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Tube Amp with the "Good Kind of Distortion"

DanielT

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He he :)

Good work! What is it you have DIY now then? :) Singel end ....KT 88? 300B? Then you know the question every DIY with tube amplifier gets: What do you have for output transformers?

Edit :
Found yours. ... Output transformers - the Hammond 125ESE...

Cool project. Satisfied? :)
 
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mhardy6647

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He he :)

Good work! What is it you have DIY now then? :) Singel end ....KT 88? 300B? Then you know the question every DIY with tube amplifier gets: What do you have for output transformers?

Edit :
Found yours. ... Output transformers - the Hammond 125ESE...

Cool project. Satisfied? :)
No, actually, on this particular morph, the OPTs are the Taiwanese (if memory serves) "James" branded transformers, which were popular, and popularly priced, at the time -- they're NLA, unfortunately.
Also -- ahem -- in full disclosure: it is indeed a DIY amp, but I didn't make this particular one. I could have, but it'd have been much uglier cosmetically if I built it. :rolleyes: It was built by "Redboy"(as he is known at audiokarma and hifihaven), or, as he is also known:
 

mhardy6647

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Since I mentioned it above, there's an HH Scott 260 review in
(magazine pages 32 & 34)

1633656098393.png
 

Ken Tajalli

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Below is one example of that kind of behaviour. Notice too how in this tube amplifier the 3rd harmonic is not far behind the 2nd harmonic in size. The plot is for the spectral response of a 1kHz sinewave, for the Balanced Audio Technology VK-56SE, low output tap, running at 1W into 8 ohms, which produces 0.4% THD+N. At 6 watts output power, this amplifier is producing about 1.0% THD+N using a 1kHz test signal.
519BAT56fig14.jpg

Source: Stereophile, https://www.stereophile.com/content/balanced-audio-technology-vk-56se-power-amplifier-measurements
The amp in question uses minimal feedback (only 3dB) and to get higher powers it is biased more into class B.
Hence the distortion pattern and high output imp.
I have built an OTL amp using the same tubes, and I get 1ohm output impedance, as opposed to BAT's 6.7ohm.
My speakers never go below 6ohms.
mine sounds very clean.
 

Doodski

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Yes, they were made in Germany.

The box says Munich, although that's possibly just the HQ.

If I'm reading the date code correctly, they're from 1960.
CooL. Nice vintage stock. Are those rare and expensive?
 

watchnerd

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CooL. Nice vintage stock. Are those rare and expensive?

I guess so, and they're going up in price every year.

I got these a while back, but this is what they retail for now:

 

Doodski

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I guess so, and they're going up in price every year.

I got these a while back, but this is what they retail for now:

It appears they match pairs if ordering pairs. I suppose they have a old tube tester/O-scope curve tracer setup? I was just starting working in home audio in the early 1980s when the tube testers and all the tubes where being pulled out of the stores that I worked @ and trucked away to wherever. Probably the dump. :facepalm:They where about 5-6 feet tall, ~2 feet wide and had a bunch of tube sockets, meters and stuff on the front for testing them. What a waste. One of these with a tube testing adapter that fits all Tektronix curve tracers would be ace.>
tek_576.jpg
 

antcollinet

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I guess so, and they're going up in price every year.

I got these a while back, but this is what they retail for now:

Holy hell - that is one expensive light bulb.

I know nothing about tubes - are there no equivalents manufactured now? Or are modern equivalents massively inferior?
 

DimitryZ

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Holy hell - that is one expensive light bulb.

I know nothing about tubes - are there no equivalents manufactured now? Or are modern equivalents massively inferior?
No, modern tubes are just fine. There is lore about old vintage that some are willing to pay 10-100X for.
 

sophie smith

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Decware Amp with measurements published by the builder. Seems like the 2nd harmonic is dominant. P-P design. Overall not bad measurements for tube amp if you trust the mnfr specs.
 

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MakeMineVinyl

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Decware Amp with measurements published by the builder. Seems like the 2nd harmonic is dominant. P-P design. Overall not bad measurements for tube amp if you trust the mnfr specs.
Second harmonic are not, that's a pretty dirty distortion spectra. Ideally you'd want to see the second, third, forth, and maybe just a little bit of the fifth harmonic at most, with nothing after that.
 

MakeMineVinyl

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True, but the higher order ones are at about -100db. Likely not audible.
But what's up with that spike at about 6.25kHz that they didn't label?
 

watchnerd

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It appears they match pairs if ordering pairs. I suppose they have a old tube tester/O-scope curve tracer setup? I was just starting working in home audio in the early 1980s when the tube testers and all the tubes where being pulled out of the stores that I worked @ and trucked away to wherever. Probably the dump. :facepalm:They where about 5-6 feet tall, ~2 feet wide and had a bunch of tube sockets, meters and stuff on the front for testing them. What a waste. One of these with a tube testing adapter that fits all Tektronix curve tracers would be ace.>
tek_576.jpg

So I've used them for a few days now.

Comments:

--Probably the quietest tube I own in terms of microphony and noise
--Doesn't sound very "tubey"
--If tested you me blind, I'm not sure I'd be able to tell it's going through a tube (unlike some of my other tubes)

As an aside, the Mjolnir 2, in high gain mode, is open loop with little to no feedback, just the tube + SS output buffer, at least according to comments in interviews from Jason Stoddard.
 
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watchnerd

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Holy hell - that is one expensive light bulb.

I know nothing about tubes - are there no equivalents manufactured now? Or are modern equivalents massively inferior?
No, modern tubes are just fine. There is lore about old vintage that some are willing to pay 10-100X for.

I have a few NOS tubes that, like this one, were best in class offerings from the golden age of tubes and stand up well to current production.

From a performance POV, is it 10x better than current production? Absolutely not, especially if you spent the time grading and sorting current production tubes to get the top 5% or so.

Probably 1/3 - 1/2 of my NOS tubes are not technically better than modern production.

I don't buy into most of the mythology of NOS tubes.

But I do like having the old boxes, learning the history of the old tubes, and collectability.

I might spring for some of the Telefunken CCa that have recently come on market again as a self Christmas present.
 
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