Spitfire & Lightning schematics - screen supply

[Gee]

There are 2 different versions of each of these schematics available online. One shows the screens being fed straight after the choke, and the second version shows the screens being fed through a 22k 1W and 22uF node connected after the choke.

I would think that first version would appear to be the correct one. Looks like maybe one version was originally drawn incorrectly because of the slightly different way that the power supply is chained and branched. However, I see that Trinity Amps Lightning (TC15) schematic has the extra 22K and 22uF node.

Does anyone know which is correct?

[Structo]

I suppose it depends where you end up on your screen voltage.
If you need to drop a few volts so it is lower than the plate voltage then that is best for extended tube life.

[M Fowler]

I don't have an answer but I used Ken Watt's version but you need to reverse the Master Volume leads there wrong and the first one post below is correct. Oh and no choke on this version.

I used this amp on Halloween gig with a 112 cabinet and the guys in the band said that it sounded great. I think they meant the low volume sounded great. I built thise about 2 years ago and enjoy this 18w amp. It uses Heyboer 18w Marshall iron.

Mark

[M Fowler]

Here is some photos from my Spitfire

[Gee]

That's a very clean looking build you have. Out of interest, did you use the 8K primary of the 18Watt OT or mismatch the impedance to get 4K?

The .bmp schematic you posted is the most correct one IMHO. The last one has a .022uF pre amp coupling cap instead or the original 0.0022uf cap. Also I can't see how the Fat Boost switch would be much of a boost at all.

However, none of those schematics or layouts have the extra 22k/22uF screen feed, so I am still convinced that the extra 22k/22uF feed is incorrect.

[Darkbluemurder]

It's not incorrect, it's just two versions of the same amp.

I read in an Ampage discussion (from www.blueguitar.org) that Mark Sampson may have been worried about the screen grid voltage being too high and later came to the conclusion that the additional resistor and cap were not really necessary.

Folks who have tried both arrangements in the same amp report that the version with the additional resistor and cap (and thus lower screen grid voltages) was less bright and fuller sounding. I did a similar arrangement on my build (10k resistor plus 22uf cap) and found indeed that the tone got less bright.

BTW the Lightning has this variant, too.

Cheers Stephan

[M Fowler]

The Ken Watts Turretboards.com 18w Marshall tranny set came with 8 and 16 ohm secondary. A recent buy from him produced a different set for my Hammond AO-35 Carmen Ghia build?

I used a 16 ohm 112 cabinet for this amp and only used it once for gigging and it went very well using my Fender Roland ready Strat/Roland GR33 midi. Which by the way for $650 this strat is a heck of a nice playing guitar. The midi went into my Rocket with 16 ohm 112 cab for a nice mini stack. More room on stage

Your right the Fat boost does practically nothing not noticeable. I think I will try the changes you two mentioned for less bright but the guys did like that bite I had going.

[Gee]

It's not incorrect, it's just two versions of the same amp.

I am now convinced that the version with the 22k/22uf (dated 2-9-94) is incorrectly drawn. The reasons for this are:
1. The schematics drawn by the same person (Mark Sampson ?) for the Hurricane (dated 2-20-95) and Tornado (dated 2-10-94) which have the same PT and Choke, do not have the 22K/22uF.
2. The DC30 does not show the 22K/22uF.
3. Having such a huge resistor to drop voltage to the screens is totally uncharacteristic of Matchless and BadCat amps (and all others I can think of) and would alter their characteristic tone.

I think it was a mistake during the no doubt time consuming hand drawing of the Spitfire. It was probably easier to just remember to not wire up the 22k/22uF than to redraw that early schematic.

[M Fowler]

Those are old pictures of initial build and fireup.

The chassis picture of the master volume is before I switched the wiring as the way it is wired in the picture is wrong. It didn't work that way and I noticed two different versions and moved the wires over and bingo she rocked.

Mark

[Darkbluemurder]

Also I can't see how the Fat Boost switch would be much of a boost at all.

Absolutely. I wired it this way (22uf + 22uf boost) and could not hear a difference between the two settings. I switched the 22uf cap on the board to 1uf and kept the 22uf for the boost. This works way better.

[Darkbluemurder]

It's not incorrect, it's just two versions of the same amp.

I am now convinced that the version with the 22k/22uf (dated 2-9-94) is incorrectly drawn. The reasons for this are:
1. The schematics drawn by the same person (Mark Sampson ?) for the Hurricane (dated 2-20-95) and Tornado (dated 2-10-94) which have the same PT and Choke, do not have the 22K/22uF.
2. The DC30 does not show the 22K/22uF.
3. Having such a huge resistor to drop voltage to the screens is totally uncharacteristic of Matchless and BadCat amps (and all others I can think of) and would alter their characteristic tone.

I think it was a mistake during the no doubt time consuming hand drawing of the Spitfire. It was probably easier to just remember to not wire up the 22k/22uF than to redraw that early schematic.

Gee,

Good points.

Ad 1. I noticed that, too. Indeed it does not make much sense why the Spitfire and Lightning have it and the others don't.
Ad 2. The DC-30 is obviously AC30 inspired, and you are right the AC30 does not have such arrangement.
Ad 3. Indeed it does change the tone, making it noticeably less bright.

I am still not convinced that it is a mistake. Why would a designer like Mark Sampson make the same mistake on two different drawings?

Of course the definite answer could only be given by owners reporting of their amps and by posting pictures. Has anybody seen an actual Matchless amp with this arrangement?

Cheers Stephan

[Gee]

Why would a designer like Mark Sampson make the same mistake on two different drawings?

One explanation, could be that he drew the first one (say Spitfire) without noticing the mistake, and then used that drawing layout to copy the common circuit to the Lightning. Two nights later when he realised his mistake he let out a loud DOH!

NB Hand drawn schematics are a real work of art and we don't see enough of them.

[orrong65]

It seems this exact same topic comes up every 5 years or so, when someone builds one of these remarkable amps which are still widely used in recording studios around the world.

I built a Lightning clone from the schematics, and have ironed out nearly all of the bugs. It is the best amp I own (out of 12). I have it in a 2 x 12" combo with a Celestion G12H anniversary and a Weber signature 12s alnico. Pure heaven.

There are two Lightning schematics readily available:

1/ a crude hand drawn version called "Matchless Lightning 15" with pre-and power-amp, and half the power supply (supposedly the original schematic), and

2/ a better hand drawn version of the complete circuit called "MATchless LightNiNg" and dated 2-9-9? and signed MS?

The schematics are very similar, but I wanted to build the original version as it is supposed to have much better harmonics. So I built the original true to the schematic, including as much of the original power supply that was shown, and then used the later power supply for the rest.

But something was not right. I found that there was quite a bit of noise despite adequate power filtering, and the amp struggled a bit above moderate volume with a big signal. It also lost a lot of its punch, either overdriven or clean.

Going back to the original schematic, I noticed the EL84 screen supply was connected to the OT B+ supply, and came off the power rail at the same point (which was not shown). This is unusual and not present in the later version, or in many other amp designs at all.

What I did was to leave B+ supply connected to the power rail before the choke (where I had put it) and moved the screen supply to the rail after the choke, and after a 22k step down resistor to drop the screen voltage and 25uf of filtering, recreating the later schematic.

This cleaned up all of the noise instantly, improved the tone clarity, and preserved the amp power right up to 10 on volume (if you ever need to do that!).

So after trial and error, I ended up with and original pre amp and power amp circuit, with the complete later power supply circuit, and this worked just fine. In my view the original circuit with the screen supply joined to the B+ supply must either be an error, or just an early version of the circuit.

Note that I kept the original design 4.7k step down resistor on V2 supply instead of the 22k shown in the later schematic (Y supply), running the V2a voltage amp and V2b cathode follower stages at higher plate voltages. I think this is a big part of the better amp harmonics.

The only other significant difference between the two Lightning circuits is the 100pf treble bleed cap across the master volume on the original (as someone else has mentioned). This certainly brightens up the tone, and is ideal for studio recording. Installing an on/off switch on this cap is a simple way to add a new tone to this great amp. Another option is to experiment with a ceramic cap (for a 'velvet' tone) and a silver mica cap (very clean) in this position, or switch all 3 - off, ceramic, silver mica.

An amp to cut through any mix.

Dave

[M Fowler]

Dave,

Good report and I like your build using the 212 combo.

At some time down the road I will build a Lightning and thinking a 112 combo for that. I am very pleased with my Ken Watt's Spitfire version and great amp for gigging in small venues.

Mark

[Gee]

There are two Lightning schematics readily available:

1/ a crude hand drawn version called "Matchless Lightning 15" with pre-and power-amp, and half the power supply (supposedly the original schematic), and

2/ a better hand drawn version of the complete circuit called "MATchless LightNiNg" and dated 2-9-9? and signed MS?

I have attached the schematics I think you refer to below, together with a version that IMO is a corrected version from Dockery Amps. But who really knows?

Going back to the original schematic, I noticed the EL84 screen supply was connected to the OT B+ supply, and came off the power rail at the same point (which was not shown). This is unusual and not present in the later version, or in many other amp designs at all.

I agree. It has to be a drawing error done in the pre CAD pen and paper days.

So after trial and error, I ended up with and original pre amp and power amp circuit, with the complete later power supply circuit, and this worked just fine. In my view the original circuit with the screen supply joined to the B+ supply must either be an error, or just an early version of the circuit.

I agree.

Note that I kept the original design 4.7k step down resistor on V2 supply instead of the 22k shown in the later schematic (Y supply), running the V2a voltage amp and V2b cathode follower stages at higher plate voltages. I think this is a big part of the better amp harmonics.

This was discussed over at the Trinity Lightning forum and from memory some liked it but others preferred the original 22k. So simple it is at least worth trying.

Another option is to experiment with a ceramic cap (for a 'velvet' tone) and a silver mica cap (very clean) in this position, or switch all 3 - off, ceramic, silver mica.

Really good idea. What sort of ceramic cap?

An amp to cut through any mix.

Absolutely.