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Old 16th April 2008, 03:35 AM   #1
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Default My First Tube Amp

I just bought a Lafayette 224A and should be receiving it next week. It looks pretty cherry from the photos, but of course the proof is in the pudding, so i have to wait.

My main concern with the amp is whether it needs to have any caps, resistors, etc. replaced in order to keep it in top form.

I posed this question to the seller and was told:
"Both of my Techs claim that replacing caps is stupid!They both told me the old caps are far superior to anything you can buy today!(I Quote)I tend to agree,I have had no trouble with any of my old amps that havent been recapped!"

I have read many posts here and am not sure how accurate that statement is. Is this something I should be concerned with. The unit was serviced last year.

If it is something to be concerned about, how do I go about checking it out? I realize I will at least need a multimeter (I used to have a real nice one but misplaced it many moons ago). Any reccomendations for a good, inexpensive multimeter?

And what concerns should I have about the tubes? I have no way to test them.

Last but no least, I am want to build my own amp later this year as well, any suggestions for a decent, inexpensive digital soldering station?


Thanks for any help!

-Steve
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Old 16th April 2008, 04:32 AM   #2
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"Both of my Techs claim that replacing caps is stupid!They both told me the old caps are far superior to anything you can buy today!(I Quote)I tend to agree,I have had no trouble with any of my old amps that havent been recapped!"
Well thats a pretty dumb statement....

Electrolytics dry out after 40 odd years obviously. They may work fine also, but sometimes its best to replace them. Modern caps have much higher tolerances than older ones, and even cheap ones will be better than your original coupling caps. Older capacitors have higher internal resistance and therefor affect bandwidth as well. Old paper, plastic, and wax capacitors generally sound like crud nowadays and its best to replace them to get the amp back in spec. Replacing capacitors is only cheap insurance, as leakages in capacitors can lead to failed tubes, as well as the other parts they take out with them when they go. A leaking coupling capacitor can put high DC on the grid of an output tube and destroy it, or cause the amp to have very poor performance.

Filter capacitors are very prone to drying out/leaking/shorting after their expected life. They were only meant to last 10 years or so...

I have a few amps that have multisection capacitors in them that are just fine after almost 50 years, but a day will come when they need changed.

If your amplifier hums real bad when you turn it on, chances are you need the filter replaced.

As a final statement, capacitors absolutly were NOT made to better tolerances than they are today. Paper in oil capacitors are the only exception to this, but its very unlikley you will have any of those in a consumer grade amplifier like a lafayette.

Resistors: They should be fine, check for obvious burning or charring and replace with higher rated resistors. Carbon comp resistors are prone to drifting after a while, so check that their within 10-20% of their rated resistance. Any that are WAY off should be replaced, but you are likley only to see this in resistances of 1megohm and above. Carbon comp resistors are also noisy, so you might consider replacing important signal path resistors and plate resistors with carbon film or metal film.

As far as tubes go, find someone that has a tube tester to verify that they are good. Check for obvious signs such as output tubes with glowing plates which would indicate a serious problem. To check for this turn out all your lights at night and let the amplifier idle- if any of your tubes PLATES ( the large metal structure inside the glass) are glowing orange shut it off. Note that this is different than glowing heaters, which are normal.

Multimeter: Get an inexpensive fluke ( ~$80 at your local sears ) or a cheap radio shack DMM for ~$30. Either will be fine for what you need.

All this being said, if the amp has been serviced properly you more than likley are fine. However, before I power on a vintage peice of equipment that has been serviced, I look for obvious stupid mistakes that the previous technician may have made such as improper or sloppy wiring/ connections/solder and improperly rated voltages. If everythig looks ok, power it up and watch for smoke/weird smells/obviously hot or misbehaving components. Remember that with a tube amp you should ALWAYS have a load connected to the out put ( a speaker) so that the amp does not blow up its output transformer.

Google didn't turn up any schematics other than someone commenting that it didn't make it to the Sams photofacts

I would sugguest tracing the circuit out on a peice of paper carefully in case you need any help with it.

Good luck!
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Old 16th April 2008, 05:13 AM   #3
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With just about any older gear be on the look-out for pots that are shot - esp. the volume and "tone" pots. Switch contacts need to be checked and connectors often need to be replaced. On older tube equipment the heat can get to the insulation on the wiring and tube sockets.
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Old 16th April 2008, 11:04 PM   #4
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Thanks for the help, everyone. I am really excited to get my amp. I have a nice set of Cerwin Vegas that have been in storage for about 6 years that can't wait to be played again.

Plus, I just closed on a new house!!!! So now I don't have to worry about annoying the neighbors in my condo complex!!

--Steve

ps. Still looking for some recommends on a decent and inexpensive digital soldering station.
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Old 16th April 2008, 11:30 PM   #5
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I used one of these for about 3-4years now and absolutely love it!
http://www.circuitspecialists.com/prod.itml/icOid/3528
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Old 17th April 2008, 01:15 AM   #6
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Cheaper here: http://www.howardelectronics.com/xytronic/137ESD.html
Yes, those are nice and not as expensive as Weller brand.
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