replacing tubes, AR sp6A preamp

Hello Phil. The arc sp6a is a very good preamp even by todays standards. I used one for a 2 or 3 year period before acquiring the SP-10 mk2 back in the mid 80's. As Newbee correctly pointed out, as long as a tube is in the sockets of the phono stage they do not have to be great sonically as your using the line stage only. You didn't mention the manufacturer of the tubes that are in it now. When it was first introduced, I believe ARC was delivering them either with amperex holland 12ax7's or seimens. Quality tubes like the Amperex, mullard, seimen and telefunken 12ax7's were not so scarce in those days. My all time favorite tube for the any of the ARC sp series preamps, from the sp3a right up to the sp-8 was the seimens 12ax7, although the mullards,telies, and amperexes were all very good as well. The preamp was just so suave and more articulate with the seimens 12ax7's. You may want to test the tubes that are in it as most nos 12ax7s will traditionally last a good 3000 hours unless they turn noisey or microphonic. The 3 tubes in the phono stage could be rolled into the line stage if they still test strong. Hope this helps. All the best. cheers

I had a -6B a LONG time ago. The first tube in the fono stage (V1?) will be the best one graded by noise and microphonics, then probably V2, then V4, then V5. The cathode followers (V3 and 6) are the least-important tubes in the preamp. If I were using it only as a line stage, I'd simply switch the tubes between the 2 sections, maintaining the same relative positions.

BTW, when 'testing' for audible noise, be sure to short the input you're using or at least have something not turned on plugged into those jacks.

Lucky, the SP-6 series responded VERY nicely to coupling-cap upgrades, and the 'A' version came with pretty mediocre-sounding versions. If I remember correctly, the 'B' used a pair of 0.47/400 interstage couplers and a pair of 8/200 section-output couplers. Know anyone who could install new caps for you?
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Thanks to all three of you for the info. you've given me. I've done a ton of research on most things you've said and now have whole sets of letter and number combinations that get me viscerally excited without having any direct experience whatsoever (12ax7;12ad7;12dt7;5751, gold brand,jhs;caa;jan, etc.)
I'm about to begin very carefully opening my preamp and start gaining some experience.
Do I understand you correctly, that because I am using only a CD player as a source in my preamp (AR SP6A), the phono stage slots ( I think V1,2) and the cathode following tubes, V3 and V6, can have any tube as long as they draw current, and I can experiment with the V4 and V5 line stage tubes to affect sound quality? So far every question I have researched becomes much more complex as soon as I get into it, so I'm imagining this may also.

Also, without owning a tube tester, are there places to get tubes tested?
Thanks again for the info you shared.
Phil Del Prince

Lucky3: "...because I am using only a CD player as a source in my preamp (AR SP6A), the phono stage slots ( I think V1,2) and the cathode following tubes, V3 and V6, can have any tube as long as they draw current, and I can experiment with the V4 and V5 line stage tubes to affect sound quality?"

Yes, if they're the correct type, but I'd still make my 1st 'tube roll' simply moving V1 & V2 to the V4 & V5 positions and visa-versa.

On tube testing, you might post your location and look for another 'GoNist to help.
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