18 watt "Lite Tremolo" - Help wanted.

[WaZaK]

Yeh, I know I've not finished my plexi yet but I'm planning the next one ...

I have a normal channel amp (LiteIIb) and don't want another. Nothing wrong with the LiteIIB - in fact it is b***dy marvellous. I just don't want another. In the same way that I like each of my guitars to have it's own neck, (and yes I did once have a twin, way back when!) I like my amps to have their own box, PA and speaker.

So, an 18 trem it is to be. But I can't find one. If only it were as easy as cutting V1 or something off the schemo , and chopping the last 4" off the faceplate on the layout with a sharp pair of scissors to get rid of the "normal" bit!

I'm still a newbie when it comes down to "first principles" in tube amp building - or I'd design my own.
Did I miss a circuit somewhere?
Can anyone help?

[bahrens]

I believe you want the original. This, for example: http://www.18watt.com/modules.php?name= ... etit&lid=2

[WaZaK]

I believe you want the original.

Unfortunately not. A two channel amp is exactly what I'm NOT looking for!
I'm looking for something just like the single channel TMB (SuperLite) I recently built
- but a "SuperTrem".
Thanks anyway.

[bahrens]

Oh ok, sorry. I reread your post and now see what you were getting at.

[bahrens]

So.. looking at the original schematic..

You should be able to just build w/o the normal channel. That 0.022uF cap at the grid of v2A get's grounded, I think, and the rest of the normal channel goes away. I had a similar idea to build just the HiWatt side of a MarWatt and that was the advice I was given. Or I suppose you could probably take the trem channel from the original schem and run it into the PI/power section of the liteIIb.

[WaZaK]

No problem. I did try the search (as usual) but my life probably won't be long enough to go through the 6,782 results that came up for "single channel tremolo" ......... Lololol.

Thanks for the ideas. Sadly I don't know enough to start hacking. I'm OK with cut and paste and producing working drawings once I understand what I need to do - and why!

[malt]

S2 posted a layout of a single channel trem years ago but i cant find it, but if you do some searches around here (single channel trem) you will find some info. Or you can send S2 a mail asking him for the shem http://stvnscott.websitetoolbox.com/

[WaZaK]

if you do some searches around here (single channel trem)

Lolololol. (Been there: done that!)
I'll try the email. Thanks.

To be honest, I'm surprised I'm not falling over suitable schemos on this site. I can't imagine why the concept is not a popular option.
Maybe someone will tell me "cos it's a bad idea" or something. Lolol.

[bahrens]

if you do some searches around here (single channel trem)

Lolololol. (Been there: done that!)
I'll try the email. Thanks.

To be honest, I'm surprised I'm not falling over suitable schemos on this site. I can't imagine why the concept is not a popular option.
Maybe someone will tell me "cos it's a bad idea" or something. Lolol.

I think most people who care about simplifying ala the Lite and it's variants don't really care about trem. Also, changing the original schem is little more than a bunch of erasing and drawing a ground for that cap. Maybe you'll be the one to do the schem/layout.

[malt]

The trem channel is a fvorite to many of the bilders on 18watt, BTV the 18watt is a forum to ask qestons on and to have a god time!

Chek this out hehe

http://www.18watt.com/modules.php?set_a ... _photo.php

[katopan]

You did get the bug bad! The attachment is a 2 minute hack, but I think is what you're after. The grounded R29 makes it more time to make it neat than just dragging the trem preamp up to where the normal one used to be. The trem input into the PI C18 and the grounded C1 can be swapped in terms of which side of the PI the trem is connected to - it doesn't matter. Your comment about cutting off V1 and 4" of faceplate and layout is not far from all that's needed. Just need to ground the cap on that unused side of the PI (just like on the Lites).

[WaZaK]

Chek this out hehe

Nice one, Malt! You found it! Thanks. That should be enough to get my brain kick started .......

EDIT - Just missed your post Katopan. Thanks for that. Another nice one!
Got it bad? I'm laid up with a new knee - nothing else to do! (Well, that's my excuse!) Have you got that submin done yet? It's almost Christmas .......

[katopan]

Nothing else to do? Surely there's a heap of other things you'd rather be doing. It is a fun hobby. Well, you're going to have quite a nice little collection adding the two you're working on.

It's been a quiet few weeks for the submini but I've made some more progress in the last couple of days. Another problem is I got it working before it was all finished. I keep having to plug in for more 'testing' instead of just getting the thing all done.

Painted the inside of the box today. Just need to cover it and that bit will be done. The chassis looks finished from the outside but still has a temporary circuit board I had to add to fix a small problem. Need to make up a proper one to replace that, buy some knobs, and she's finished. Hopefully I can write up a post on it in a week or so. Definitely before Christmas anyway!

[WaZaK]

A few questions:
This would seem to be yet another ideal situation to use PA&PI VVR. Unregulated first stage will offer full voltage to the oscillator at all times. Right?
(1) But the first stage voltage rises up to 20% with max VVR. Would the increased voltage adversely effect the tremolo?
(2) My previous builds use 290-0-290+EZ81=B+ of 360V. This build shows 300-0-300+EZ81=325V. I don't see a large load to pull down the B+, so where did the volts go? I note the PA screens have only a shared 100 ohms (why bother), not sure if this is part of the equation. (Sorry if this one is more dumb than usual!)
(3) With the tremolo switch closed, does that effectively kill V3b by decking all the tremolo effects, leaving a low gain (V3a), clean channel?

PS

Definitely before Christmas anyway!

Thanks for the update.

[WaZaK]

A few questions:
This would seem to be yet another ideal situation to use PA&PI VVR. Unregulated first stage will offer full voltage to the oscillator at all times. Right?
(1) But the first stage voltage rises up to 20% with max VVR. Would the increased voltage adversely effect the tremolo?
(2) My previous builds use 290-0-290+EZ81=B+ of 360V. This build shows 300-0-300+EZ81=325V. I don't see a large load to pull down the B+, so where did the volts go? I note the PA screens have only a shared 100 ohms (why bother), not sure if this is part of the equation. (Sorry if this one is more dumb than usual!)
(3) With the tremolo switch closed, does that effectively kill V3b by decking all the tremolo effects, leaving a low gain (V3a), clean channel?

OK, so weekend is over. No more cucumber sandwiches till next weekend! Or has everybody been out gigging? I thought my questions were dumb enough for anyone: no replies?

[zaphod_phil]

This build shows 300-0-300+EZ81=325V.

How do you mean it "shows" - ie how are you measuring those voltages?

I note the PA screens have only a shared 100 ohms (why bother), not sure if this is part of the equation. (Sorry if this one is more dumb than usual!)

The 100 ohm shared resistor provides a bare minimum of protection to the screen grids. Possibly the higher screen voltage also results in more anode current draw and lower B+.

With the tremolo switch closed, does that effectively kill V3b by decking all the tremolo effects, leaving a low gain (V3a), clean channel?

It kills the LFO, leaving a typically dirty 18W preamp stage, not too different from what you will be used to with the Lite IIb. Being a little brighter than the Normal channel, a lot of folks like using it with LPs.

HTH

[WaZaK]

How do you mean it "shows"

Early planning stage: no measurements. The circuit Katopan supplied- http://www.18watt.com/files/18w_trem_only.jpg - "shows" the voltages I mentioned. The low B+ seemed strange ........

not too different from what you will be used to with the Lite IIb.

Ah, didn't realise I'd get a Lite(ish)/Trem out of the build. The (real) Lite uses both halves of V1 and the Trem uses only V1a, correct? How would they be similar?
Thanks ZP.

[katopan]

Sorry for the voltage confusion. The schematic I posted was a two minute hack of the combo reference schematic from the downloads section, and it's voltages are lower than normal. You should expect and target more normal voltages in line with what you have with your Lite IIb.

From the photo of your Lite IIb I think you built it with the parallel & single input jacks. You can hear for yourself the difference between parallel triodes and just a single. Parallel is a bit thicker.

The Lite IIb is sort of a mix of the classic combo channels, with its parallel triodes like the normal preamp and the tone control of the trem. The trem channel with the tremolo switched off will sound very close to the Lite IIb plugged into the single input. In other words the trem only is very close to a LiteIIb with no parallel input jack and valve tremolo effect added.

I've never built a trem and so didn't delve too quickly into your other questions. I remember others writing that whole amp VVR didn't work because it stopped the trem oscillating, and they went for PA only. I think PI/PA VVR would work well again with this one. Don't remember anyone saying the rise in preamp supply of PA only caused any problems, so should be OK for PI/PA - searching will find these threads. Also, there are tremolo improvements floating around by Ritchie that fix a lot of the problems people have, and I believe make it less sensitive to valve selection.

[WaZaK]

it's voltages are lower than normal.

Thanks. And I had forgotten it was a hack. Thanks for taking the time, btw.

I remember others writing that whole amp VVR didn't work because it stopped the trem oscillating, and they went for PA only.

Me too, that's why I thought it should be good with PA&PI

there are tremolo improvements floating around by Ritchie

Thanks. I have read bits about instability (which obviously I don't want!) so I must do some research.
It's very early planning: something I can do with one leg till everything is back to full power ..... Lolol.
(I gave up trying to carry a chassis from bench to bench with crutches!)

[rjgtr]

The two tremolo improvements that helped me the most were using shielded wire on the PI plates and putting a 100p cap across the tremolo footswitch jack. The cap eliminates low end oscillation that can sometimes happen with the tremolo. I don't think the shielded wire would be necessary in a Lite Trem configuration, since the plate wires can be both shorter and won't go near the trem channel's tube socket, like on a normal 1974 layout. The cap might or might not be needed. You can build without it and add if you get low frequency thumping.