[00940]

Rozenblit has presented in 1990 an otl, capless power amp giving 25W@8ohms, based on 4 6AS7/channel. But the design is very different (see here )

His alimentation uses choke + tubes regulation (and ss rectification). Alimentation for the power stage is just CRC.


Voltage of 250 and 150 with regulation make me think of using old step-down/isolation transformers, from the old times of the linears xformers, before switchers invaded the market. In Europe, i've seen many of those on flea markets, with outputs at 120 and 220 vac, often rated at 500W or more, weighting tons (ok, more like a few kilograms). And they cost like nothing (5$?).

I just wondered... what happens if output tubes fail during listening ?

 

[kevin gilmore]

Yep another of the futterman variations. Push Pull. Top tubes have
no voltage gain. Bottom tubes have significant voltage gain.

My design is single ended. Significant difference in the sound.

quote
I just wondered... what happens if output tubes fail during listening

In general BAD THINGS... If you are using one of these for a speaker
amp, then the fuses MAY save you. (including the fuses built right into
the 6as7's)

For headphones a fast integrator circuit and a shorting relay are probably
a good idea.

 

[robzy]

I may know nothing about amps, but what i do know tells me that: DUDE! That is awesome.

Rob

 

[philodox]

Quote:

Originally Posted by kevin gilmore This amp has a sweetness and powerful presentation that no other tube amp i have listened to can match.

Ahhh! Pure Evil!

 

[00940]

Before I forget my question...

How does it compare to the 6AR8 hybrid with grado ?

 

[trbl]

Quote:

Originally Posted by kevin gilmore Yep another of the futterman variations. Push Pull. Top tubes have no voltage gain. Bottom tubes have significant voltage gain.

Not to quibble, but I think this can leave a false impression. Julius Futterman's designs did have genuine balanced push-pull output stages.

There are actually 4 different variations: two using a single tube section in a modified split load stage (like the circuit posted by 00940) and two using two tube sections in a modified long tailed pair. For each type driver stage there are two further variations: the combination of driver stage plus output stage could have near unity gain and lower output impedance, or higher gain and output impedance. In each case the secret was to bootstrap the correct end of one of the driver tube load resistances to the output of the circuit, and this in turn depends on which of the two driver outputs goes to the upper or lower set of output tubes.

When this is done correctly, the bootstrapping of the driver stage to the output stage creates a local feedback loop. The result is a balanced output stage: for the driver plus output stage as a whole, the top half of the circuit has the same gain and output impedance as the lower half (assuming the upper and lower output tubes have the same characteristices, of course).

People sometimes modify Futterman style circuits to "improve" them by not bootstrapping the driver stage to the output, or by connecting the wrong driver output to the upper tubes, etc. Then it's not a real Futterman anymore, and the output won't be balanced. But the four correct versions are real Futterman circuits and you can do the math to prove that both output stage halves have the same gain and output impedance when you consider the driver and output stages as a whole.

 

[palchiu]

Is Dynatoob project still going?

 

[pabbi1]

Good question.... is the Dr. in?

 

[pabbi1]

Is the Dynatube still a viable project, or did the fit of madness pass and fade?

 

[gsferrari]

It killed a few people when the output tubes failed

Otherwise all is well

LOL

Just kidding...anyone have the cojones to build this goliath?

A couple of mortgages or automobiles will take care of the costs

 

[kevin gilmore]

Fit of madness??? I don't think so. I'm completely sane. Its everyone
else thats nuts.


I have an initial board design. The design is huge. (10 x 6.85 inches)
Partly because of the layout space for the ultra trendy teflon coupling
caps. I never got around to typing in the parts values. And there are
things i definitely want to change when i get around to the
production boards.
I do have 2 prototypes and they sound absolutely amazing.

For people who have a gerber viewer and want a look...

http://gilmore.chem.northwestern.edu/dynatoob2.zip

I'm really busy lately so this is not progressing as quick as i want.
Things never do...

 

[pabbi1]

Just knowing it is alive gives us hope... and the thought that it sounds amazing is, well, distressing.

Thanks for the update.

 

[Kenny12]

dr overkill strikes again

jesus 5 psus?

my wallet is dying at the cost of 1 dynahi psu

 

[rellik]

are the production level gerber files ready?

if the prototypes sound as good as you say, this is very tempting

has march madness actually cooled?

 

[philodox]

I'm wondering how this design compares to the mig and mig2?