What do you guys know about these

[transformer]

i'm curious as to opinion of recapping? as those appreciating the natural/original integrity of the altec designs, ... do you feel that recapping the unit with higher performance components is a positive or negative thing?

[bfish]

"do you feel that recapping the unit with higher performance components is a positive or negative thing?"

IMO, at least partial recapping is warranted on most any tube gear 25 years or older, especially items that have been out of service for years at a time. Replacing all the electrolytic-type caps is #1, as they're already well beyond their expected lifespan, and when they die, it's usually a short, so they take other parts out with them, often the irreplaceable transformers. Your noise problem may be caused by leaky electrolytics, if there's 60 or 120hz hum. Blind replacement of the film caps is seldom needed unless the originals are of the paper/wax variety. Ceramics and micas live forever, as do most PIOs.

Don't get caught up in the "magic" capacitor nonsense, or, for that matter, the "bigger is better" philosophy. Use the exact values for capacitance and voltage ratings if at all possible. Classic models became such because they excelled in performance, not because they needed 'improving'! The engineers that designed them were sharper than any dozen online 'gurus'. Buy NEW caps, not NOS! (FWIW, NOS electrolytics are more likely to be bad than the ones you're replacing!)

HV caps for tube gear are harder to find, but are still readily available from sources like Mouser, JustRadios, and Antique Electronics, all of whom I buy from regularly, and highly recommend. I'm personnally a Sprague (brand) devotee, but most all of the current-production caps will outperform (and outlive) the ones you're replacing.

I'd recommend some study time be invested prior to ordering a slew of caps. Learn to recognize the various types, and how to correctly read their ratings. GET YOUR INFO FROM SOMEONE THAT'S NOT TRYING TO SELL YOU SOMETHING! unfortuneately, many forums are lousy with bad info too. Choose what to believe because it's logical, and can be proven, not because it's magic. As in most cases, the right road isn't the easy road, but WILL get you where you're going.

BTW, the most common cause of noise is from poor or incorrectly wired connections, particularly on gear with both balanced and unbalanced I/O. BobR has a recent post with excellent info on that topic.

[transformer]

"BobR has a recent post with excellent info on that topic."


how do i find this post? i dont think its the issue with my unit but i want as much info as possible so i need to read what his post says.

and thanks for all the great info on that last post....it was real helpful.

[bfish]

Guess it was a little older than I thought, it had already been archived;

http://www.hostboard.com/cgi-bin/ult...&f=3729&t=1863

The archives can be searched (while logged in), from the link at upper page-right.

Some good interconnect info is also in the Rane tech library;

http://www.rane.com/note110.html

A third possible noise source could be a tube gone microphonic. A light tap with a pencil on each tube while operating should reveal this audibly.

Always glad to help someone willing to listen!

[Richard C.]

The thing I see when looking at these pictures is the beautiful "point to point" wiring done on this quality piece. It is done in layers from the chassis out, and it is VERY difficult to replace all the caps without butchering up the remaining circuitry. I have done this and it requires much time and patience to do a job that looks "right" when done. If you think anyone can do this, just look at some of the older kits. Heathkit, Dynakit, Eico, etc. I have seen assembly techniques that looked like they were racing to power up & do the smoke test! I think the majority of the smaller coupling caps will test just fine, and will last forever. The paper caps with wax dripping out of the ends should be replaced. Definitely replace the power supply caps, and Don't substitute a solid state diode (or full wave bridge) for a tube rectifier. Not a good mod unless you dump the extra voltage that is gained. Some tubes don't like B+ applied too quick, either! One thing I have noticed is the older carbon resistors usually increase in value as much as 20% over time; especially if they run hot. There are places that sell original carbon resistors, too. And, yes "old" NOS electrolytic caps would be in terrible shape after years on the shelf. IF the NOS caps were charged thru a resistor to the working voltage about once a year, and held there a few days (called reforming); they could be kept usable for several years.

All this work is gonna cost $$$, unless you do it yourself. Get some tube type "junk" and practice your soldering technique on something that doesn't matter.

Richard C.

[scott fitlin]

My opinion on recapping is that over time electrolytics do deteriorate! BUT, be careful when deciding to recap. many very high priced caps out there advertised as the Holy Grail of Sonic Nirvana! B*ll5hit! When you change caps, you can alter the sound of the unit, but not always for the better!

Let a good technician repair whats neccesary to be changed, and knows what to use, it will keep your unit sounding as it was designed to sound!

Too many times, amatuer DIYers change caps and resistors, spend a small fortune on esoteric parts, only to have horrifying results in the end!

The designers of the gear knew what they were doing, and there are technicians that are equally as good and knowledgable in restoring older vintage electronics, and keeping the sound proper!

Ive heard items utilizing the very best of parts, some sound good, and some dont! And i have also heard items utilizing off the shelf, readily available parts from " anywhere electronics " sound really good, too!

Recapping an old unit can be good, let a tech find and fix what needs to be fixed.

[bfish]

Since it's such an important issue in regards to vintage electronics, here's another dissertation. Once you've "got it" the reasoning behind blind replacement of all original electrolytic capacitors in 30+ year old amplifiers will become clear.

NOTE:THE ELECRONIC PARTS DISCUSSED HERE CAN HOLD CHARGES THAT CAN KILL YOU! EVEN LONG AFTER UNPLUGGING THE DEVICE!

Capacitor manufacturers long ago discovered that in order to cover the entire spectrum of values needed, different construction methods were required for various purposes. For values generally larger than 1 microfarad (mfd), the "electrolytic" variety was chosen. The majority of 'lytics you'll encounter will be of two types, the round, aluminum cans on top of the chassis, and the large, paper-encased "shotgun shells" underneath. The word "electrolytic" defines the active process that literally keeps the capacitor functional.


Let's say we have a couple of strips of aluminum foil, each 2 inches wide, and 50 feet long. Let's connect a short wire to one end of each strip, lay one strip on the other, and roll both strips up together, into a tight, tiny, cylinder. We just made an electrolytic cap, and the two short wires are the leads. By now, the sharper tacks are sqwauking "That's a dead short, not a capacitor!", and they're right. we forgot to put a dielectric film between the strips, something all capacitors must have. We can, however, form one, even with the foil still rolled up! By applying a tiny, DC voltage to th leads, the entire surface of the facing foil strips begin to oxidize, and by this "electrolytic action", an insulating film is created, effectively separating the two strips. Increasing the voltage slowly increases the film thickness, until the proper level is reached. We just saved several dollars by making our film from the thin air rather than buying some. Just one problem.......the process isn't permantant.


As soon as power is removed, the process begins to reverse, though at a much slower rate than during formation. Application of rated voltage for only a minute or two each day can keep the film in good shape for years. Periods of disuse can see signifigant reduction of the film. At some point, small areas of film become so thin they no longer separate the foil, and ZZZZAP! Just a small short, but the area that shorted out is no longer usable surface area, so the capacitance value has changed, and now there' a tiny DC current leaking through, first to cause hum, later to weld the transormer windings together. And all you noticed was a little "pop" when you powered it up!


The film can be restored by using the original method of incremental voltage increase (why we use a Variac, to "bring it up slow"), but damaged areas cannot be restored. Mfg. data suggested a 10-15 year expected lifespan for electrolytics made in the 50's and 60's. Do the math. Modern materials and methods have greatly increased their useful life.


'How' to do it's another story, this was just the 'why'.