A directly heated triode or Pentode SE amp on a Budget

[avisa]

I recently finished building my diy 6l6SE amp to complement my diy Open Baffle Speakers, my room size is small so the output is sufficient.

However I would like to experience the sound of a Directly Heated Tube, and am scouting for a suitable tube for my next project, The 300b's are way beyond my budget so are the 2a3's and the 45's - I was think of using either the 811a or 813 or the GM70 tubes.

I have seen as simple 811a class a2 amp schematic on this forum or will build a amp which operate the 813 or the GM70 on low voltage.

I do not mind if it is a triode or a pentode SE amp - I am looking for around 5 to 12 watts of power, which is more that enough for my needs.

I have searched, but the above tubes seem to be the most popular ones. Which other directly heated tubes will be suitable for my SE amp.

Any help is appreciated.
Thanks.
- Avi.

[Miles Prower]

Originally posted by avisa
However I would like to experience the sound of a Directly Heated Tube, and am scouting for a suitable tube for my next project, The 300b's are way beyond my budget so are the 2a3's and the 45's - I was think of using either the 811a or 813 or the GM70 tubes.

Doesn't leave very many options. You might see about getting some 6A3s (6.3V version of a 2A3). The only DH beam former that might suit your purposes is the 1624.

Most of the rest of the DH tubes are the high power RF finals. That means operating at some bigvolts to get the best out of them.

[avisa]

Originally posted by Miles Prower


Doesn't leave very many options. You might see about getting some 6A3s (6.3V version of a 2A3). The only DH beam former that might suit your purposes is the 1624.

Thank you for your kind reply. The 6A3 will give a out put off only about 2.5 to 3 watts, and would like to avoid running the tubes in parallel, I checked on the data of the 1624 - seem to be like a direct heated 807. may be it will work.

Are there any other tube I can use?

Thanks again.

- Avi.

[kmaier]

You don't have too many options... sorry to say. The 6B4G (octal 6A3) can yield a solid 4+ watts output but you also need DC filaments to knock out the hum. Still, you're looking for more power.

When you get into the older transmitting triodes, the expense also climbs as you need plate caps, fancier (read more expensive) sockets and high voltage power supplies and in many cases custom transformers.

One uncommon option is the 3C24. Thoriated-tungsten DHT which uses the same base as a 45/2A3 but does require grid and pate connection caps. Pd is rated at 25 watts and should be good for a solid 5-watts but will require A2 operation. They are also easily obtainable at reasonable prices and are sorta pretty when lit up (orange glowing plate). As I have a small quantity of these, I plan to build such an amplifier sometime in the near future. There are a few designs available, Tossie built one... quite pretty too. Here's a link:

http://www2u.biglobe.ne.jp/~tossie/KY-3C24-J.html

Regards, KM

[avisa]

Originally posted by kmaier
One uncommon option is the 3C24. Thoriated-tungsten DHT which uses the same base as a 45/2A3 but does require grid and pate connection caps. Pd is rated at 25 watts and should be good for a solid 5-watts but will require A2 operation. They are also easily obtainable at reasonable prices and are sorta pretty when lit up (orange glowing plate). As I have a small quantity of these, I plan to build such an amplifier sometime in the near future. There are a few designs available, Tossie built one... quite pretty too. Here's a link:

http://www2u.biglobe.ne.jp/~tossie/KY-3C24-J.html

Regards, KM

Thank you for replying, the 3C24 is a very good option that you have suggested, I checked the link you posted, it look beautifull when lit up, the ckt also is not too complex.

I do not mind running tubes in A2 - are there any more options.

Thanking you once again.
-Avi.

[kmaier]

Yes, Tossie has many A2 designs with other tubes... another of my favorite old tubes is the 808... still have a couple of these too.... also pretty when lit up... cherry red plate.

http://www2u.biglobe.ne.jp/~tossie/YM-808.809-J.html
http://www2u.biglobe.ne.jp/~tossie/M808-J.html

... and a A1 4E27 amp... orange plate glow and 18W output:

http://www2u.biglobe.ne.jp/~tossie/FJ-4E27-J.html

Take a look thru these links too:

http://www2u.biglobe.ne.jp/~tossie/gallery2007.html
http://www2u.biglobe.ne.jp/~tossie/gallery2006.html
http://www2u.biglobe.ne.jp/~tossie/gallery2005.html
http://www2u.biglobe.ne.jp/~tossie/gallery2004.html

Regards, KM

[avisa]

Originally posted by kmaier
Yes, Tossie has many A2 designs with other tubes... another of my favorite old tubes is the 808... still have a couple of these too.... also pretty when lit up... cherry red plate.

http://www2u.biglobe.ne.jp/~tossie/YM-808.809-J.html
http://www2u.biglobe.ne.jp/~tossie/M808-J.html

... and a A1 4E27 amp... orange plate glow and 18W output:

http://www2u.biglobe.ne.jp/~tossie/FJ-4E27-J.html

Take a look thru these links too:

http://www2u.biglobe.ne.jp/~tossie/gallery2007.html
http://www2u.biglobe.ne.jp/~tossie/gallery2006.html
http://www2u.biglobe.ne.jp/~tossie/gallery2005.html
http://www2u.biglobe.ne.jp/~tossie/gallery2004.html

Regards, KM

Thank you for the links, - Class A2 dose open up a lot of options.

I read in other posts in the forum and there they have mentioned about Class A2 sounding Diffrent than Class A operation.

Could you or others kindly explain that to me.

Thanking you for your kind help.

Regards,
- Avi.

[Bandersnatch]

hey-Hey!!!,
There is also the HY69. Its DH pentode, and with a Thoriated Tungsten cathode like the 845/813/811A. They are more like an 807 than the 1624( whose curves are more like a 6V6 ). There is also type 1619 which is *VERY* close to the 1624. Consider also the 2E22...its 5-pin base like HY69 and 807/5933.
cheers,
Douglas

[revintage]

Hi Avi,

Can not see anything wrong with using the easily obtainable 813 as you suggested in your first post.

If triode-strapped you could get away with the wished power at quite low voltages.

It would also be quite easy to drive. Personally I would stay away from A2 as this complicates the driver.

http://www.pmillett.com/file_downloads/813%20curves.gif

The offset might might be the heatersupply needed.

[Sheldon]

Originally posted by revintage
Personally I would stay away from A2 as this complicates the driver.

True, if you want all tube. But if you don't mind a Mosfet follower to drive the grid, it's three extra cheap parts; two resistors and the FET.

Sheldon