Bugera 1990 Amp preamp tubes

[TomCarlos]

Team MEF:

A friend has asked me to look at his Bugera 1990 amp. I think the amp will need typical servicing (dirty pots, tubes, etc).

I found a YouTube video on this amp and it addresses the low quality output tubes. The suggestion is to replace the cheepo 5881s that came with the amp and use 6L6GCs. I think a better pair of 5881's oughta do it. Anywhere, here is that YouTube video - https://www.youtube.com/watch?v=OFn0qDDo02M

My question for now if with the preamp tubes. In the owner's manual, it calls for two ECC83A and one ECC83 tube. I have also seen Bugera sell the ECC83B preamp tube. To me, an ECC83 is a 12AX7, every day of the week. But some guys are tube snobs and insist on using the specific tubes Bugera suggests.

Any opinions on this?

Thanks in advance.


Bugera_1990_Manual.pdf

Bugera_1990_Schematic.pdf

[Chuck H]

As far as I know there is no difference between those tubes. The "A" suffix typically means "premium". Which to me would be low microphonics and noise. Though I've purchased new A suffix tubes that were just as bad in one way or another as some non premium tubes. So for my understanding Bugera is suggesting two "good" 12ax7 tubes and one that's at least fully functional

[mozz]

I think it's a gain designation these days.

[Chuck H]

I think it's a gain designation these days.

I do know some 12ax7 types seem to have more gain. This is always confusing for me because the specs for all of them say 100 regardless. And that is the spec for use of that model number.

I've never read anywhere that the A suffix (eg:12ax7A, 7025A, ECC83A, E83CCA) means higher gain. Though this might be lore circulating on gear forums. That wouldn't surprise me.

[TomCarlos]

Thanks Chuck...

I guess it is marketing. Here is a link to the ECC83B tube on Sweetwater - Bugera ECC83B Preamp Tube

The only other thing I know about this amp (without yet seeing it) is that is has two of the original Bugera branded 5881s (stock) in the center position and two Tung Sols (on the outside). And supposedly the plate voltage is around 475 volts. So I will deal with that when I get the amp. But for now, I will make sure to have some extra 12ax7s on hand.

[Chuck H]

That Ecc83B looks to be a spiral grid tube. I remember the Sovtek spiral grid tubes having excellent tone but tended toward microphony. Anyway... B as a tube suffix has never had a standard meaning like A meaning premium. B usually denotes some OEM request which can be anything from logo paint color to spiral grids or gold pins, etc.

[Enzo]

I don't think it is a industry term, I think it is a Bugera term. BUgera labelled tubes may have been sorted for gain or noise or whatever, so they recommend a Bugera type A versus B for whatever reason. I wouldn't look any deeper into it.

[tubemonster]

You know, I totally forgot that I contacted Bugera a while back about their tubes and they responded back and also gave me a link to a data sheet.
Here is a copy and paste from that email (thankfully I saved it) and the data sheet they sent to me:
------------------------------------------------------------------------------------------------------------
Thank you for contacting us. All BUGERA tubes are Shuguang.
The datasheets are available here ->
http://analogmetric.com/download/Shu...heet%20Analog% 20Metric%20Limited.pdf

All BUGERA 12AX7 tubes are Shuguang 12AX7B.
The BUGERA 12AX7 A,B,C rating relates to gain and balance:
A is highest gain but not necessarily balanced, best to use in earliest preamp stages.

B is lower gain than A and still not necessarily balance, best to use later in preamp and tone stack recovery.
C can be high or low gain and is balanced, best to use as the phase inverter.

I hope this helps for you and please let me know if you have any further questions.

Let's keep in touch,
------------------------------------------------------------------------------------------------------------

Shuguang Beijing Vacuum Tube Datasheet Analog Metric Limited.pdf

[tubemonster]

This is the full address link to the data sheet, in case the what I attached above doesn't work for some reason.

http://analogmetric.com/download/Shu...%20Limited.pdf

[Chuck H]

Apologies to mozz for poo pooing the A designator meaning higher gain. Though I don't recall this ever being a standard it looks like that's what Bugera has done. So I digress.

[TomCarlos]

Thanks again guys and to TubeMonster for providing that link.

[mozz]

Apologies to mozz for poo pooing the A designator meaning higher gain. Though I don't recall this ever being a standard it looks like that's what Bugera has done. So I digress.

I know the old 12ax7 and 12ax7a had some slight differences. There was also a 12ax7wa which was a military type but today that meaning is useless as they sell WA,WB,WC and that is a gain designator also. (Sovtek)

I lost all faith the first time i saw a "copied" original data sheet with some other companies name on the bottom. I'm 1 year younger than this book.

[g1]

Apologies to mozz for poo pooing the A designator meaning higher gain. Though I don't recall this ever being a standard it looks like that's what Bugera has done. So I digress.

I think Sovtek was doing it even earlier with their 12AX7WA,WB, and WC. I recall doing a test of a pile of them in the shop back in the nineteen hundreds.
With Sovtek, the B is higher gain than the A and is marketed as such. At that time the difference did show up in our testing.
Agree with you that 'A' is traditionally a premium quality, or improved version, which should have nothing to do with the gain factor. Gain of a 12AX7 should be a specified value with a tolerance.

Attached is the Sovtek datasheet, only difference between the types is min. plate current and amplification factor.

[Helmholtz]

Attached is the Sovtek datasheet, only difference between the types is min. plate current and amplification factor.

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

[g1]

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

I know that when we tested them, it was a much more significant difference. More like if the higher gain one was considered 'normal', you would look at the lower gain one as being on the border of 'defective'.