2. amps-preamps
  3. 1105990413

replacing tubes, AR sp6A preamp

HI,
I am on a steep learning curve with tube equipment. I have an AR SP6A preamp. For reasons too long to go into, I bought it 12 years ago, and just hooked it up two weeks ago.
I don't know how old the tubes are.
My two questions are:
My system uses only a CD player as a source component. When I replace the preamp tubes, do I have to replace all of them, including phono stage, or just some (if some, which ones).
Second question, Can I do it (simple, take out and put in?), and do you have a specific tube preference?
Third, though I imagine this is a tough simple answer, since i don't know how it sounded when tubes were new, is there any way to tell if the tubes are just fine, or not so good?
Thank you for any help you have the time to give.
Phil Del Prince
lucky3

Showing 2 responses by jeffreybehr

jeffreybehr's avatar
jeffreybehr
805 posts
 
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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jeffreybehr's avatar
jeffreybehr
805 posts
 
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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