Lawrys 8 Watt Valve Amp with Tremolo

[lawry]

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.

[lawry]

This is what mine looks like in an old Behringer Thunderbird box.

[lawry]

Oops. Forgot to attach the pics. Git!

[wokkaboy]

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

[kells80aus]

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

PK

[WeirdBits]

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. **

[Gavin1393]

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!!

[keloooe]

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

[lawry]

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.

[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.