The Value Of Using A Variac With Vintage Audio
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- Опубліковано 13 сер 2022
- Lookie Lou's Episode 2: So you bought a vintage piece of gear? Are you properly prepared before turning on and testing? Here's your first tip before buying used audio gear!
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Couple of questions: I was advised to use a variac on my 100 watt tube guitar amp that has been sitting in the closet unplayed for about 10 years. (this might be obvious answers), 1) After connecting the amp to the variac, Do i turn the amp on 1st, and then start the gradual turn up on the variac? 2)which version of variac should i buy ...500VA, 1000VA, etc.... Any advice on the steps in correctly preparing/variac my old amp before I play it would be greatly appreciated!
0 Variac, turn on amp, turn on variac. Raise variac to like 40. Let set 1/2 hour. Up to 80 for 1/2 to 1 hour. Then proceed to standard voltage. As for which unit, look up the power consumption of the amplifier and that will guide you into which to buy. Convert Watts to volt amps to determine the version you need.
I have some vintage SS audio equipment from the 70's, 80's, and 90's that I inherited. However, they have sat unpowered for 30 years (mostly NAD and McIntosh brands, but also some Japanese receivers) and I'm wondering if I should use a VARIAC and dim bulb tester to power them up or just go for it and hope for the best. Is reforming caps possible with SS? I'm reading this is mostly for tube gear. How about Class H switching power supplies that are common in some pro amp gear? Is it safe? If so, what is the procedure that you recommend (specifically voltage increments and duration)? I'm reading a lot of mixed reviews regarding using a VARI-AC for SS equipment. You sound like you know what you are doing and might have some sound advice (pun intended 😀).
Thanks in advance. I will subscribe.
Hello and thank you for suscribing.
Certainly, most agree about their use for vacuum tube electronincs and I have used that approach even on fairly current Audio Research amplifiers.
On solid state, well, I know of a very recent case where a mid 70s receiver went up in smoke when a start up was tried without a variac. Now, in that case, the unit had been in a flooded basement and while there was no clear sign of water damage, it was in a very humid environment. So, the exact cause is unclear and I don't honestly know if a variac would have made a difference. I am still, personally, inclined to use one in such cases, however. Mid 70s electronics did not use 2 power supplies.
With the advent of remote control, second power supplies were introduced. The second power supply was used to power the remote control circuitry. In that case, a variac is of little practical use as all the functions are electronically controlled. This is easily observed with units that have a standby button. Sadly, it's often the failure of the smaller "stand-by" power supply that kills the product completely and replacement parts for those events are spotty, at best.
With switch mode power supplies, those either work or not. I tend to agree with comments that variacs are likely useless in such cases and problematic at best.
Hope these observations help you.
I appreciate the response. Good to know. How about a procedure? What do you recommend to best incorporate a dim bulb tester with a VARI-AC power up? I imagine I'd plug the audio unit into the tester and the tester into the VARI-AC but what about voltage and duration increments, from start to finish? It sounds like from the video presentation that I should plan on 10-12 hours to slowly bring it up to full power. Being 30 years without power, should I take longer?
Also, what size bulb should we use for Class AB amps? Is there a formula based on the current draw from the wall or the power output itself? (I.E is it based on idle current or full power?) Lastly, should the device be in the 'ON' position or left in the 'OFF' position during the conditioning process? I imagine based on your remote secondary power supply comment/example that the unit in question needs to be powered "ON" to get the benefit. A faulty secondary remote power function will not allow for that to happen. Is that right?
Lots of questions but I think all are important to get the info that your subscribers will appreciate. This is something extraordinary for most of us but necessary in many situations. For that, thanks in advance and I look forward to future content.
Scott @@audibleeleganceinc
Well, I think you are making this much more of a project than needs be. I appreciate the intense care considered but I think much of it is unnecessary. Personally, I start out at about 30 to 40 for about 10 to 15 minutes, then around 80 for about 15 minutes and the up to 110 for about half an hour.
(What I am principally trying to avoid is a sudden in-rush of power causing the capacitors to short on the surge of power.) After that, out comes the variac and it is plugged in as normal and left on for a few hours. If nothing has gone wrong. I test it with a signal so see what I get. I don't use light bulbs or anything like that. Not sure what is accomplished by that, actually, and certainly with LED bulbs today.
The unit does need to be switched on and as I noted, with remote systems, I rather doubt that a variac actually helps with the capacitors unless it somehow the unit trickle charges capacitors in the standby mode. I rather doubt that. As I noted earlier, that becomes case by case and I don't think there's a data base for that anywhere.
Clearly, it's always case by case. Please also understand that regardless of your care, most capacitors have a life expectancy of 10 to 20 years, depending upon quality. Many are less. All you are trying to do is to see what you have. Most products from the 60s and 70s are well past their accurate life and re-capping the main power capacitors is not unusual.
There are a lot of other details in vintage equipment far beyond using contact cleaners and calling it good. But, we are talking about initial power-up to see what even works. Kinda like Apollo 13, I suppose.@@djscott9207
I agree with your comments regarding life expectancy or at least a lack of specified performance with age. Since they have been sitting for 15-30 years unplugged, I'm wondering if the caps will even reform?
The dim bulb test is used with an incandescent bulb to limit current in the event there is a short or dropped rail to prevent further damage. I was told because the units have sat with no power for so long, it would be wise to wire an incandescent light bulb with socket in series that the amp or pre-amp, receiver, radio, etc. will plug into. This bulb "tester" acting as a resistor (a visual fuse) would then plug into the variac or wall. The dim bulb "test" is a somewhat common procedure for techs who are servicing a unit with no known history to help protect the unit from further damage and to know (if it goes bright) to not plug it directly into the wall without further inspection because something is seriously wrong. Anyway, while researching this, I came across your video here talking about a variac. I thought it might be smart to incorporate both when powering the units on for the first time.
That being said, are you a believer that old capacitors can be reformed with a variac? There are some who attest that it works and others who are not believers. I certainly will remove the covers and do a good visual inspection and cleaning before powering them on. @@audibleeleganceinc
Oh, I am not going to get into that arguement. Just getting them to work without nuking is my goal. Now, if you see caps that appear to be expanded on their ends, that's a bad sign. Some have cross hatches on them and if you see the quadrants splitting, it's over. Don't even plug it in. Thanks for the info about using an incandescent bulb while you can still find them. You are not even allowed to sell them on ebay anymore in the States due to mandates.@@djscott9207