CJ Premier Five refresh story with happy ending

[Pynchon]

Hello,

I am new to the forum as I acquired a pair of P5s, first CJ, about 8 weeks ago. I was considering SET tube amplifier build project when I across the P5 monoblocks - available for a song. The amps would power up and play but clearly had a number of known and unknown issues and almost assuredly ripe for a refresh. Given the limited information and reviews I could find, I quickly decided on the P5 refresh path even though I had never worked on electronic equipment - much less tube amplifiers.

Thanks to this CJ forum, the schematic and manual documentation and some quick supply sourcing guidance from the folks at ModWright (my tube preamp manufacturer), I began my journey by searching replacement capacitors.

First step, focus one the eight, large electrolytic capacitors. I eventually settled on Kemet units which met the specs and bolted right in. Success! Though there were continued issues with the amps, I played them for a while and felt there was a marked improvement in the sound to my ears.

Stay tuned. I will post this in stages.

[Pynchon]

Part B

As I geared up for the next phase, I stuck with the advice from ModWright folks: use www.octoparts.com and only source from quality suppliers. Most of my purchases were via Mouser and Digi-Key. Rather than getting completely overwhelmed by the capacitor mystique and debate, my guiding principle was to source replacement parts from quality manufacturers, sourced from reputable part suppliers and reasonably priced. I sought all parts (caps and resistors) with the same spec but, at every opportunity, tighten the tolerances from the original CJ build whenever I could.

As I dug in, additional issues presented themselves such as a burned out circuit on the PCB on for the first amp, a couple blown 20 ohm/5 watt resistors

On the second Amp, I found out of spec resistor "repair" with some capacitor issues which I am sure was rather startling when it happened!

Additionally, all the tube bias adjustment potentiometers were completely worn and erratic. In the end, I also opted to replace all of the tube sockets with the new Belton Audiophile, gold plated units.

A few phots of how things looked when I pulled the boards. In the second, you can see the wire jump I installed to repair the burned circuit.

[Pynchon]

Work in progress. These photos show what things look like as I was replacing caps and resistors. These do not show the boards with replaced tube sockets and tube bias potentiometers.

[admin]

First,
Welcome to CJO, great to have you with us.

Wow, this is one of the biggest repair/replacement jobs I have seen for a CJ unit. Must have taken a good amount of time to troubleshoot and find all those individual faults. Really amazing.

In terms of capacitor replacement, did you decide to go all with one brand? How did you make the choice?

Very cool project. The units are looking great.

[Pynchon]

Finally, I replaced the input tubes with Sovtek 5751s and RCA clear tops. When I purchased the amps, the seller provided me all the spare and spent tubes which included a total of 21 Svetlana EL34 tubes (including 16 installed). The seller claimed that the tubes had been replaced recently for about $1K. Be that as it may, I tested all and found 3 tubes were blown.

Before power up, I thoroughly researched videos on tube amplifier repairs and safety advice and acquired what I thought I needed. Variac, multimeter, oscilloscope, signal generator, a Tripp-Lite ground isolator and endless numbers of insulated alligator jump wires rated at 1000v. I could never find a PCB mount set up that was large enough and suitable for power up, so I elected to purchase some lab beaker stands with insulated grips that would rotate 360 degrees. Finally, I built a dim bulb tester and purchased a couple 8 ohm, 100 watt speaker load units.

[Joe Appierto]

Welcome. What an ambitious project as Admin has said.

Out of curiosity, is the power cord in the first photo a TARA Labs RSC Decade? I have one and like it quite a lot.

Good luck with your project.

[Pynchon]

Success! Both amplifiers powered up successfully without incident. I let them warm up for 30 minutes with the 8 ohm speaker loads, adjusted the tube biases and they both played music from a small speaker while on the bench!

When I placed installed the PCB boards, I also updated the speaker binding posts to modern units.

Before getting into the good stuff, a word about my based of comparison:

My primary system is anchored with an ARC Reference 75SE primarily running with:
1) [ModWright SWL 9.0 Linestage tube preapmp recently upgraded by Dan Wright with a new, tube rectified power supply (not original) and full cap upgrade;
2) Metrum Menuet DAC
3) Auralic Aries Streamer
4) Focal 1038BE Speakers which are very efficient for their size
5) Focal SW 1000BE Subwoofer with 13" speaker & internal 600w amp.

The ARC Ref75SE is is a beautiful amp. So clean and precise. With 75 watts per channel and lots of reserve current, what's not to like given the Focal 1038 BEs are very efficient??

I have now integrated the P5s into the primary system. I even built to amp stands from a substantial, single piece of reclaimed hemlock.

I work from home and have been able to run the P5s for hours & hours and they sound like they are really settling in.

The P5s are simply stunning. The bass and midrange have a presence and punch just not delivered by the "little" ARC.

The ARC Ref75 moved upstairs to play with my Focal 1008 BEs, my father's Luxman CL-34 tube preamp and another Metrum DAC.

Happy to be part of the CJ community. Wonder what will be next?!

[admin]

Congratulations. That is awesome. Great setup.

Question, do you find you need the sub with the Focal speakers, they seem to be full range? Of course everybody's liking is different.

I love those amp stands. Really nice. I was about to ask, where did you buy those, and then I read that you made it. Outstanding.

[Pynchon]

Hello Admin,

Thank you. Glad to be part of the community and enjoying the P5s.

As I touched upon Part B, my primary driver was to find capacitors that were of good quality (manufacture) met the original specs. That being said, I would always try to tighten the tolerances when and if possible. They were mostly plus or minus 10%, so I would install the best tolerance rating I could find 1%, 2% and/or 5% if available. Manufactures varied from Vishay, Cornell Dud, Kemet, etc.

I did NOT get spun up about esoteric materials and the expense associated therein. This was my first ever project like this and, frankly, I was not sure how successful the outcome would be.

As for the large electrolytic caps, I found an old P5 upgrade post in which someone started replacing the original Sprague units with Riva. With all the M&A over the years, the older Rivas may have a similar origin story as the new Kemets I installed. The point was, Kemets provided quality, was a single manufacturer that met the spec for both 1300 and 3300 and fit in the original mount points like a glove. Would have been nice if both configurations came in black...

[Pynchon]

Hi Joe,

Good to hear from you.

To be honest, I did not focus on the power cords. However, this sale post on Reverb is for two P5s clearly show different power cords. Incidentally, they were selling the two P5s made right before my two units. They ended in 115 & 116 and my units or 117 & 118. Small world.

Here is a photo of the cords on mine.

[Pynchon]

Hello again, Admin.

I purchased the subwoofer when I was still running the Focal 1008 BE bookshelf speakers (with stands). Almost immediately after the sub arrived, I took the plunge on the larger 1038s.

With the 1038s, I definitely adjusted the sub to the lower range frequencies given the substantial low end capabilities of the 1038s compared to the 1008s.

Be that as it may, I find the sub is always nice to have. No tone or frequency adjustments with the ModWright preamp. With some music, such as older jazz recordings, it is nice to be able to give the bass frequencies a more pronounced lift with the subwoofer.

[Big Dog RJ]

G'day mate!

Now that's an outstanding refurb project! A remarkable level of commitment and dedication, plus the willingness to learn... that's the key!
Like I've stated before, CJ gear is very simple to follow and understand. There are no major gizmos in these circuits nor any bells & whistles... circuits are simple and based on the 50's/60's Classic tube circuit. CJ has refined and simplified these classic tube circuits over decades, so nothing really new as such. Once you get a hold of these designs and a thorough understanding of what's going on, refurbs and mods can be done with the right skill and level of knowledge, plus a very very steady hand... of course!

Only recently, a very similar project was completed with all my CJ tube gear, where it was modded towards a higher Class A bias operation and the results are stunning! Going from 125w monoblocks in Class AB, now operate at 60W Class A, and they're very stable! They will switch into AB if pushed over 80w... leading upto 150w Class AB if required. Funny thing is, at normal human hearing levels... we really don't require anything more than a handful of watts. The human ear cannot continuously listen to over 100's of watts, you'd go deaf! With high-end audio gear, such as these wonderful Premier series amplifiers, it's all about the current capability and stable voltage that really drives speakers with a full grip. That's the key and Class A has more of this high current capability. CJ's top of the line stereo amps & monoblocks (ART27A & ART108A) are all Class A output, and their more powerful ART series amps, ART150 & ART300 series have higher Class A bias, so these can really perform at very high levels.

Now, I'm no technical expert nor do I have the time or a steady hand... I still like to enjoy a six pack of beer, and a couple bottles of wine... so even if I poked around I'd probably break something anyway! So all of my mods were entrusted to my CJ tech, who has vast decades of such experience, and has a steady hand! All parts sourced were original and certified, and it took approx two years to complete, since I got it done in stages. Each part was sourced then paid, and installed, and finally tested so that nothing goes into thermal overload... over long listening periods. Adjusting the Class A bias is not for the faint hearted, and if I had attempted it, I would have burned down the service center.

When I saw those pics of the Prem5's being redone, I understood the dedication, commitment and most of all passion of such a project. For when it finally all comes together, it's a beautiful thing! At this stage, you'd be very pleased with the results, there's absolutely no requirement to further upgrade, unless you were really desperate. I certainly feel the same exact way...happy as!

Now this deserves a massive WOOF!!!
Cheers, and do enjoy those fine tunes!
RJ

[AnotherJohnson]

A true labor of education and love!

Congratulations!

FWIW, I have the REF 75SE, and a pair of the LP275Ms.

I think that REF 75SE is special too.

[admin]

When I saw those pics of the Prem5's being redone, I understood the dedication, commitment and most of all passion of such a project. For when it finally all comes together, it's a beautiful thing!

I am really impressed by this repair. Not just a "replace a blown cap."

Pynchon,
The board and components look almost brand new after your fix. Did you clean the inside and parts? If so, with what and how?

[Pynchon]

Hi RJ,

Thanks for the support! I have to agree, the project was relatively straight forward. The entire project did not take more than about 6 to 7 weeks to complete. Again, I believe it was well worth the time to carefully test continuity after each component was soldered in.

Interesting project to Class A. It sounds like the results were so good, it was well worth the wait.

I too considered a conversion to Class A and discussed this extensively with my father - a bottlehead from the old days. He built a number of tube amplifiers in the day including Heathkit, etc. I still remember his Harmon Kardon - Citation II. In fact, the turntable in the photo above is his original Empire Scientific the model 108 and 1962 date etched below with his Rabco SL-8 linear track tone arm (installed a machinist on his carrier during Vietnam).

Though I have no idea how to do it at this point, I still may attempt modification to enable me to go back and forth from Class A to Class AB with the P5s at some point. In the end, I elected to stick with AB for the time being in order to test two pairs of speakers I have had in storage: The Magnaplaner MG1s my father purchased in the early 1980s and the Martin Logan CLS IIs I bought in grad school and have not touched since the mid 1990s. Both should benefit greatly from the power of the P5s!

I am enjoying the P5s as they continue to settle in. Admittedly, I have not turned the P5s up more than about 20% to 25%. Even though the 1038s are rated up to 400 watts power handing capability, they are so efficient, I fear blowing the roof off of the house if I turn it up too much!

[Pynchon]

Hi AnotherJohnson,

I am still familiarizing myself with all the CJ models but the LP275Ms look superb.

What speakers are you using the the LP275Ms and the Ref75SE?

[Pynchon]

Hi Admin,

I did some clean up - particularly removing soot from the PCB boards and chassis. However,I think the PCBs may appear more pristine in the photos. They still show browning in spots with resistors heating up in the past.

As for material, terry cloth shop towels dampened with a little water and restrained use of Windex.

Photos show soot on the underside of one chassis and the other show the new potentiometers installed with heat discoloration evident on the board.

[admin]

Still looks like you did a great job. Congrats.

[AnotherJohnson]

What speakers are you using the the LP275Ms and the Ref75SE?

The LP275Ms were most recently being used with Revel F228Bes. The REF75SE is being used with Wilson Sabrinas… but Sasha DAWs are ordered and are expected in late December.

Since early in 2020 we have been transitioning from one house to another in different nearby city. So I’ve been running two (or more) systems. We finally finished the move this year. The LP275Ms and Revels are idle for lack of suitable space to support more than one high end system.

[Big Dog RJ]

Modding those Prem5's to Class A is a bit tricky... such that it will rely heavily on the trannies and output tubes. EL34's are more known for their high resolution in midrange, the tangible benefits in the midband and that magical expansive soundstage. Therefore, they're more suited to Class AB in ultra linear mode. So modding the Prem5's to Class A is somewhat unnecessary.

There's only one other brand of amplifiers that uses EL34's in Class A output that I can think of, and that's the Overture integrated amp from Kondo Audio Note. It uses just four EL34's to produce 32w in Class A, and in this sort of application it's a beautiful sound. I tried one with my Quads ESL 2905's few years ago, and really enjoyed my time with it. However, the price tag was around 10grand for a demo model... so I settled for the CAV45 instead, just as good!

It is more practical though to do Class A mods with larger power supplies using either KT88, KT90 or KT120's. Amplifiers in this line up, such as the LP160M, LP260M and LP275M's have well designed power supplies that can easily handle Class A, and they sound superb! Their trannies are much larger and the power supplies are capable of higher current. So no issues modding these.

One of the very reasons why I engaged in such a mod was knowing that CJ will put out a higher powered Class A monoblock version after the ART27A was introduced. I could feel it happening... and I also had a feeling that the price was going to be right up there... and so it was!

I managed to get hold of all the required schematics, consulted with over a dozen EE's and got the ball slowly rolling...two years considering all the trials and errors plus burnt out tested parts, I guess was well worth it at the end.
It was also done solely in focus to fully grip and drive the CLX's full range, so I wouldn't have to turn things up so much, especially during my very late night sessions. For me and my particular system requirements, Class A proved to be perfect in this type of application.

Pynchon, looks like you certainly have a nice collection of speakers including Maggie's and ML stats! The CLS will sound marvellous with these Prem5's.
Back in the day I used the Prem11A with Maggie's and the CLSIIz's, it was fantastic! Later on took delivery of the Prem12's and then onto the Prem8A's driving Apogee Diva's with the ART preamp. That was at another level altogether but the Prem11A with the CLSIIz's was one of my favourites. I used to listen for endless hours.

You've done really well in bringing these legendary monoblocks back to life. I'm sure those are playing some wonderful tunes. Keep those tubes glowing!

Cheers, RJ