EL34 in place of a 6AS7G (used in the supply circuit as a pass tube). how?

[tubetvr]

I won't be using a 500-0-500V xformer though. It'll only be a 280-0-280.

In the drawing it is a 500CT transformer that is 250-0-250V which is not enough, 280-0-280 should be better as it will give a raw DC of ~375V, at this voltage there will be ~65V over the EL34 which can pass ~ 50mA but no margins. I still recommend a higher AC voltage and a better design.

According to Philips datasheet the max voltage between heater and cathode is 100V, (Philips Electron tubes, March 1975)

Regards Hans

[jarthel]

Originally posted by tubetvr


In the drawing it is a 500CT transformer that is 250-0-250V which is not enough, 280-0-280 should be better as it will give a raw DC of ~375V, at this voltage there will be ~65V over the EL34 which can pass ~ 50mA but no margins.
Regards Hans

the connected circuit will used about 70mA. does that mean the EL34 is not suitable?

how did you find out about 65V and 50mA? can you tell me what graph can I find such info?

Thank you very much

[tubetvr]

Look here http://www.mif.pg.gda.pl/homepages/f...129/e/EL34.pdf
at page 9, you can see that an EL34 triode connected will pass ~50mA at 65V and 0V on the grid, it can pass more at positive grid voltage but then it will draw current from the reference Zener chain which will affect the output voltage. A 6AS7 will pass ~150mA already at 40V. with 0V on the grid. Find a better design which use feedback to get a better stabilised voltage.

Regards Hans

[jarthel]

Originally posted by tubetvr
Look here http://www.mif.pg.gda.pl/homepages/f...129/e/EL34.pdf
at page 9, you can see that an EL34 triode connected will pass ~50mA at 65V and 0V on the grid, it can pass more at positive grid voltage but then it will draw current from the reference Zener chain which will affect the output voltage. A 6AS7 will pass ~150mA already at 40V. with 0V on the grid. Find a better design which use feedback to get a better stabilised voltage.

Regards Hans

thank you.

the page you linked above contains circuit that are for "advance DIYers" IMO

[jarthel]

would I encounter problems using the circuit above (still using 6as7) if my target Vout is around 150V?

[tubetvr]

would I encounter problems using the circuit above (still using 6as7) if my target Vout is around 150V?

Max dissipation of a 6AS7 is 13W per plate so as long as you don't exceed that it should be OK, however the regulation of this circuit is bad and therefore the voltage will vary if the current varies.

Regards Hans

[cogsncogs]

Did anyone notice that the reg circuit in question uses BOTH sections of a 6AS7? So when Eric suggested an EL34 would that mean two EL34's in //?
Regardless the regulation of the circuit is poor, in otw not that great. That's not to say it wouldn't work as far as for his Brute Force Line Stage. It's a pretty darn simple series pass regulator, about as simple as you could get. To get better regulation one would add an error amplifier which would add to it's complexity unfortunately. There are other tubes, triodes or triode strapped pentodes that can be used. From the article I believe one reason he used the 6AS7 was for it's looks.

@jarthel here's a nice tutorial by Steve Bench:

http://members.aol.com/sbench/reg1.html

Cheers
Wayne

[jarthel]

Originally posted by cogsncogs

@jarthel here's a nice tutorial by Steve Bench:

http://members.aol.com/sbench/reg1.html

Cheers
Wayne

I have read that article twice already. very good one.

He mentioned changing R1 and R2 to change Vout but he never said what formula to use. I was thinking simple voltage divider was used which according to my search is:

Vout = Vin x R2 (R2 + R1)

But for a newbie like myself, that's only a guess. It's probably right but most likely it's wrong.

Thank you all for the help