Opinions on vintage cj amps and Teflon cap mods

Mrtennis, I enjoy much of what this amp has to offer. I'm hoping I can improve it without altering its virtues. Think of it like buying a vintage house that you love for its woodwork and craftsmanship of a bygone era. Would it be inconsistent to tear out the coal burning furnace and replace it with a modern heating plant?

The power supply is responsible for much of your amps sonic signature. If you send it back to CJ for these updates, I can assure you that it will sound nothing like it did. My advice is to have it restored to spec. Buy a new amp if you want the modern "teflon cap" sound.

I had a chance to compare CJ's proprietary teflon Caps to VH Audio and Relcap teflon caps as coupling caps in a tube preamp.
CJ's caps do not sound at all like VH caps. Both are excellent, the CJ caps retain the CJ "magic" while increasing resolution, however they do not go over the edge.
VH caps are excellent choices if your aim is maximum transparency.
The Relcap TFT cap would be my third choice.
In summary, if you want to bring your amp to modern CJ specs, I believe you can not go wrong with the factory mod.

Phaelon, most vintage tube amplifiers (not CJ) were designed to a price point and to make the tubes last long (to the detriment of sound quality). Tubes were under-biased (or to put it technically, an "easy-on-the-tubes", low current operating point was chosen), transformers had limited bandwidth, oil caps were used for coupling and the power supplies used a minimum of capacitance, mostly electrolytic caps have a specified shelf life of 10 years.

With rare exceptions (Harman Kardon, Fisher, Marantz, Quad), the output transformers did not pass a wide frequency response. This was partly compensated through heavy use of negative feedback, which wreaks havoc with soundstaging and dynamics.
In summary, vintage tube amplifiers in mint condition sound mellow, limited in the frequency extremes and undynamic as compared to modern tube amps. Soundstaging is also affected.
If one factors in dry power supply caps, out-of-spec resistors due to 30+ years of aging and leaky coupling caps, we have the usual mellow/bloated, lo-definition sound quality of vintage amps.
I am not saying that all vintage amps sound bad, I have tried to explain in general the "vintage sound"

SNS, about parts life expectation: Parts with a limited life span are tubes, potentiometers, carbon resistors and electrolytic caps.
Nowadays, CJ uses mostly film caps in their power supplies.

Transformers, hook-up wire, modern resistors, modern film capacitors, connectors and well-engineered tube sockets have an indefinite life span. 100 years in a non-salty/corrosive environment is not unheard of.
I own a 1938 tube radio that works perfecly after the electrolytic caps were replaced.
So, a properly cared-for CJ amp should last the owner's lifetime, if he/she replaces the output tubes when the bias indicator sez so.
Input tubes last aproximately 10,000 hours or 5-8 years of normal usage.

I hope this helps

Casouza, I hear you on the V-Caps, can be too much of a good thing, the reason I would hesitate to recommend them in this case. I wonder who manufacturers CJ's film caps?

Granting that what you say about transformers being band limited is true (I hear it), it would seem somewhat pointless to upgrade most vintage amps. These amps will never be able to reproduce those things I most like about the modern amp sound (I don't know about Phaelon), ie. the dynamics, immediacy and soundstaging. These things my Art Audio does magnificently, my CJ likely doesn't have a hope in these areas.

Hi Casouza, Your post helps tremendously. You addressed all of the issues in question. Ultimately, I have to make a decision and it would seem to come down to this: 1) Would I be better off trying to restore these amps to as close to original spec as possible, 2)sell them, combining the revenue with the cost of the upgrade and buy a different amp or 3)taking a chance on the upgrade and hope that lightening strikes. Regardless of which I choose, your post is most appreciated. They all are.