[zjj_wwa]

Any sound impressions or photos?

Pls. find photos of my OTL on my blog page: http://hiend-audio.com/2014/01/03/the-otl-challenge
Have you ever been to the mountains ? Have you ever drunk water directly from a stream high up in the mountains ?
Yes, you did ? If so, how do you compare the taste of that mountain stream water with the water that you can drink from your kitchen tap ?
Feel the difference ? The former is "Crystal clear". That's what it is. A similar experience I found when comparing the sound between an OTL-OCL and an Output Transformer based tube amplifier. Can't find a better comparison / allegory from the top of my head.

On that blog page, hobby page of mine there is a fair share of my texts that relate directly, or indirectly, to subjects specifically relating to the OTL stuff, as well as to "tube audio" in general. You may like it. You may not like it. Either way, I hope to hear some feedback on those ideas of mine, if you find the time to look into them.

My current "future plans" relating to OTL would be to either make 288 ohm speaker cabinets, and/or to make an impedance multiplier circuit (or current multiplier - whatever name you prefer) for my 8 ohm speakers. Obviously, the aforementioned is all OTL related.I am also thinking about creating a newer version of the OTL, but this time ... not based on the 6s33s triodes, but rather on SuperTriodes:  6s33s + N * TOSHIBA 2SC5200.
 
A long time has passed since that discussion back in Aug 2011 ... Did you actually build that Tim Mellows OTL in the "meantime" ?
Cheers.
Ziggy.

[zjj_wwa]

B.T.W .... Has anybody tried to modify this OTL and convert it into a CURRENT DRIVE OTL ?
I mean converting it from a voltage drive device, i.e. one that is a voltage source with close to zero output impedance,
into a modulated current drive device, i.e. one that is a current source with close to infinitely high output impedance ?
Cheers,
Ziggy.

For all those who believe that OTL is good stuff ... I suggest going one step further: 
OTL Current Drive  ( = Nirvana ). 

[FullRangeMan]

Thanks for the link photos, its a beautiful amp, It looks nicely micro controlled, congratulations.
I would like be able to build a tube amp, proplably I would do various mistakes.

Why do you use many big capacitors?
I dint see a power trafo, its underside?

[zjj_wwa]

Thanks for the link photos, its a beautiful amp, It looks nicely micro controlled, congratulations.
I would like be able to build a tube amp, proplably I would do various mistakes.
Why do you use many big capacitors?
I dint see a power trafo, its underside?

Many thanks. I'm glad you like it. Indeed, there is a fair share of extra bells and whistles inside, of my design and making, which are a result of my moods and fantasy.
Stuff like multi-stage soft-starts, intelligent timer circuits, precision fillament heating control, electronic voltmeter circuits, quick discharge circuits, intelligent charge-up sequence, basic speaker protection, and some more.

>>> Big caps ...
Did I mention that I am a bit psychopathic in this respect ?  I am a fan of the BRUTAL FORCE strategy.
I have over 100 000 uF of high voltage capacitors in the device.   Why ?   
... indeed, because I ... can.   Simply stated: I wanted to have them. So I put them in.
Because 99,9999999% of the population would say that they do not change a thing. But they do. 

>>> the trafo ...
Actually, the "thing" on the pictures that you see - is just the signal box, of a dual, split box setup.
The Power supply is in a separate chassis ( a black box, to be seen underneath, on some photos). 
This power supply chassis weighs c.a. 40 kg.  It has a 1500 Watts mains toroidal transformer, of my own tweaking / making.
Yet another example of my BRUTAL FORCE thinking in terms of oversizing.
The toroid is slightly oversized, as the power consumption of the whole unit is around 300 Watts at idle.
This signal box chassis is another 35 kg.
In total, the amp weighs about 75 kg, give or take. 
Thereof, I reckon, some 25 kg of iron (chokes, mains toroids, etc), then you have some 20 kg of capacitors ... more or less.

It takes about 3 minutes to switch it on.   
Tried to do it quicker, but the fuses in the apartment building can not cope).
Initial surge current is limited so that it does not exceed 13 A.
 
On the other hand ... after pulling the plug from the wall, it keeps on playing for a minute or two, at normal listening levels.

I departed from the basic, "plain vanilla" design, from which I started off with, and put in a lot of my own "extras" ...

[zjj_wwa]

... the "technical" reason for the vast amount of capacitors is that I wanted to achieve a stiff power supply.
One that is capable to produce a peak current of say 3 Amperes at +/-160 Volts,  but in such a manner, that the voltage from the supply does not sag, neither in LF nor in HF.
Well, OK, it actually does sag a bit, as can be dynamically seen by the voltmeter displays, but not more than 0.1 Volts. 

According to my BF strategy, the optimal solution would be a miniature, pocket sized nuclear power plant, but they don't provide those in surplus stores. 
Lacking the aforementioned, the next best thing that came to mind was a CLCLC HV filter, with an extensive amount of capacitors within.

[FullRangeMan]

It takes about 3 minutes to switch it on.   
Tried to do it quicker, but the fuses in the apartment building can not cope).
Initial surge current is limited so that it does not exceed 13 A.

Man I like your style!! 
You have respect the 6C33 tube, the amp and for the music lover security.

In the past I said in the DIY Forum all 6c33 amps that dont use a delay of several minutes for the B+ are poorly designed and received a barrage of criticism.

When I mention the Michael Boele 6C33 datasheet say the tube minimum warm-up time to steady state are 600 seconds for military use(just 1K hours life) and for Hi-Fi it most be at least 10 minutes, I almost got stoned.

Today I think a pot for the B+ delay are the best low cost solution as used inthe ham radios.
I fell this pot is used at the input of the B+ PS.

[Ericus Rex]

You have respect the 6C33 tube,

Is anyone still manufacturing that tube?  Seems prices have skyrocketed on it the past 5 years.

[zjj_wwa]

Is anyone still manufacturing that tube?  Seems prices have skyrocketed on it the past 5 years.

As long as the MIG's are flying around, I would not consider that as a problem.
Never underestimate the Russian Army Surplus.
Stocks will last for 3 more generations ....
Price fluctuations are a function of less than optimal distribution channels.

[Steve]

Thanks boys for your support. I just got the Audioxpress article, it say it is PP indeed, and NFB have two options, 26dB and 11dB(removing some capacitos maybe C3 and C4.

............

Thanks, Gustavo

The audioxpress article is incorrect. NFB is variable depending upon the volume control setting. As the
volume control is turned up (more output power), the NFB increases.

The low frequency response is also variable due to the NFB being frequency dependent due to the input capacitor's
reactance increasing at low frequencies (C1).

Such a design, connecting the feedback after C1, allows for a little better low frequency response,
with a trade off of a little higher distortion figure. I don't think the slightly higher distortion is any big deal though.

Cheers

[FullRangeMan]

Is anyone still manufacturing that tube?  Seems prices have skyrocketed on it the past 5 years.

According various guys on DIY audio no.
The Ulianov plant ceased 6c33 production in the 90s, so she is NOS now.
The good news are the current stock in Siberia are around 750K pieces, but as its a military item I suspect it is much greater.

OBS.1: Price increase? Not in Russia. Only in US and Ebay due smart brokers.

OBS.2: Same is happening with the GM70, after US market sure it can do great sound quality(DeHaviland etc) the price begin up ladder.

OBS.3: Suggestion buy in Moscow.

[FullRangeMan]

The audioxpress article is incorrect. NFB is variable depending upon the volume control setting. As the
volume control is turned up (more output power), the NFB increases.

The low frequency response is also variable due to the NFB being frequency dependent due to the input capacitor's
reactance increasing at low frequencies (C1).

Such a design, connecting the feedback after C1, allows for a little better low frequency response,
with a trade off of a little higher distortion figure. I don't think the slightly higher distortion is any big deal though.

Cheers

A hobbist builder of this amp informed the sound is very crispy, whatever it means.