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A directly heated triode or Pentode SE amp on a Budget

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A

avisa

Member
Joined 2008
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

Miles Prower

Member
Joined 2005
dolphin-hsl.com
avisa said:
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.
Click to expand...

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.
 
A

avisa

Member
Joined 2008
Re: Re: A directly heated triode or Pentode SE amp on a Budget

Miles Prower said:


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.
Click to expand...

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

kmaier

Member
Joined 2007
3C24 anyone?

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
 
A

avisa

Member
Joined 2008
Re: 3C24 anyone?

kmaier said:
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
Click to expand...

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

kmaier

Member
Joined 2007
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
 
A

avisa

Member
Joined 2008
kmaier said:
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
Click to expand...

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.
 
B

Bandersnatch

Member
Joined 2003
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
 
R

revintage

Member
Joined 2007
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 curves.gif

The offset might might be the heatersupply needed.
 
B

Bandersnatch

Member
Joined 2003
Sheldon said:


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
Click to expand...


hey-Hey!!!,
Use a cascode FET, deals with the screwey gate-drain capacitance, or maybe a $2 12HL7 pentode. The smaller tubes will be quite able to run the power requirement, and without the filament supply the bigger tubes need.
cheers,
Douglas
 
R

revintage

Member
Joined 2007
This is a Soundlab-inspired A2 solution. Had no model of 2SK2700 so I took what I had:
 

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S

Sheldon

Member
Joined 2003
Bandersnatch said:
Use a cascode FET, deals with the screwey gate-drain capacitance, or maybe a $2 12HL7 pentode. The smaller tubes will be quite able to run the power requirement, and without the filament supply the bigger tubes need.
Click to expand...


In this application, at pretty high voltages and used a a follower, the D-S voltage will be high enough for most FET's that the CRSS will be low and flat. I've used FQPF2N80 for a couple of projects. It's an 800V part, and the CRSS is about 6pF at 25 Vds and doesn't rise much until Vds goes below 6V. It's also an insulated package, which is handy as long as you don't need to run too much bias current.

Sheldon
 
S

Sheldon

Member
Joined 2003
Bandersnatch said:
I'd still protect for it whilst designing the circuit.
Click to expand...

Not sure I understand what mean there.

You could substitute a current source for the resistor under the follower. I tried that on one amp with DN2540 or the IX chip for the current source, because both are depletion devices and simple to set up. But with either one it would occasionally oscillate. Tried playing with stopper values but couldn't seem to make it perfectly stable, so I just went back to about a 10k resistor. Sims might help sort that out.

Sheldon

edit: when I said earlier that only three extra parts are needed, I neglected to include the negative bias supply that wouldn't be there unless the design already is fixed bias. Not difficult or expensive to do, but it is more parts.
 
A

avisa

Member
Joined 2008
I Thank you all for your kind help.

It looks like the 813, is the tube that will meet my needs - to start with, I could operate it at a lower voltage, and if required, increase the operating voltage to get more power.

I have been reading a lot of info about 813 on this forum, and on the net, in the past few days.

Also another thing about the 813 tube that i have understood is, that the driver stage can remain common for both the higher and lower voltage operating points of the 813 tube.

Thanking you all once again.

- Avi.
 
rcavictim

rcavictim

Member
Joined 2004
Bandersnatch said:



hey-Hey!!!,
Use a cascode FET, deals with the screwey gate-drain capacitance, or maybe a $2 12HL7 pentode. The smaller tubes will be quite able to run the power requirement, and without the filament supply the bigger tubes need.
cheers,
Douglas
Click to expand...


Doug,

Do you have a schematic to show what you are speaking of with using a 12HL7 or perhaps in my case a 6CL6 (also a video power pentode). Does the FET still have to be used?
 
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