VARIAC for idiots please.

[Daddy Dee]

I want to bring up a couple of old amps with a VARIAC.

There are some threads on this I'm unable to locate on search, so am asking here.

Part of what I remember is removing power tubes before starting up. Is this right?

Does the amp need to be connected to speakers for a load?

Any help or advice is appreciated.

Also, how long to bring up?

Thanks.

[JJkizak]

What good is the Variac going to do? Just turn the unit on and if it croaks get it fixed. Some components don't like low voltages and your procedure may burn the thing up anyway depending on where you start the voltage inputs. This is a total waste of time in my opinion. Checking the tubes, cleaning corrosion, inserting the correct fuse, replacing burned resisters with new low noise parts, replacing the caps would be a much better procedure.

JJK

[sfogg]

Usually I take out all the tubes but the rectification when bringing it

up on a variac. Start at like 20 or 30 volts and let it sit there for 5

or 10 minutes. Increase 10v and let it sit again and keep repeating.

With just the rectifier in it don't go up to the full 120 line voltage.

Stop a little short as without the additional voltage drain of

the rest of the tubes in the amp I have seen some amps voltages get

higher then they should.

Obviously if you let the smoke out cut power and figure out what failed.

After the above I usually will bring it up fairly slowly again with all

the tubes in. When you have the tubes in you should have a load across

the outputs. Keep an eye on the bias voltage(s) while doing this. It

won't be correct till your voltage is all the way up but if you see it

running away earlier then that you likely have a problem to track down.

Shawn

[DRBILL]

Regards, Bro.,

Does JJ have it in for you?[]

Bill

[Daddy Dee]

JJ,

I'll take that under advisement. As to what good it does... well, I don't know. I hear it allows the caps to re-form, but I certainly don't understand that. My lack of technical understanding is the reason I'm asking.

Shawn,

Thanks.

Dr.Bill

Hey soul man! I've been hoping that your schedule will allow you to show in Hope in June.

[PrestonTom]

By all means use a variac!

I certainly question why someone would negate that idea.

For those who are unaware, large capacitors in the power supply may need to be "reformed" if they have not been used for a long time. By bringing up the voltage slowly (hence the variac or even light bulbs in series) the capacitors will "reform" and not send a large amount of higher frequency AC to the rest of the unit (the power supply rectifies then low pass filters the electrical from the outlet to give you DC power).

A common mistake would be to remove a tube that is the rectifier (the rectifier may or may not be a tube). This would negate the procedure.

If the amp is in any way suspect, certainly fuse the speaker or better yet place a load on the output with a radio shack power resistor (10 watt / 10 ohm & it costs about a dollar).

Reforming the capacitor is not to be confused with the audiophile nonsense that has a similar name.

Good Luck,

-Tom

[artto]

Take out all of the tubes!! I always use large load resistors (10 watt).

Another tip is to use a series wired low wattage incandescent lamp (less than 25 watts, preferably 10 or 15). You can actually use the series wired lamp in place of the variac but I use both just as a precaution. The lamp will act as both an indicator of when the power supply capacitors are formed, and as a current limiter should anything catastrophic happen. Slowly turning up the variac, gradually increasing the voltage over a period of time is safest. When the series wired light bulb begins to glow dimly, the capacitors are formed. You can then shut the amp down, replace the tubes and fire her up.<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

[JJkizak]

No, I don't have it in for anyone. But reforming the capacitors sounds like total baloney to me. If they are 20 years old just replace them and be done with it, one less thing to worry about. Those capacitors were not designed to last more than 20 years anyway. Same with carbon pots. Replace them with a 5 turn wirewound and reduce your noise and gain added precise control. Bust all of your ground connections and remove the corrosion then refasten. Look for burned resisters and replace with oversize low noise precision. Re-solder any suspect looking joint. If you have solid state rectifiers just replace them and don't even ask why. They are lucky to last 20 years. If the tube sockets feel loose when you insert the tube replace the socket as this will cause noise. I assume you know how to solder. If you do not then you had better learn, preferably from someone that has taken the "NASA" course. Wire positioning is critical for hum control so don't go bananas moving wires around. If you have coax with shields do not modify how they are hooked up as this is critical.Don't mount your amp on top of a huge magnetic thingy like an unshielded sub woofer. Huge magnetic fields are how they control electron flow from in high power klystron tubes. Magnets disrupt electron flow. If I were considering a tube system I would buy new only knowing what I know about old stuff. Good luck and may you stumble on a warehouse full of old NOS tubes. I am really trying not to be caustic here as I am really a nice guy.

JJK

[artto]

JJK, my Luxmans are about 30 years old and the caps are just fine. In fact the amps are still quieter than some (most?) of the best SS stuff out there.

On the other hand, a long time ago, I once "just fired them up", as you recommend, after they had been in storage a couple of years. One by one the power tubes began to blow. Three amps, six power tubes, 5 of the 6 blew. You probably don't know how much an 8045G goes for so lets just say I blew a around a grand fast real fast!

You may think using a variac and/or series wired lamp is hogwash. But not using it may turn out to be stupid hogwash. Better to be safe than sorry.

And BTW, don't new power supply caps have to be "formed" before use? These things may hold a charge for a long time, but not forever, hence the need (safety?) to reform the caps after the amp hasn't been in service for some time, at least with tube amps, power amps in particular.

[JJkizak]

Artto:

I really and truly do not buy it. I never had to do that in the 50's, 60's, 70's and 80's. I have an old cheapo console out in my garage (Admiral) all tubes and never have to do that. I turn it on once a year and it's fine. I have another old all tube motorola radio in my barn and the same thing. In my opinion something else caused your problem, possibly corrosion. And all of the amplifier designs I have worked with the caps discharge to ground within a few minutes, computer caps being the exception.

JJK

[artto]

Some components don't like low voltages and your procedure may burn the thing up anyway depending on where you start the voltage inputs.

JJK

This statement alone indicates that you don't know what you are talking about.

IF you didn't remove the tubes, didn't have a non-reactive load on the amplifer, and were driving the amp with an input signal, then yes, you risk doing damage running the amp at a line voltage lower than it was made for. And if you don't use a variac or series wired lamp as a current limiter you risk damaging the amplifier upon startup, or at the very least, risk damaging the output tubes if the caps haven't been reformed. End of story. PERIOD.

If YOU want to practice potentially unsafe or damaging startup methods, by all means, BE MY GUEST! And if YOU want to repair a vintage piece of equipment that doesn't necessarily need repair, go ahead, IMO that also is stupid.

[BEC]

artto said "Take out all of the tubes!!

You really don't mean to take out the rectifier tube in this, I hope. You would not reform the electrolytics without DC present.

Bob Crites

[artto]

hehe....you're correct. Got me on that part of the equation Bob [:$]

BTW, love that "audiophile" stuff. Yoy't mind if I copy it and post it in my room woood ya?

[efzauner]

Caps reforming? I have a Heatkit w5m that dates from the 50s. It is all original. Had not been used in years and it worked no problem! Are there any technical references on cap reforming?

[JBryan]

I used to flip the switch and roll the dice but that was with garage sale finds that cost less than $20 but it only took one catastrophic failure to show me the way. Now I use the Slow-Start method as others have suggested.

"The following is an excerpt from Bill Bittle, an avid collector of vintage tube hi-fi... Follow along, as Bill takes us through a "soft start" procedure of his vintage H.H. Scott 299C using a Variac.

[First]... I remove the tubes and plug the unit into my Variac and bring the power up while monitoring the AC voltages coming out of the power transformer. I check the filament, bias and high voltage values to make sure everything is there and within specification. I remove and inspect the fuse and often replace it with one of lower known value.

Assuming everything looks good, I next will install all the tubes and again connect it to the Variac. I will start off at about 30-40 volts on the Variac and just let the amp run till things start to glow, and I begin to get high voltage in the power supply. At this point, I look for any unusual voltage drops in the power supply circuit. Such voltage drops could indicate a shorted capacitor or an open resistor. I also monitor the amps' current or wattage draw.

Next, I will crank the Variac to around 55 volts. At this point, I will usually be able to hear a little hiss and hum in the speaker, and the amp will also, if everything is working, pass a signal. It may not sound too great, but it should be there.

It was at this stage that my first Scott 299C exhibited the "leaky (filter) capacitor" phenomena. When I pushed the Variac to 80 volts, the B+ did not increase and the first filter capacitor began to get noticeably hot.

This amp actually worked as long as I kept it's line voltage below 60 volts! But by using the Variac, I had the time to safely ascertain that I did have a leaky (filter) capacitor.

Hot Hint: If you do not have access to a Variac, you can make a substitute dim-bulb tester (a.k.a. poor-boy's safe soft-start rig) by carefully wiring a light socket in series with the amp's power cord and the AC wall outlet. Here's how it works:

You use progressively higher wattage bulbs to gradually raise the voltage seen at the amp's power source. Always start out with lower-wattage bulbs, i.e., 15-watt, 30-watt, and gradually work up to 60-watt, 75-watt, 100-watt. If the lower wattage bulbs, get bright STOP IMMEDIATELY! This indicates a high current fault within the amp. For an excellent, illustrated, construction guide, see: Phil's Old Radio's, Dim-Bulb Tester.

But if you are really into collecting and restoring antique radios and vintage tube audio gear, you owe it to yourself to purchase a Variac. Used, I have seen them as cheap as $20.00 and new they range from $80.00 - to over $200, depending on their size. They are reliable too, so don't be afraid of buying an old one.

Now, after the amp has successfully operated at 60 - 80 volts for a while, it is now time to increase the Variac to 100 volts and plug in a signal source, such as a turntable and tuner.

Switch the amp's input selector to tuner and see if both channels work and sound clear using the tuner as a source. Let her rip for a while paying special attention to any abnormal distortions of the sound, or any unusual noises like squeals, pops and hisses.

Turn the volume control down and see if there is any hum. Sometimes an amp will be quiet for the first several minutes of operation, then it will start to hum. This can be indicative of a power supply capacitor problem, weak or gassy tubes, and improperly balanced and biased tubes. Some amps have a hum balance control that can cause the problem as well.

Next, give the phono section a check out by selecting the turntable and playing an LP. If everything is all right, you should hear a nice clean crisp signal coming from both speakers. I don't care what anyone says, tube amps from the 'golden era' of hi-fi (1955-1965) have the best sounding phono preamp sections. So, if you have been listening to those old LP's on a solid state amp (that is if you hadn't become so disgusted with the sound you tossed them and the turntable!) you won't believe how good they will sound through a tube amp.

When I finally got my first 299C going, I plugged a Techniques SL3300 turntable into it, plugged it into a pair of Mirage 190is speakers and felt my jaw drop at the sound. I couldn't believe it! This thing sounded better playing an LP then new solid-state gear does playing CD's. (Bear in mind that my LP's are, for the most part, in quite good shape. If you have LP's that have been played extensively on inexpensive 'close-n-play' quality turntables then they are probably trashed and nothing is going to make them sound great.)....."

Works for me. -Bryan

[JBryan]

BTW, If you don't frequent hamfests or can't find a suitable variac locally, I found a pretty accurate 2000VA model for $100 - new. I use it to regulate my coffee roaster when I'm not bringing up old gear. I found this one here...

http://www.sweetmarias.com/prod.roastkits.shtml

[JJkizak]

Like I said, replace the caps and be done with it. They are designed to last 20 years period, and don't even last that long. If the caps were replaced running up the amp with low to high voltages is a waste of time, as proven by the previous thread. Tube balance must be set at normal operating input voltage or it is not valid.

JJK

[Piranha]

You must have quite a bit of expendable cash? Unlike me. []

[JJkizak]

There is no such thing as "reforming" capacitors. This is total nonsense.

JJK

[PrestonTom]

There is no such thing as "reforming" capacitors. This is total nonsense.

JJK

There is some ambiguity here. As I mentioned on the first page of the thread, a variac or series of bulbs should be used when bringing up an old tube amp. Others have agreed. I also mentioned the reason/mechanism was to reform the caps on the power supply. This is still true. I also mentioned that this should NOT be confused with voodoo about "reforming" caps when installing new ones on crossovers etc.

I agree, on THAT application it is nonsense. However, you have been very negative about the need to slowly power on an old tube amp. Perhaps this is the source of confusion. I reiterate this because I think you are unintentionally giving some very bad advice.

If you find an old tube amp in the attic, bring it up slowly. Several methods have been outlined. If you have not done this in the past and had no ill-effect, then consider yourself lucky.

Good Luck,

-Tom