Current in production 6072/ 12AY7 tubes

[gyraf]

Not distortion, but linearity of spectrum. There is kinda' a generic limit to the ECC83 if you want full >20KHz bandwidth, namely its miller capacitance - which prevents you from using two stages of this without having to resort to adding feedback to linearize it, trading gain for linearity, but also significantly changing it's overload behavior. This off course nice for som instrument processings, not so much for full-bandwidth use (but as always, ymmw)

 

[ruffrecords]

Not distortion, but linearity of spectrum. There is kinda' a generic limit to the ECC83 if you want full >20KHz bandwidth, namely its miller capacitance - which prevents you from using two stages of this without having to resort to adding feedback to linearize it, trading gain for linearity, but also significantly changing it's overload behavior. This off course nice for som instrument processings, not so much for full-bandwidth use (but as always, ymmw)

As I said, the problem is not the tube it is the designer. Miller capacitance is only a problem when driving an ECC83 (or any tube for that matter) from a high source impedance when simultaneously trying to squeeze the last ounce of gain out of the stage. A good designer will avoid one or both of these unless forced to do otherwise by bean counters.

Cheers

Ian

 

[gyraf]

Aah yes - but the ECC83's own (rather high) output impedance is half the source of the trouble - preventing you from running two consecutive stages without adding feedback

Back in the topic, my favorite try-it-out replacement for the now extinct 6072 is the JAN6201 - yes, it's somewhat different (being sorta E81CC 'ish), but often behaves really nice in mics made for the 6072

/Jakob E.

 

[emrr]

Probably falling into the color camp, and currently (pun intended) heretical observation - all of the AX equivalent higher gain tubes in historic preamps that I’ve liked have had much smaller plate resistors than expected. I might guess it changes the distortion spectrum to one I prefer.

 

[Clakejr]

Can you use Telefunken tunes in the twin amp pcbs

 

[RuudNL]

I have good experiences with the EH 6072.
In the past I have used JJ tubes, but I have the impression that they don't test them at all...
Usually it takes some time for a new tube to reach a lower noise level, but the difference between 'just out of the box' and 30 minutes later was with the JJ tubes sometimes 10 dB! (The difference with the EH tubes was usually in the order of 0.5 to 1 dB, giving me the impression that the JJ tubes were never heated up before.)
Also I have had JJ tubes that didn't work at all, or had an internal short.

 

[Rusan]

Years ago, when I used to repair, mod and build a lot of tube gear, I gained a lot of experience with JJ tubes. Their 5AR4/GZ34 and EL84 were definitely superior to Sovtek or Shuguang, but their big pentodes, beam tubes and power triodes weren't quite as spectacular or reliable. Their 12AX_/ECC__ family was bad enough that I learned to avoid them altogether; their 12AX7 was especially bad. Surprisingly, despite the 6922 being a frame grid tube that's more difficult to manufacture than an ECC83, their 6922 was solid, reliable and quite pleasant sounding.

 

[gyraf]

I'm pretty sure that JJ built their reputation of making good 6922 by simply rebranding very-large batches of NOS EI/Yugo stock

the verified new production E88CC/6922 I've tried are terrible

 

[PermO]

I've never heard a JJ tube sound good, tried a couple and my opinion is "avoid at all cost"

NOS is a gamble, there's some really good stuff out there, and a whole bunch of overprized crap.

I really miss my 10$ Tung Sol tubes from the Reflector factory

 

[KIDVOX]

another very old thread that has been given the kiss of life

 

[Rusan]

I'm pretty sure that JJ built their reputation of making good 6922 by simply rebranding very-large batches of NOS EI/Yugo stock

the verified new production E88CC/6922 I've tried are terrible

I didn't know that. I haven't had a lot of experience with Ei Yugoslavia tubes, except for a few EL84s and some EL34s I have that are decent. Interestingly enough, the evacuation stems of the EL34s are on top of the bottle instead of under the base.

I've used some quite old, pre-JJ era tubes with the Teslovak branding from the same factory, that were mostly pretty good. I'd say they were better than the JJ stuff in general.

Thanks to the Shuguang fire and the XPO-Pul/Reflektor factory being in the unfortunate situation it's in, I don't see anything but tube quality going down and prices continuing to rise from here on. On the topic of 6922s, thankfully I have a good stash of Bugle Boys and early Mullards on hand, that'll far outlast me.