Brand New Spitfire

[telentubes]

Here's a Spitfire I just finished, based on the Watt's Tube Audio layout. Although it ain't no Rocket, it's a sweet little amp and should prove to be lots of fun. It has Volume, Tone, and Master Volume. Along with the tone control, Bass response is also affected by the relationship between Volume and Master Volume.

Overall, the tone is pleasing... except for that "ice-pick treble" that's present when everything else is well balanced and dialed in pretty well. So here's the question...

Is there a good way to alter the circuit to get rid of that super high piercing frequency? Which components are in charge of that, and what values might they be changed to.
Thanks,
TNT

[M Fowler]

Looks good welcome to the Spitfire club, I like mine and it's a Watts version as well.

Mark

[Bear]

Add a Vox-style cut control. It's also in the Trainwreck Rocket, schematic in this thread: https://tubeamparchive.com/viewtopic.php?t=5684

[M Fowler]

Or replace the MV with the cut control.

[Gee]

The bright cap on the volume can make the Spitfire very bright. It's an ideal place to put a switch to switch it in and out. I removed the tone control on my clone and replaced it with a cut control which I prefer as it removes just the treble and can be adjusted to trim out what you don't want to hear.

[telentubes]

Seems like the cut control is the answer. I've built an AC15 as well as a Rocket so I can probably figure a schematic from those.

If I want to use the Master Volume pot space for a cut control, can I just measure the Master Volume's pot resistance value, at a setting that I like, then replace the pot with a resistor? Is it that simple? The other option would be to add another pot, but I kinda wanted this amp to have as few knobs as possible (for no particular reason).

[telentubes]

Hey Gee,
Can you tell me how you made the mod you described on your Spitfire. That might be a good way to go as well.
Thanks

[Structo]

What value is the bright cap on your volume control?

That is most likely the source of the ice pick.

Either decrease it or put it on a switch or both.

EDIT:
I see the bright cap is 220pf.

That's pretty large.

I would try a 120pf, or even a 50pf but just put it on a mini toggle or push/ pull pot to make it optional.

[Gee]

Hey Gee,
Can you tell me how you made the mod you described on your Spitfire. That might be a good way to go as well.
Thanks

Here's a schematic of what I ended up with:

[telentubes]

I had a 240pf bright cap, which I changed to a 47uf during my lunch break (I also lowered the 220K resistor to the first E-cap to 200K, to lower the gain a little, while I was at it)

It's still got too much ice-pick for my taste, but it has diminished with the 47pf cap. The mid-range seems to be a little stronger, but that could easily be my inaccurate memory. I still want to dial out that super high end so I'll try other ideas. Thanks everyone (Gee for the schematic!)

[Structo]

Try it without the bright cap.

[ampmike]

Nice build Bro!!Very clean,Enjoy,Mikey

[telentubes]

I got rid of the bright cap, changed the 1st coupling cap to a .047 from a .022, and used Gee's high cut mod, loosing the Master Volume, but keeping the Tone control. Now it's pretty cool. I think I need a coupling cap half way between the .022 and the .047 to dial in the bass a little better. One is too much, one not enough.
Thanks everyone (the schematic saved me some head scratching).

I'm running this as a combo with a Celestion Alnico Blue. It's a nice practice amp, as tonally it's no match for my Rocket, but plenty of fun.

[M Fowler]

I think the Alnico blue is messing up the tone of the amp.

It is a fantastic speaker but I don't think it goes well with this amp.

The speaker I like the best with the Spitfire is the Epiphone 112 cabinets that came with my Epi valve jr. 16 ohm cabs.

[rp]

The speaker I like the best with the Spitfire is the Epiphone 112 cabinets that came with my Epi valve jr. 16 ohm cabs.

So what you got in there, curious to know? Matchlesses don't play well with many speakers.

The first thing everyone says plugging into a matchless, real or clone, is, "Bright!". I'm sure Samson, Perrotta, Jamison were/are well aware. My experience with my Lightning clone is trying to tame the brightness in the circuit takes some of the life out of the amp, it's losses sparkle is the best I can describe. I think the original designers dealt with it by choice of speaker and custom treating them, maybe extra dope, certainly acetone break in. It's almost the universal opinion that Matchlesses sound best through their own cabs. The spifire had a V30 I believe, I consider that a bright speaker too but haven't tried it on the lightning. Of what I have I like it best with greenbacks, the g12h30 anni is bright. V10-60s are good but still bright. With an Altec 417 your nuts will retract. Truly awful sound.

I needed to plug an extra hole in my chassis and put in a 3 cap switcher. I thought it was useless at first, cause of the sparkle thing, but it's proved very useful with pedals.