At your risk. All safety precautions must be followed. A fuse must be connected in series with any battery for protection. Any voltage or current apcan be dangerous.
Direct heated cathode power consumption is less than 50mA at 1ess than 1.5V per electron tube !!!
This Daven? low level amplifier was found by chance yesterday in a Pleiades cupboard. (Not sure even this is Daven, that had been long time ago the eBay's listing title. There is nothing written on this module except a very small stamp inside it that seems to say Daven.)
It had been bought on eBay for not much as probably nobody was looking for such a thing or nobody knew the existence of such a thing. It had been watched almost by chance. Not remembered how. Probably while looking for Daven constant impedance attenuators.
It looks it is coming from space.
It must be at least 50 years but it looks like newborn. No trace of age. The chassis has a color between gold and silver. No corrosion trace. There are unside some circuit board tracks, they look like made of gold and probably they may be.
It must have come from a medical, university, space laboratory?
It can be shock mounted to a bigger chassis. There are 3 space quality conical rubber aluminum mount supports with threads.
All 3 stages are in class A, ie electrons flowing all the time. Music modulates such flow of electrons.
On the left is a big UTC input transformer. Input impedance is 600Ω. It feeds a front end 1U4 (low battery consumption electron tube).
Then a top quality potentiometer. Then another 1U4 then another 1U4 as single ended output stage with a smaller UTC output transformer. The first 2 stages are RC coupled. The output stage is output transformer coupled. The UTC output transformer is designed to be able to carry DC current.
No electrolytic capacitors. Everything must be top quality film or very small can paper in oil with excellent mounting hardware.
Today after a lot of watching or eye signal tracing it was decided to power it up.
A 1.2V AA Recyco rechargeable battery was used for filaments.
On 1st and 2nd electron tube there is a series dropping resistor. So only the output stage is directly connected to battery. The other 2 electron tubes must be deliberately under heated. For lowest noise?
Initially 12V was applied to anode circuit. It didn't it work. Only a couple of micro amps measured.
Anode current is increased abruptly with increase of tension of anode supply.
At this stage it is supplied with 57 volts and anode current consumption is of the order of 0.7mA.
Sennheiser HD 580 were directly connected at the 2400Ω output.
Power out capability is still low.
But the sound quality is amazing. It sounds like a vinyl record playing nice recorded vocals.
There were s problems due to clipping etc with the Shure VP64 mic.
When the Fostex M80RP was connected S problems stopped. Amazing transient response. Amazing treble detail. So natural as if no amplification is employed.
Not even a single trace of bass heaviness.
Sounds like When I Fall in Love - Nat King Cole.
Low noise too. By connected a 0Ω male XLR, slight hiss disappears.
It is also striking that when the omnidirectional Shure VP64 mic is connected out of phase, that the background noise is canceled when mic is approached to ear while wearing headphones (very dangerous practice). This experiment is not recommended and could lead to ear damage should feedback become positive and a very loud ear damaging oscillation may occur. Taking all safety precautions is most important. The ambient canceling effect is to such high degree proving the amazing sound quality of such amplifier.
This is the first time an all electron tube signal path from mic to headphones with amazing low battery power consumption is tried at Pleiades. It is hardwired. Mic and headphones are connected to the barrier strip.
The input transformer is a UTC E-3832 TF1RX10YY. The output transformer is a smaller size but still big enough UTC E-3833 TF1RX13YY.
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