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Old 12th January 2009, 07:00 PM   #1
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Default 12AY7 preamp schematic

hello .....

i found this schematic but i only have some high quality 12AY7 tubes

do you think that since the schematic is made for 12AU7 will work directly or needs to be moded to fit in the 12AY7

excuse my limited knowledge about tubes i am a transistor guy and only have a lot of these tubes and wanted to do something with them

thanks
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Old 12th January 2009, 08:06 PM   #2
kmaier is offline kmaier  United States
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Hi Sakis,

The schemaric shows either a 12AX7 or 12AU7. These two tubes are at opposite ends of the mu table... 100 vs 20. I would also comment that with a 330K plate load resistor and a 100V plate supply, they are barely conducting. I would not waste time building something from this schematic.

The 12AY7 is a wonderful tube... it has a mu of ~40 and has been used in high-end products from tube condensor microphones to microphone preamps and more. I would search for for some schematics that either use a 12AY7 or 6072 (almost identical). Good luck.

Regards, KM
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Old 12th January 2009, 08:15 PM   #3
rdf is offline rdf  Canada
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That's one strange schematic. Why the blocking cap on the first grid? Doesn't the bypassed cathode result in a gain >>100? 0.02uF output and interstage coupling caps?
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Old 13th January 2009, 05:58 AM   #4
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Default thanks so far

Quote:
Originally posted by kmaier
Hi Sakis,

The schemaric shows either a 12AX7 or 12AU7. These two tubes are at opposite ends of the mu table... 100 vs 20. I would also comment that with a 330K plate load resistor and a 100V plate supply, they are barely conducting. I would not waste time building something from this schematic.

The 12AY7 is a wonderful tube... it has a mu of ~40 and has been used in high-end products from tube condensor microphones to microphone preamps and more. I would search for for some schematics that either use a 12AY7 or 6072 (almost identical). Good luck.

Regards, KM
thanks for your help ..... do you have any scehmatic that might help my case ????
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Old 13th January 2009, 07:57 AM   #5
Yvesm is offline Yvesm  France
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Default Re: thanks so far

Quote:
Originally posted by sakis


thanks for your help ..... do you have any scehmatic that might help my case ????
Depends on your target !

This schemo is obviously designed for a guitar input stage ... or so ?
Link caps values and op points being deliberatly pushed at some limits, it can be seen as a kind of "Sound Processor".
It deserves to be tested in a such usage.

If you need a preamp for another usage, please precise wich.

Yves.
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Old 13th January 2009, 08:11 AM   #6
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Default i had an argument

about this in a previous thread ......

i belive that this preamp is made as a hifi preamp ....at least this is what is stated by the designer .....

also i had a serious argument with some "Quitar" forum members in a similar thread some long time ago cause they insisted that 12AY7 can only work in quitar amps .....

so much for that i found so many 2.000 dollar phonostages that work with this tube .....

let us please not make that a quitar issue cause its not !!!!

my target is a line hifi preamplfier

thank you very much for your help
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Old 13th January 2009, 08:39 AM   #7
kmaier is offline kmaier  United States
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In general the 12AY7 has been used in microphone preamps over the years. You can find a balanced schematic in the Radiotron Designer's Handbook. Yes, it's also been used in guitar amplifiers for the preamp section, but that certainly does not limit it.

I would not consider the schematic you posted as a preamplifier for home audio use, regardless of what the "designer" stated. You can find a list of recommended bias points in the back section of most vacuum-tube manuals (like a RCA RC-30). This will give you values for cathode and plate resistors, supply voltage and list gain, distortion, maximum output voltage, etc.

Depending on what your target is (gain, output impedance, polarity) you can either make a single gain stage (hence inverting polarity), add a cathode follower for lower output impedance or cascade two stages for higher gain and non-inverting output.

Simply stating a line preamp is not quite enough information. Do you have an overall gain requirement? What are you driving with it? What is the input impedance of the source you will drive?

Regards, KM
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