I built a tube amp from Tubes 4 hifi (ST120) and it works like a champ, issue is my electrical.
I am the first house off a transformer and generally get 120-125v at the outlet; anything over 122 volts leads to blown fuses or arc'd rectifier tube. A variac if my solution.
Any advice on a good power regulator so I can quit fiddling with a variac.
I am the first house off a transformer and generally get 120-125v at the outlet; anything over 122 volts leads to blown fuses or arc'd rectifier tube. A variac if my solution.
Any advice on a good power regulator so I can quit fiddling with a variac.
Use a small transformer to buck the input AC voltage down.
You get -5% with a 6.3VAC filament transformer, or -10% with a 12.6VAC unit.
I'd go with the -10% option.
The transformer's secondary current rating should be more than the amplifier.
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While that will drop the voltage I would still have issues with fluctuations resulting in fluctuations in my bias setting. It can swing a couple volts over a couple hours, really annoying.
Unless you get a SOLA ferroresonant transformer (1% regulation), that's hard to fix.
Priced around $1000 new for the 500W unit, but there's a $100 used one on ebay
which looks like a really good deal. And the Variac is no longer needed as well.
SOLA HEVI-DUTY POWER CONDITIONER, 23-23-150-8, 120/208/240/480 V INPUT 13227066063 | eBay
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I don't see how you can go wrong, as long as it works.
They apparently don't do any testing though, so if it's bad
you could be out for the round trip shipping, around $90.
Other used 500W SOLAs on ebay are $100-$200 more than this one.
The SOLA part number you want is # 23-23-150-8.
Please have an electrician install it if you have any doubts about
whether you can do it.
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What about something like a Furman P-1800 pfr? I know it is more expensive.
Supposedly it will maintain 120v +/- 5. Granted that could result in blown fuses or rectifiers unless that +/- is only a second or two.
I am sick of fiterring with a variac and my wife likes the stereo too and is worried she might screw it up, thus, make it as easy as possible.
Supposedly it will maintain 120v +/- 5. Granted that could result in blown fuses or rectifiers unless that +/- is only a second or two.
I am sick of fiterring with a variac and my wife likes the stereo too and is worried she might screw it up, thus, make it as easy as possible.
What about using an ac/dc power supply and then an inverter to produce a more constant voltage, some inverters made for on grid solar systems produce very good sine waves.
Im using this setup for my VPI turntable to produce 110v 60hz from 220v 50hz grid, speed is spot on so at least the frecuency produced by the inverter is very stable.
I have 2 furman voltage regulators also but their spec is -+ 5%, so its more swing that what you are looking for.
Im using this setup for my VPI turntable to produce 110v 60hz from 220v 50hz grid, speed is spot on so at least the frecuency produced by the inverter is very stable.
I have 2 furman voltage regulators also but their spec is -+ 5%, so its more swing that what you are looking for.
Frankly your diagnosis sounds far fetched to me. I assume the kit came with a current production transformer? So why would swinging above 122V on a current production 120V transformer cause serious problems? I think there is most likely something else going on here.
+1
If the amplifier is indeed designed such that it can't handle at least ±10 % variation from nominal mains voltage, I'd consider the design rather flawed. If that's indeed the case, the bucking transformer has the most going for it, I think. You don't need a large transformer. A 5-10 VA type is likely plenty.
I suggest sending tubes4hifi an email about this.
Tom
If the amplifier is indeed designed such that it can't handle at least ±10 % variation from nominal mains voltage, I'd consider the design rather flawed. If that's indeed the case, the bucking transformer has the most going for it, I think. You don't need a large transformer. A 5-10 VA type is likely plenty.
I suggest sending tubes4hifi an email about this.
Tom
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It may seem far fetched, however, I have blown a couple fuses and arc'd my rectifier tube prior to learning my electrical is out of whack. I then contacted Tubes4Hifi and thats when I learned about the over 122v issue - it is also in the build sheet but I skimmed past it like a dope.
I keep the variac between 119-120v and have no issues for more than 2 months.
I did contact them and thats how I learned it was an over voltage issue. They do mention them on their website and manual, however, I had no idea my electrical would be an issue. I assumed my voltage was fine - 50 year old house, new electrical panel, new wires from pole to panel. Ooops.
I am new to all this, my first piece of kit I have ever built. I really do not know my options aside from Variac, bucking transformer, or something like the furman.
In the US anything between 108 VAC and 132 VAC is within specs. There's something wrong with that amp and I suggest you get to the bottom of it before you use it.
Mike
Tubes4hifi's position on mains voltage and their response ridiculous. So what if they put it in the instructions, it's a design deficiency! It's so ridiculous I'm not even sure what the real design deficiency is, maybe 1 transformer covers both Japan and the Americas?
You might want to start a thread in the Tube forum on really diagnosing what the design issue is and fixing it more elegantly.
You might want to start a thread in the Tube forum on really diagnosing what the design issue is and fixing it more elegantly.
Since I am a bit new here and VERY NEW to building my own gear - I am trying to learn as best I can - I was not sure where I should put this thread. Maybe I will post over there with a link to this thread for backstory.
How about an ATX computer power supply powering a 12V inverter? I've found stepped sine to be fine.
122V has been common for decades.
I had a house run 127V normal. Incandescent lamps died young. I called the company and said "I'm scared!!", they turned down to 122V.
My present house runs 125V unless I turn on some appliances. It can dip to 109V when the pump starts. Having NO trouble, though I have no tubes (except radar-range).
My last lab was wired for 117 on the nose, but backhoe ate a cable, and I lived on 108 for several years. I did develop tube-amps on this supply, merely correcting results from 108 to 120V.
I spent a couple summers touring with 750 Watts of tube amps, eating every sort of bad power. I did carry a volt-plug; I have seen 150V in wall outlets. But if it was in sight of 117V I just used it. No re-bias, no failures.
Really: if incandescent lamps give good service, your voltage is fine. Incandescents are MUCH more fussy than any other common electrical load. And until 2010, incandescents were THE load that the power company had to cater to.
You may have bad rectifiers, or a bad design.
The design is basically a modified Dynaco ST-70 from what I understand. I wonder if the desire to maintain the lineage of the design has resulted in a questionable power supply.
I have a desire to rebuild this one with a few modifications and maybe I can learn enough to fix this issue too.
Honestly, I had ABSOLUTELY no idea residential power had such variance. I also have no idea how to deal with this other than a variac or how tube manufacturers deal with it.
I have a desire to rebuild this one with a few modifications and maybe I can learn enough to fix this issue too.
Honestly, I had ABSOLUTELY no idea residential power had such variance. I also have no idea how to deal with this other than a variac or how tube manufacturers deal with it.
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