Heptode oscillators

[LoFi Ninja]

Hi..

I'm wondering if it is possible to make a varible oscillator with ECH81 for audio use ? Like a little noise toy..

Also I found these tubes in an old, battered radio, do you got an idea what I should do with them ? Anything really..

EM80
EZ80
EABC80
'ECH81 X2
EL84
ECC85
EBF89

[Wavebourn]

If you got also both transformers you can make a nice mono amp using EL84. EZ80 you may use as a rectifier, EM80 like a magic eye indicator. If there is a B+ filtering choke in that radio you can get a very nice small mono amp.
Was it Telefunken?
Does it have a vibrator to make AC from DC?

[LoFi Ninja]

Damn.. I only took the tubes.

I was on foot far away from home, and then suddenly the radio was just chucked in the road side.. I didn't check the brand or anything.
I guess I could try and see if it's still there.

The EZ80 is a Telefunken tube and the rest is Phillips Miniwatt.

Do you have a schematic somewhere for the amp ? I found a Mullard SE amp using an EZ80, EL84 and an EF86. I don't have spare money to spend on tubes so that one is a no go. Only ones that uses the tubes I found.

[m6tt]

ECC85, EL84 and EZ80 would indeed make a nice little mono amp. The ecc85 looks like a lower-mu 12AT7, so somewhere between AT7 and AU7. Probably makes an excellent driver for the EL84, and hopefully a nice voltage gain stage. It's not the *most* linear triode, but it's linear enough to look like it'll work from the curves. Sometimes those heterodyne mixers (ECH tube) are quite linear as voltage stages with the extra grids tied to plate, so that's another option. I'd use an isolation transformer to rectify the 230v mains into the ez80 for the B+/HT supply, and a seperate 6.3v filament transformer for the tube's filaments. The output transformer will need to be approximately 5-8k depending on bias points and desired power out, gapped for SE.

If you can find one more EL84, you can approximately double the power out and buy a cheaper output transformer by switching to push-pull. In that case, the ecc85 would be voltage gain + cathodyne phase splitter into the two el84 grids, both el84 cathodes connected to shared approx. 130 ohm cathode bias resistor. If that doesn't have enough gain, triode the ECH and put it in front of the ECC85.

Anyhow, that's what I'd do if I was dead set on making an amp from those tubes. Good luck!

[m6tt]

The EABC80 seems to have a nice linear triode in it as well, the duodiode-pentode tube would make a good CCS, at least...you have a few options for preamps!

[LoFi Ninja]

Oh damn, most of what your saying I'm not getting.. I know basic electronics, but nothing about tubes..

[m6tt]

Please look at the stickied threads about high voltage safety & information sources in this forum, they're quite good!

Here's some links that may help with theory etc.:
http://www.freewebs.com/valvewizard/
http://www.tubecad.com/articles_2003...ier/index.html
http://www.angelfire.com/electronic/funwithtubes/
http://www.tpub.com/neets/

Here's some links for datasheets etc. for the tubes:
http://www.tubedata.org/
http://www.nj7p.org/Tube.php
http://tdsl.duncanamps.com/

Don't be afraid to experiment with cheap or free tubes! Next time grab the transformers too though Check second-hand stores for old tube radio consoles, music amps/equipt., or something like that to experiment with, esp. if you learn better with your hands and eyes than by reading. Good luck, it'll make more sense after some reading and soldering!