,which layout & schematic are you using?
have a look at Josh's lite2 b"ish" layout in the downloads,it shows you clearly the wiring to the ez81 and the other tubes using the 3 amp supply.

[mehfuzhoss]

Im using josh's layout. I wired up the ez81 with white yellow 6.3v and grounded the CT. For rest of the tubes i will use the two green taps. This is where i got confused are these 3.15v each or 6.3v each?
In josh's layout shows the PT has 3.15 each but mine is a hammond 290paz. Will there be any change in the wiring?

Thanks.

[JMPGuitars]

Im using josh's layout. I wired up the ez81 with white yellow 6.3v and grounded the CT. For rest of the tubes i will use the two green taps. This is where i got confused are these 3.15v each or 6.3v each?
In josh's layout shows the PT has 3.15 each but mine is a hammond 290paz. Will there be any change in the wiring?

Thanks.

Just to be clear, the center tap you grounded is the green/yellow wire, correct? The yellow/black wire doesn't get connected to anything. You can heatshrink tube the end of it to be extra safe after cutting off any exposed wire.

The 6.3VCT or 3.15 + 3.15 heater wires are different ways of writing the same thing. You can follow the schematic/layout as normal.

Also note that in my layout I used two different color greens for the heaters. This is because you want to connect them consistently across the tubes. The first connection from the PT is arbitrary, and everything after that should match.

Thanks,
Josh

[mehfuzhoss]

Thanks I will finish up the amp in the next week or so still waiting for tubes to arrive. I will post how it went. thank you for the nice layout.

[mehfuzhoss]

hello,
i finished up wiring the lite ii as per josh's layout. i am using a hammond 290paz.
- when i do a continuity test, the heater wire 4,5 for the el84 seems to be grounded. is this normal?
- the 290paz has a center tap for 6.3v. it is the green-yellow wire and it is grounded.

thank you.

[JMPGuitars]

That's normal when the amp is off. Don't do a continuity test with it on.

[mehfuzhoss]

The amp is working. Awesome. Thanks. I have a pilot light 115 ac. how should i wire it?

Thanks

[geoff 1965]

can you add some pics of the wiring from the mains input to your PT and the power and standby switches?

[mehfuzhoss]

Pics posted.

[mehfuzhoss]

When i plug in the ac to the wall the lower light comes on. And then i switch the pw and then standby the amp works as usual but the pilot light shuts off. Did i wire it wrong? Am new to amp building.

Thank you for help.

[JMPGuitars]

You definitely wired it wrong.

With the AC plugged in, and the amp off, if the light is coming on, then it's connected directly to the AC. It needs to be wired so that it's connected only when the amp is on.

[colossal]

When i plug in the ac to the wall the lower light comes on. And then i switch the pw and then standby the amp works as usual but the pilot light shuts off. Did i wire it wrong? Am new to amp building.

Thank you for help.

Mehfuzhoss,

When you have an issue that you would like help with, I will ask you to please start a NEW thread, or pick up on one of your own (such as this one: viewtopic.php?f=4&t=25478). Adding on to someone else's thread is considered bad forum etiquette and serves to confuse existing conversation and discussion coming from fellow members with the original poster.

Thank you

[mehfuzhoss]

Thank you guyz for your help. I didn't realize it was some one else's topic. However, my amp bug bitten time is over. you guyz have fun now ...cheerzz