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Starved-heater operation
Starved-heater operation
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Old 20th January 2019, 02:46 PM   #11
Printer2 is offline Printer2  Canada
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Don't know if it will display, one is at Free stomp boxes.
Click the image to open in full size.
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Old 20th January 2019, 03:51 PM   #12
JMFahey is online now JMFahey  Argentina
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Quote:
Originally Posted by Printer2 View Post
Don't know if it will display, one is at Free stomp boxes.
Click the image to open in full size.
Won´t show for non logged in Members:

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You are not authorised to download this attachment.
Can you please download/save the relevant image to your own computer and then upload it here?
If possible as an image, if not as an attachment.
Thanks.
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Design/make/service musical stuff in Buenos Aires, Argentina, since 1969.
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Old 20th January 2019, 05:59 PM   #13
Printer2 is offline Printer2  Canada
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I'll try. Oh, it worked.
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File Type: png CT-01_02_03Servicemanual_Page_03.png (368.2 KB, 58 views)
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Old 20th January 2019, 10:57 PM   #14
Gnobuddy is offline Gnobuddy  Canada
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Quote:
Originally Posted by Printer2 View Post
I'll try. Oh, it worked.
Thanks for the schematic!

To me it seems that this pedal was designed by someone who knows their way around analogue audio electronics. It isn't a blind copy of something from the 1950s or '60s like most of these "real tube" pedals, and the design shows awareness of more sophisticated techniques that are lacking from typical hobbyist designs like the Valvecaster.

As an example, this VOX preamp uses an op-amp in a servo feedback loop to monitor the anode voltage of the 12AU7, and continuously adjust the grid bias voltage to bring the anode voltage exactly where the designers intended. The op-amp only operates at very low (near DC) frequency, so it doesn't interfere with the audio signal passing through the valve.

This means no need to hand-select 12AU7s for this unusual operating point (which is so far below normal operation that you can't even see it on normal datasheets.)

By the way, Takamine claims their Cool Tube preamp uses low heater voltage to avoid having a hot tube drying out and damaging the nearby wood of the guitar body. It could be pure marketing BS, but it is at least a plausible reason, unlike some of the nonsense we often see in ad copy!

-Gnobuddy
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Old 20th January 2019, 11:45 PM   #15
audiostrat is offline audiostrat  Greece
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Originally Posted by JMFahey View Post
Thanks.
Would you please post it?
Yep, here you go:
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File Type: pdf vox big ben overdrive.pdf (581.1 KB, 34 views)
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Old 21st January 2019, 02:49 AM   #16
Printer2 is offline Printer2  Canada
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Much easier on the eyes.
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Old 21st January 2019, 08:15 PM   #17
djgibson51 is offline djgibson51  New Zealand
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Beautiful. Yummy engineering.
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Old 21st February 2019, 09:11 PM   #18
mozz is offline mozz  United States
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Have a valvecaster on my bench right now. It is a starved plate design. Mine is actually run from a 24vct transformer so i have the full 12.6v on the filaments and about 30v on the plate. These sound great and there are a lot of mods for this on one of the pedal sites. Mostly a 12au7 or 12at7 work great and a 12ax7 sounds like crap. They do not like the starved plate. Reason i built it was because i have a few hundred of the variants, 12au7, 12at7, 12av7, 12az7, 6201,6211,5963, 5965, 6414.
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