[jarcher]

Hi folks : just won a flea-bay auction for a Conrad Johnson MV75A1 tube amp, but it comes with no tubes.  Was wondering whether folks could give me recommendations based on their experience - whether with this amp or others.  Here is what it needs :

(4) 6550
(2) 6FQ7 / 6CG7
(1) 5751

I had previously heard another of these amps with Sovteks or something Russian for the 6550's, probably GE's or RCA for the 6FQ7 and 5751's.  I was really surprise by the depth and power of the bass along with the transparency / detail / resolution but musicality of things such as cymbals, electric guitars, etc. 

My sound preferences : I like my sound more "analytical" but on the same hand smooth (i.e. without getting too etchy). 

Some tubes I'm considering :

6550 : SED / Svetlana Winged C ; new production Tung-Sols. Something Russian & not to expensive.  I know I can try KT88's and maybe even KT120's (willl try those later), but I think I should start at least with what the amp was originally designed for.  And I was pretty happy w/ the detail + power of the 6550's I heard w/ this amp originally.

6FQ7 / 6CG7 : Don't know what CJ's came with originally.  Was thinking of experimenting with the Mazda ones that Upscale Audio is raving about.  Otherwise maybe RCA's?

5751 : I'm assuming the grade / choice here is not as critical (?).  Perhaps just an RCA as well?

Thanks all for the help!

[DustyC]

I had a pair of these a few years ago, running as monoblocks. I used 6550 Svet's and Sylvania 6fq7's and a GE 5751. I would be careful about running KT120's in this amp as the power transformer runs pretty hot and plugging those in might be just a little more than it can handle.
C-J "voiced" this amp for the GE 6550's but I think the Svet's are pretty good and cheaper to get.
Enjoy 

[jarcher]

Interesting : I was thinking some day to maybe get another to run them in mono-blocks, one of the attractive thing about them along with the price, sound and relatively compact size.  Using them w/ Magnepan 1.7's ,so those do like more power.  Did you find you were getting significant / more noticeable power running monoblocks vs one in stereo?

I had my reservations about trying KT120's as well, as you noted I also found that this amp runs "hot".  Will have to check w/ CJ + owners before making a costly mistake......

Which "flavor" of Svet 6550 did you run?  I'm seeing 6550WE (plastic base), 6550WD, and 6550C.

[JakeJ]

Hi jarcher,

I am not familiar with the amp but my VAC amps take 6550/KT88s and although I have not tried any 6550 variants I have tasted JJ KT88, Penta Labs KT88, and Gold Lion KT88 (all tubes I consider "affordable") and my ears like the Gold Lions best with the Penta Labs a close second.  The JJs sound nice but seem colored with a lot of emphasis on the treble, ie. very "sparkly".  I know this doesn't help much since the amps are from different mfrs but I also had a very similar experience with a pair of Quicksilver monoblocks with these same tubes.  Just thought I'd throw that out there.  Good luck on your search.

[mikef]

When I had my MV75A1 amp I liked the GE 6550s. Better than the Svets or Sovteks.

You might look into having Bill Thalmann of Music Technology update your amp. Worked wonders on mine.

Mike

[jarcher]

Yeah - would like the GE 6550, but a quad would set me back $350+.  Will keep my eyes peeled for a used set. What was it you liked vs the Russian equivalents?

Bill + CJ are both only 15 minutes from my house. Hopefully I'd only need them for updates. Taking a chance on such an old amp from a flood damaged estate, but the photos and price were good. Previous owner updated the RCA's + power cord with cardas stuff, but don't know if the power supply caps, etc were done.

[Ericus Rex]

A couple of Russian options to try for cheap:

http://app.audiogon.com/listings/tube-3-quad-6550-for-sale-sovtek-6550wa-and-svetlana-6550b-for-sale-2013-07-15-amplifiers-30071-norcross-ga

[pstrisik]

I have a Premier 11A that uses the same tubes.  I've been running KT120's after trying stock tubes, KT90 (or was it KT88), and the Tungsol 6550 reissue.  You might check on the dedicated CJ forums as there is quite a bit of discussion about this tube.  The KT120 has it all, IMO.  It extends more in both directions, is generally more dynamic, and adds no harshness.  CJ is using this tube in new amps.  In fact, I just acquired a demo pair of LP125M that originally came with 6550's and CJ now ships them with KT120's.  Definitely worth checking with CJ about the suitability though.  Both the Premier and current LP lines are said to use higher quality parts, so the concerns about heat might or might not be warranted.

I also experimented with the other tubes in my 11A.  I first tried NOS RCA Triple Mica 5751 but was still feeling some grain.  Brent Jesse, where I bought them, suggested trying the RCA blackplate 5751 double mica which I did like better.  Note that I err on the side of easy to listen to/warm - opposite of edgy/grainy.  But I think I'm more sensitive than most in the upper ranges.

For the other tubes, I tried RCA 6CG7/6FQ7 Clear Top and stayed with them. 

You can check out Brent's site at www.audiotubes.com.  The site is a bit of a mess, but he's very helpful with advice.

[mikef]

Yeah - would like the GE 6550, but a quad would set me back $350+.  Will keep my eyes peeled for a used set. What was it you liked vs the Russian equivalents?

If I remember correctly (8+ years ago), the GEs imaged better (deeper soundstage) and had better bass.

[jarcher]

A couple of Russian options to try for cheap:

http://app.audiogon.com/listings/tube-3-quad-6550-for-sale-sovtek-6550wa-and-svetlana-6550b-for-sale-2013-07-15-amplifiers-30071-norcross-ga

Thanks - that's a good deal.  I've made the guy an offer @ his asking price & asking him if he'll through in shipping : though what he's asking is super cheap as it is.  I believe the first time I heard this amp it had Sovtek 6550's, and I was pretty happy w/ it as it was.  The PS caps had been upgraded, and a few fixes, but otherwise stock.

I've also ordered some used SED / Svetlana Winged "C" used off of ebay (for hald off new).  So will have a fleet of different Russian 6550's to try out (fortunately I also have another tube amp that can use 6550's). 

For the input tubes I ordered some used RCA (not clear top), GE and Sylvania 6FQ7 / 6CG7 to try out (all 3 pairs we're like $30).  Fortunately these tubes types seem to be in ample supply so I don't see crazy prices.

5751 will probably start by using an RCA I have around and get whatever later as it doesn't seem so critical.

Anyway - still value suggestions on tubes - particularly for the input stage.  If I don't end up having to put a lot of money into this amp to get it fixed, may try out those GE 6550's if I can find them at a reasonable price used. 

[jarcher]

I have a Premier 11A that uses the same tubes.  I've been running KT120's after trying stock tubes, KT90 (or was it KT88), and the Tungsol 6550 reissue.  You might check on the dedicated CJ forums as there is quite a bit of discussion about this tube.  The KT120 has it all, IMO.  It extends more in both directions, is generally more dynamic, and adds no harshness.  CJ is using this tube in new amps.  In fact, I just acquired a demo pair of LP125M that originally came with 6550's and CJ now ships them with KT120's.  Definitely worth checking with CJ about the suitability though.  Both the Premier and current LP lines are said to use higher quality parts, so the concerns about heat might or might not be warranted.

I also experimented with the other tubes in my 11A.  I first tried NOS RCA Triple Mica 5751 but was still feeling some grain.  Brent Jesse, where I bought them, suggested trying the RCA blackplate 5751 double mica which I did like better.  Note that I err on the side of easy to listen to/warm - opposite of edgy/grainy.  But I think I'm more sensitive than most in the upper ranges.

For the other tubes, I tried RCA 6CG7/6FQ7 Clear Top and stayed with them. 

You can check out Brent's site at www.audiotubes.com.  The site is a bit of a mess, but he's very helpful with advice.

Thanks - I've been trying the KT120's with a Jolida 502A amp, and definitely like what I hear vs the Electroharmonix KT88H it was running before.  A bit more power, bass, and somewhat more refined & warmer / rounder. This may ultimately be my power tube of choice for the CJ once I confirm it's ok.

RE: the 5751, I use these in the preamp section of a Darep MP5 hybrid tube amp, RCA 5 stars.  Best of the few things I tried : detailed but refined.  For the CJ the 5751 is just the rectifier (?) tube, so the choice perhaps is not as critical (?).

[Ericus Rex]

RE: the 5751, I use these in the preamp section of a Darep MP5 hybrid tube amp, RCA 5 stars.  Best of the few things I tried : detailed but refined.  For the CJ the 5751 is just the rectifier (?) tube, so the choice perhaps is not as critical (?).

The 5751 is likely first stage voltage gain, the 6FQ7 is probably the driver.  I would imagine the 5751 would have more impact on the sound but I don't have first hand experience with this amp.  I don't think this amp uses tube rectification.

[DustyC]

Interesting : I was thinking some day to maybe get another to run them in mono-blocks, one of the attractive thing about them along with the price, sound and relatively compact size.  Using them w/ Magnepan 1.7's ,so those do like more power.  Did you find you were getting significant / more noticeable power running monoblocks vs one in stereo?

I had my reservations about trying KT120's as well, as you noted I also found that this amp runs "hot".  Will have to check w/ CJ + owners before making a costly mistake......

Which "flavor" of Svet 6550 did you run?  I'm seeing 6550WE (plastic base), 6550WD, and 6550C.

I used the 6550C version. Got them from Kevin Deal at Upscale Audio.

Having 2 amps allows you to flip that switch on the back deck to tie the input jacks together (so you can use either one) and then connecting the hot taps from each channel togther along with the ground (1 only). You are connecting the channels in parallel to double the output power (150 watts). Since that is only 3 db more volume level I didn't think that it was worth it from a power standpoint.

You must listen fairly loud. I have 3.6R Maggies and drove them with a single MV75 for quite awhile. 

[DustyC]

The 5751 is likely first stage voltage gain, the 6FQ7 is probably the driver.  I would imagine the 5751 would have more impact on the sound but I don't have first hand experience with this amp.  I don't think this amp uses tube rectification.

You're right, no tube rectification.
The input 5751 made more of a difference in sound than the output tubes did. I borrowed a couple from a friend and found differences in the treble to be most apparent. I don't remember what brands they were since I wanted to keep the stock C-J "sound" that was voiced around the GE tube. I didn't think the change in sound was of the "oh my god" variety so I didn't note the brands. (RCA maybe?)

[jarcher]

So, sorry for the ignorance : the single 5751 is the input tube & the 6FQ7 / 6CG7 pair are the driver tubes?  Used to all the other tube amps that I have using a pair of tubes for the input tubes, so assumed that the 6FQ7 / 6CG7 were the inputs tubes.......

[jarcher]

You must listen fairly loud. I have 3.6R Maggies and drove them with a single MV75 for quite awhile. 

My previous experiment was using an MV75A1 in stereo w/ a passive preamp / dac (Bel Canto 1.5) and on occasion felt that I wanted just a little bit more power.  And thought it might be good to have a bit more headroom as well for the heavy stuff.  Even used as monoblocks MV75A1s seemed to be one of the better tube deals out there for the power and sound quality.  Nice to be able to start with one.......

[pstrisik]

I had a bel canto 2.5 and tried it as a preamp.  I found that it suffered from a lack of gain. you'd probably find that your amp seemed more powerful if you used a fulfledged pre.

[JakeJ]

Hey, does anyone have any opinions on the Tung-Sol 6550 reissues?

[Ericus Rex]

So, sorry for the ignorance : the single 5751 is the input tube & the 6FQ7 / 6CG7 pair are the driver tubes?  Used to all the other tube amps that I have using a pair of tubes for the input tubes, so assumed that the 6FQ7 / 6CG7 were the inputs tubes.......

No sweat!  We're all learning about this crazy tube world.

The 5751 is a twin triode which means it has basically two tubes in one glass bottle.  That's why you only need one.  Some designs use two bottles but only one section in each (a waste, IMO) and others use both sections of both bottles.  All depends on the design.  No hard and fast rules here.

[jarcher]

I had a bel canto 2.5 and tried it as a preamp.  I found that it suffered from a lack of gain. you'd probably find that your amp seemed more powerful if you used a fulfledged pre.

Yeah, I think the 1.5 / 2.5 / 3.5 are essentially passive preamps only outputting up to the stock 2v or whatever vs actually providing gain.  I'm still going back & forth trying to decide whether the advantages of direct from the dac as passive preamp outweigh the additional gain and body (even if it is "coloration") that an active preamp can provide. 

Somehow I see a vintage CJ preamp in my future - though wonder if that's not going too far in the "tubey" department.