New Amp Day - StewMac Mojotone '65 P-Reverb Princeton Reverb Assembly & Review

[jonfields45]

First, we have my StewMac main eyelet board. A perfect recreation of the mid-60's original assembled with genuine 1950's technology (ignoring the small axial lead electrolytic's).



Next we have the Headstrong version. All the passive components are the latest, quietest, longest lasting, and physically tiniest that today's technology has to offer. The solid core cloth insulated wire is used to maximum Manhattan geometry perfection in a way no factory run by Leo Fender would ever come close. It is much loved by the cork sniffing crowd :~).



Last we have the Fender 64 Princeton. The components are higher end consumer grade. The eyelet board is made from modern glass epoxy. The wiring is plastic insulated stranded (I think) and not obsessively placed (Leo would be fine with it). The main ganged chassis mounted electrolytic capacitor is replaced with eyelet mounted axial lead individual electrolytic's (like the higher end Fenders of the 60s). This amp is much maligned by the same crowd that loves the Headstrong.



So what do I think, as a retired EE whose opinion is tilted towards the modern??? The Fender 64 is way better!

[clintj]

The Headstrong and modern Fender arrangements have one advantage in serviceability. They didn't tie the cathode resistors to the cathode bypass capacitors like Mojotone does. Those resistors will last for decades, while those caps will need replacement in 15 to 20 years and you end up either trying to separate them or throwing out a perfectly good resistor. It also puts the soldering heat right against the body of the capacitor which can lead to damage and shortened lifespan.

[jonfields45]

Originally Posted by clintj

The Headstrong and modern Fender arrangements have one advantage in serviceability. They didn't tie the cathode resistors to the cathode bypass capacitors like Mojotone does. Those resistors will last for decades, while those caps will need replacement in 15 to 20 years and you end up either trying to separate them or throwing out a perfectly good resistor. It also puts the soldering heat right against the body of the capacitor which can lead to damage and shortened lifespan.

Luckily (?), at 66 years old, I suspect the StewMac design will outlast me.

[Jeff Scott]

Originally Posted by jonfields45

First, we have my StewMac main eyelet board. A perfect recreation of the mid-60's original assembled with genuine 1950's technology (ignoring the small axial lead electrolytic's).



Next we have the Headstrong version. All the passive components are the latest, quietest, longest lasting, and physically tiniest that today's technology has to offer. The solid core cloth insulated wire is used to maximum Manhattan geometry perfection in a way no factory run by Leo Fender would ever come close. It is much loved by the cork sniffing crowd :~).



Last we have the Fender 64 Princeton. The components are higher end consumer grade. The eyelet board is made from modern glass epoxy. The wiring is plastic insulated stranded (I think) and not obsessively placed (Leo would be fine with it). The main ganged chassis mounted electrolytic capacitor is replaced with eyelet mounted axial lead individual electrolytic's (like the higher end Fenders of the 60s). This amp is much maligned by the same crowd that loves the Headstrong.



So what do I think, as a retired EE whose opinion is tilted towards the modern??? The Fender 64 is way better!

After having owned three 7ender amps with fiber tag boards (1962 Concert Amp, 1966 Band-Master head, and an early '70s Princeton Reverb Amp) I am all in favor of glass-epoxy boards.

[jonfields45]

Originally Posted by Jeff Scott

After having owned three 7ender amps with fiber tag boards (1962 Concert Amp, 1966 Band-Master head, and an early '70s Princeton Reverb Amp) I am all in favor of glass-epoxy boards.

I had a similar Concert (brown vinyl and panel) amp in the early 70's. At only 10-15 years old the carbon comp resistors were quite noisy. Hopefully my kit will do better!

[GoPappy]

Originally Posted by jonfields45

Luckily (?), at 66 years old, I suspect the StewMac design will outlast me.

It's the same philosophy as riding a motorcycle. If you ride one long enough, it will probably kill you. The goal is to avoid that long enough that you die of something else first!

[rockabilly69]

Originally Posted by Jeff Scott

After having owned three 7ender amps with fiber tag boards (1962 Concert Amp, 1966 Band-Master head, and an early '70s Princeton Reverb Amp) I am all in favor of glass-epoxy boards.

I'm also in favor of the glass epoxy boards as I have two vintage Fender amps ('64 Deluxe Reverb and '69 Vibro champ) that needed solder joints re-flowed with the warping of the original fiber boards.

[jonfields45]

A little progress. The left most main eyelet board bolt was very inconveniently placed next to the output transformer. The instructions mention only two of the three main eyelet board bolts, but one of the two was that one by the transformer... They included a 0.047 Orange Drop for the faux ground switch which is left unconnected in the instructions. Figuring out why I had an extra cap at the end of eyelet board assembly was a little irritating.

[Bluside]

I love following this thread. Keep posting your progress. Looks great.

[Jeff Scott]

Originally Posted by jonfields45

I had a similar Concert (brown vinyl and panel) amp in the early 70's. At only 10-15 years old the carbon comp resistors were quite noisy. Hopefully my kit will do better!

Originally Posted by rockabilly69

I'm also in favor of the glass epoxy boards as I have two vintage Fender amps ('64 Deluxe Reverb and '69 Vibro champ) that needed solder joints re-flowed with the warping of the original fiber boards.

One issue I believe is that the fiber boards tend to collect and retain moisture.

[jonfields45]

Originally Posted by Jeff Scott

One issue I believe is that the fiber boards tend to collect and retain moisture.

I had a 74 Twin Reverb that at a couple of years old produced an oscillating noise that would go away if I left it on overnight. Something another person might have ignored. The local Fender repair shop, Time Electronics near Kean College in NJ, said the eyelet board was conducting and they could float some of the components over the top to fix it. I declined and contacted Fender. They offered to repair it if I shipped it to California. I guess unethically I ran it overnight and traded it in on a Sunn Concert Lead at Rondo Music.

[jonfields45]

Originally Posted by rockabilly69

I'm also in favor of the glass epoxy boards as I have two vintage Fender amps ('64 Deluxe Reverb and '69 Vibro champ) that needed solder joints re-flowed with the warping of the original fiber boards.

As I finished my EE degree I was asked by friends to repair their amps. I never successfully repaired a solid state Peavey of that era, but did good work with Fenders and NJ made Ampegs. For the Fenders, I would always reflow the eyelet board solder joints, given it was not the usual blown open B+ power supply electrolytic and that the owner checked the tubes. I attribute this problem to the size of the solder joints and thermal cycling. Most of the time that was that was all that was needed. My preference for glass epoxy is more the tactile feel of quality.

[redir]

Looking good! I've been thinking about one of those kits and now you're killing me! I built a Mojo Tone 18w Marshall about a year or so ago and liked it so much it's my gigging amp now. One thing I did, since I am a total armature and don't at all understand the electronics but simply follow the directions, was to take my amp to my VERY good amp repair guy to go over it and make sure I didn't do anything that would kill myself.

[jonfields45]

Originally Posted by jonfields45

I would always reflow the eyelet board solder joints

as one of the first steps in Fender amp repair.

Just to clarify, the eyelet is likely nickel plated steel and the solder joint mostly tin. Given enough temperature cycles it will eventually fail due to different coefficients of thermal expansion and stresses that build up in tin over time. Lead free solder is much worse. And like many things in life, size matters :~), however in this case smaller wins.

[redir]

So for you guys that know this stuff, when you solder a high voltage, or any I suppose, wire to a lug so you want first, a mechanical contact? IOW maybe not wrap the wire around it but at least be sure there is wire to lug contact before locking it in place with solder?