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Old 6th February 2005, 12:06 AM   #1
Trout is offline Trout  United States
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Default Will This Blow Up?

Trying to put together a few circuits from various amps into a toy for my brothers 40th Bday.

Using junk I have laying around,And Limited budget for this project, My Question Is Simple Will "THIS" Blow Up?

Are there any huge fundamental mistakes?

Edit: Oh,, I left out the preamp tube,, Its a 12AX7A rca orange label(60s)

This is supposed to be a guitar amp, But hey,, might even be better with some input.
Gene
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Old 6th February 2005, 02:50 AM   #2
SY is offline SY  United States
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One thing immediately jumps out: the 1K resistor in the power supply feed to the output tube. Why such a high value? If the output stage idles at 40 ma, you'll be dropping 40 volts across it (and, incidently well exceeding the 1W rating).

And do you really want a 15K bias resistor in the first stage? If I were you, I'd steal plate/cathode resistor values from the tube handbook.
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Old 6th February 2005, 03:07 AM   #3
hacknet is offline hacknet  Singapore
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my gut tells me the power supply is not stable.. try increasing the 5uf to something larger... having 1k in the psu is not really desieable... but it will do as long as the wattages are met.
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Old 6th February 2005, 03:51 AM   #4
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Lol, I could see some hot resistors if the caps were enlarged and someone happened to put Si diodes in for the tube rectifier.
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Old 6th February 2005, 04:11 AM   #5
Trout is offline Trout  United States
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Quote:
Originally posted by SY
One thing immediately jumps out: the 1K resistor in the power supply feed to the output tube. Why such a high value? If the output stage idles at 40 ma, you'll be dropping 40 volts across it (and, incidently well exceeding the 1W rating).

And do you really want a 15K bias resistor in the first stage? If I were you, I'd steal plate/cathode resistor values from the tube handbook.


Yawn,, I've been trying to post the updated schematic for about an Hr,, But our FTP things acting up tonite,, I'll post it tomorrow.

The 10 ohm 1 watt is actually a 10 ohm 5 watt. Though a 10 watt might be better. I posted prior to correcting the value. Optionally, I had planned on a choke in place of the 1K resistor. Just to clean up the sound if necessary.

As far as the 15K bias resistor on the 1st preamp stage. That value is borrowed from this cute little Preamp project I had built earlier this winter. The McTube by Fred Nachbaur.
His article is located Here

Cute little thing works very well, I though It would be starting point on this project.
Gene
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Old 6th February 2005, 05:06 AM   #6
Trout is offline Trout  United States
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OK, Finally got it uploaded again. My space was full and I couldnt get it uploaded, House Cleaning time lol.

Anyway, Here where I am on this schematic now Fresh Drawn

Hopefully Im a little closer to having functional circuit now.
Gene
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Old 6th February 2005, 07:41 AM   #7
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Why not just build a champ clone(5F1)? Very cool little amp and real close to what you have. Or if you need tone control look at the Princeton.
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Old 6th February 2005, 11:00 AM   #8
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Cloning a Fender isn't a bad idea!

OK, you're unlikely to smoke the power supply now. There may be more hum than you'd like, though, depending on the sensitivity of the speaker. Do be careful about stray capacitances- the 1M series resistor off the preamp plate ought to be placed as physically close to its load as possible.
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Old 6th February 2005, 12:52 PM   #9
Trout is offline Trout  United States
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Quote:
Originally posted by SY
Cloning a Fender isn't a bad idea!

OK, you're unlikely to smoke the power supply now. There may be more hum than you'd like, though, depending on the sensitivity of the speaker. Do be careful about stray capacitances- the 1M series resistor off the preamp plate ought to be placed as physically close to its load as possible.

Welp,,
I'll know more by maybe monday night, Last night in a burst of energy, I stuffed most of this into a re-used 6 1/4 X 6 1/4 X 2 chassis. Tight fit indeed.

Mind you EVERYTHING in this project came from box lots I purchased at an estate auction. Caps, Resistors,Sockets,Pots nib,
Everything LOL, Even a pair of vintage 70s Utah/Musicman 12 inch speakers.

My biggest worry was melting down the OPT. Everything I had previously looked at used a 5000 ohm primary. When I started this project all I had were 2 of 2500 ohm units.
I ordered the fender replacement and got it yesterday,along with a nice little PP Tranny rated up to 25 or so watts.( next project).

Thank you so much for all of your inputs, I'll get more pictures up soon I hope.
Gene



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