tubes...any 12v fodder here ?

[petemoore]

12av6, data sheet doesn't say much beyond pinout and heater supply info..
12au6 http://www.nj7p.org/Tube4.php?tube=12AU6
12aq5
12be6
    12a7, the HTML Says comination rectifier and power pentode...for half wave rectification and power amplification...? seems like it might be useful? max plate voltage is 135.

[Ice-9]

I'm busy working on a 12ax7 design myself,  but also using (don't hate me) op amps, i have a non inverting op amp to drive the first part of the vale. The op amp has been worked out to give a clean sound at full gain to drive the 12ax7. I'm looking at powering the valve at about 90 volts. I hope i'm not off topic as i will be using just a 12v ac adapter.

From the 12v ac adapter using a C/W voltage multipier , i think i will only get a max of 5 - 10 ma at 90ish volts, does tis sound ok

[esdiezy28]

I'm not sure if that will work, but I haven't worked with voltages that high yet. I did though, successfully, use a 12V DC adapter, a 7812 voltage regulator, and a TC1044 (same as a Max1044, Charge Pump DC to DC) in my recent Valvecaster build. Rick, aka, FrequencyCentral shows how to use a the 1044 to increase voltage for the plate resistors. Look at the "Murder One" schematic, version 2, its at the bottom of the page here http://www.diystompboxes.com/smfforum/index.php?topic=71381.0. In my Valvecaster I used only one 10uf cap to pin 2, and one to ground before taking my voltage, it rose from 12V to 21V with just one stage! Someday gonna reboard the whole circuit to provide more than 21V, but I'm VERY PLEASED with the improvement running the plates at 21V instead of the 12V. It worked at 12V but had alot more volume and tonal richness IMHO. Hope it helps!

[Minion]

If You Take one 12v ac transformer and connect the ouput primary to the output primary of another 12v ac transformer you will get 120v ac at the output which will rectify to about 160v DC for the Plates and if you Tap off the 12v ac from the first transformer you will have 12v ac for the heaters...

So useing two 12v ac transformers will give you close to the Plate voltage for a 12ax7 tube and the proper heater Voltages without buying those expensive High Voltage transformers needed for Tube preamps....


Cheers

[Cliff Schecht]

All you starved plate tube lovers take a look at this schematic as well (I posted it somewhere else yesterday..), it's a mix of op-amps and tubes used in a mic preamp to great effect. With the sets of mods I'm posting, this thing will compete with some high-end mic pre's.
Paia Mic Tube Pre schematic:
http://www.paia.com/prodimages/fantusch.gif

Mods:
http://www.tapeop.com/magazine/bonuspdfs/paiamicpremods.pdf
http://www.paia.com/ProdArticles/tmpmod.htm

Hope this helps

[Ice-9]

I've just had a look at the schematic over at paia for that mic preamp you mention. The voltage multiplier using the 4049 is the same as i'm using except i have extra stages to the multiplier ladder.

[Minion]

PAiAalso makes a starved plate Tube Guitar preamp with Speaker sims and a DI and a bunch of other stuff...

I used one to build a 100W Head with a 15 band EQ...

here"s the schematic...

http://www.paia.com/prodimages/siabsch.pdf

I did a few mods on mine like useing Fet opamps for the input , and increased the Gain by useing a 100K Gain pot instead of the 10k , and I used matched resistors on the output opamps to give better CMMR for the Ballanced DI....

Here"s the Amp...




Cheers


PS: it sounds freaking awesome , especially with the 15 Band EQ , very versitile in the tones you can get....

[beans_amps]

If you are looking for tubes to use, get your hands on some 12SL7's very nice sounding tubes.  If you wan to use some from the list, the 12AV6 is the same as 1/2 of a 12AX7 with two small signal diodes thrown in.  Can be used a s clipper but share a common cathode.  The 12AU6 pentode can sound pretty good with a 90 volt rail.  The 12AQ5 is a good sounding power tube and can be used just like a 6V6 except for the heater ratings.  The 12BE6 can be used as a compressor (some are microphonic) the diodes in the 12AV6 can be sued to rectify the signal voltage for the compressor. 

It sounds as though you may have found a load of tubes in a old radio.  The 12A7 was used in the old tabletop sets as a combination rectifier and power output tube.  The rectification noise was low enough that it did not show up in the output.  Some where on the internet is a stereo set with a pair of 12A7 tubes with a full wave power supply.

the 12AB5 is a nice sounding power tube and is the same rating as a 6V6.

Sean