Spitfire & Lightning schematics - screen supply

[orrong65]

Thanks Gee,

good post, those are indeed the two schematics I referred to. And thanks for the Dockery Amps version, it is spot on! I like the idea of the Tone cut control without the bypass cap on the master volume, it sure would tame that top end, although there are some times when that piercing high is useful, especially if the PA is not running JBL horns.

I tend to use 70s and 80s american ceramics (cornellDs, CRLs etc) as they have this "velvety"quality. The modern Jap/german ceramics are much better quality, but often sound more brittle. Lots of the 80s Fender amps have snubbing caps everywhere (like across every plate-grid-cathode you can find) and the first thing I usually do is take them all out and start from a "standard tone". So I have plenty of these ceramics around.

Having a 3-way switch on the master volume with - no bypass - ceramic cap - silver mica cap - (caps not necessarily the same value) allows me to tailor the brightness to match the venue - eg: room, club and stadium with a 2000Wpa. I might add the tone cut as well to see what it can do.

[jlatrace]

I am about to convert a prior build to a lightning and noticed that there are two resistors (220K in lline and 100k to ground) after the treble pot and before th phase inverter that are not shown on the Dockery Amps schematics. Any ideas why Dockery would have omitted these?

[rp]

Yes, these same question do pop up for everyone googling a Spit/Light build. I still have all my research, FYI this was the most informative discussion for me and includes two posters who actually mapped their originals:

http://www.blueguitar.org/new/text/thre ... itfire.htm

Funny I totally overlooked the part on the hand-drawn schematic where the plates and grids share the same cap and wasn't sure what people were referring to, good thing as I would have chosen the earlier version too, but I should learn pay closer attention to schematics. Here's a pict of my Lightning layout and some images I stole off the web of an original if anyone wants to struggle trying to make the thing it out. I like my layout much better - Samson could have used me

https://picasaweb.google.com/lh/photo/y ... directlink

I used the 4.7K dropping resistor, didn't try the 100pf MV cap yet (seems plenty bright) and I used the TDS trainees an couldn't be happier with how it turned out.

w/ respect to the original posters.

[mick]

Just to pitch in to the debate about the schematic's, when I bought my transformers for a lightning I knew nothing about electronics or schematics, but a guy I knew at the time supposedly did, the place where I purchased the TXs said there was a mistake on the lightning schematics that he had seen and we should look at the spitfire power section, the amp builder guy took a look and said about the 22K dropping resistor not looking right. Now I searched for any info I could find to give to the guy building my amp most of which he ignored and was only really interested in the layout, now I understand much more and can read schematics, this thread made me look back at all the stuff I had kept from that time which included some gut shot's of a real lightning, the site where I downloaded them from is now gone, however I just found a place hosting the exact same photo's, so take a look and see what you think, hope this helps.

http://spinoo.free.fr/projetG5/Images%2 ... ning%2015/


Mick

[jlatrace]

OK I see that Ceriatone has the 220k and the 100k resistor. Also I see that the AC30 has the 220K resistor. So I am going with the 220K and 100k resistor, just like Trinity and Ceriatone (and the older schematics).

[Darkbluemurder]

OK I see that Ceriatone has the 220k and the 100k resistor. Also I see that the AC30 has the 220K resistor. So I am going with the 220K and 100k resistor, just like Trinity and Ceriatone (and the older schematics).

I bet that that 220k/100k voltage divider's primary function in the DC-30 was to provide a slightly lower impedance to the non-buffered and primitive effects loop. I guess Mark Sampson just carried everything over when he designed the Lightning. Since the Lightning does not have an effects loop you are free to experiment with the 100k resistor to ground value. Higher values provide more bass and a bit more push to the phase inverter. I have put a 150k in series with a 500kA pot wired as a variable resistor. Dr Z uses a similar arrangement in the Monza.

And BTW: that 0.01uf grounded grid cap in the PI is also most certainly a carry-over from the DC-30. In the DC-30 it made sense because that amp used both inputs to the PI. In the Lightning it would be better to use a 0.1uf.

Cheers Stephan

[rp]

My amp is ptp making it kind of tough to mess around but if I had it on a board I'd experiment. If the OP tries DBM suggestions please report your findings and if anyone else has played around with the 220K/100K divider or the .01 PI cap please chime in.

I'm of the opinion that Samson (and crew) were attentive tonemeisters and were aware of these oddities but preferred what they heard, just like the 4K Pz for the Lighting/Spitfire OT, the happy accident thing, but you never know.

Anyone have info on the 15W Bad Cats if they changed that divider? That would suggest DBM is right.

[Tdale]

Hi.

I took these pictures of a Lightning, maybe you can see something there?

http://spinoo.free.fr/projetG5/Images%2 ... ning%2015/

[jlatrace]

So what I am understanding is I can remove the 220K voltage divider (as sis done on the dockery Amps schematic) because it is a one channel in the amp (nothing to divide)

As for the 110k to ground, I can experiement with values as suggested above.

I'm going to build it as drawn in the older schematics and then mod it to remove the 220k (step 1) and remove the 100k (step 2).

I'll report back what I learn.

[jlatrace]

So what I am understanding is I can remove the 220K voltage divider (as sis done on the dockery Amps schematic) because it is a one channel in the amp (nothing to divide)

As for the 110k to ground, I can experiement with values as suggested above.

I'm going to build it as drawn in the older schematics and then mod it to remove the 220k (step 1) and remove the 100k (step 2).

I'll report back what I learn.

[Gee]

The 220k/100k divider is there to reduce the signal to the PI. From memory the Voxes have it and also the Top Hat and Bad Cat versions of the Matchless/Vox.

[jlatrace]

Thanks, that is what I thought.

[jlatrace]

After some more thought, should I consider cutting the voltage divider in 1/2 (from 220k to 110k) since there isn't another 220K resistor in the divider circuit?

Seems reasonable so I'll give this a try too.

[jcat5503]

I'm thinking of building a spitfire from the Watt's document

What mods would yall suggest?

I'm curious if a tone bypass switch would be cool..

[M Fowler]

Jason,

I'm probably the only person that enjoys the Ken Watt's Spitfire stock no mods. I do agree the Fat Boost switch doesn't add much with the cap values used.

But the rest of the circuit I left stock.

Mark