12v car radio tubes. Possibilities?

[BluegrassDan]

Just restored a 1961 Ford F-100 vacuum tube radio that uses 12FR8 and 12FX8 tubes. It got me wondering whether anyone has experimented with these 12v plate tubes for things like preamps, guitar pedals, or DI boxes. They seem readily available NOS.

 

[ruffrecords]

Interesting tubes.

Cheers

Ian

 

[emrr]

Yes, on and off you hear of people doing these things. My partner at one time 20-25 years ago built a number of things, pedals, battery powered amps, etc.

 

[CJ]

Fender makes a tube stompbox,

https://www.fender.com/en-US/effects-pedals/boost-gain/mtg-tube-distortion-pedal/0234539000.html

 

[abbey road d enfer]

The 6205 tube in the Fender MTG is not a low-voltage tube. It's a subminiature designed to operate with standard HT. The MTG includes a DC/DC converter that goes from 9 to 150V.

 

[abbey road d enfer]

They seem readily available NOS.

Indeed they are. The main thing that let them down is the high heater power. Typically 0.3A at 12V, that's double a 12AX7. That definitely rules them out for anything phantom-powered, and makes them unattractive for stompboxes, particularly considering the standard power is 9V.

 

[gyraf]

Elektor once described a low-voltage preamp, based on ECC86 and EF98 - running off +30V:

 

[abbey road d enfer]

There's no doubt most of the common low-power tubes (EF8x, ECC8x...) can be used with very low HT voltage.
I remember a discussion with PRR about a distortion pedal that used an ECC83 with a 9V HT. It was a cath-follower with a variable cath resistor.

 

[gyraf]

..the EF98 and ECC86 were dedicated battery-voltage use tubes - Plate voltage down to 6.3V (!):

https://cdn-reichelt.de/documents/datenblatt/A300/EF98_DB-EN.pdfhttps://frank.pocnet.net/sheets/035/6/6GM8.pdf
Although the ECC83 and similar can also work on low voltages, they perform horribly compared to the dedicated ones

/Jakob E.

 

[trobbins]

Just restored a 1961 Ford F-100 vacuum tube radio that uses 12FR8 and 12FX8 tubes.

Does anyone have the service manual or schematic that shows how the 12FX8 was implemented?

I just finished a pedal using 2x 12FX8 and 1x 12AU7 that is based on a standard Magnatone vibrato circuit and it works well, but I did learn a few lessons about the 12FX8 along the way. So apart from the original Wurl organ use of the 12FX8 in oscillator/divider circuitry, I'm keen to find out where-else it has been used.

 

[Tubetec]

A tube stereo vibe/trem would be nice ,
maybe theres a clever way to use triode/heptodes to provide feedback via the extra grids or a seperate LFO per channel ,
There must be some circuit from the old tube organ days that fits the bill .

 

[trobbins]

The original Wurlitzer schematics using the 12FQ8 that I know of were:
https://dalmura.com.au/static/Wurl 4100B 12FQ8 schem 1.jpg
https://dalmura.com.au/static/Wurl 4100B 12FQ8 schem 2.jpg

My vibrato clone pedal schematic using the 12FQ8 is:
https://dalmura.com.au/static/Vibrato clone pedal schematic.pdf

 

[Wavelength]

I use to fix car radios when I was in college. Mostly used the 6GM8/ECC866 (low voltage 6922/6DJ8) and another pentode which I can't remember. The 6GM8/ECC86 can run the plate down to 6.3V, but you have to watch it will start to pull gird current. Like the 6418 and the new Korg tube both will draw grid current unless the circuit is right. I use the 6GM8/ECC in a USB DAC I built since 2003 called the Cosecant. I run it at 30V on the plate and it works great there. I have a clean boost I make with the 6418 in triode mode and it works well at 20V (30V supply) on the plate, but has really high Rp so I buffer it with a JFET (LSK187) in source follower.