[steve f]

After reading all of the recent posts about an OTL, my only question is how far down the road is it?

Steve

[Roger A. Modjeski]

Yesterday I pulled out the prototype that became the Counterpoint SA 4. It was well liked and I can do something better now. For better sound and reliability mine will be hardwired and simper. I really can't say when though I would like to hear what power and price people want.

It takes eight output tubes to get 100 watts into 8 ohms. How many people need 100 watts these days?

[steve f]

I could personally get by with 15 wpc and 25 for sure. In this economy, the idea of an integrated is very appealing.  The fewer output tubes, and less waste heat, the better. I am most curious about what others want too.

Steve

[Roger A. Modjeski]

I could personally get by with 15 wpc and 25 for sure. In this economy, the idea of an integrated is very appealing.  The fewer output tubes, and less waste heat, the better. I am most curious about what others want too.

Steve

Thats what I have in mind. Two output tubes, one driver per channel and a very quiet preamp tube.

[airhead]

For my Stax loudspeakers, notoriously difficult to drive and inefficient, I would need 100 watts per channel.  I suppose that would mean 8 output tubes per channel, which I seem to recall that SA-4 had.  Since 6LF6's are no longer available, what are you planning to use?  I  don't remember what the Transcendant OTL uses, but I have heard that there isn't a good source of those available any more either.
Are you planning on using coupling caps a la Futterman instead of the servo (is that what it was in the SA 4?) to block DC?   Despite what conventional wisdom says, I found the Futterman to sound better and to be more reliable with my speakers that the SA 4.
These two amps sounded much much better than anything else I tried at the time.  I'm still using the Futterman, but it can't last forever, but when it goes I would probably want an OTL to replace it, based on my experience in the past.

[steve f]

Transcendent uses 16 of the JJ octal base EL509 tubes per channel.  That makes one heck of an expensive re-tube job.  Output impedance is 2/10 Ohm and we are talking about 160 WPC into 8 Ohms.  The amp will drive anything. 
I can't afford to feed it though.

[Roger A. Modjeski]

For my Stax loudspeakers, notoriously difficult to drive and inefficient, I would need 100 watts per channel.  I suppose that would mean 8 output tubes per channel, which I seem to recall that SA-4 had.  Since 6LF6's are no longer available, what are you planning to use?  I  don't remember what the Transcendant OTL uses, but I have heard that there isn't a good source of those available any more either.
Are you planning on using coupling caps a la Futterman instead of the servo (is that what it was in the SA 4?) to block DC?   Despite what conventional wisdom says, I found the Futterman to sound better and to be more reliable with my speakers that the SA 4.
These two amps sounded much much better than anything else I tried at the time.  I'm still using the Futterman, but it can't last forever, but when it goes I would probably want an OTL to replace it, based on my experience in the past.

I am curious which Futtermans you have. I do have a good stock of 6LF6 tubes and they are on tubeaudiostore.com.

I can go either way on the output. Coupling cap or Servo and relay. The coupling cap is simpler, however, given the thoughts of listeners about capacitors I wonder which they would prefer.

[Clio09]

I prefer a design that does not use coupling capacitors.

[Roger A. Modjeski]

I prefer a design that does not use coupling capacitors.

How is your Transcendent (and his other amps) coupled to the load? Does it have bias and centering (offset null) pots? Is it easy to set up?

[Clio09]

I no longer own the T-16 but it used pots to adjust the DC offset null. Prior to connecting the amp to speakers it was recommended to place 10W 10 ohm resistors across the speaker terminals and let the amp warm up a bit. Then using a multimeter take readings on each channel and use the pots to zero out. After doing this connect the amp to the speakers and recheck the readings. To me it was an easy set up procedure but I found the pots to be very sensitive.

On the other hand the Atma-Sphere S-30 has a built in meter and a toggle switch that allows you to check the readings for DC offset null. Pots are also used and adjustments are very easy to perform. Both amps were auto-bias.

[poseidonsvoice]

I no longer own the T-16 but it used coupling capacitors between the driver and output stages. Pots are used to adjust the DC offset null. Prior to connecting the amp to speakers it was recommended to place 10W 10 ohm resistors across the speaker terminals and let the amp warm up a bit. Then using a multimeter take readings on each channel and use the pots to zero out. After doing this connect the amp to the speakers and recheck the readings. To me it was an easy set up procedure but I found the pots to be very sensitive.

On the other hand the Atma-Sphere S-30 has a built in meter and a toggle switch that allows you to check the readings for DC offset null. Pots are also used and adjustments are very easy to perform. Both amps were auto-bias.

The Transcendent Beast is as straight forward as the Atma-Sphere S-30. It has a built in meter with a toggle switch and dc offset is very straightforward. Pots are not sensitive on this design. No coupling capacitors for the output, it is direct coupled.

Anand.

[airhead]

I am curious which Futtermans you have. I do have a good stock of 6LF6 tubes and they are on tubeaudiostore.com.

I have the NYAL OTL3a.  They have 6 6LF6's per channel.  I bought a set from you a few years ago; they
are still in my attic.  I think I get about 80 watts per channel from these amps.  The stax's, unlike most
ELS's, have a very low impedance at low frequencies, and, after the speakers were repaired, the amps couldn't handle the bass, so I bought a pair of your subwoofers, which solved my problem.  I'm hoping that the tubes will last longer now.   Despite what is now conventional wisdom, these amps sound very good although they use coupling caps and lots of feedback.    I am told that the octal base EL 509's are not made to the correct spec anymore.   What tubes are you planning to use for output?





I can go either way on the output. Coupling cap or Servo and relay. The coupling cap is simpler, however, given the thoughts of listeners about capacitors I wonder which they would prefer.