Matchless to Rocket conversion

[mojotom]

First of all Hi everybody and thanks for that great forum full of great posts. I have read the Ampage posts about the Trainwreck but you really gives us more about thoses amps.
I'm like everyone trying to build an amp, I foolishly try to build the best amp on earth on the first try so it's still unbuilt for quite some time now...

I plan to build a Matchless Lightning kind of amp so I have all the parts, drilled chassis, transformers... I build an Hotbox clone to test ideas but the original tonestack sucks and I was unable to found a good sound out of it (even with a TMB tonestack). At that point I really doubt about the amp so I search to try one of the original by myself (a Badcat) and was really dissapointed. It didn't like effects and it was almost impossible to find a good sounding setting for both bridge and neck pickups.

My main goal now is to build something in the line of my 64 Vox (red panel) or even more likely in the line of a Rocket.

I found two differents versions (one schem and one layout) and the layout seems the way to go from the posts I read.

I have an issue too because my West Labs tranny are a bit of for that purpose (4k output for 2*EL84 and 350V to the plates) and the power supply is quite different. I bought a London Power scaling kit so I can install it to vary the voltages.

I know I have to build it and tweak it later but sourcing parts is not easy for me so I have to start somewhere


I really need to know if I had to follow the schematics or the layout and what kind of power supply should I use as well as the RC on the EL84, I had the chassis mounted for almost a year now I really need to build that amp.

I would be pleased to know what you are thinking about the too high power supply and 4k output tranny, somehow it reminds me of the voltage article found on the files section where Ken Fisher explained he has two taps for the Rocket, one at 315v one at 370v.

Thanks for all

I will try to post a pix of the chassis.

Tom

[Bear]

The Lightning and Rocket are fairly similar, though with some obvious differences.

(I take the 15 vs 30 watter issue as irrelevant. If I were to build a Rocket, it'd be 15.)

On the transformer mismatch in the Lightning, remember that an OT's impedences are about the ration of nominal load to nominal load. You can re-match the amp by using a different speaker load.

One thing about the Lightning is that it's pretty gainy due to using parallel triodes at the input - this parallel stage is not found in the Rocket or old Vox Top Boost amps. Some really like the extra gain potential, though - the paralleled input is also used in the Top Hat Club Deluxe, which is yet another tweaked Top Boost design. If you build a Lightning and don't like the gain, try only hiting one triode stage on the input. From there, tweak to more appropriate values for that topology.

Since you've got the parts for the Lightning build, build it and live with it for a while. The Treble/Bass tone stack is a bit trickier to work out then you'd imagine, so keep working those knobs until you know the ins and outs. Look at the Lightning forum at Trinityamps.com for specifics on the design and tweaks.

The Rocket is tantalizing, but there isn't as much info out about it as there is about the Lightning and Vox designs. So the knowledge here might work very well to perfect on that base of general knowledge and get the last few percent going. We're really talking of incremental differences in most amps of this family, so some things will be matters of taste, other things matters of insight.

Bear

[mojotom]

Thanks for the answer.

I read all my notes once again and the main question is about the power supply. Either a standard one like the schem (with all the preamp and PI tubes B+ supplied by the sceen voltage tap) or a Trainwreck like power supply (like a Liverpool).

I'm a bit worried about the 350v supply using the trainswreck supply but I hope the scaling kit will do its job lowering the voltages if necessary.

The input resistor, first coupling cap, PI resistors and coupling caps could be tweaked after.

I don't know about the power tube bypass RC, I started with 120R and 33µ.


I have started the build now (filaments wiring).

Can't wait to fire it up !

Tom

[MarkB]

My suggestion would be to pick a known design - like the Lightning - and just try to get it right. Sometimes you get lucky on your first try, but you're liable to have problems with your first build. If it works at all, there's hum, buzz, hiss, squeal, and other assorted gremlins to deal with. Then you might want to tweak for less treble, clearer distortion, etc. When you get that build near perfect, then start worrying about your "dream" amp. By then you'll probably have learned a lot that you can use perfecting the amp you really want.

[mojotom]

In fact I've read some great reviews concerning a Rocket clone, mainly the fact that it works great with open cabs and strat.

I really didn't like the sound of the Badcat, the bass was not tight and I didn't like the high gain settings so I'm really not that convinced to build a lightning clone. I have another amp project on his way but I had hard time drilling the chassis and sourcing parts for this one so I have to use it for something.

The main concern is about voltages as I have a 285-0-285vAC out of the power transformer, something like 350v on the plates...way too much. I have to low it down. i have thought about the power scaling kit but I haven't that much space inside the chassis. I have read here something about a zener diode between the B+ center tap and ground.

Do you have tried this mod ?

What voltages do I need ? 315v on the plates ?

I'm using the trainswreck type power supply.

Thanks.
Tom

[RossH]

This is interesting timing. I put my pseudo-Lightning on the bench for tweaking recently but have not yet made any changes. I didn't realize that it was so close to a Rocket. Here are the basic differences I can note short of the voltage differential and the PS cap values.

How to modify a Lightning in to a Rocket:
1. Change 1st stage grid resistor from 68k to 24k
2. Change 1st stage post bypass cap from 1200pf to a paralleled 470p/47p arrangement
3. Change the volume pot from 1M to 500k
4. Change the treble bright cap from 180p to 100p
5. Lose the 22u cathode cap on the second stage
6. Change the pre tone stack cap from 51p to 500p
7. Change the bass-wiper-to-ground resistor from 10k to 1k
8. Lose the post-treble wiper 220k resistor
9. Lose the 100k resistor connected to the PI-tail resistor
10. Change the pre and post PI caps to .047u
11. Change the PI cathode 1.2 resistor to a 1.5k resistor per tube arrangement

It looks like this list covers the basic stuff. I wish I could hear a cranked Rocket to compare.

This lightning thing sounds real chimey and jangley. I love that part of it. What isn't my personal taste is the distortion character when you wind up the volume. It is a bit too fine or fuzzy. I am looking for more of a thicker grind...if that is possible. In comparison I find myself gravitating to my 18 watt Marshall more often.

Might have to start experimenting.

Ross

[RossH]

Oh yeah...and the paralleled first stage would either need a plate and cathode resistor and cap adjustment or remove the paralleled status.

Ross

[mojotom]

It's exactly what I thought about the Badcat (not too found of the high drive sounds).

If you followed the layout and the last schem, I think the main thing to look at is the lower voltages (300-315v instead of 350v) and the Trainwreck power supply (18k/10k/10k or 1.8k/1k/1k).

Tom