ECC83 with 12V on the anodes?

[Mike-repairman]

Just a query; would an ECC83 actually work with just 12VDC on the anodes? Most circuits I have seen in the past have at least 70V and often up to 120V HT supplies.

I came across a Valve overdrive unit for guitar with a 12VDC PSU on ebay and was curious how it would work.

Mike.

[ITAM805]

Hi Mike

this homebrew guitar pedal is popular and uses 9V-12V anode volts... Valve Caster

ps - you edited your post while I was writing!

[Mike-repairman]

Thanks ITAM805; I never knew these low voltage circuits ever existed; amazing what you didn't know even at 70 years old LOL.

Mike.

[G6Tanuki]

I've used a 12AT7 (which is rather similar to an ECC83) in a homebrew regenerative medium-wave broadcast-receiver using 12V on the heater and the anodes.

It needed a few more turns added the regeneration coupling-coil than would have been the case for the more usual +150-odd volts onthe anode, but it worked!

[barretter]

If you read the Valve Caster thread it uses an ECC82, not an ECC83 and the man says that using an ECC83 with 12VDC on the anode produces terrible sound, which is not surprising.

[Peter.N.]

Pye made a car radio with 12v supplying all the valves but with a single transistor in the output stage and it sounded very good, I had one in my car. TRC1000 I think it was.

Peter

[Herald1360]

If you look at the curves for an ECC82 you will get a modest anode current at 12V HT and near zero bias volts. Enough to make a low level audio stage with not a lot of gain. In the guitar pedal, I suspect that the horrendous distortion available is part of the musical effect desired. This will vary considerably with different valves!

[kalee20]

I have used an ECC82 in an LC oscillator circuit with about 40V on the anode. Wondering how low the supply voltage could be before it stopped oscillating, I reduced the HT ... Would you believe it still worked with 50mV of HT!

[Mike-repairman]

Quite surprising Kalee20. As a matter of interest what volts did it need to fire it up again?

Mike.

[Tractorfan]

Hi,
The Pye car radio mentioned in post no.6 used valves that were specifically designed for 12volts HT but still had 6.3volt heaters. My first car had one and I often caused surprised looks among folk by saying that I had a Morris Minor Twelve Valve!
It'd be interesting to see what other valves would operate on very low HT. PL509 perhaps?
Cheers, Pete.

[turretslug]

Originally Posted by kalee20

I have used an ECC82 in an LC oscillator circuit with about 40V on the anode. Wondering how low the supply voltage could be before it stopped oscillating, I reduced the HT ... Would you believe it still worked with 50mV of HT!

Brings into question the whole meaning of "HT" and "LT"! The US "A" and "B" would at least be less ambiguous in this case.

There's the well-known case of the ECH81/83- I wonder how many other "conventional" (i.e. no special measures for low-voltage working) valves ended up being used at low voltage? The BC1206 beacon receiver which used 28V for its HT supply is an example with mainstream loktals that would have been familiar in domestic table sets (apart from the output valve, a twin-triode which I believe was developed for 32V "farm" radios, almost a baby 6080).

[turretslug]

Correction! The 28D7 output valve was a twin beam tetrode, rather than twin triode. Nonetheless, there's a common thread here, all the way back to the original post- the heater power dwarfs the HT consumption in all cases, the guitar overdrive unit could almost be run from a PP3 HT-wise but heater consumption would exhaust it very quickly.

[kalee20]

Originally Posted by Mike-repairman

Quite surprising Kalee20. As a matter of interest what volts did it need to fire it up again?

Can't remember, was about 50mV though. Naturally, amplitude of oscillations was only some tens of mV's. As a matter of detail, the oscillator was for 75kHz, used both sections of the ECC82 in push-pull, a pot core coil (which gave a high Q), tuned with a polystyrene capacitor. Feedback was via a separate anode winding (with HT centre-tap).

With a bit of tweaking, it may even have worked to ZERO volts HT, relying on the emission velocity of the electrons to operate. May be a project to re-create...

[Mike-repairman]

Thanks for the reply, a very interesting project Kalee20.

Mike

[4cx250b]

Originally Posted by Mike-repairman

would an ECC83 actually work with just 12VDC on the anodes?

Yes, it will work. When I was at university, I was not allowed to use voltages in excess of 30v, except in exceptional circumstances.

I ended up building a hybrid amplifier in my spare time which ran with an HT voltage of 24v.

It wasn't particularly efficient (obviously) but it did work, and it used a standard valve in the pre-amp (an ECC88 if I remember correctly, but I wouldn't swear to it.) You don't have to use space charge valves, at least for low power.

A couple of years ago, I was going to research this idea further, but never got around to it - too many ideas, not enough time!

[G8HQP Dave]

To use 'normal' valves on low voltage you need low mu, so an ECC88 might work where an ECC83 will not. Even then you have to accept significant distortion.

[daviddeakin]

You can use any valve at low voltages, even the ECC83, but you have to think very seriously about grid current. There's a good article on starved circuits here:
http://valvewizard.co.uk/Triodes_at_...s_Blencowe.pdf