How beneficial, and important is stable voltage for vintage tube equipment?

RS Steve

Tube Junkie
Subscriber
I haven't really seen too many detailed posts about this subject, but having a pair of Dynaco MK II's that run on the ragged edge with their output tubes even at 115V, I thought I would get opinions and experienced advice on the subject.

I have personally seen my wall voltage go as high as 131 volts, and as low as 118. So that being said, I have also noticed slight red plating at times while using the amps for an extended period. We all know that good output tubes are not cheap, and we all would like them to live a full service life.

I have everything needed to build bucking transformers for the amps to get their voltage down closer to 115V level, but before assembling them I did a recent purchase of a power stabilizer / cleaner that keeps the voltage at a stable 120V no matter what the wall voltage.

So in my mind, the stable 120 volts is much more desirable than doing the bucking transformers. The extra 5 volts being a constant, and not a huge amount, should allow me to bias the tubes to a level that keeps them from ever red plating from voltages going way high at the outlet.

Being a fairly new person to understanding electronics in depth, I would very much appreciate any educated, and experienced advice / opinions on the subject.

Thanks!
 
Arguably, supplying a "perfect" voltage, i.e. 120 to an amp intended for 120, means the amp is working at the intended operating point.

However, from a practial operation standpoint, I feel if you can supply the amp with a voltage that is at it's intended operating voltage, then normal line fluctuations shouldn't be causing any damage.

Bear in mind they had line fluctuation back in the good old days too. Probably more than today.

Personally, I think operating my 115V amp with a bucking transformer providing 115V, give or take, most of the time is probably better than operating the 115V amp at fixed 120V all of the time.

If it's that nerve-wracking then connect the bucking transformer to the 120V constant source and supply the amp with constant 115V (or whatever).
 
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If it's that nerve-wracking then connect the bucking transformer to the 120V constant source and supply the amp with constant 115V (or whatever).


Nothing nerve wracking, I'm simply trying to get experienced opinions from members that found the best way to deal with this. I didn't expect to find this Monster Power Stabilizer for 100.00 in a thrift store, so just wondered if it made it less important to need bucking transformers for the Dynaco Mono amps.

I would think not letting the voltage get to 131V anymore has got to help a bit, I feel much better about running my vintage tube equipment now, and that the bias settings should stay somewhat more stable. So using the bucking transformers and the power stabilizer would put me at a stable 113 to 114 volts, this should make the Dynaco twins happy.

20160304_095127.jpg Dynaco MK II.jpg
 
Things get out of hand in high voltage power supplies very quickly with high line voltage. Any weakness in the filter caps and bang! Dissipation in everything goes up and reliability goes down. Bias moves away from optimum. I wouldn't knowingly run anything on a 130 volt line, but then I'm a bit paranoid. Use a stabilizer or a big Variac or something to get it down to 120 or a tad less.
 
If mains voltage is high at times, you can reduce bias, thus reducing the power losses in the tubes.
If it's a "stock dynaco" try to reduce from 1.56V to 1.4 V

It's not the higher mains voltage that is the greatest problem, it's the increased power consumed in the power tubes. That why it's important to reduce power losses and the only way
is to reduce bias.
 
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I wouldn't knowingly run 115-120V devices at 130+ volts either, if that was somehow implied.

Nor would I consider 130V a normal line swing.

If I saw 130V at my place on any semblance of a regular basis I'd be on the horn with the utility.

Could even be an early sign of deteriorating neutral connection, particularly if voltage on the other mains leg drop an unusual amount as the one noted increases an unusual amount.
 
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I wouldn't knowingly run 115-120V devices at 130+ volts either, if that was somehow implied.

Nor would I consider 130V a normal line swing.

If I saw 130V at my place on any semblance of a regular basis I'd be on the horn with the utility.

Could even be an early sign of deteriorating neutral connection, particularly if voltage on the other mains leg drop an unusual amount as the one noted increases an unusual amount.


I only saw it hit 131 V once, but 128 V a bunch of times. They recently serviced the connections at the transformer behind my house, I see an average of 124 V most of the time lately. The incident really got my attention, they told me they found loose connections at the pole.
 
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Back in the days when vacuum tube stability and longevity were absolutely critical to defense,industry,communications and other demanding applications,many studies were done to determine which variables had the greatest impact in these areas.

It always came down to two factors:
Maintaining filament/heater voltages within the specified tolerance ,and preferably AT the prescribed value.
Reducing plate dissipation to the lowest practical level.

In my case,regardless of voltage stated on the nameplate,I have always adjusted my line voltage to provide the proper heater voltages.
Like most folks today,my line voltage averages somewhere in the 120 to 125 volt range,which has always put my heater voltages at an uncomfortably high level.
Needless to say,I've built so many ''little buckers'' I might just trademark the name and start a company:rolleyes:

Also,when I was first looking at Monster power conditioners,I found a lot of discussion on the net concerning reliability issues that resulted in fires.
Based on that,I chose to stay away from them. Between soldering iron and welding mishaps,I really don't need any help lighting myself on fire:cool:

Cheers, Art
 
Back in the days when vacuum tube stability and longevity were absolutely critical to defense,industry,communications and other demanding applications,many studies were done to determine which variables had the greatest impact in these areas.

It always came down to two factors:
Maintaining filament/heater voltages within the specified tolerance ,and preferably AT the prescribed value.
Reducing plate dissipation to the lowest practical level.

In my case,regardless of voltage stated on the nameplate,I have always adjusted my line voltage to provide the proper heater voltages.
Like most folks today,my line voltage averages somewhere in the 120 to 125 volt range,which has always put my heater voltages at an uncomfortably high level.
Needless to say,I've built so many ''little buckers'' I might just trademark the name and start a company:rolleyes:

Also,when I was first looking at Monster power conditioners,I found a lot of discussion on the net concerning reliability issues that resulted in fires.
Based on that,I chose to stay away from them. Between soldering iron and welding mishaps,I really don't need any help lighting myself on fire:cool:

Cheers, Art


Great information, I'd like to see your little bucker's. :thumbsup:

I looked all over the net about information on this power stabilizer, only found a few negative replies concerning getting it fixed if out of warranty.
 
Heater voltage is my primary guide too.

Information posted in other threads seems to indicate nominal to slightly higher heater voltage is preferable to low/lower heater voltage.
 
Heater voltage is my primary guide too.

Information posted in other threads seems to indicate nominal to slightly higher heater voltage is preferable to low/lower heater voltage.


I have been one of those persons not comfortable measuring voltages inside tube equipment, but I have gradually, through more understanding, started to do some.
 
Steve-just out of curiosity, I did some surfing to find the ''smoke and flame'' threads that specifically referenced Monster power conditioners.
Hmmm,they have all ceased to exist,even on the tech forums. And there were quite a lot! Strange,very strange indeed. Mind you,out of warranty repair issues abound,as you have said.

Little bucker photos coming soon.
 
A good thing about being a bucker is that due to the small voltage being bucked, it doesn't take a big mother bucking trafo to have a lot of bucking capacity.
 
I refer to my largest model as the Fat Bucker....
Oh crap,what have I started here:rflmao:
.
 
I refer to my largest model as the Fat Bucker....
Oh crap,what have I started here:rflmao:
.


Ok, this thread is going bucking no where, I'll start it back in the right direction. :p

I think the answer to buck, or not to buck has been answered. I plan on moving forward with the bucking plan, and build or buy one for each mono amp. Possibly if it was a big bucker I could run both amps off it at the same time. Your thoughts would be appreciated on this bucking matter.:idea:
 
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