700M...the legend of Greystoke

This is going to be a three-parter. The first post is just pics of a finished unit, the second and third, the nuts and bolts of it.

Before I get going though, I just want to shout out to Yoda, uhhhh Echowars! for insight he'd contributed to past 700M threads. Prior to tackling this beast, I went into infomaniac mode and parsed through as much data as I could in the 700M threads,so I wouldn't have to reinvent the wheel. Saved a BUNCH of time! Thanks, Glenn...for all you contribute.

 

Tarzan like.

 

That looks just fabulous!! You are going to love this amp!

 

Where to begin...first off, I apologize, I don't have the infinite patience of hopjohn to do a play by play tutorial, so bear with me, or just ask later.

With the exception of the two resistors to the headphone jack (oops, forgot ... shipping is more expensive than the resistors ) and the transformer, all components were replaced. Resistors, transistors, diodes, caps, relays...we did it all! For starters, I'll list what I'd culled from Echowars' insider tips so if anyone who wants to restore one of these gets bored reading this, they can at least see the dirt, then bail.

The first EW tip is the most salient one, Qe5 pin orientation on the driver boards:
** "Qe5's collector connects to Qe7's emitter (and the output line). Qe5's emitter must connect to the base of Qe9."
** C303 & 304 caps in the low current power supply upped from 1000uF, to 3300uF (found some 3300s almost the exact same dimensions with wire leads. Purrfect!)
** Cq4 cap on the meter board is installed opposite the polarity of the board markings
** .56uF film cap diode bypass between the bases of Qe9 & 10
** upping wattage of soft start resistor from 10W, to 25W (still 4 ohm)

What's in the photos...

I used solid electrolytics everywhere I could. With the exception of leakage current, they excel in performance over wet electrolytics in the form of low ESR, low ESL, high ripple current, and low dissipation factor. They're not normally used in an audio signal path because audio doesn't have a 1600MHz bus speed. They are however used in switching power supplies where things are turning on and off pretty fast! Do they have a sound? While this would be a hotly debated subject, I'm of the opinion that they have a more clinical sonic signature than a wet electrolytic. I'll leave it at that. Ce1, the first cap at the driver board input was upped from a 1uF film cap to a 3.3uF PP one. And of course, all resistors were changed from carbon film to metal film.

Besides the low current PS caps upped to 3300uF, I also increased the capacity of the main filter caps from 22,000uF, to 47,000uF. Both sets of caps are bypassed with film caps; 2.2uF/250V for the big dogs and .1uF/630V, for the smaller pair. I also added a .1uF/630V film cap across the power switch contacts. We also nixed the oil-filled caps from the low current PS to the bridge rectifier in favor of film caps.

Connector pin cleaning...here's a way to get it done very quickly, but with a caveat: don't overdo it! Fine steel wool. Gently rub fine steel wool over the contacts and in short order, they're clean! Magic? No, because if you overdo it and pull too much material from the contact pin, the connector may not fit tight over the pin Aaaaand, the pins are plated. Too much rubbing and you'll hose the plating. Also, steel wool inherently flakes apart so using steel wool to clean board contacts needs to be done with the boards removed from the unit. Steel wool the contacts, use compressed air to evacuate steel wool particles, then spritz some Deoxit on a rag and wipe the contacts. Of course, car wax works too.

Soft start resistor...YES, it is a PITA to remove! We'll fix that crap...I chose an Ohmite cylindrical one for mounting purposes. Ran down to Home Depot and picked up a 3/4" cable clamp with rubber insert, wrapped a bit of electrical tape around the center of the resistor, got a larger diameter flat washer to make up for the clamp's large mounting holes and used the factory screw and mounted that bad boy! Instead of soldering the wires to its posts, I terminated the wires with ring terminals and used screws and nuts to attach them to the resistor. If it ever needs to be re-replaced...no sweat!

Another PITA is replacing the large power resistors on the protection board. No not those ones, the other ones with the concentrically-mounted inductor. This called for patience and harsh language.

Powder coating: the bottom and top sheet metal AND the normally white-colored piece of sheet metal behind the glass were powder coated grey. Okay, gray. If I find the bottom piece of sheet metal will either take too long to clean, or the finish isn't as pristine as I'd like, I powder coat it.

I know I'm forgetting something...

 

...ahhh, remembered! If you look at the pic, on the right side of the pic between the two center bulbs and the outside pair of bulbs, you'll see a small black block of foam. From the factory, Kenwood had low compression, open cell foam pieces there and I can only assume they were there to keep the white light dispersion of the center bulbs, from leaking into the meter housings which are covered with a blue transparent/tranlucent plastic sheet...hence, the blue hue on the meters. The factory foam was essentially dust, so I cut a couple of pieces of that black foam (normally used to ship transistors and/or chips) and mounted them with contact cement. No leakage, though I will say that because I'd powder coated that white background behind the glass, the light output from the front is less, but nothing to be worried about. I replaced all bulbs with 8V/300ma wedge bulbs as well as both fuses replaced.

The sound to me ... it sounds nothing like a vintage amp! It sounds like a modern day brute force power amp, extension at both ends and effortless watts. It's clean when loud! My preference is for a more clinical sound, than the normal sort of mellow which vintage gear exudes, so this amp is to my liking. Having said that, my front end consists of a recapped (solid caps) McCormack ALD-1 Deluxe preamp and a recapped Integra DBS 50.3 Bluray player...no vinyl. Between the front end gear and component choice for the Kenwood, I don't think the results are surprising.

Oh yeah, the blue plastic on the meters cleans right up with glass cleaner, BUT...when cleaning the glass, use an isopropyl alcohol/water mix. It doesn't streak.

 

Well put. My impressions are pretty much the same.

 

Robert, looks beautiful and I am sure it sounds as good as it looks. Your attention to detail blows me away. Hopefully it will still be around when I drop off my Pioneer Spec 1 for your magic. (I wanna have a listen) I fill very fortunate that you are local and I don't have to ship gear to get excellent service. Your restoration on my Spec 2 was stellar. You the man here in SoCal. Craig (70's Silver)

 

Thx, Craig! Your check is in the mail.

 

I'll take it. !

 

My favorite scene...scared the hell outta her into sleeping with him. Classic.

 

???

 

I'd named the amp, "Greystoke" ... the jpg was from the movie: Greystoke, Legend of Tarzan. OR, it's another non sequitur for which I can't remember why I'd posted it.