36 Watt Lite

[JTone]

Does anyone have a design for a 36 Watt Lite (with just volume and tone controls)? You know, an amp to fit into a smaller cab.
Thanks.

[phsyconoodler]

Same as the 18 watt lite.Just the same filtering and two more power tubes as the 18 watt.And of course the bigger PT and OT.

[zaphod_phil]

And a bigger rectifier tube, rather than the EZ81. But you're right. Basically, it's just a cut and paste of a 36W power section, (including the power supply) onto any of the Lite preamps. It's been done a few times.

[wiseowl]

I've just built said amp, and very nice it is too. Will have to post some pics when I get time.

Basically I took the pre-amp design from the 18 Lite2b in the downloads section and connected it to the power section of the 36 watt design from the downloads section.

I don't have a drawing but it's simply the 18 watt pre-amp as far as the 10n capacitor connected to the 22n capacitor on pin 2 of V3 of the 36 watter.

If you need more info I'll cobble together a schematic for you.

Martin

[menix]

Wiseowl, would you be willing to still cobble together a drawing and perhaps post some build pics? Lately I find myself wishing my LiteIIb amps had a bit more volume and increased headroom. Strangely enough, this does not seem to be a popular request, so the info out here is limited. Any help would be appreciated!

[zaphod_phil]

The difference is very small. You can just cut n' paste the drawing of a 36W power section onto a Lite IIb preamp + PI drawing.

Check out the clips and discussions from this thread http://www.18watt.com/modules.php?name= ... ic&p=21174

[Ben32]

I built one of these last year and use it as my main gigging amp. Very happy with it and it sounds great, although it does suffer from quite a bit of HF/radio interferance!

Here's a link to the schematic i used.

http://i1227.photobucket.com/albums/ee4 ... 6wlite.jpg

Hope it helps!

[menix]

Ah, that is perfect! Thank you. This will be my first pass at a point to point amp. I've built a few of Terry's PCBs. I will be going slowly!

[zaphod_phil]

You could easily build this using a Baby Will PCB for the preamp and PI sections. And just build the power section off board. If you look closely, you will see the 36W power stage is actually just two 18W power amps in parallel, going into the same OT. So you could even build the whole Baby Will PCB and just add the one extra 18W push-pull section off board.

The other nice thing about this power amp design is that you can pull one pair of tubes out and run it as an 18W when you want. You just need to run a 16 ohm speaker load on the 8 oh output tap, or an 8 ohm speaker load on the 4 ohm output to correct the load impedance for a single pair of EL84s.

Here's a link to the schematic i used.

http://i1227.photobucket.com/albums/ee4 ... 6wlite.jpg

Hope it helps!

I would love to use this schematic in the 36W Downloads section, once this site has been rebuilt and is fully working again. Would you be OK with that?

[Gary]

re pulling two el84s to get 18 watts...... how would you set up the four sockets from the point of view of bias resistors? e.g there's a 150r resistor for the push side and the same again for the pull side in the schematic just referenced.

cheers

[zaphod_phil]

there's a 150r resistor for the push side and the same again for the pull side in the schematic just referenced

Oh darn - I thought I had checked the schematic, but I misread that part. Well spotted, Gary! OK, that 36W power amp won't allow you to pull a a pair of EL84s. Nor can you use the power section of a Baby Will PCB this way.

The better way is to tie the EL84 cathodes into push-pull pairs like they would be in a regular 18W power stage. So like I said before, you in effect have two 18W power stages tied in parallel.

[Ben32]

Here's a link to the schematic i used.

http://i1227.photobucket.com/albums/ee4 ... 6wlite.jpg

Hope it helps!

I would love to use this schematic in the 36W Downloads section, once this site has been rebuilt and is fully working again. Would you be OK with that?

Yes Phil, feel free. It's literally copied/pasted from a couple of schems in the download section.

[Gary]

on the tube pulling question....
my 2x el84 blackheart bh15 amp uses separate 250r resistors and 100uf bypass caps for each valve. Presumably this is another option on a four hole amp. But it begs the question - why design it this way if you can do it with fewer parts? Is there a tonal difference depending on which cathodes are tied together or kept separate. And what about the capacitance affecting bias, the 'big cap' trick etc etc.

Any thoughts?

[zaphod_phil]

Joining the cathodes of a push-pull pair together helps reduce extreme swings of cathode bas voltage, because it tends to average the current draw of the two tubes through the shared resistor. So you would be more likely to need to do the huge cap trick if you separate the cathodes. Separating the cathodes is however sometimes done to allow use of lower wattage rated resistors. However, you then have to double the resistor value. So for a single EL84 in Class AB you would use something like a 300 ohm resistor, rather than 150 ohm for a pair. Doubling the resistor value would also mean halving the cap value to get the same frequency/time-constant. HTH