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
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
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.
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.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
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
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.
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.
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.
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.
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!
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!
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.
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
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
Hi Victoria,
Tube amplifier equipment should always have a load when powered up. This can be cheaper speakers or dummy load resistors.
Do a visual inspection first. If you see a white deposit around the terminals of an electrolytic cap, replace it before applying power. Part way up in powering up, measure the voltage on both sides of the smaller coupling caps. If they are passing DC, stop and replace them.
Like burnedfingers suggested, replacement of coupling caps should be done anyway. Better now than later (before they "get you").
-Chris
Tube amplifier equipment should always have a load when powered up. This can be cheaper speakers or dummy load resistors.
Do a visual inspection first. If you see a white deposit around the terminals of an electrolytic cap, replace it before applying power. Part way up in powering up, measure the voltage on both sides of the smaller coupling caps. If they are passing DC, stop and replace them.
Like burnedfingers suggested, replacement of coupling caps should be done anyway. Better now than later (before they "get you").
-Chris
i do suspect i would prefer the 1000A
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pre-historic beaver
http://www.cnn.com/2006/TECH/science/02/23/jurassic.beaver.ap/index.html
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pre-historic beaver
http://www.cnn.com/2006/TECH/science/02/23/jurassic.beaver.ap/index.html
Am I correct in assuming that the " coupling capacitors", for the 500C, are the four .047 's, 2 per side, which connect a pin on each of the 7591's and the 12AX7's? If so they look original and OK. All are W. German and have a black band on the ends closest to the 7591's. Is that the + end?.
In fact, the whole under side looks good. The only mark on the under panel is a little oil stain under a brown jelly bean .oo47 cap just behind the ON-OFF/Volume switch.
My plan is, with speakers connected, to bring it up slowly with the mode selector switch in Aux with nothing connected to it. If the amp finally goes a couple of hours at 110/118 (house voltage) I will back it down, enable the FM tuner, and slowly bring the FM/Amp combo up. I will have a 100W light bulk hooked into this test setup.
The 500C has options for 4/8/16 ohm speakers . My speakers are ESS AMT 1B's which are 6 ohm. I assume I should hook them to the 8 ohm tap. Is that correct? Thanks again, Vic
In fact, the whole under side looks good. The only mark on the under panel is a little oil stain under a brown jelly bean .oo47 cap just behind the ON-OFF/Volume switch.
My plan is, with speakers connected, to bring it up slowly with the mode selector switch in Aux with nothing connected to it. If the amp finally goes a couple of hours at 110/118 (house voltage) I will back it down, enable the FM tuner, and slowly bring the FM/Amp combo up. I will have a 100W light bulk hooked into this test setup.
The 500C has options for 4/8/16 ohm speakers . My speakers are ESS AMT 1B's which are 6 ohm. I assume I should hook them to the 8 ohm tap. Is that correct? Thanks again, Vic
Re: Re:Old Tube Equipment Turnon
by Victoria
The 500C has options for 4/8/16 ohm speakers . My speakers are ESS AMT 1B's which are 6 ohm. I assume I should hook them to the 8 ohm tap. Is that correct? Thanks again, Vic
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might try the 4 ohm to see how the amp settles
then try both
could you post a pic of the underside?
by Victoria
The 500C has options for 4/8/16 ohm speakers . My speakers are ESS AMT 1B's which are 6 ohm. I assume I should hook them to the 8 ohm tap. Is that correct? Thanks again, Vic
````````````````````````````````````````````````
might try the 4 ohm to see how the amp settles
then try both
could you post a pic of the underside?
Experimenting with both the 4 and 8 Ohm taps is in order to determine which way sounds best. FWIW, I think the 4 Ohm taps are indicated, as that arrangement maximizes damping factor and minimizes distortion. If your speakers have significant dips in their impedance curve, using the 4 Ohm taps is (IMO) clear cut. Net power O/P will be lower using the 4 Ohm taps.
Use shorting RCA plugs inserted into the Aux RCA jacks.
Hi Victoria,
The coupling caps can look to be in perfect condition and still be leaky. This would then cost you much, much more.
So if I understand you, you will use a variac to power up your unit? Somewhere over 1/2 voltage (leave it there) your will start to get some B+. At that point look at your bias supply and coupling caps. If it's cathode biased (can't remember off hand) the grid voltages should be mV within ground. If there is a neg. supply, the grids should be with mV of that set voltage. This is very important. Continue to check these voltages as you bring the unit up.
If you see any plates turning red, shut down. Same if you hear a big hum from a speaker.
-Chris
The coupling caps can look to be in perfect condition and still be leaky. This would then cost you much, much more.
So if I understand you, you will use a variac to power up your unit? Somewhere over 1/2 voltage (leave it there) your will start to get some B+. At that point look at your bias supply and coupling caps. If it's cathode biased (can't remember off hand) the grid voltages should be mV within ground. If there is a neg. supply, the grids should be with mV of that set voltage. This is very important. Continue to check these voltages as you bring the unit up.
If you see any plates turning red, shut down. Same if you hear a big hum from a speaker.
-Chris
Yes, triodes presently rule.
An interesting chart, but is it useful?
It quotes efficiency (which is arguably useful) but doesn't quote the power level at which the distortion measurements were made. Suppose that the distortion for one measurement was 0.1% and for another 0.25%; you'd assume that the 0.1% configuration was superior. But what if the 0.25% configuration produced 30W, and the 0.1% configuration produced only 10W? Then, (if we make the sweeping assumption that distortion is proportional to level), the 0.25% configuration would produce a little less distortion at 10W than the 0.1% configuration...
We really need graphs (and lots of them)...
An interesting chart, but is it useful?
It quotes efficiency (which is arguably useful) but doesn't quote the power level at which the distortion measurements were made. Suppose that the distortion for one measurement was 0.1% and for another 0.25%; you'd assume that the 0.1% configuration was superior. But what if the 0.25% configuration produced 30W, and the 0.1% configuration produced only 10W? Then, (if we make the sweeping assumption that distortion is proportional to level), the 0.25% configuration would produce a little less distortion at 10W than the 0.1% configuration...
We really need graphs (and lots of them)...
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