red bear pre amp tubes?

[bagudan]

Hi. I have an old Red Bear mke 60 head.  I think these amps are russian designed/american made(by gibson i think).
The pre-amp tubes are: 6n2p-ev... Do you guys know of a replacement tube for this, or do i need to re-wire it for 12ax7´s?

[anchovie]

Ebay is full of 6N2Ps, no surprise the majority are from Eastern European sellers. The EV suffix denotes a military version.

If you opt to mod it to take 12AX7s you'll just need to move the connection from pin 5 to pin 9 and jumper pins 4 & 5 together.

[Ripthorn]

The 6N2P's are dirt cheap.  You can get 10 for like 15 or 20 bucks on ebay.

[bagudan]

thanks... guess i´ll be looking at ebay then

[bagudan]

You´re right! They are cheap, and there are loads of them.
Havent dealt with tubeamps before, but I was told it would be ok for me to put in new pre-amp tubes myself.... the hard part would be the powertubes, right?
They are 5881´s.... the matched pair and bias-adjusting, is only when you change powertubes, or am I wrong? Do powertubes need to be changed often?
A lot of questions, I know

[maarten]

Matched output tubes are only needed when you can not bias each tube individually. Time period for changing your outputtubes depends upon the configuration of your amp and the intensity of use, e.g. when you are using very high voltages (see the limits in the tube specs) and are using your amp very often, you might want to change your outputtubes maybe even 2 times a year. At lower voltages and especially when also the voltage at the 2nd grid is much lower than your platevoltage (at 40 or 50% of plate), your tubes will last much longer. Quite a lot of guitaramps use voltages for grid #2 which are quite high, however. I think I recall that the "Tonelounge" site has some more information on this. It is a matter of design and of taste, I guess.... In most of my amps I have never changed the tubes, and started out with old tubes to begin with. But maybe I am just sitting here soldering too much and not be playing enough...

Maarten

[bagudan]

thanks for the reply. Ifound some info regarding the output tubes on this site:

http://www.angelfire.com/ok2/joseph3000/redbear/faq.html

"what are some substitutes for these tubes?
the 6n2p-ev/6h2n-eb is very rare. not many have had success in locating it. the information obtained from svetlana about the american 6jk8 being a more common tube that could be used as a substitute has recently been proven to be false. the 6jk8 does not work as a substitute. the svetlana 6n1p will work in the 6n2p-ev sockets, but is a medium-gain tube as oppossed to the high-gain 6n2p-ev. svetlana sv6l6gc can work in place of the 5881 power tubes without rebiasing. novik currently uses 12ax7wa for preamp tubes (an equivalent to the russian 6n2p) and should work as a replacement in red bear amps."

Does this mean that, if I find 5881´s, I can put in new ones, and avoid having to open up the amp and mess around with high voltage, or do I need to re-bias?

Thanks again

[edvard]

On this page they say the 6L6WGB is the direct replacement for 5881's.
I would make sure of the bias no matter what you're replacing with.

All the info I can dig up on 6N2P's is to do the mod James (anchovie) recommended and use 12AX7's.

Otherwise, snag a few bags of them off ebay and be done.

[bagudan]

thanks for the replies....got 10 pre-amp tubes for 10 dollars on e-bay. That is certainly cheap!

[m-theory]

A buddy of mine just got a 120w head back from the shop, after a thorough checkup and a bit of tinkering.  They converted the preamp sockets for 12ax7.  I really can't imagine a reason to keep the original oddballs, and neither could the guy who worked on the amp.  Why gig something that nobody makes tubes for, when you don't have to? 

If a single one of the tubes acquired through Ebay turns out to be good, being of acceptable gain, conductance, and microphonics, I'd be shocked.  I've not personally had very consistently favorable results in buying tubes from the bay, nor has anyone I know of.  YMMV, of course.  Then again, if you're just going to plug them in and go and don't care whether the gain is optimal, all that really matters is that they light up and that the microphonics aren't so drastic that they're unusable. 

These are pretty cool amps, btw.  Very old school, and built like a Russian tank.  They, along with the other Russian amp maker, Sovtek, also happen to quite a bargain at the moment, but don't tell anyone!   

[bagudan]

I wont tell
Will give these cheap tubes a try, and if it´s crap, I´ll get the mod done at the when I´ll let some tech-guy change the power tubes as well. it is a nice sounding amp...