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Hey all, I just got my Spitfire with a twist up and running this past weekend. It's got a 6SJ7 pentode preamp, a 6SL7 phase invertor, and the normal power section, although I'm running a 5Y3 recto for lower voltages.

I did include a cut control which I really like. The last bug I'm working on is that the Master Volume is wide open untill the last 1/4 turn where it rapidlly drops the volume to zero. I think I need to wire it like the DC 30 setup with cut and MV.

I'm discovering the awesome tones from this amp with the different settings!!! The 6sJ7 is setup to achieve a voltage gain of 238. So I can set the volume low for clean, jangly and compressed, or crack it wide open for over the top gain, and control it with the Master Volume and guitar volume. Yes, very responsive to the guitar volume. Love it!!!!

Sounds very interesting. If you want me to post a schematic, I'll pop one up for you.

On the MV, what happens if you remove the cut control? Is it wired up in reverse? It's a pretty simple MV control so that behaviour seems quite abnormal.

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Thanks Stephen, I just got visio and will work on a schematic.

Yes, it seems like the MV is wired in reverse, I'm going to work on it tonight, and post back with results.

Denny

I just looked at the trinityamps layout of the spitfire. I definatly need to shift my wire connections on the MV over 1 terminal and have the N/C terminal on the other side of the pot. I should have known better...

A Spitfire with a 6SJ7 on the input? Hmm... sounds yummy. But you don't get a paralled triode with that... oh well, it's a morphed amp anyhow.

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PJM

http://www.diyguitarist.com

Trust me Paul, you would'nt miss the parallel input. I may eventually change the plate, screen, and cathode resistor on the 6SJ7 for a little less gain. Maybe...

MV is now working correctly, I think. At least it's not working in reverse like I had it. It s still most effective for the first 1/3 rotation, after that the volume change is very slight. Anybody else's MV like this?

Denny

Yeah, I suppose. But I have heard that the parallel input triode is part of what gave the Spitfire its characteristic sound, too...

Anyhow, I really like the 6SJ7 on the input of a SE amp. My Octal Fatness has one of the best amp distortions I have ever heard!

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PJM

http://www.diyguitarist.com

The MV on my Lightning acts the same way, maybe it is just a function of the mixing of the two out of phase signals. I may try changing it to a dual pot and see if that gives better control, similar to this one for an 18 watt, although the values would end up being a little different.


Eddie

hmm, is that a GA-20 in your avatar? Inspiring amp isn't it?
jef

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"Remember, there's a big difference between kneeling down and bending over" Frank Zappa

[/quote] ...I may try changing it to a dual pot and see if that gives better control, similar to this one for an 18 watt ... . Eddie[/quote]

That's a post PI MV. IMO, I would'nt recommend that configuration for an 18. Most of the great 18W tone come from the PI. Overdirving it with a pre-MV should get you more of those tones. I can't see, doing a post PI would work as well.

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Jef, Yes it is. I have 2 of those sweet babies. That is my inspiration for the preamp and PI section of my Twisted Spitster.

Erl, I don't know if it will make any difference with the Master Volume, but I see the DC 30 amp uses all 3 lugs of the pot, where the spit uses 2 with the third not connected. Looks like CCW and Wiper lug wired together. I will give it a try at least. Let me know if your dual gang pot works out, I do have one of those.

CoCo, the Spit Fire Master Volume is post PI, right?

Yes, the Spit [and Lightning] Master Volume are post PI.

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

For a full swing on your MV, use a 470k or 500K Pot.

CR ><>

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WoodCross Amps

http://www.geocities.com/woodcrossamps/

Did you use a metal can 6SJ7? How is it for noise and microphonics?

The metal can 6SJ7s that I have used haven't been too noisy or microphonic as far as audio amplification goes, but some of them have had a lot of hum from the heater filament which required me to make a few changes to the original circuit (Octal Fatness) in order to take it down to acceptable levels. It was really just some hum with the gain maxed, but I thought it was a little too much. Anyhow, others have had no such problem(s) with their 6SJ7s. Mine were NOS RCAs, BTW.

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PJM

http://www.diyguitarist.com

I'd like to try a fully octal amp. 6sj7, 6sc7 then 2X6v6. Any thoughts on that? Seen one?

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

I was thinking of building a 5C5 Fender pro, only using 6v6’s instead of 6L6’s. BBQ has a schematic and layout and a 5c3, which already uses 6v6's Schematic and layout, on his site. Either might be interesting.

Eddie

Coco, that is what the early GA-20 Gibson used, like the one in my avitar.

Check this:

http://www.informatik.uni-bremen.de/~dace/gg/ga-20.gif

Although the schematic says 6SL7 for the phase inverter, both of the GA-20's that I have came factory stock with 6SC7's for the PI.

Denny