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Foxhunter
Intermediate Member
Username: Foxhunter
Post Number: 115
Registered: 4-2008
| | Posted on Wednesday, September 03, 2008 - 2:55 am: | 
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As some parting words, I was told by a seller of vintage/antique radios that some of the older things I'd just bought would be best "fired up gently" with the use of a "Variac".
He'd said that basically it would be wise when first applying voltage/current to an older device that gently increasing the voltage upwards would be the safe way to power on an old radio piece to avoid blowing capacitors or anything else. That appeared to make sense.
From what I've read briefly it would seem that a Variac (brand name) aka "variable voltage transformer"---is the equivalent of an adjustable "DC voltage regulator" or similar to what we use on our variable DC power supplies---or similar to even a Rheostat like on some of our good-quality soldering stations.
Have any of you used or are using them? Do you agree that buying one is an excellent recommendation or is it really "going overboard"? It would seem to make good sense to me in my humble opinion. Let me quote the following about why one should be used with vintage radio gear:
"Your vintage guitar amplifier is almost certainly not running on the proper AC line voltage. Why?
Most of the older radio's & amps in use were designed at a time when the AC power out of the socket was lower. 115VAC is a common rating on power rating plates, some older ones may carry 110VAC or 112VAC ratings. Over the years, the nominal AC voltage rating has crept up; 115VAC was "standard" for a while, then came 117VAC, 120VAC. Now many cities have AC that is most commonly 125VAC or so.
This means that amps designed for 112VAC are running at 10% higher AC voltages---all the time. AC voltage can run even higher at times when the average load on the power net drops off - like in the early evening in spring and fall when all those air conditioners cycle off.
Obviously, most amps will survive life with higher input voltages - they have and do - but it's not necessarily good for them or you, either from the standpoint of repairs costs or tone.
The continuously high AC line voltage means that all the voltages inside your amp are running about 10% high all the time. This steady overvoltage can cause your power filter caps to wear out sooner, make tubes die sooner from the higher filament voltage, in general cook things from the extra heat the parts will dissipate."
Is there an alternative to buying a high-priced Variac-type unit? Any recommendations of what or where?
I have several Heathkits, Hallicrafters and other older units that I've never even plugged in after hearing the warnings about these older pieces and the effects of age on tubes, transformers/supplies and capacitors.
Anyone willing to share anything about these devices? |
Bruce
Senior Member
Username: Bruce
Post Number: 4803
Registered: 9-2003
| | Posted on Wednesday, September 03, 2008 - 8:05 am: |
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THIS IS TRUE ..... it will help save those old caps ..
I bring up voltages on all older radio with a " vairac " transformer.
But even with this it is wise to recap old power supplys and radios.
On 6 since 66
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Foxhunter
Intermediate Member
Username: Foxhunter
Post Number: 116
Registered: 4-2008
| | Posted on Wednesday, September 03, 2008 - 9:02 pm: |
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Once again thanks Bruce your willingness to help or share is noticed and appreciated.
At some point I would like all my older pieces "gone over" and the capacitors changed and necessary upgrades made. For instance I was told on the Heathkit SB-200 I should not use it unless the "Harbach Mods" are installed due to occillations that would harm the amp. It would seem there are several other "highly recommended" upgrades for this amplifier too.
Almost with every older unit I have, when I've looked up reviews of them....they all seem to need important upgrades to function properly or to protect them from harm. I can see this will be quite expensive in the long run.
I was just talking a few minutes ago on the phone with an Extra Class Licensee who does have one and also highly recommends using one. He is selling some of his things locally here but won't sell the Variac.
He said with alot of these older radios and amplifiers that you should start each unit out at about 30V and let it warm up for an hour or more before increasing the voltage.
I do know that some electronics & appliances DON'T LIKE to be run at low voltages and it could harm them actually. So am I correct that there is nothing to worry about with doing this on most Amateur Radio equipment?
I will look into trying to find one reasonably here soon. |
Tech833
Moderator
Username: Tech833
Post Number: 1696
Registered: 8-2002
| | Posted on Wednesday, September 03, 2008 - 11:53 pm: |
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Almost every piece of radio gear here is tube type. Much of it older than me.
The idea behind a variac is to bring up voltages slowly (like over several hours to several days) in order to allow capacitors to reform slowly. Caps that are drying out when bumped with HV instantly will fail. If allowed to reform, the caps will not fail.
However, this isn't a solution for everyday power-up. The variac trick is usually for those times when you are bringing up a piece of gear that has not been powered up for months or years. If you want to bring gear up day-to-day without the inrush 'bump', especially fatal to transformer type tube gear, then use an inrush current limiter. It's a small component that looks a lot like a ceramic disc capacitor, but used in series in one side of the power cord to the power transformer in old gear. It solves the power 'bump' from power being applied to the transformer, which is looking at a lot of 'short circuits' in those cold filaments and discharged power supply caps.
The difference between 115 and 120 v is well within the parts tolerances of most gear. Don't sweat it. But, if you do sweat it, the proper way to deal with this is a buck/boost transformer wired in series with the power transformer primary in 'buck' phasing.
A variac is not cheap, don't skimp on one if you decide to buy one. If you can't afford a good one, just pass on this idea until you can. |
Foxhunter
Intermediate Member
Username: Foxhunter
Post Number: 119
Registered: 4-2008
| | Posted on Thursday, September 04, 2008 - 7:38 pm: |
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Most of my collection of older gear has not been plugged in at all recently *BY ME*. I am a "worry-er" and cringe to think of how some of these things may have lived their past "lives" or what a seller may have unknowingly done to "test" the pieces before selling them to me. I few weeks ago I was buying a mobile radio from someone and they were going to key a mic right in front of me with no load attached. Things like that and maybe worse.
Anyway---sorry I was getting side-tracked. I will try and find a Variac or the equivalent. Many of the transmitters/receivers/amplifers I have that are vintage have been sitting unused for quite some time. A few I'm told were at a working station 8-months ago but I'll be safe and assume they weren't.
Here's another thing:
I was reading last night (I believe on Hamuniverse) that all of these older units (if they have 2-prong AC cords) will electrify the units' cabinet if plugged in "backwards/incorrectly" by inadvertently inverting the plug and not knowing/observing polarity. That could be an easy mistake to make if the plugs are 2-prong straight plugs without the one wide spade to make it "idiot proof". So the installation of 3-prong grounded plugs will be a necessary upgrade as well. I'd guess that any of you with "vintage gear" have done this? |
Tech833
Moderator
Username: Tech833
Post Number: 1698
Registered: 8-2002
| | Posted on Thursday, September 04, 2008 - 11:59 pm: |
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2-prong plugs on transformer type equipment are not a problem.
The fear is in the 'All American Five' type of radio that does not have a power transformer. In this type of vintage gear, one side of the power cord is connected almost (and sometimes) directly to the chassis. Not a problem for the equipment, but it you plug it in 'wrong', then the radio is at AC potential!
On my AA5 radios, I install polarised 2-prong AC plugs. Assuming your home is wired properly, the danger is diminished.
Wiring a 3-prong plug on a transformerless chassis is asking for big trouble. |
Foxhunter
Intermediate Member
Username: Foxhunter
Post Number: 122
Registered: 4-2008
| | Posted on Friday, September 05, 2008 - 1:59 pm: |
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Just to be sure I'll be looking up the "All American Five" radios as I've never heard this term and I'm not sure if any of mine qualify as one. I have a number of older radios & amps that are mainly Heathkits and Hallicrafters as well as Lafayette and Hammarlund.
I'll be sure about the radios that don't have polarized plugs to put them on and I can do that myself. At some point I'm really going to need the services of a qualifed "vintage radio repair center" to have these radios "gone over" and necessary upgrades made/done. I don't want to botch any of them myself somehow and have made a costly mistake. I'm not qualified. Any recommendations? (who? where?)
I've seen two Variacs for sale: a 2000W ($160+shipping) and a 3000W version ($235+shipping). Would these prices be considered good, fair or average? |
Tech833
Moderator
Username: Tech833
Post Number: 1703
Registered: 8-2002
| | Posted on Saturday, September 06, 2008 - 1:04 am: |
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Prices are average.
All the old radio restoration people I know are expensive, but good. Email if you want to go further. |
Foxhunter
Intermediate Member
Username: Foxhunter
Post Number: 127
Registered: 4-2008
| | Posted on Monday, September 08, 2008 - 2:10 pm: |
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Ok so that is an average price for the Variacs. When I do get one I'll try and get the larger version.
I'm going to try and have some of the radios gone over in the next year. I had a couple of places in mind after about 30 hours of careful sifting through countless websites. I'll e-mail you if you won't mind perhaps steering me in the right direction. Thanks Tech833 |
