"Low" B+ Voltage Amplifiers

[Wavebourn]

Are 6N14P and 6N24P semi-remote cutoff triodes? Is this a problem for audio use -- i.e., distortion will be higher than if using 6DJ8/ECC88 in equivalent circuit? (Let's say Va = 90V, Ia = 7mA)
--

No, they are not. They are quite linear. The difference is in gm.

http://istok2.com/data/541/

http://www.goldenmiddle.com/files/6N24P.pdf

https://frank.pocnet.net/short/054/2/284.pdf

https://frank.pocnet.net/sheets/106/6/6ES8.pdf

 

[Shoog]

Just wanted to report that I have retro-fitted one of my low voltage amps with a 12V SMPS power supply which supplies the heaters and a DC-DC boost converter for the B+ of 220V

The units are :
AC 85 265V TO DC 12V 8A AC DC 50 60Hz Switching Power Supply SMPS Moudle Board | eBay
150W Inverter Battery DC 12V TO DC 220V Voltage Step UP Boost Converter Module | eBay
The SMPS seems to be better built but they both work and supply a stable B+ without running excessively hot. the amp draw about 1A of heater DC and about 220mA of B+. The scope show that there is quite a bit of ripple on the B+ - but not anything worse than most Linear supplies. I am thinking of adding a beefy cap after the booster, to further smooth things out and to see if it alters the balance of the amp to a bit more bass authority.
As an experiment in cheap alternative Power supplies it gets a thumbs up from me.

Shoog

 

[petertub]

Very interesting use of a dc/dc step-up.
How much high-freq noice does it emit ? Is this acceptable for hifi use ? And if so,
how much external components are needed ?

 

[Shoog]

Very interesting use of a dc/dc step-up.
How much high-freq noice does it emit ? Is this acceptable for hifi use ? And if so,
how much external components are needed ?

There is no noise bleeding into the circuit as far as I can tell. However its an emitter of FM RF interference as it is blocking out a channel on my analogue tuner at 89mhz.

The two boards simply wire up back to back and I have added an extra cap of about 400uf. It struggles a little to charge up the cap on power on - but once it is charged it runs fine for long periods.

Shoog

 

[ericj]

Have you checked how it behaves with a smaller cap?

.:Sent by pneumatic tubes

 

[Shoog]

Not yet, I will see if its a problem over extended use. It goes into current limiting mode and its LED goes out once or twice until the cap is fully charged.

Shoog

 

[Sorento]

6N14P and 6N24P double triodes were also designed to work on low voltages:

just an observation:
6n14p, 6n24p, ecc89, ecc189 all have dissimilar capacitance specs for the two triodes in the bottle
e.g. c(g1-a) typically 0.25pF for one triode and 1.5pF for the other triode;
not so for ecc88 ...