±10% variation (108-132 V) is normal. Wider excursions are not uncommon either. If your amp gets cranky at 122 V, it's broken. If the vendor says it's supposed to be that way, it's a flawed design.
In the EU, the mains voltage was normalized from 220/240 V to 230 V ±5 % to make it fit within the old limits. Still, that's 218-242 V. Even small percentages can look dramatic at high voltage. 🙂
Tom
In the EU, the mains voltage was normalized from 220/240 V to 230 V ±5 % to make it fit within the old limits. Still, that's 218-242 V. Even small percentages can look dramatic at high voltage. 🙂
Tom
Exactly as Tom says. It's just the way it is, depends on many things such as the distance of your installation from the main distribution transformer, and the electrical load on the system at a given point in time.
And that voltage is to your point of supply. From there, within your installation you will have a max permissible voltage drop from the main switchboard to the furthest power outlet from that point, 2.5vAC is about right for 120vAC supply, And in your situation, works in your favour. All to say voltage will vary, and this is not only normal, but also unavoidable unless somehow regulated.
Further, you cannot simply call the power company and ask for them to 'turn it down', that was amusing. Nor can you wire an installation for any 'prescribed voltage', and expect the voltage at the outlet remain constant unless you regulate it.
10 percent line fluctuation will equate to 10 percent B supply variation, so if your B supply is 400V, expect 440V. The bias supply will also increase in the negative direction by the same percentage, which will limit current flow - unless it is regulated, which is not something that you want.
If this is an isolated incident amongst owners of the same amplifier, I suspect you have a problem. Measure the current consumed by the amplifier from start up and for 5 mins afterward, and compare with the rated current, this will give some clues.
My question to the manufacturer would 'can I reliably use you amplifier with a mains voltage which complies with standard, in so far as line voltage fluctuations are concerned?'.
Any response outside of 'yes', is unacceptable. I'd ask them again.
And that voltage is to your point of supply. From there, within your installation you will have a max permissible voltage drop from the main switchboard to the furthest power outlet from that point, 2.5vAC is about right for 120vAC supply, And in your situation, works in your favour. All to say voltage will vary, and this is not only normal, but also unavoidable unless somehow regulated.
Further, you cannot simply call the power company and ask for them to 'turn it down', that was amusing. Nor can you wire an installation for any 'prescribed voltage', and expect the voltage at the outlet remain constant unless you regulate it.
10 percent line fluctuation will equate to 10 percent B supply variation, so if your B supply is 400V, expect 440V. The bias supply will also increase in the negative direction by the same percentage, which will limit current flow - unless it is regulated, which is not something that you want.
If this is an isolated incident amongst owners of the same amplifier, I suspect you have a problem. Measure the current consumed by the amplifier from start up and for 5 mins afterward, and compare with the rated current, this will give some clues.
My question to the manufacturer would 'can I reliably use you amplifier with a mains voltage which complies with standard, in so far as line voltage fluctuations are concerned?'.
Any response outside of 'yes', is unacceptable. I'd ask them again.
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This is a known "issue". The manufacturer notes in on the website and it is in the build instructions. Mine is not messed up, it sounds great and zero problems after I started using a variac.
I agree, something should be done or offered that does not require a variac but this is the path I am on at the moment.
Humbuck circuit as others have suggested.
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Why do they prescribe a fuse who's value cannot hold in with the current draw of the amplifier when line voltage goes high?.
Insulation rating for the winding within the power transformer? - doubtful.
Voltage rating of the B supply capacitors? - entirely possible.
I'd be interested in the reason behind their decisions, given the problems which are inevitable; lifecycle, reliability, useability, brand reputation etc.
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From what I understand, the UK went with 230V +-10% so a max of 252V!
From :UK Mains Voltage
"Nominally, all of the EU (with the exception of the Isle of Man and Gibraltar, who are at 240V) is supposed to center around the voltage of 230V single phase. Becaause the mainland countries were all at 220 and the UK and Ireland were at 240V, they were allowed to vary by the aburd amount of +10%/−6% (216.2V to 253V) and this was made worse by being widened to 230V ±10% (207V to 253V) in 2008. This means we have single standard that is not a standard but a wacky, wide range of voltages that can and does burn stuff up at the extremes of variation - though this is rare. "
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If it blows up at 122V I'd set the variac to 110V and call it a day. Also "Known issue" sounds like "We screwed up so be careful". If this design flaw was found in a car, there would be a mandated recall 🙂
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Do you have a schematic of the amplifier?
The original Dynaco ST70 had no such issues.
Just the opposite, it was extremely reliable.
I'm not sure there's much to add that already hasn't been said. I'll press on anyways 😀
It sounds like you are not on board with challenging the manufacturer, either because you accept that by identifying the problem, they have absolved themselves, or that it is a waste of time because there is little chance that they will change their position. Fine, if that's the case we can move on.
The point is that issues at 122V is ridiculous, and if it were me I would not accept having to always have it on a variac.
The most likely culprits are:
Bad rectifier. If you have been trying just Russian or Chinese types, could be that you got 2 bad ones in a row, assuming that's how many times this happened to you, especially if you replaced it the 1st time with the same tube.
Bad design PS. Maybe B+ or heater supply or another rail was poorly designed for the components used, and rising above 122VAC has an exaggerated effect.
Bad transformer choice. Maybe they picked what's nominally a 100VAC or 110VAC transformer and use that for all 100VAC-120VAC countries they export to.
As I said, if it were me, I'd diagnose it and try to fix so it's all nice and self contained in the amp enclosure.
It sounds like you are not on board with challenging the manufacturer, either because you accept that by identifying the problem, they have absolved themselves, or that it is a waste of time because there is little chance that they will change their position. Fine, if that's the case we can move on.
The point is that issues at 122V is ridiculous, and if it were me I would not accept having to always have it on a variac.
The most likely culprits are:
Bad rectifier. If you have been trying just Russian or Chinese types, could be that you got 2 bad ones in a row, assuming that's how many times this happened to you, especially if you replaced it the 1st time with the same tube.
Bad design PS. Maybe B+ or heater supply or another rail was poorly designed for the components used, and rising above 122VAC has an exaggerated effect.
Bad transformer choice. Maybe they picked what's nominally a 100VAC or 110VAC transformer and use that for all 100VAC-120VAC countries they export to.
As I said, if it were me, I'd diagnose it and try to fix so it's all nice and self contained in the amp enclosure.
Most likely the real issue, not excess line voltage. Poor quality current production 5AR4 like JJ, Sovtek, Shuguang. Just place a silicon diode in series with each rectifier plate connection, voila, end of problem.
heff
That's what I would like to do. Sadly, I am not educated enough to know how to do so. I am reading a book on tube amps, doing a lot of looking around, and hopefully will gain the knowledge required.
This is what I built: tubes4hifi amplifier KITs page
I've only blown one rectifier and and three fuses. Its been on a variac since day two of its existence.
Do you have this circuit installed? It cannot hurt anything,
and may fix your problem completely.
I do. I bought the diodes and variac the same day. Thus, I have not run the mod without also using the variac to keep voltage under 122.
Then if the problems are still present with the diode mod, but without the Variac,
I'd suggest getting a schematic so we can see if there is a design problem.
What size and type of fuse do you use?
I built the mono m125’s last week and blew a fuse when my rectifier arced while I was adjusting the bias. The mono version of this amp is running right at the edge of what a 5ar4 rectifier can supply and I suspect your version as well since they are basically the same output. I switched to a Weber wz34 rectifier and have not had a problem since. My Monster Power conditioner says my voltage swings between 118-124 constantly which is why I’m getting the companion Monster Power AVS 2000. I will try tube rectifiers after I get that unit.
The WZ34 seems to be worth trying for this amp.
WZ34 Copper Cap
The W51 that they recommend instead for "hi-fi" amps only drops 1V instead of the 17V in the WZ34,
so the W51 would raise the B+ by 16VDC, and possibly cause other problems.
I'd think that you would want the sub to drop about the same voltage as the 5AR4.
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