Spitfire Assistance Please

[ncusack]

Hey everyone im looking to build a Spitfire for my next amp im just wondering about some of the specs for it. I've found a number of schematics and layout for it but none seem to reference any transformer values. Closest i found was a reference to west labs 15 watt transformers but they don't have the voltage or impedance specs. Basically just looking for any pointers as a start up for this project.

Thanks

[Bruce / Mission Amps]

Hey everyone im looking to build a Spitfire for my next amp im just wondering about some of the specs for it. I've found a number of schematics and layout for it but none seem to reference any transformer values. Closest i found was a reference to west labs 15 watt transformers but they don't have the voltage or impedance specs. Basically just looking for any pointers as a start up for this project.

Thanks

I would think a 270v@120ma-150ma PT would be right on and the OT will need to be at least a 15 to 20 watter (guitar amp watts not Hi-Fi watts) at around 7500 to 8500 ohms with any normal speaker load.

[ncusack]

Cool sounds like I already have the Iron lying around. Hammond 270EX at 275-0-275 at 115VAC and I have a push pull with 8k and 6.6K Primaries into 4,8,16 ohm loads. Any idea if there are any problems with the schematics that are available out there?

[axpro]

I've built a few clones with the schematics floating around... a buddy still swears by his. All i can say is that (as usual) lead dress and cleanliness are BRUTALLY important on these, simple circuit, and you tend to hear every small change (in my opinion)

I think when i did it, i tweaked the gain a little, but nothing major... cool sounding amps, just not for me.

[ncusack]

Hey axpro if you wouldn't mind what are some of the key issues with wire dress i should try and avoid in the spitfire?

[ncusack]

Here are two of the spitfire layouts ive been able to find. I was thinking of using a 32x32uf can cap I have from another build for the first power supply filtering section so it will be a little different then these.

http://www.diyguitarist.com/PDF_File...ireChassis.pdf

http://www.turretboards.com/layouts_...s/kits/msf.pdf

The second one here uses a star ground and looks like there is no choke involved with that one either.

Any thoughts would be appreciated

[axpro]

The second looks closer to what i've done in the past

[cminor9]

I built one a while ago using the layout at DIY guitarist.

Here are some pics: Spitfire build - a set on Flickr

It sounds great! Mine uses a triad 10 H choke, a 32/32 cap can, and a couple of 22uf caps, which I have upgraded to F&T caps since the pics were taken. Epoxy glass turret boards, silver plated PTFE clad wire. I really tried to use good parts because that's how Matchless builds em. Although I have built a few other amps (Fenders) using more traditional buss type grounds with good results, I tried a true star ground here, with insulated jacks and all, and it worked great.

I had to get creative with the layout, and spent a good deal of time working it out, since my chassis is smaller than the one on the layout seems to indicate. It's a pretty quiet amp in terms of hum, makes no more noise than a Fender HRD I bought many years ago.

I know the wires look like they are routed willy-nilly in the picture (I just don't take the time to make perfect 90 degree bends, perfectly straight component leads, etc) but actually I spent a good deal of time making sure that AC-carrying wires crossed at 90 degrees, are far away from B+, the grounds were rock solid, and other minor details.

I did the labels by masking with stick on letters and painting over them, then applying lacquer over it all. It worked well, but now that I have moved on to silkscreening I find the labels inferior. I just don't feel like taking it apart to make a faceplate for it.

Hope these pics help!

If you've never played one, they are a blast. I am running mine through a pair of 12" speakers in a large cab. Using a Warehouse Veteran and a Reaper (Vintage 30 and Greenback) which is a pretty highly regarded speaker combination. That little amp through that cab sounds like a freight train!

[kkregsg]

I'm working on my first build, also Spifire, and let me pass along some info I've received from several people. First, Chuck H, a member here had these recommendations on transformers: PT, the Hammond 270 EX is a good choice, as the schematic calls for 285v, and the 270 EX shows 275 at 120 AC, but with the rise in voltage at the plug to usually 125 volts, it will be spot on. OT, 1608, and choke, 156G.
Second, there are several layouts available: Watts which is above, Ceriatone on their website, Paul Marossy with the 2 Spitfire schematics at Schematic Heaven (post '70's amps), one schematic has voltage readings included, House of Jim on the Blue Guitar site, and one that I received via email on a different site.
I've been scouring the web for as much info as I can find. I ordered my chassis from Dirty Dawg as shown on the ax84 site, and while you have to drill it, the price and quality are great. There's a lot of info on making your own turretboards, too.
Good luck on you build.

[Chuck H]

the Hammond 270 EX is a good choice, as the schematic calls for 285v, and the 270 EX shows 275 at 120 AC, but with the rise in voltage at the plug to usually 125 volts

The Hammond actually has a 115V primary. With a 120VAC mains voltage It works out to be 287-0-287. So, pretty damn close. At 125VAC mains you get 298-0-298. So that's a little high. But AFAIK they don't make a PT that accounts for mains drift. Here in my house you can count on the voltage shifting. With a low of 120VAC and a high of 127VAC. A lot of areas throughout the US are more steady though. But sometimes steady at 125VAC rather than 120VAC. I think I've seen some transfomers in the last few years become available with a 125V primary. So that's telling. For now I'm still designing with the 120VAC "standard".

[kkregsg]

Thanks for the correction, Chuck. I should re-read before posting!
As far as lead dress, just do a search online, and you'll get a number of hits. They give some points to be aware of as to wire routing, some of which cminor9 pointed out above.
Kkreg