Spitfire with VVR

[Gee]

I modified my LiteIIb 18 Watt into a Spitfire as I was curious to hear how different it was to a LiteIIb. So far I am really very pleased with it after a bit of tweeking to get it to sound less harsh.

I built it into into a Fender Pro Junior chassis and cab with a 10" Celestion Greenback. It has a VVR that scales the PA & PI leaving the pre amp at full voltage. As it has a VVR I didn't need the master volume.

I initially built it just like the main schematic that is floating around. I used a choke I had spare - a Hammond 157L choke which is a 14H 75mA 425 ohm choke which has more inductance that the original Spitfire one but I figured more smoothing is a good thing. Also I used an 18 Watt OT and put a switch on the 8 and 16 ohm taps so that I could compare the 8 ohm speaker into the 8 ohm tap for 8K primary and the 8 ohm speaker into the 16 ohm tap to get 4k primary.

At first I found the amp to be so bright that I had to turn down the tone control a long way and this killed the sound of the amp. After a lot of trying different coupling caps and tone caps I still wasn't there and was about to give up when I removed the tone control and rewired it as a cut control (250K with .0047uF) - BINGO. Finally that was it. The gain was increased a bit so I used a 5751 for V1. Also I increased the screen resistors to 1K as that seemed a sensible thing to do.

It still wasn't quite there after a bit more playing and I added a centre off DPDT switch with a few different caps for the bright switch. I found that getting the bright cap sized right was also a critical factor in getting the harshness under control. So far 100pF sounds about right with a Tele and 180pF works with my Strat.

Two other things that were worth doing was a switch on the V1 cathode to have .68, 2.2uF and 22uF options to tune out any boomyness and also a switch on the PI cathode to give 1k2, 820 and 470.

Overall I am very pleased with this amp - it has more clarity and note definition than as a LiteIIb yet gets pretty crunchy.

I am not decided on the 4K or 8K primary yet. The 8K is louder so it is difficult to make good comparisson but both sound good enough.

I have attached circuit diagram with some voltages.

[M Fowler]

Great work

You should have just built the Ken Watts version and saved a lot of work.

I played my Spitfire at a gig on halloween and boys in the band said that amp sounds fantastic and if they can tell then something is working right.

I used the Epi 112 Eminence cab that came with my Epi Value Junior. The other Epi cab I used with my Rocket for my keyboard sound from my Roland GR33 midi for a nice short stack.

Mark

[Gee]

You should have just built the Ken Watts version and saved a lot of work.

I did consider that version but for me the .022uF pre amp coupling cap would be too big. I found .0047uF a bit boomy and .0022uF just right.

[Darkbluemurder]

Yes, it's a bright amp indeed. That tone control is indeed useless. You did the right thing by installing a cut control. I did the same to mine and it works much better.

The "incorrect" screen circuit (see other topic) warms up the amp a lot. I like it better than the "correct" version.

I have a 0.022uf coupling cap after the first stage. OK with single coils but too muddy with humbuckers. I guess I will reduce that cap gradually until the amp just does not get muddy.

However I am not sure whether I will keep that amp. Got to fiddle with it a bit more to decide.

[Gee]

Yes, it's a bright amp indeed. That tone control is indeed useless. You did the right thing by installing a cut control. I did the same to mine and it works much better.

The "incorrect" screen circuit (see other topic) warms up the amp a lot. I like it better than the "correct" version.

I have a 0.022uf coupling cap after the first stage. OK with single coils but too muddy with humbuckers. I guess I will reduce that cap gradually until the amp just does not get muddy.

However I am not sure whether I will keep that amp. Got to fiddle with it a bit more to decide.

Interesting that you also didn't like the tone control. On one hand, it is a crazy tone control that has a 0.0022uF coupling cap followed by a 0.01uF cap to ground - for me it killed the tone that this amp is capable of.

I am still very pleased with this build and how the amp sounds. After more blind listening switching between the 4K or 8K primary, I am not convinced which sounds better to my ears, both sound good.

My thoughts are that the Spitfire is one of those amps that needs the right speaker and correct tone shaping component values for the right guitar, otherwise it doesn't have the magic that it is capable of. It is interesting because, with the same circuit rebuilt as an 18Watt LiteIIb, it is much more tolerant of speaker and guitar.

[M Fowler]

Yesterday I changed the PI cathode from 1k2 to 820 like the Marshall and it made a good difference. The tone control needs something better but what.

[Gee]

Yesterday I changed the PI cathode from 1k2 to 820 like the Marshall and it made a good difference. The tone control needs something better but what.

The 18 Watt LiteIIb is a tried and tested tone control. Maybe change to Vol and Tone pots for 1M and you would be done. However, I highly recomend the Cut control with no Tone control. Also you get a gain boost with no Tone control.

[M Fowler]

I buttoned the Spitfire back up and I am going to run the amp as is for now to see how she works gigging with no change to the MV or tone control.

[Gee]

I'm still really enjoying playing through this build. I really can't find any big difference between the 4K and 8K primary settings that would make the 4K preferable.

[M Fowler]

From what I have for specs there is no difference on the turns ratio.