Verellen Octal

[agedhorse]

For those of you who would like to learn a little more about the history of solid state vacuum tube replacements, my dad worked for a military division of the company that was the largest manufacturer of such devices in the world, Teledyne Semiconductor, during the time period that these devices were being developed.

While they focused on signal tubes primarily, there were also replacement devices designed for the 6V6 and 6BQ5 power tubes, but the demand wasn't there to justify production.

Below is a really good (technical) article about these devices, and especially about the need to adjust the design for different types of circuits. It's not an easy task, in part because tubes are more forgiving and in part because of the many possible circuits that are out there. It worked for these devices because they were targeted for specific applications within rigidly controlled equipment designs (telecommunications, test equipment and military) where the number of devices used for maintenance in these specific applications were enormous (in the millions). This was all big company stuff (though Randy did incorporate some in the V1 position of a few early guitar amp models with moderate success).

I have followed this since the late 1970's, in part because of my dad's interest in audio/small signal amplification (especially 48 volt applications because the extremely long life and power savings in large switching and repeater installations using thousands or tens of thousands of tubes is significant, his own applications were aircraft and satellite based where he worked mostly with sub-miniature and Nuvistor tubes).

https://lampes-et-tubes.info/sd/FETRON.pdf

 

[darev]

https://lampes-et-tubes.info/sd/FETRON.pdf

"The greatest thing since the winning of the West"

 

[agedhorse]

"The greatest thing since the


"The greatest thing since the winning of the West"

For those industrial and commercial users users of the tube types they covered, it was in fact the greatest thing ever, saved some customers millions of dollars.

Western Electric also had a similar device (for their unique tubes that had a much higher heater voltage), but never went into commercial production AFAIK.

[edit: They may have been produced, possibly exclusively for Western Electric's own equipment and service departments because those particular tubes had a unique 20V parallel/40V series heater circuit]:

 

[cfortner]

I decided to put them first in my Fender Bassman 135 (4 power valves, 135W) and Studio Bass (6 power valves, 180W) and will measure them before and after swapping. These amps work with anode voltages of 500V, for trying them more secure.

I presume, in similar circuits without special tricks they will behave like we know from tube rolling. With the benefit, that BIAS-voltages are unnecessary and are blocked by the ac-coupled grid1.

 

[agedhorse]

I decided to put them first in my Fender Bassman 135 (4 power valves, 135W) and Studio Bass (6 power valves, 180W) and will measure them before and after swapping. These amps work with anode voltages of 500V, for trying them more secure.

I presume, in similar circuits without special tricks they will behave like we know from tube rolling. With the benefit, that BIAS-voltages are unnecessary and are blocked by the ac-coupled grid1.

Just beware that the circuit will behave differently in both the Bassman 135 and the Studio Bass because of the UL connection that produces local feedback around the tube back to the screen. The Octals remove that feedback path, which changes other parameters. The Bassman 100 does not use the UL output topology as a comparison point.

 

[cfortner]

Ok, I don't know the exact topology of the Octals, but this is from Verellen's FAQ:

ANY ISSUES WITH AMPS USING ULTRALINEAR OUTPUT TRANSFORMERS?​

Early tests with a vintage Sunn Model T, which uses an ultralinear output transformer, have been great.



Interessant if the Octals use the UL taps at G2, but for a normal tetrode mode it has to use G2. Triode mode isn't possible. FAQ:

WILL THE OCTAL WORK IN MY AMP?​

The Octal is designed for amps with:

• PUSH/PULL CIRCUIT
  Not single-ended or triode connected
• STANDARD 8-PIN POWER TUBE
  EL34, 6L6, KT series, 6V6, or similar common octal pinouts

Does this mean, that G2 is internally fix connected?

 

[cfortner]

In the moment Verellen seems to be very busy, they answer on my questions, but very short and little delayed.

I'll ask them to the funktion of G2 in tetrode and UL-circuits.

 

[baxter_x]

So, did you manage to try those Octal in you amp?
Any noticeable change in tone or presence?

 

[cfortner]

Sorry, no time...

 

[coreyfyfe]

So, did you manage to try those Octal in you amp?
Any noticeable change in tone or presence?

Ben has been sharing some third party reviews and demo videos through his social media pages

 

[baxter_x]

Very interesting

 

[WG Plum]

They sound pretty great to me, would be good to hear some bass demos.

 

[baxter_x]

They sound pretty great to me, would be good to hear some bass demos.

You can find some on his website. There is the tone bat also the presence of a tube amp. Unfortunately you can't feel it through a video.

 

[WG Plum]

Well. Sounds real damn good in the Meatsmoke.

 

[baxter_x]

Well. Sounds real damn good in the Meatsmoke.

That's what think so. I'd really like to try those in my SVT 2 pro and Sadowsky SA200 to see if it can really replace real tubes.

 

[Balog]

Definitely interesting if these work out. I assume if they're successful enough they'll license the design to one of the big manufacturers. It'd be interesting to get an SVT from the factory with these in it.

 

[Sparky Mark]

Definitely interesting if these work out. I assume if they're successful enough they'll license the design to one of the big manufacturers. It'd be interesting to get an SVT from the factory with these in it.

I can understand fully why current owners of tube amps might move to these solid state output devices to extend their amp's life when tubes become too expensive, unreliable or non-existent. However, there are so many excellent, lightweight, more cost effective, more powerful, efficient modern solid state amps (with or without tube preamps) out there, that I'm not convinced a new amp market would exist for a company like Ampeg.
I guess it all comes down to whether these devices really do sound and feel identical to genuine vacuum tubes, that no other new amp topology can reproduce?

 

[6thplanet]

Exactly. Which is a big slap in the face to tube amp owners that tout there's nothing like a full tube amp.

I guess next we need a solid state transformer?

 

[cfortner]

I just measured my old Fender Studio Bass, first with six 6L6GC, then with 6 Octals.

Studio Bass 6x 6L6GC (8 ohm load):


38,3V RMS, 183W, 8% THD+N

Now with six Octals (I started the amp with a variac) (this foto is wrong, all six Octals are glowing):

At 8% THD+N 253W at 8 ohm, a clearly improvement of power.

At 2,5% THD+N app. 220W

But some oscillation with the Octals:

Connected to a 115 box you can hear the amps oscillation, not good.

At full power the Octals get warm, not very hot (I'll measure the temp next time).

Good result with power improvement, but some oscillations, may be because it is an UL amp?

With the valves 6x 6L6GC no oscillation at all:

I will report this to Verellen, next I'll test my Hiwatt DR405 clone (300W with 6x 6550 at 660V):

 

[baxter_x]

But some oscillation with the Octals:

Is this a problem?
While playing, do you notice any difference?