Opinions needed for Conrad Johnson rebuild

inspiredsports

I've been auditioning my recently acquired vintage Conrad Johnson PV-5 tube preamp versus my recently acquired vintage Conrad Johnson PV-7 tube preamp and have decided I prefer the sound of the PV-5 by a slight margin.

I think the sound of the PV-5 is a bit warmer in the middle, and slightly more detailed at the high end of the spectrum. The PV-7 is sweet too, and the bass register seems to be better controlled, but overall the PV-5 wins.

I've heard a cap/power section rebuild will move the PV-5 to near world-class status.

Where should I send it? Ed Deitemeier at Conrad-Johnson Design and Bill Thalmann at Music Technology are my two top picks so far.

Are there other options?

inspiredsports

No one has had any experience rebuilding a CJ ??

bikerboy

Why dont you rebuild it yourself? Why do you think it needs to be rebuilt? A power supply rebuild isnt very difficult. What are the 2 places asking to do a rebuild?

ViperZ

Are we talking rebuild or upgrade here? Like bikerboy said, rebuild should be easy if you have the tools and the skills. Upgrade is a whole different beast.

inspiredsports

For sure, I want new diodes, caps and IEC input. I could probably muddle through the caps, but the space is really limited for the IEC upgrade. Silver Buss wires I don't know about.

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Music Technology is not cheap at $600, but they:

1) Replace metal can electrolytics with polypropylene (high voltage) or dry film electrolytics (heater supply).
2) Replace capacitors in the signal path with Auricap polypropylenes.
3) Install hyperfast, soft recovery diodes in the high voltage supply.
4) Improve the heater elevation circuit for lower AC ESR (surprisingly important)
5) Replace the buss wires from the I/O connectors with pure silver.
6) Lower the noise floor from the power supply regulators
7) Install an IEC power cord connector.
8) Repair anything that is needed electronically to get the preamp to operate as new, except for tubes.
9) Optionally, bypass the balance control for a subtle, but audible improvement (this is easily reversible).

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CJ proper is quite a bit less, but they use parts closer to original mid '80's specs that don't correct all of the minor criticisms (mostly less than perfect bass reproduction) of the past couple of decades. They perform more of a restoration versus upgrade

disneyjoe7

Do you care to pull the cover and post a picture in the PV-5 pre amp? I own one and I think the original person had it update once, I could post a picture also so we could compare both of them.

inspiredsports

disneyjoe7 wrote: »

Do you care to pull the cover and post a picture in the PV-5 pre amp? I own one and I think the original person had it update once, I could post a picture also so we could compare both of them.

Thanks Joe,

I've attached a huge image so you can see cap values, etc, and it may take a bit to load.

I don't think anything has been replaced with the exception of tubes.

The only problem within is what appears to be melted rubber, I think from a cheap tube damper, on resistors in the phono stage.

disneyjoe7

Hmm....., I was thinking that my volume controller was changed I seen another and the volume was look the balance controller. Mine does have different caps on the power supply by the volume controller, I can post a picture later.

Jed Leland

Hello,
Those circuit path resistors look like Corning glass composition types. We used those on the original Dyna PAS 3X and ST70 mods, way back when. They were certainly an upgrade from carbon composition types. Once the Roederstein Resista and later Vishay bulk foil resistors became available they fell out of popularity.
Cheers, Ken

inspiredsports

Wow, this is crazy. After buttoning it back up after the photo and turning it back on, the unit will not kick out of "warm up" mode. :mad:

It has a relay that kicks in after 45 seconds to send full signal to the outputs. I guess the warm up period is to protect the amp from the strange noises most tubes output when they are cold.

Looks like my tune up is going to need to come sooner rather than later unless this is something simple.

inspiredsports

disneyjoe7 wrote: »

Hmm....., I was thinking that my volume controller was changed I seen another and the volume was look the balance controller. Mine does have different caps on the power supply by the volume controller, I can post a picture later.

A picture would be great. I know the 3 metal power caps in the front right corner generally get noisy or fail early on, and get replaced in many of this era CJ preamp. My PV-7 was done by the folks at Conrad-Johnson Design in early 2006 by the prior owner.

I'm guessing that is what has just gone wrong with the PV-5 now.

I'm sure glad I still have the PV-7 so I don't have to go back to solid state while repairs on the PV-5 are being arranged.

disneyjoe7

The update was also done by Conrad Johnson, still no picture but soon

disneyjoe7

This one is a close up of the work I done for my auto HT bypass. It's a little dirty work as I wasn't sure if I would be happy with it. This work was done prior to PF09 so if you heard this pre it worked thou these relays. I used 2 relays to reduce any crossover talk being introduced, the wire is copper with a silver like coating making it sound beautiful.

dorokusai

Yea, that looks familiar and awful.

disneyjoe7

dorokusai wrote: »

Yea, that looks familiar and awful.

And Awful, not sure why at least the wiring of my relay thing should be familiar to you I twisted it grounding one end for noise, I couldn't tell the difference before or after the mod.

dorokusai

LOL Steve, I rolled when I saw that wiring....I get nausea when I see it at work.

disneyjoe7

Ok from you point of view, yes I would feel sick also. But makes one great sounding pre, which everyone can work the system. Read "Wife" proof

dorokusai

I'm a huge fan of that era of CJ...excellent tube pre-amps.

disneyjoe7

Looking at these pictures I see some difference in the power supply circuits. So I'm adding some pictures in the area.

Dawgfish

Greg,

I'm sorry to hear about the power up problem. I hope it gets resolved quickly. I've been wondering how the PV-5 has been treating you and how it compared to your PV-7. Good luck with everything.

Steve

inspiredsports

Dawgfish wrote: »

Greg,

I'm sorry to hear about the power up problem. I hope it gets resolved quickly. I've been wondering how the PV-5 has been treating you and how it compared to your PV-7. Good luck with everything.

Steve

No problem. I'd planned to rebuild one or the other, and I'm just glad I got a good chance to audition both and determine the PV-5 was the keeper before the glitch. Thanks again for your exceptional help in relaying this unit from your almost nearby Craigslist guy to me!

inspiredsports

disneyjoe7 wrote: »

Looking at these pictures I see some difference in the power supply circuits. So I'm adding some pictures in the area.

Yep, your old metal power caps have certainly been upgraded. This part I could tackle myself, but I will just let the rebuilder do when they are into the more critical signal path upgrade

disneyjoe7

And may the diodes near that black cap, then look at your output leads to the output jacks, yours in a gray wire mine are silver?

inspiredsports

Well this dates all the way back to Jan 14th (2010) when Dawgfish (Steve) posted that he found a CJ PV-5 for sale in Jacksonville: http://www.polkaudio.com/forums/showthread.php?t=94950&highlight=Conrad+Johnson.

I mentioned on the 18th that I was interested if he bought another pre he was considering at the same time. Well, Dawgfish ended up going with an Anthem and graciously offering to liaison the deal between me and the Florida seller. I sent funds and Steve made the deal for me with a considerable investment of his own time and driving miles. (THIS KIND ACTION IS ONE OF THE THINGS THAT MAKES ME MOST PROUD TO BE A PART OF THIS GROUP ).

Long story short, the PV-5 arrived, I listened for a bit, decided it was here to stay and sent it out to Bill Thalmann at Music Technology for a $600+ 2010 makeover. I waited for what seemed like forever, and received the unit back today.

It is all plugged in, warmed up, and playing some Jethro Tull as I write.

I'll get photos posted later.

As far as the sound . . . . naturally I should wait until it seasons a bit. I will say no more than, "Wow!" and "My ear to ear grin couldn't be any bigger!"

(This is my first "real" preamp)

inspiredsports

Here's an image of the insides after the upgrade (Post #11 above contains an image of the original components and Post #5 lists the upgrades).

I know this sounds trivial, but the addition of an IEC Power Cord connector so I can swap power cords is one of my favorite parts of this tweak. (I know, I know; simple things amuse simple minds )

inspiredsports

24 hours in and I'm convinced I made the right choice. The phono section REALLY shines versus the few preamps with phono or free-standing phono stages I've had prior (NAD 1700, NAD 7600, Conrad Johnson PV-7, Bellari VP-130, Thorens MM 001).

The one last thing I would like to do for the PV-5 is obtain 4 HIGH-LINE 5751 tubes as the Sylvania's in there are still strong, but getting older. The phono section uses just 1 and the line stage 3 so I would only need 3 matched and 1 could be a bit different in spec.

DeusExa

Did this have anything to do with the Carver challenge?

inspiredsports

Nope, I just like to have lots of vintage gear brought up to 21st century standards as I fall deeper and deeper into the rabbit hole.

inspiredsports

I have "stock" GE 5751 gray plates in the PV5 and am going to upgrade to GE Triple Mica black plates, and then look for a decent deal on Raytheon's or Sylvania's moving forward.

I've read a lot of reviews and the way I take it, they rank approximately as I have listed them below.

I've also heard that while Sylvania black plates sound best, they might not last as long.

Am I missing anything?

1 - Sylvania Gold Brand grey plate - gold pin
1 - Sylvania Gold Brand black plate
1 - Sylvania black plate government contract gold labels (JHS, CAA, etc..)

2 - Raytheon

3 - GE black plate

4 - Siemens grey plate

5 - GE grey plate

inspiredsports

I found a great deal on a matched quad of late 1950's NOS Black Plate Triple Mica GE 5751's ($125 delivered) and have had them installed for just over a week now. Tube strength values (with 140 = maximum) on my calibrated Eico 667 are 140/130, 138/128, 125/130, 120/130.

The GE's seem like a very, very good match for the PV5. The width and depth of soundstage, vocal focus and decay are absolutely better than the NOS 2 Mica Gray Plate GE's I replaced. (duh!)

I wonder what would happen if I replaced the 12AX7's in V1 and V2 (100% gain) with 5751's (same values with the exception of 70% gain).

I guess my next rung on the ladder are the highly touted Sylvania's, but I'm going to stay with the GE 3Mica Blacks for now.