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Old 20th February 2006, 09:56 PM   #1
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Default Old Tube Equipment Turnon

I would like to begin using at least one of the tube units I have salted away in the past 20 years (at least?).
My choices are:1. A Sansusi 1000A , 2. A Fisher 500C, or 3. A Dyna ST70 with PAS.
I am not the original owner of any of these pieces and have not used them. Hence, I do not know whether or not they have problems. But I assume, that having sat all these years, they all will have problems.
So two questions.
1. Is there a procedure somewhere on the web outlining how one could safely fire them up and how to sort out the problems?(I just bought a variac today assuming lower voltage would make sense.) I am not the second coming of Tesla so the simpler the procedure the better!!! I have a VOM, a frequency counter, an audio oscillator , and an old Textronic RM35A oscilloscope. I am not proficient in the use of the last 3.
And,
2. Which of the three is the better unit?
Thank you for your help, Vic
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Old 21st February 2006, 09:50 AM   #2
SHiFTY is offline SHiFTY  New Zealand
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Nice stash!

The main danger with these is that some of the old electronic components may have degraded, and may cause damage to the unit.

Most of the time the tubes are just fine; and won't require replacement (at least to begin with).

But over time, the signal capacitors may have gone bad, the resistors drift in value and the selenium rectifiers can also blow up. Sometimes power supply capacitors are bulged and leaky, sometimes they are ok.

The good news is that these components are easy and quick to replace- a few hours with a soldering iron and you will have an amp that is likely to be better than new.

If I were you, I would hook up some old speakers and a source, then use the variac to bring up the amp over a minute or so, and see if it plays ok on both channels. Watch out for loud crackling noises or tubes that glow a dull red on the plate- turn it off immediately.

If it does seem to work ok, then unplug it and order some new caps and resistors and do a restore job on it.

You should restore all three but I think the DYNA and the fisher have the best representation.
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Old 21st February 2006, 10:50 AM   #3
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What shifty said.. and make sure that you arent leaning over the amp when you power it up, the electrolytic power supply caps can be quite nasty if they blow up in you'r face..
Personally i would have a look over the amp BEFORE you power it up and make sure there arent any obviously dodgy capacitors, i mean electrolytics that are bulgeing and so on, if there are replace them before you power it up to be on the safe side..
Owen
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Old 21st February 2006, 05:37 PM   #4
kevinkr is offline kevinkr  United States
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Better still in addition to the variac wire up a lamp in series (hacked extension cord works great for this) with the amplifier and bring the variac up slowly and reform those electrolytics before applying full voltage to them. The lamp with should be about 100W will limit the current in the event that there is a serious fault and prevent the power transformer and a lot of other expensive parts from being destroyed.

If these are low hour pieces and have been properly stored you may have some life left in them prior to restoration. (I have an old scott that has all of its original electrolytics and they are all fine so far.) Coupling capacitors should be replace regardless.
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Old 22nd February 2006, 06:05 PM   #5
rickl is offline rickl  United States
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Quote:
Originally posted by DoomPixie
What shifty said.. and make sure that you arent leaning over the amp when you power it up, the electrolytic power supply caps can be quite nasty if they blow up in you'r face..
Personally i would have a look over the amp BEFORE you power it up and make sure there arent any obviously dodgy capacitors, i mean electrolytics that are bulgeing and so on, if there are replace them before you power it up to be on the safe side..
Owen
I even use safety glasses and ear muffs for some suspect gear.

I also bring it up a bit slower - full power in a couple hours at 15-12volt increments.

Once up to full power with inputs shorted and speakers connected, measure voltages at *all* pins.

rick
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Old 22nd February 2006, 06:23 PM   #6
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Simple procedure? Plug it in, turn it on and run like h e l l. Watch for puffs of smoke with a spotting telescope or binoculars.

I'm kidding!

I approve of rickl's procedure to increase applied voltage in increments with a variac over a couple of hours with a light bulb in series with the power cord. That will restore the elecectrolytic capacitors the best of all methods discussed.
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Old 22nd February 2006, 07:27 PM   #7
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you laugh! My first two valve amp's i just plugged into an extension lead and turned on from the other side of the room! they both worked fine but i wouldnt recomend it! lol.. better safe than sorry!
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Old 22nd February 2006, 07:31 PM   #8
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Quote:
Better still in addition to the variac wire up a lamp in series (hacked extension cord works great for this) with the amplifier and bring the variac up slowly and reform those electrolytics before applying full voltage to them. The lamp with should be about 100W will limit the current in the event that there is a serious fault and prevent the power transformer and a lot of other expensive parts from being destroyed.

If these are low hour pieces and have been properly stored you may have some life left in them prior to restoration. (I have an old scott that has all of its original electrolytics and they are all fine so far.) Coupling capacitors should be replace regardless.


There is no better advice than this!
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Old 22nd February 2006, 08:54 PM   #9
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Of course, when contemplating any restoration work, it makes sense to have a schematic to refer to. Some are available free on line and scanned copies of others are often available at a *reasonable* cost from eBay sellers. The 500-C, with its tuner and phono sections, is pretty complex; for that reason the Dynaco might be the place to start.
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Old 24th February 2006, 04:42 PM   #10
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Default Re:Old Tube Equipment Turnon

Thank you very much for your help!!! The variac will be here Tuesday, along with the rain, so it will happen next week. Will use the light bulb as suggested.
The Fisher 500C thread has inspired me to start with it.
Should the unit have only the power connectted to it, no speakers?
What input mode should it be set at: Aux. Tape, etc?
One pair of the output tubes are Sylvania. The other pair are unmarked
except for "USA" on the under side of the bottom plastic piece. I am old enough to have grown up with tubes and I think that is a first for me.
Thanks again, Vic
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