Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: davidwpack on December 11, 2017, 04:23:37 pm
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Ello! I'm doing a layout drawing from a schematic. I'm wanting to put the bright switch on a push pull volume pot but I'm not exactly familiar with anatomy and function of push pull pots. Can anyone provide a drawing or link to a drawing of using one of Doug's CTS push pull pots as a volume with a bright switch? If so it would be completely excellent! Thank you...dave
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(http://www.prestonelectronics.com/audio2/ttip/images/switch.jpg)
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Hey THANKS! Looking at example #5, does the input and output to the amp still go to the top set of lugs as if it were a regular 3 lug pot? Or the bottom 2 lugs??? I've never used these and I'm not familiar. Thanks again...dave
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Thank you!
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The cap does not connect between the switch terminals. It connects between the hot terminal of the pot to one of the switch terminals. Then connect a jumper between the pot wiper and the other switch terminal. Like this...
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Gotcha. Thank you muches!
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OK, I finished me drawering and will try to post it. The layout is of the Ampeg B25-B which in my opinion is one of the greatest sounding amps to my ears and has become the mainstay of my sound out of all my amps. I Hoffmanized the layout and made a few minor modifications which I'll number below. For the interminably bored, (like me), that actually look at this, feel free to point out any errors I've made. I'm a novice at best with schematics and until now the most complicated schematics I've tried to figure out were mostly a few single channel fenders so their could be mistakes but I've yet to find anything to be terribly erroneous by myself. Figuring out the PI and changing it to accept the 6GH8 nearly drove me to madness. :help: Ok, the changes:
1. I used single input instead of 4. I used the channel switch like on Sluckey,s Supro.
2. I put the bright switch ("ultra hi") on a push/pull pot with help from Sluckey. Thanks!
3. I omitted the "ultra lo" switch entirely because I simply do not like it.
4. The "shift" pot was added per Merlin's illustrations of the James Tone Stack in his preamp book.
5. PI tube was changed from a very expensive 7199 ($90- $120)to a much cheaper 6GH8 pentode/triode ($8). (Pin numbers are different.)
6. Added 470R to screens.
7. Changed bias circuit...is adjustable.
8. Wired octals to accept 6L6. The Ampeg used 7027A. Disconnect pin 1 from pin 8 if you want to use 7027. Pins 1 and 4 are internally connected on a 7027.
I'll get Visio or something comparable in the future but for now here's the drawings. I'll post them in a new reply. Hope they're legible...and correct.
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Some pictures.
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The schematics I referenced.
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Couple other things. It would be easy to add a presence knob to the feedback. I halved the 100k resistor from the input jack because I dropped the low input jack. I think it was correct to do this? It says 50k in the drawing but I think 47k would be the actual closest value... anyways