Pre-Amp with russian tubes 1j24b

[holger1]

Hi,

I bought from Pollin in Germany some small russian tubes, direct heating, 1j24b. These tubes are pentodes, I would wire them as triodes, and the tubes are pretty cheap as well. Has anyone some experiences with tubes like this? Heating voltage is 1.2 Volts, anode voltage might be 40 Volts, anode current might be 1 mA. Planned is a pre amplifier with these tubes, and I hope so far, this will provide a good sound quality. Just interesting is to me, can I expect a more convenient quality, or would the sound more poor?

Every answer is appreciated.

Best wishes, Holger

 

[artosalo]

I have build a short wave receiver only by using 1j24b, not done any audio measurement.

Below is the link, maybe usefull to you.

Russian Subminiature Tubes

 

[piano3]

Does anyone actually know the triode mu of this 1j24b? ( My guess would be about 15 )

 

[artosalo]

Must be higher. My estimate is some 28...32.
The method I used is presented at page 35 of Radiotron Designer's Handbook 4th edition.

 

[piano3]

Based on this method I would have to agree with you; do you think the method applies to these tubes which are so different in construction?

My crude estimate was obtained by comparing with tubes of known mu in a line stage circuit but since I only used a resistive load, I would not be surprised that my estimate was out by a factor of 2.

 

[artosalo]

I think the method should apply because 1j24b acts electrically as an ordinary pentode.

 

[piano3]

Yes, that is a convincing argument; so it should be a useful gain stage although the dynamic resistance will be pretty high. Many thanks for your input!

 

[Sorento]

ug1g2 = 20 according to
1j24b various triode connections.

 

[Sorento]

By the way:
does anyone have Spice Model of 1j24b rod tube ?

 

[piano3]

I imagine it is unlikely that many have tried this tube for audio yet but the link you have most helpfully provided has a very useful set of curves. Have you any reason to doubt them? There is a good datasheet at the Klausmobile site.

 

[piano3]

I just did some filament current draw measurements on this tube; very consistant at the data sheet value of 13mA @ 1.2V
However, I decided to do some similar measurements on the big brother of this tube, 1P24B-V and most were close to 200mA which was far from the expected 255mA. Admittedly the datasheet was not specifically for the "V" variant. Has anyone else found this? Good news for D cell battery use.

 

[piano3]

ah! stupid me- just found the datasheet for "V" variant; indeed, 190mA +/- 20mA

 

[piano3]

Hi Holger1; Did you complete your project? I just finished and tested an easily portable microphone amplifier (without input transformer and power supply in the same box(!) ) with 2 cascaded stages of 1j24b in triode mode for use with small diaphragm and fairly low output condenser microphones and a hand held recorder with only single ended input. Direct coupling to mosfet source followers interfaces with the recording device and the filament supplies are batteries (the main attraction of proceeding from design to build). The bias is achieved with a IN4148 diode and with a CCS supplying 1.1 mA the anode-cathode voltage settles at about 65 volts. The sound is crystal clear and there are no microphonics. There is some thermal hiss with headphones on full volume but this is not noticeable on loudspeakers when recordings have been made at a reasonable distance. It might be an issue if distant recording were attempted and I would not use this valve at first stage of RIAA. My conclusion; definitely good for audio.

 

[artosalo]

Have you already checked the mu of triode connected 1j24b ?
Can you show the schematic of your mic. amp ?

 

[dovla]

1j29b & 1p24b

I made a battery-powered headphone amp with 1j29b & 1p24b but had to wire them in pentode because of insufficient gain with my low B+ (27-32 V).
http://www.diyaudio.com/forums/tube...amp-all-tube-direct-heated-portable-fits.html
I did try trioded 1j29 with 60V on and it sounded quite nice into EL84. 1j24 should be similar apart from the lower current.

 

[piano3]

I cannot check the mu directly but the voltage measurements made suggest that the triode connected curves in the link posted by payloadde are reliable. Unfortunately my IT skills are extremely limited and I have no idea how to use engineering CAD. I work from scribbled drawings in my notebook. I will try to make a neat hand drawing of the schematic and then scan it and ask my niece to show me how to post it on this forum; it is probably worth doing so for the efficiency of cramming everything in together rather than any innovative circuitry. The phantom supply, for instance, is provided via an emitter follower from a potential divider across the main HT(which is 180 volts) but this is only reasonable because the mics. I am using draw less than 1 mA from the phantom.