Bugera 1990 Amp preamp tubes

[Chuck H]

I wonder where a gain difference of maybe 1dB could matter.

Agree. In fact I had a "high gain design" (as it were) I did for a company that spec'd the Sovtek 12ax7WA for the first gain stage primarily because they were typically low in microphonics. Other offering that touted higher gain were problematic at the time. The gain differences being so slight can be usually be dealt with otherwise in the circuits. The WA was a "dark" sounding tube though. I know that most believe ALL tubes are essentially linear in the audio range, but... No way. All I can say is that hearing is believing. My own personal favored amp is the proto for that design and I use selected tubes other than the Sovtek 12ax7WA in the V1A position. But the WA was a good tube for that project with consistent performance. The WB wasn't available at the time or I would have tried it. Really short electrodes on those tubes. They reminded me of the old GE tubes. And sounded similar.

[Helmholtz]

The WA was a "dark" sounding tube though.

I recall that I noticed the same.
Explanation could be a somewhat larger than typical (I think 1.6p) grid to plate capacitance.

[TomCarlos]

Again, my thanks for the replies. Lots of good info.

How about this - "B" is for balanced? So if you consider a phase inverter circuit, you want balanced gain on both sides of the ECC83? Maybe that is what they are after.

While it makes good sense, I don't know of any other guitar amp pushing a "balanced" P.I. tube.

[TomCarlos]

And going back to one of my questions (in #1).... shall we use either JJ 5881 or maybe a Sovtek 5881 WXT? I don't know if either of these tubes are good for 475 on the plates. That is why I asked about using 6L6GCs (as was suggested in the video.

[Chuck H]

And going back to one of my questions (in #1).... shall we use either JJ 5881 or maybe a Sovtek 5881 WXT? I don't know if either of these tubes are good for 475 on the plates. That is why I asked about using 6L6GCs (as was suggested in the video.

To be honest I've had all manor of trouble putting the screws to current JJ tubes. I haven't had any problems with the Ruby offering though. In fact they came through for me in a similar case where I had 475Vp and all the JJ's exploded in the overdrive test. ( I may have been pushing the screens too hard, none the less...). The Ruby's took the heat and lived where the JJ's failed. So if it were me I'd probably go with Ruby selected tubes. 6L6's if necessary. JM2C.

[Delta362]

I used to use Ruby as they were inexpensive, reliable, rugged and sounded good. Now they've pretty much gone the wayside. I've since switched to the Sovtek 5881WXT and 6L6WXT+. I have not tried the JJ 5881, but unless the customer asked for that specifically, I'll stick with the Sovteks.

[Chuck H]

I used to use Ruby as they were inexpensive, reliable, rugged and sounded good. Now they've pretty much gone the wayside.

???

What did I miss? Is this a Covid thing? I haven't bought tubes in a while. It looks like the Magic Parts site is selling a lot of JJ and Sovtek tubes and only a few Ruby branded power tubes now. And indeed, alas, no 6L6 or 5881 offerings. And I have to wonder if the JJ or Sovtek tubes are going through the same selection/culling process that Magic Parts was doing for their Ruby offerings. If so I think I'd still buy from Magic Parts.

As I said, it's been a while since I bought tubes, but I do remember the Sovtek 5881wxt being very rugged and having good reputation among members here as well.

EDIT: Yes, it seems even Doug's Tubes has a *note on their Ruby offerings specifying they are actually JJ or Sovtek products respectively. But they also note that these tubes are indeed put through the rigors of the Ruby selection process. How much we can believe that I don't know.

[TomCarlos]

But here is what I don't get (but probably should by now) ....

-The Bugera amp is Class AB and I measure 475 volts at the plates. (and has a switch for Triode or Pentode mode).

-The JJ 6l6GC is rated at 450v for Triode, 500V Pentode.

-The Sovtek 6L6WXT shows a max plate voltage of 350v, Class A.

How does any 5881 tube work in this amp with 475 volts on the plate?

[Enzo]

Ruby never made a secret of where their tubes came from.. Their alphabet soup told the tale. SO a tube ending in CZ was from the Czech Republic, in other words JJ.

[DrGonz78]

As I said, it's been a while since I bought tubes, but I do remember the Sovtek 5881wxt being very rugged and having good reputation among members here as well.

Just a link of reference to the 5881WXT tube reputation here on MEF.
https://music-electronics-forum.com/...es-pleeeeeease

The Sovtek 5881WXT will have no problem running at 475VDC. I personally had these tubes running at near 500v without a hiccup. The datasheet is only giving an example of class A type max ratings which it says is 350v but it does not state AB push pull.

When they sell these on the Antique Electronics Supply website they state...
"Built to rigid military standards, the 5881 will tolerate higher voltages than any other 6L6. In fact, they're frequently used as replacements for the old 7027 model in vintage Ampegs. Extremely consistent from piece to piece."

I always bias an amp on the cooler side to make sure the tubes last longer.

[TomCarlos]

Thanks Doc.... the "Last word on Sovtek 5881..." thread answers my questions. Much appreciated.

[tubemonster]

I used to use Ruby as they were inexpensive, reliable, rugged and sounded good. Now they've pretty much gone the wayside.

Same here - I don't think I ever got a bad Ruby tube out of the box.