[MaxCast]

I am looking for a pair of 12AU7's.  I have a Foreplay preamp and would like to replace the tubes.  Is spending $75 for a matched pair necessary??  I would like to spend <$40 for a set of tubes.  I see tubes for $8 each but feel these are like trying to pick the best HT receiver for $250 i.e.  it dosen't matter.

Here are my issues.  I think I have some bad microphonics going on.  The little I've read says the 12au7A's are a bit better in this regard.  Is this true?  I also see tubes that say they test 49/50 or 125 vs a usual 119.  What do I look for in buying second hand tubes?  Is a matched pair important?  I've seen the recommended clear tops for $30 a pair.  Almost bought them.

Sources?  I've been to tube world, upscale, and another I can't remember (all recommendations from a thread I read at Agon).  Does anyone have a fav they would recommend?

Thanks,

[Pez]

If it's a matter of microphonics why don't you try Halos? They work wonders in my system. I admit I've never had a problem where I felt I had to replace tubes in order to solve an issue, but when I put the Halos on my tubes everything improved top to bottom.  Try em.

[JohnR]

75 bucks is a bit much I reckon... check your PMs

[Hantra]

Go to the Tube Store.  They are absolutely fantastic!  

No need to match pre-amp tubes.  I got a pair of NOS Tesla ECC082S from them, and they weren't matched.  They are amazing though!  Much less microphonic than my old Chinese tubes, and way better frequency response.  A lot quieter as well.  

BUT, they are $80 a pair.  Jon at the Tube Store can recommend a good one for your budget.  He burns them in before he tests them too.  

L8z,

B

[markC]

If anyone has a line on Raytheon 5751's, I'd certainly be interested. Got about 8 months on my first set and only have one back-up pair. I use them in my qds-15 cdp and love them!

[MaxCast]

If it's a matter of microphonics why don't you try Halos? They work wonders in my system. I admit I've never had a problem where I felt I had to replace tubes in order to solve an issue, but when I put the Halos on my tubes everything improved top to bottom.  Try em.

Been there done that   I should have explained a bit more.  I was so excited to try the Foreplay when it was done I didn't put the little rubber feet that come with it.  Plus I picked up three tripod/point/isolation thingamajigs that I planned on using.  With a bare base  I could tap the self the unit is sitting on and get noise through the speakers.  I can "yell" at the tube and get an echo from the speaker also.  

After trussing up the pre with the points the echo pick up was greatly reduced, but still there.  I could tap the shelf and get wee bit of noise with a solid tap.  I then ordered from Herbie and got another small improvement.  I have not tried with no points but with halos.  That would be interesting to test.  Taping the controls of the pre still yields a tap at the speaker.  I have an offer I can't refuse  coming and will try a different set of tubes.

This brings me to another question.  Is the microphonic phenomenon related to tubes, component or both?

Any truth to 12au7A's being "more rugged"  "less microphonic?"  I suppose it depends on the tube more than anything else??

Hantra, thanks for the rec of the tube store.  I will try them out after I try another set.

Thanks all,

[audiojerry]

fwiw, I have found preamp tube rolling to make a more signifcant audible difference than in amps or cdp's. My Audio Valve uses 4 12AU7, and when I switched from the stock Chinese to a set of vintage Telefunkens ($160), the improvement was substantial and well worth the cost.

Finding a trustworthy supplier of reliable tubes is more difficult. I had a couple of bad experiences buying used tubes over the internet, and have learned the hard way, that it's better to pay a little extra to work with someone you can trust.  My source is Bruce Wangerin of BWS Consulting, www.bws-tube.com,
This guy really knows tubes.

[Audio Al]

I have another question regarding 12AU7 tubes.  I have two tubes in my preamp and I'm looking for a good "tubey" sounding current production tube.  The original Sylvania tubes that came with my preamp rang like a bell so I purchased some HP's from Rogue which were not much better.  I then got some French   (those bastards)NOS Radio Technique tubes that got very noisey after a few months...waste of money.  I now have the Electro-harmonix installed.  These tubes are low noise but they sound more like SS than tubes.
Has anyone compared the JJ/Teslas, Yugo EI's/or gold pins,  to Electro Harmonix?  I want a tubey 12AU7 and don't want to spend NOS prices again.
I appreciate your advice
BTW I've used Triode as a source for tubes.  They have good prices and I receive my order the next day!