Tube Amp with the "Good Kind of Distortion"

[Doodski]

--Doesn't sound very "tubey"
--If tested me blind, I'm not sure I'd be able to tell it's going through a tube (unlike some of my other tubes)

The only tube gear I've owned was a Sherwood. It sounded very tuby but the tubes where old and soft sounding. It was great eye candy and attracted a lot of attention.

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.

So the tubes are not the final gain stage? Oh I see it's FETs. Interesting. I like!

 

[watchnerd]

The only tube gear I've owned was a Sherwood. It sounded very tuby but the tubes where old and soft sounding. It was great eye candy and attracted a lot of attention.
View attachment 167465

So the tubes are not the final gain stage? Oh I see it's FETs. Interesting. I like!
View attachment 167466

Nope, it's a hybrid, so it can swing plenty of current, too.

Which is why I (and others) like it with planars.

 

[Doodski]

Nope, it's a hybrid, so it can swing plenty of current, too.

Which is why I (and others) like it with planars.

I've been checking out tube testing with curve tracers. Very nice. The price of curve tracers has ~doubled or ~quadrupled since about the mid 90's when I was working at a instrumentation shop/metrology lab part time. One very vintage unit is $4995.00 for a operational device. Tektronix made a proper tube socket jig for the 576 curve tracer and some have been known to make a DIY jig. A model 576 is about $1000-$4500 @ebay They where pretty common in the day and I'm sure they can be found for sale @instrumention shops.

 

[watchnerd]

I've been checking out tube testing with curve tracers. Very nice. The price of curve tracers has ~doubled or ~quadrupled since about the mid 90's when I was working at a instrumentation shop/metrology lab part time. One very vintage unit is $4995.00 for a operational device. Tektronix made a proper tube socket jig for the 576 curve tracer and some have been known to make a DIY jig. A model 576 is about $1000-$4500 @ebay They where pretty common in the day and I'm sure they can be found for sale @instrumention shops.

Can't you do the same thing with a modern digital oscope?

 

[MakeMineVinyl]

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.

I'm ready for my service call.

 

[Doodski]

Can't you do the same thing with a modern digital oscope?

I'm not a expert on O-scope curve tracing with tubes but I found a source of info:

Yes, it's tedious, possibly dangerous and simple designs may not be calibrated for current and voltage parameters. A basic design req's voltmeters, DC power supply, variac, resisters and a suitable potentiometer. More comprehensive designs are more complicated. I have a <.pdf> if you want it. It's 3.5MB It has schematics and explains how to do simple circuits. Or you can download it here. OSCILLOSCOPE TECHNIQUES ALFRED HAAS 1958 Refer to starting page 108.

I think it's better to use a safe to operate Tektronix curve tracer.

I also found a dedicated Tektronix curve tracer for tubes. Vintage de jour from ~1950's design.

 

[watchnerd]

I'm ready for my service call.

View attachment 167490

It looks like you have everything except the 6922 (and soon to be 6SN7) tubes I use.

 

[Doodski]

It looks like you have everything except the 6922 (and soon to be 6SN7) tubes I use.

So that's pretty much all the various tubes used for audio amps? What about those huge light bulb+ sized tubes?

 

[MakeMineVinyl]

It looks like you have everything except the 6922 (and soon to be 6SN7) tubes I use.

There's several 6922s in there but some are labelled 6DJ8; my Ampex 354 uses them for the line output stage. I've got a bunch of 6SN7, 6SL7, 300B, 2A3, EL34 but they wouldn't all fit in the tube caddy.

 

[MakeMineVinyl]

So that's pretty much all the various tubes used for audio amps? What about those huge light bulb+ sized tubes?

I have spares for all my tube gear and also some oddball tubes for an RCA 1956 vintage table radio and a few other oddities. The 300B and 2A3 are the big ones used in my SET amplifier. The 2A3s produce 2.5 watts and when I want to really party, I plug in the 300Bs for a massive 7 watts.

 

[Doodski]

I have spares for all my tube gear and also some oddball tubes for an RCA 1956 vintage table radio and a few other oddities. The 300B and 2A3 are the big ones used in my SET amplifier. The 2A3s produce 2.5 watts and when I want to really party, I plug in the 300Bs for a massive 7 watts.

300B looks pretty.
2A3 is cool too.

It appears there is money to be made in tubes. Or have they all been bought up and the few people with quantity are reaping the rewards?

 

[watchnerd]

So that's pretty much all the various tubes used for audio amps? What about those huge light bulb+ sized tubes?

No, not at all.

Those are just the only types I use for home audio, as I only have small signal applications (headphone amps, phono stages).

I also have some 12AX7 that I use in my bass guitar amp, but I just use cheapie current production tubes for that.

 

[Doodski]

12AX7

Must be very common the musical instrument store sells them.

 

[watchnerd]

Must be very common the musical instrument store sells them.

Correct.

 

[MakeMineVinyl]

300B looks pretty.
2A3 is cool too.

It appears there is money to be made in tubes. Or have they all been bought up and the few people with quantity are reaping the rewards?

Some tubes like original production Western Electric 300B can sell for truly insane prices. Fortunately most of the common audio amplifier tubes are still being produced today and prices are reasonable.

 

[MakeMineVinyl]

Must be very common the musical instrument store sells them.

The 12AX7 is probably the most common tube of them all. My Ampex 354 and a lot of the other vacuum tube Ampexes use them for the first amplification stage from the playback head. If you listen to any music from the days of vacuum tubes, there's probably a 100% chance the music went through one at some stage. They were common as dirt in the days when tubes were used in consumer audio. Almost every company who makes tubes today makes them.

 

[watchnerd]

The 12AX7 is probably the most common tube of them all. My Ampex 354 and a lot of the other vacuum tube Ampexes use them for the first amplification stage from the playback head. They were common as dirt in the days when tubes were used in consumer audio. Almost every company who makes tubes today makes them.

I think McIntosh uses them a lot, too.

McIntosh C8 Vacuum Tube Preamplifier

The C8 Vacuum Tube Preamplifier has an open chassis industrial design and can help deliver a lifelike audio experience in your home.

www.mcintoshlabs.com

 

[MakeMineVinyl]

I think McIntosh uses them a lot, too.

McIntosh C8 Vacuum Tube Preamplifier

The C8 Vacuum Tube Preamplifier has an open chassis industrial design and can help deliver a lifelike audio experience in your home.

www.mcintoshlabs.com

Yep. My McIntosh C-11 preamp, MR-66 tuner and MC240 power amp all use the 12AX7.

I still hate those silly green LEDs under the tubes though. YUCK!

 

[watchnerd]

Yep. My McIntosh C-11 preamp, MR-66 tuner and MC240 power amp all use the 12AX7.

I still hate those silly green LEDs under the tubes though. YUCK!

I thought you could at least turn them off?

 

[Doodski]

Hmmz. Surfing how to parallel tube amp output tubes and found a curve tracer assembled kit and vacuum tube tester.

Buy online

etracer digital vacuum tube curve tracer/tester project's website

www.essues.com