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AUDIO FORUMS >> General Discussion and Support >> SE84UFO3 regulator tube not powering up
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Message started by Tapatrick on 11/21/20 at 16:54:45

Title: SE84UFO3 regulator tube not powering up
Post by Tapatrick on 11/21/20 at 16:54:45

My SE84UFO3 monoblocks have been working fine of months, but on switching amp on earlier the Regulator tube (the back one) on left channel flashed then went dead. All other tubes are lit up. Rectifier is fine but also flashed before regulator went off.
1. Switched the regulator tube from the other mono block (which was working fine) and it does not power up either when inserted. I checked that all pins/slots are good and in good contact as far as I can tell.
2. I presumed it must be a blown fuse but all fuses inside are fine.

Any suggestions what the problem might be? Thanks in advance

Title: Re: SE84UFO3 regulator tube not powering up
Post by HockessinKid on 11/21/20 at 17:15:23

Did you check the fuse located in the IEC, where you plug in your power cord? There is one in there.

HK

Title: Re: SE84UFO3 regulator tube not powering up
Post by Tapatrick on 11/21/20 at 17:18:10

all the other tubes are powered up...

In addition looks like there is no voltage getting to the regulator tube, all other tubes are powered up. On the good amp it is 70volts to the reg but on faulty amp it reads as zero. So looks like something powering and before the reg is faulty.

Title: Re: SE84UFO3 regulator tube not powering up
Post by CAJames on 11/21/20 at 20:42:22

Did you try another rectifier tube? If that is good then it sounds like something in the power supply.

Title: Re: SE84UFO3 regulator tube not powering up
Post by Tapatrick on 11/21/20 at 23:57:26

Thanks for the input. I swopped the rectifiers and no didn't work either. But frustratingly neither regulator works in either amp now. I'll have a fresh look again tomorrow and order some new regulators as I don't have spares.

Title: Re: SE84UFO3 regulator tube not powering up
Post by Archie on 11/22/20 at 00:28:55

Sounds like the amp shorted both tubes then. I don't think I'd try a 3rd until I talked with Steve.

Title: Re: SE84UFO3 regulator tube not powering up
Post by CAJames on 11/22/20 at 00:31:54

^^^Agree. Once is an anomaly, twice is a trend. Probably time to seek professional guidance. I hope you didn't lose both rectifiers too.

Title: Re: SE84UFO3 regulator tube not powering up
Post by Steve Deckert on 11/22/20 at 05:46:19

Quote:

Rectifier is fine but also flashed before regulator went off.

The regulator needs both high voltage and a load to light up. When a rectifier tube shorts (the flash) there is no longer any high voltage so consequently the regulator tube won't stay lit.

A common mistake is to think that a rectifier is good when the heaters are still working. Most shorts happen in the high voltage plates of the tube which will always take out the internal fuses usually instead of or in addition to the mains fuse.

Sometimes the fuse board itself shorts in pre 2019 models when the rectifier arcs which results in the board sacrificing itself instead of the rectifier. This has only happened 3 or 4 times in the past two years so it is not common, just possible.

Most likely just get yourself some new fuses and a new rectifier tube and you'll be fine. Rectifiers can arc without actually failing, but the arc can blow a fuse. When you try the rectifier in a different amp it seems to work fine.

Anyone having even a small arc in a rectifier tube should immediately order themselves a New Old Stock 5U4G as a replacement. That will end the whole pre-mature rectifier tube failing problem and make your life less stressful, not to mention have the bonus of improving the sound by as much as 20%. A New Old Stock Rectifier tube should last easily 5000 hours and often well surpass that figure in these amps.

Steve

Title: Re: SE84UFO3 regulator tube not powering up
Post by Tapatrick on 11/22/20 at 13:59:23

Thanks for your help Steve! Yes it was as you described. I changed the 500ma fuses (which strangely did not look blow) and replaced the rectifiers with older ones I had and both amps all firing up. And I've ordered some new 5U4Gs.

Since I bought the amps in 2017 the only problem has ever been with the rectifiers going. I'll watch out from now on to catch any early signs of them fading...
Now back to the music... :)
Patrick

Title: Re: SE84UFO3 regulator tube not powering up
Post by Dunning1 on 12/08/20 at 09:31:18

The aftereffect of this arrangement vacuum tube power flexibly is a finished impeding of intensity gracefully sounds, clamor, hash, grain, and spikes.

Title: Re: SE84UFO3 regulator tube not powering up
Post by Steve Deckert on 12/12/20 at 17:31:14

Rectifier tubes are by far the most failure prone over all the other tubes. This is because today's current production rectifiers are made in China, Yugo, Russia. The only decent ones are Russian, and even those can be a little hit and miss. China has no quality control. You are the quality control. Russia has quality control, but it's not like 1950's American tubes which were built with the same resources and seriousness as the NASA space program.

My advise to everyone with a Decware amplifier, or any amplifier using a tube rectifier would be this: Find yourself a new old stock 5U4 from America or Great Britton. The China rectifiers has proven to have on average a 500 hour life span, then they short and try to damage your amp. Russian ones are much better but a good new old stock will almost always last a minimum of 5000 hours and sound better the entire time.

Steve

Title: Re: SE84UFO3 regulator tube not powering up
Post by Steve Deckert on 12/12/20 at 17:36:32

Side note:

The internal fuse holder contains two 500mA fuses on in the case of the smaller amps, 200mA fuses. These are connected between the high voltage secondary of the power transformer and the rectifier tube socket. If one of these blows there will be no high voltage.

Also, the internal fuse holder contains a third fuse for the heater of the rectifier tube. The heater is low voltage (5 volts AC) and the fuse for that is always 6.3 A. If this fuse blows, the rectifier tube will stop glowing since the heater is the part that you see glow inside the tube.

The only way to know if a fuse is blown when it looks fine, is to check it with an ohm meter.

-Steve

Title: Re: SE84UFO3 regulator tube not powering up
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Title: Re: SE84UFO3 regulator tube not powering up
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