• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

Gemtune GS-01 blows second rectifier tube

Captain Slack

Captain Slack

Active Member
I bought a Gemtune GS-01 new from Amazon this past January. Two days after hooking it up, the rectifier tube blew. I can't remember which tube it came with, but it was an older NOS one I replaced it with a SovTek 5AR4 and it worked beautifully.

Until the other day, that is.

I was moving some speaker cables around and the fuse blew. Replaced it with the spare only have it blow a short time later. (No, the amp wasn't powered on when I was messing with the cables.) Ordered some fresh fuses and it worked for a few hours. Today when I switched it on, the 5AR4 blew as well. That's two rectifiers it's gone through almost a year's time.

So, am I just cursed when it comes to tubes or is something wrong internally that's causing this? I hate to spend the money on a third tube only to have it blow in a few months.
 
Register to hide this ad
Dunno about nowadays, but even a few years ago, the consensus (as I recall) on the Sovtek 5AR4 was avoid at all cost.

I guess the fundamental thing to do is find out the HV requirements of your amplifier and also check the first filter capacitor's value and see if the amp simply asks for too much from a 5AR4 (particularly a modern 5AR4).

http://audiokarma.org/forums/index.php?threads/5ar4-sovtek-shuguang-or-other.204963/
https://www.thegearpage.net/board/index.php?threads/reliable-gz34-5ar4-any-recommendations.1714637/
 
Last edited:
Open the amp and look (high voltage inside! Don't touch anything!!!). I have seen several of these amps with capacitors leaking brown goo all over the place.
 
Don’t think it actually came with a 5U4, despite what the link says. Whatever tube it did come with was an equivalent to a 5AR4.
 
I had a similar issue with my GS-02

The proper rectifier is a 5U4. My original issue was defective and the seller sent a 274b as a replacement. I'm currently using an OEM Winged C 5u4 grey plate and for $11, it has performed flawlessly. Also, I found that most new 6SN7 driver tubes die quickly in this amp, killing the rectifier. Either stick with the stock driver tubes or go whole-hog and get the PSVane UK-6SN7.

I wouldn't play around under the hood. There's nothing is there you want to mess with.
 
Captain Slack said:
I bought a Gemtune GS-01 new from Amazon this past January. Two days after hooking it up, the rectifier tube blew. I can't remember which tube it came with, but it was an older NOS one I replaced it with a SovTek 5AR4 and it worked beautifully.

Until the other day, that is.

I was moving some speaker cables around and the fuse blew. Replaced it with the spare only have it blow a short time later. (No, the amp wasn't powered on when I was messing with the cables.) Ordered some fresh fuses and it worked for a few hours. Today when I switched it on, the 5AR4 blew as well. That's two rectifiers it's gone through almost a year's time.

So, am I just cursed when it comes to tubes or is something wrong internally that's causing this? I hate to spend the money on a third tube only to have it blow in a few months.
Click to expand...

If an amp is destroying rectifiers something is amiss.

From what I've read on other threads some of these Chinese amps use power supply caps that are way too large for the rectifiers used, which leads to failures. Check the value of the first capacitor after the rectifier tube. The data sheet says the max for a 5U4 is 40uf. The modern equivalent would be 47uf which should be fine since I'm sure this amp is not drawing as much current as the 5U4 is designed for. If it's higher than 47uf I would replace it.

You should also check the voltages. The power transformers they use are sometimes rated for 110v. If you feed them typical US wall voltages, which are typically over 120v, the secondary voltages, including the heater voltages, are probably too high. You don't say if the rectifier was arcing internally or if the heater burned out.

I'd suggest using NOS or strong testing used American 5U4s and 6SN7s. They are common and reasonably priced unless you opt for some audiophool-approved version. But check the cap and voltages first.

KlipschFan61 said:
I had a similar issue with my GS-02

The proper rectifier is a 5U4. My original issue was defective and the seller sent a 274b as a replacement. I'm currently using an OEM Winged C 5u4 grey plate and for $11, it has performed flawlessly. Also, I found that most new 6SN7 driver tubes die quickly in this amp, killing the rectifier. Either stick with the stock driver tubes or go whole-hog and get the PSVane UK-6SN7.

I wouldn't play around under the hood. There's nothing is there you want to mess with.
Click to expand...

There is no reason why an amp should eat 6SN7s either. Input tubes are generally operated quite conservatively compared to output tubes. Vintage amps that are over 50 years old usually have input tubes that still test strong. This is another symptom that points to questionable design. I'm not sure why losing a 6SN7 would kill a rectifier either.

From the pics I've seen these amps are point to point wired using a tag board. It's not that difficult to check voltages if you have a multimeter. Obviously, you should follow basic safety procedures.
 
Do as you see fit. I am just posting my personal experiences with this product. These amps run hot and if you use inferior tubes, they'll blow.

Good luck with the amp.
 
mhardy6647 said:
That is both really fascinating and really unfortunate to watch.

:confused:
Click to expand...
It was a puzzler for a while until the seller convinced me it was a bad rectifier. Now that I've got the proper mix of fire bottles in there, it performs flawlessly. it sounds way better than it should, that's for sure.
 
KlipschFan61 said:
Do as you see fit. I am just posting my personal experiences with this product. These amps run hot and if you use inferior tubes, they'll blow.
Click to expand...

For many owners of these lower priced Chinese amps this is their first experience with tubes so they might think it's normal for tube amps to blow tubes. It is not normal IF the tubes are well made, the parts used in the amp are decent quality and the circuit is designed correctly.

The lower priced Chinese amps are known to ship with low quality tubes. Many buyers replace them immediately. Sometimes the "brand name" parts they claim to use are really counterfeit and don't meet the same specs.

Tubes do produce heat and a power transformer will get hot, which is completely normal. If an amp runs especially hot (thermally) it is usually because the manufacturer has built it with a transformer that just barely provides the necessary combination of voltage and current needed. A better design would use a transformer that has enough reserve capacity that this would not be an issue.

Heat generated by a power transformer does not blow tubes, though. If heater voltages are too high, as would happen if a 110v transformer is being fed over 120v, the tube's heater can burn out. If the maximum spec for a tube's plate dissipation is grossly exceeded or if the cheap tube they used was never actually able to withstand that level of dissipation, then the tube will die an early death. That's the result of poor circuit design and using questionable parts. Usually this would just mean that the tube wears out faster, not that it suddenly "blows". You would expect these issues to be more likely with power tubes, however, not input tubes like a 6SN7.

Tougher tubes might last longer but it doesn't solve the underlying problems.

Captain Slack said:
It arched internerally.
Click to expand...

If a rectifier is arcing internally, the first thing you need to check is the value of the first cap in the power supply. The "designers" of some of these amps seem to have never bothered to look at the data sheets for the tubes they used. I've seen where some shipped with rectifiers that only allow a maximum of 4uf as a first cap and the amp is running 47uf or even 100uf.

Newer and current production rectifier tubes (especially 5AR4s for some reason) seem to have a reputation for not being anywhere near as tough as old stock American and European. And they are not particularly expensive . . .

KlipschFan61 said:
Really?
Click to expand...

NOS (new old stock) American 5U4s from the big dealers are $15 and 6SN7s are $20. Obviously, you can spend a lot more if you choose. And there is no reason not to use strong testing used tubes either.
 
KlipschFan61 said:
After doing a little more research on the GS-01, I'm was incorrect in my assumption. The proper rectifier for the EL34 version of the Gemtune requires a GZ30 equivalent...

https://tubeworldexpress.com/collections/rectifiers/5Z3

A 5U4C is not equivalent to the 5U4 series of rectifiers. It's a Cyrillic thing. The driver tubes are also 6SL7 equivlents, not 6SN7.
Click to expand...

Ahh, yes. I forgot about that bit of confusion. This is why it's important to check the data sheets. And I didn't notice that you have a different version of that amp than the Captain. There seem to be a lot of variations of this amp. So which rectifier was in your amp as it came from the factory?

As you pointed out, the Russian (cyrillic) 5U4C is not the equivalent of any of the 5U4 versions or the 5V3 for that matter. It is the equivalent of the American 5Z4. It draws less heater current (2A vs 3A) and its max voltage is a bit higher (500v vs 450v) too but the maximum current rating is considerably less, only 125mA, which is half that of a 5U4GB and the same as a 5Y3GT. The American data sheets suggest that you can use either a 4uf or 8uf input cap, the Chinese data sheets say 4uf.

So if your amp uses 47uf, reliability would still be an issue. Either use a tube that can handle the 47uf cap or keep your rectifier and install a different cap and you're fine.

Another nice thing about the 5Z4 is that it is indirectly heated so it has slow start characteristics, which is a good thing. As long as the current draw of the amp isn't taxing that 125mA rating it should be OK.

Another issue that can have an effect is the voltage drop differences between different rectifier types. If the original internal voltages were measured with a tube that drops 50v and you substitute a tube that only drops 20v (like your 5U4C/5Z4), your voltages will be higher. That's why I asked what the original rectifier tube was. If an amp has been designed to run somewhat on the ragged edge (hot, as you say), pushing voltages higher just puts more stress on it.
 
I was also wondering if the Captain bought the amp from the seller Gemini Doctor. This was the seller willing to send a replacement rectifier for my amp.
 
No specific comment on the OP or his issue.
I'm just commenting in general. This is the 3rd or 4th thread I've seen come up in a week about amps eating rectifier tubes. Different brand , era amps. It just seems odd they all happened so close together:idea:
 
You must log in or register to reply here.
Back
Top Bottom