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Verellen Octal

#62
cfortner said:
Only fixed BIAS, look at the FAQ
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Thank you. I'm a little sceptical of the lifespan statement:-
Screenshot_20260125_155601_Brave.jpg

There should be a theoretical MTBF figure calculable for an electronic circuit that operates and cycles at up to 300 Fahrenheit / 150 Centigrade. Just to say "should continue to work indefinitely" is a red flag (for me) about the validity of other statements.
 
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#63
Sparky Mark said:
Thank you. I'm a little sceptical of the lifespan statement:-
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There should be a theoretical MTBF figure calculable for an electronic circuit that operates and cycles at up to 300 Fahrenheit / 150 Centigrade. Just to say "should continue to work indefinitely" is a red flag (for me) about the validity of other statements.
Click to expand...
Just a suggestion that if the MTBF exceeds say 100k hours, might that be considered “indefinite” for practical purposes?

Calculating and then testing such aging parameters is really difficult without testing a large numbers of devices and then quantifying (or trying to quantify) accelerated testing.

This is where qualitative “best estimates” and “marketing estimates” overlap because of practical considerations.
 
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#64
agedhorse said:
Just a suggestion that if the MTBF exceeds say 100k hours, might that be considered “indefinite” for practical purposes?

Calculating and then testing such aging parameters is really difficult without testing a large numbers of devices and then quantifying (or trying to quantify) accelerated testing.

This is where qualitative “best estimates” and “marketing estimates” overlap because of practical considerations.
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Agreed. However, it just reads as if no calculation has been attempted. If MTBF calculations indicated 100k + hours, surely that would be a better statement to make?
 
#66
Balog said:
Has anyone received and tested these yet?
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Mine have been in USPS limbo for days. They should all have been in mid week but one set keeps getting delayed and with the storm I probably won’t have them all and be able to test in a big amp until mid to late next week. Might try the pair I have in my V2 for now. A few friends locally have received and tested theirs, positive reviews thus far. Ben has been sharing a lot of posts on social media from people who have received them.
 
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#68
Gorilla Monsoon said:
I have mine. Im still waiting on early testing confirmation. Things are tricky. Internal bias needs to be monitored beyond my limited capabilities. More to follow- i picked these up as a potential replacement set for an amp i really like. Nothing wrong with the amp, i just wanted something to back it up beyond the supplied tubes.

I looked into NOS tubes and read some things. Total Dunning- Krugar here. Im trusting Ben. I don’t have any way to quantify this experiment for the time. I hope not to see smoke.

I contacted the builder of the amp im considering with replacement. He is silent. Can’t say i blame him. While i have no immediate plans to replace the tubes in the pre-mentioned setup- if it aint broke- i remain curious as well.

These were a long time coming. Ima talk to my amp person who will most likely attempt to disabuse me from using them. I am not a smart man, though…Ima do it eventually.
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From the info page on verellens website:

DO I NEED TO BIAS MY AMP FOR OCTALS?​

No, the Octal is internally factory biased for safe operation and zero crossover distortion in a push pull amplifier.

And from the datasheet:

The Octal bias current is set internally at the factory to very tight tolerances. There is no need to tune Octal bias current in your amplifier - the Octals will not respond to amplifier bias tuning.

 
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#69
Sparky Mark said:
I wonder if they would work in an amp that uses a power tube auto bias system?
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cfortner said:
Only fixed BIAS, look at the FAQ
Click to expand...

Isn't an auto bias system either cathode or fixed bias (both mentioned in the FAQ as compatible)?

And if the octal "will not respond to amplifier bias tuning" anyway, then shouldn't it make no difference what an auto bias circuit does to voltage?
 
#70
cfortner said:
Isn't it normal that solid state power circuits have a greater MTBF than valve power circuits, especially if you mention the hard road life of guitar and bass amps (mechanical- and temperaturewise)?
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If properly designed, generally yes.
 
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#71
Deadsound said:
Isn't an auto bias system either cathode or fixed bias (both mentioned in the FAQ as compatible)?

And if the octal "will not respond to amplifier bias tuning" anyway, then shouldn't it make no difference what an auto bias circuit does to voltage?
Click to expand...
Auto-bias in this context is a servo system that monitors quiescent current and adjusts the grid bias voltage to obtain the target current.

When the servo loop is opened, the bias circuit may behave unpredictably or even shut the amp down as a precaution, each servo bias system operates a little differently.
 
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#72
cfortner said:
Isn't it normal that solid state power circuits have a greater MTBF than valve power circuits, especially if you mention the hard road life of guitar and bass amps (mechanical- and temperaturewise)?
Click to expand...
Yes, but it also depends on how both the tube and solid state circuits are designed to withstand high temperatures. Tubes are constructed from thermosetting plastics, metal, glass and mica which are much more tolerant of high temperatures above 150C than transistors and the materials used commonly in PCB assemblies. It all depends upon the specifics of the design.
If tubes become unavailable, then this type of device may become the only option for keeping these amps running. Until that point it's desirable to understand cost vs lifespan compared with the equivalent tube in particular applications.
 
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#75
agedhorse said:
It’s not just thermal vulnerabilities, there are other failure modes too.
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Agreed again, but the fact these can run at up to 300F/150C is a significant reliability factor, in addition to everything thing else that you could possibly suggest.
Don't misunderstand me, I really hope these are a super reliable alternative, but at $900 to retube an SVT, personally I'd like to see a bit more data behind the statement "should continue to work indefinitely".
Screenshot_20260125_213508_Brave.jpg
 
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#77
Operating at 150 deg C, those would have to be Silicon Carbide based devices which I have no experience with.
 

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