[mcgsxr]

Recently bid on this little guy, as my first foray into tubes.

http://cgi.ebay.ca/ws/eBayISAPI.dll?ViewItem&ih=007&item=170020494714&rd=1&sspagename=STRK%3AMEWN%3AIT&rd=1

With my 96dB efficient speakers, the limited wpc should still be OK.

I bought a tube set off Jim McShane, and should have this up and running inside a month, with shipping to Canada etc.

Have been advised that I might want to replace the original PS caps, due to age, and risk of catastrophic failure etc.

Any other words of advice/experience with this unit?

Thanks,

[Scott F.]

There are a number of things that you can (or maybe should) do to the old amp. Besides the power supply caps, you will need to replace a few other parts at have worn with age and are likely to (eventually) fail.

The amp likely has an old rectifier bridge that uses selenium rectifiers. After the PS caps, this is the first thing you should tackle. When these fail (and they do fail), they take out big chucks of your circuitry. Replace the recitifiers with new super fast, soft recovery diodes. Before you change them, take a voltage reading downstream of your first B+ dropping resistor. After you replace the rectifiers (without the tubes in place), take another voltage reading at the same spot. You will need to calculate the new resistor value to meet the original voltage. The reason for this is the old selenium's are less efficient than the new diodes. Use a Caddock power film resistor (very low noise) in place of the old Allen Bradly.

Replace the cathode resistors. After passing current for so long they are likely way out of spec. A nice Dale/Vishay RN65 should usually work fine.

After listening for a while, if you find the 'sound' too soft or undefined, replace the coupling caps with a decent metallized polypropylene (or what ever flavor cap you wish, just no aluminum electrolytics). Most often the old amps use those old Sprague 'bumble bee' or 'orange drop' mylar caps. They sound OK but they are one of the main contributors to that 'tubey' sound everybody talks about. A nice MP freshens up the sound quite nicely.

Don't be afraid of those old brown Allen Bradley's (or Ohmites) in the rest of circuit path. They are likely used everywhere. If they havent turned noisey (manifested as a hiss), they sound marvelous. If they do turn out to be noisey, thats when things get interesting trying to figure out which one it is 

Oh, and if the amp is using the old silver mica caps, leave them too.

[mcgsxr]

This little bugger showed up at my office yesterday, and it was tough to get any work done for the balance of the afternoon!

Having never owned a tube amp before, I figured this would be a simple way in, and at the very least some decent insight into vintage kit etc.

It does not disapoint.  Not going to rave about it, but it is an excellent little amp, with clean mids, plenty of bass, and extended highs.  The mild downside (already alleviated by swapping in 70's EI EL84's, a Tung Sol 12ax7, and a GE 5Y3) is some grit on the highs, and some wool in the bass.

I look forward to how this comes together, with the PS cap replaced, some real binding posts, and the output caps upgraded...

Amazing synergy with my high efficiency b200 Visatons, those 4-5 wpc are really delivering, in the context of my Bolder SB3 front end, 50 year old amp, and open baffle speakers!  A really interesting mix of gear I guess, but it works!

[Brad]

Mark - we have ended up at almost the same destination 

My amp is ONLY 45 years old, but we're using comparable digital front ends and OB............

[speaker]

The amp likely has an old rectifier bridge that uses selenium rectifiers. After the PS caps, this is the first thing you should tackle. When these fail (and they do fail), they take out big chucks of your circuitry. Replace the recitifiers with new super fast, soft recovery diodes.

The amp uses a 5Y3 tube rectifier.