Lawrys 8 Watt Valve Amp with Tremolo

Seeing how the interest in this is getting a few posts on the cigar box guitar page I thought I might give it it's own thread to keep things together and easier to find.

I have reported the schematic and layout again for convenience. Some things to note...
The preamp tube I used was a 12AT7 because I wanted more 'clean' range in the volume. You can use a 12AX7 if you want more drive/distortion.
The 6BM8 output tubes contain a triode and a pentode. An equivalent is a 6F3P. You can buy these on eBay for $10-$15.
You can use a 5Y3GT tube rectifier like I did or use 1N4007 diodes. I like the sag I get with a tube rectifier. Your choice.
The transformers I used are made by ClassicTone and I bought them here http://store.triodestore.com/index.html in the good 'ol US of A. Still cheaper than OZ even with freight.
I built amp into an old Behringer 15 Watt combo amp. It was much cheaper than building one and buying a speaker. And I have to say that the speaker is surprisingly good!
I recommend putting a 270k 1Watt resistor across the 22uF 450V power supply capacitor for safety. Scott very astutely noticed that I had written 400V on the layout diagram. 450V is better.

If you build this be very careful. There will be about 300V humming around in there and that can kill you if you are complacent. Just be careful.
Otherwise have fun. As I mentioned elsewhere, this little beastie keeps up with a guitarist mate's Vox AC15.
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This is what mine looks like in an old Behringer Thunderbird box.

Oops. Forgot to attach the pics. Git!
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well done Lozza, you certainly have Pest and maybe Gavmiester keen to build one.
I might consider one down the track when I'm more confident with electronics.
Do the tubes need much bias adjustment once its built ?
I had a tube head and needed a specialist to tweak new tubes

really need it as a PDF. Not sure I can print these pics effectively. :)

PK

Those ClassicTone transformers look very reasonable, compared to Hammonds etc. *

Pest, these are the ones you need: ClassicTone 40-18027 Power Transformer and 40-18045 Output Transformer. **

Loving this thread, and Wok's the Gavmeister has already ordered the tubes! No turning back now!

..and <click> on Scott's links.....transformers on order too! Pest, you may need to save up for these $167 US!!

Hehehehehehe.... Time to have some fun with this thing now that Lozza got me into it!
Cheers for the links Scott!

Damn. Posted an update on the wrong thread after setting up this one specifically. So here it is copied and pasted with extra info.

Not behind Gav for long Woks. You should be head of the leader board before the weekend's done!
Gav. The Lamington is a 15 Watt valve amp designed by Grant Willis (from Sydney, I think) and built on a lamington baking tray. I've made a couple for mates and they're damn good!
OK. In order to see how I put the Knee Trembler together I took the chassis out and took a few pics (I called it the Knee Trembler because it has tremolo in it).
As you can see, there's not much room in there but you don't have to build one that tightly.

And here are the answers.
@Wokka. No. No re-biasing is required. If you need new tubes, just pop 'me in. All good.
@Weirdy. You're right, Scott. The Transformers are expensive but that goes with the territory. And you are also right about the Hammonds. Good trannies but you pay for them.
@Kells. Paul, if you (or anyone) wants to PM me your email address I am happy to email you a PDF of the schematic and layout.

Building these things is a bit like building a kit guitar. They're a bit cheaper than an off-the-shelf item but the satisfaction is priceless.
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Wokka wants to know if the tremolo modulates the volume.
Yes it does. It modulates the 'ground' reference of the two output pentodes thereby causing the amplitude to vary.

ok back to the correct thread. Think I've almost caught up to Gavmiesters posts !
Good news on the re-biasing.
Might have a crack at one of these amps Loz, might hunt down a cheap box/speaker that has the amp components not working

Good Gravy, this forum just gets more & more interesting . . .
Some clever dudes out there :D

Loz, I'm guessing the bottom middle circle is the output and the circle with f/s on it is the foot switch jack?
And what is on the ends of the red wire with "active" marked next to it?

Hey Pest.
You are correct. The 'circle' is the output jack and the F/S is for a foot switch to turn on/off the tremolo. Without a foot switch the tremolo is on all the time so you have to turn the Depth knob down to stop it.
The wire marked 'active' is the bitey part of the incoming mains power. That is, the Active wire containing 240 volts AC that goes to the fuse F1. In AC you have Active and Neutral.

Parts have arrived!!!!

Lawry, any chance of you sending me a PDF to gavmeister@pitbullguitars.com? Thanks mate!

@ Lawry Looks like a pretty cool little design for a Valve guitar amp, I'm going to be ordering some new bits and pieces for my Soldano amp this coming Tuesday, going to replace all the existing pots with some new CTS pots.

Quote:

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Originally Posted by lawry

Wokka wants to know if the tremolo modulates the volume.
Yes it does. It modulates the 'ground' reference of the two output pentodes thereby causing the amplitude to vary.

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I know all of those words, but when you put them together like that I'm lost :(

I’m finally going to get around to building this….it might be considered vintage given how long it’s taken…the joys of retirement!

Attachment 45162

Good luck!

Here's a suggestion for a mod to the original design, why not add a switch that allows you to switch between a Tube Rectifier and 1N4007 silicon power diodes? that way you can choose between the two.