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spitfire questions

7/9/1998 9:16 PM
Mark Buckingham	spitfire questions After I got a great deal on parts, (got the power and output transformers from a good friend for free), I've decided to build a spitfire clone. All I have left to obtain is a chassis to put it in and start soldering. So here's a couple of questions- 1. The power transformer I got puts out 326-0-326 vac. I need to know if I'm going to have too much power here, as the spitfire schematic shows a 285-0-285 vac secondary. 2. I'm planning to use 2 high speed diodes to rectify the voltage. The book I borrowed from the library says that the average value of the dc voltage is .637 * the ac voltage. This would give me 415 vdc before the first filter cap. (I think.) Is this the right way to determine this? 3. I'm planning to wire in a pentode/triode switch similar to the one on Duncan's web sight for the blues-112. In this, he uses 22k resistors to tie the screens to the plates. Should this work ok here also? 4. The master volume circuit looks a bit odd. Does this work well, or should I do the stereo volume control trick instead? 5. If the triode switch works, I'm guessing I'll get about 3 watts out of this thing in triode mode. To me, that means I can get power tube distortion much earlier. Right? Thanks for any help anyone can give. My main goal is to build something that I know already works so I can have a nice circuit to add to or change. (And having yet another guitar amp is very cool too ) -Mark

7/9/1998 9:16 PM

Mark Buckingham
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spitfire questions

After I got a great deal on parts, (got the power and output transformers from a good friend for free), I've decided to build a spitfire clone. All I have left to obtain is a chassis to put it in and start soldering.

So here's a couple of questions-

1. The power transformer I got puts out 326-0-326 vac. I need to know if I'm going to have too much power here, as the spitfire schematic shows a 285-0-285 vac secondary.

2. I'm planning to use 2 high speed diodes to rectify the voltage. The book I borrowed from the library says that the average value of the dc voltage is .637 * the ac voltage. This would give me 415 vdc before the first filter cap. (I think.) Is this the right way to determine this?

3. I'm planning to wire in a pentode/triode switch similar to the one on Duncan's web sight for the blues-112. In this, he uses 22k resistors to tie the screens to the plates. Should this work ok here also?

4. The master volume circuit looks a bit odd. Does this work well, or should I do the stereo volume control trick instead?

5. If the triode switch works, I'm guessing I'll get about 3 watts out of this thing in triode mode. To me, that means I can get power tube distortion much earlier. Right?

Thanks for any help anyone can give. My main goal is to build something that I know already works so I can have a nice circuit to add to or change. (And having yet another guitar amp is very cool too

)

-Mark

Replies:

Mark Buckingham One more question-I've got ... -- 7/9/1998 9:30 PM
Bruce Mark the general rule of thumb.... -- 7/9/1998 11:17 PM
Mike B Mark,I've built a couple of spi... -- 7/10/1998 9:08 AM