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    Building, troubleshooting and testing of these amplifiers should only be
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Woolgathering

mr2racer

Member
2009-07-09 12:53 am
Hey Anyone,

I have been looking for a while for a way to build a high power SE amp. Something along the lines of 50 watts. On another thread a friend posted a schematic of the Altec Lansing 260A amplifier using 813 transmitter tubes. I looked at the data sheet and was amazed at the power capabilities for this tube, 100 watts plate dissipation. Unfortunately the data sheet does not list class A operation.

Using it in triode would be pointless.

I would want to use it in ultralinear class A. I know the risks of building an amp with a B+ in the KV range. But the idea is intriguing.

There are some questions even at this woolgathering stage;
-Has anyone ever heard this tube? Is it a Hi Fi quality tube sonically?
-Is it even possible to use it in class A?
 
On another thread a friend posted a schematic of the Altec Lansing 260A amplifier using 813 transmitter tubes. I looked at the data sheet and was amazed at the power capabilities for this tube, 100 watts plate dissipation. Unfortunately the data sheet does not list class A operation.

I don't suppose the spec sheet would since the 813 was intended for bigwatt RF power amps, or AM plate modulators. The only audio data is for Class AB1 PP.

"Using it in triode would be pointless".

Not really. If you can keep the voltage below 1100V, you can stay within the scrfeen voltage spec, so Ultralinear or triode are possible. Trioded 813 has been referred to as the "poor man's 845".

"Has anyone ever heard this tube? Is it a Hi Fi quality tube sonically?"

SE pentode is pretty much high distortion, though some like it. No telling what that distortion profile will look like. This one may need the assistance of lNFB in addition to gNFB to sound really good.

I did a project with another RF pentode, the 807, and got a lot of h3 and higher order harmonics that made for a really nasty sound open loop. I needed lNFB as well as gNFB to clean 'em up. Definitely not like the 6V6-oids and the 6BQ6 that make mainly h3 and very little higher order harmonics. These sound overly "edgy" or "aggressive", but not fingernails on the blackboard nasty.

"Is it even possible to use it in class A?"

It's one of the few high power RF pents without a severely restricted screen voltage rating, The Vgk= 0 plate current looks pretty limited, so you may need to take it into Class A2, but a power MOSFET source follower grid driver can handle that easily.