Anyone have experience with $13 Sovtek 5ar4 in Mark III?

I need to replace the rectifiers in the Mark IIIs that I am debugging. $13 each for Sovtek 5ar4 sounds cheap... Anyone have experience with this tube in the Mark III? How about the JJ/Tesla for $20, anyone ever try those?
...j

Just completed construction of a pair of Dynakits Mk3's and chose the Sovtek 5AR4s.
One 5AR4 was problematic right out of the box resulting in inconsistent bias setting adjustments. I will continue to use the Sovtek 5AR4's in the Mk3's and the ST70 for the time being until the Sovteks flame out and switch to the Shuguang.

Precisely the sort of inputs I was looking for. Thanks.
...j

Sorry to confuse the issue here, j beede - I have run two Mesa 5AR4 tubes for well over 1,500 hours in my mark IIIs now without any issues whatsoever. I am under the impression that the Mesa tubes are made by Sovtek (plate construction looks identical, seems to be a copy of the Mullard rectifier tube).

I have so far lost two Ruby tubes in my ST-70, at a fraction of the hours that the Mesa / Sovtek / whatever tubes already gave me - I have sworn to never buy Ruby again.

Perhaps I am just lucky, who knows.
-- JunkyJan

JunkyJan wrote:...I am under the impression that the Mesa tubes are made by Sovtek (plate construction looks identical, seems to be a copy of the Mullard rectifier tube)....

WRONG!! I take that back, the Mesa tubes (available at most of the better music shops - I think it is really aimed at the Guitar Amplifier market) apparently is made by SHUGUANG.

So... That bears out then what Bob said too.

-- JN

...but you did have failures with the Ruby rectifiers in your ST-70?

Hi j beede

Yes, I lost two Ruby 5AR4 tubes on my ST-70 over the space of about 6 or 7 months... One came with the kit, the other was bought from a guitar shop on Commercial Drive in Vancouver (BC, Canada).

In both cases the tubes went in the same way - it works perfectly fine until one day when it will suddenly arc for a second or so when the amplifier is switched on. Within an hour after that it will then suddenly fail (and take the fuse with it). Any attempt to try switch the amp on afterwards (after replacing the fuse) will just promptly take the fuse out again (Yay for fuses!).

The Mesa / Shuguang 5AR4 I have in it using now seems to work perfectly fine, then again it has done 1,500 hours in a Mark III amp before, so I guess it would have failed by now if it was going to. Mesa/Boogie claims that they select, test and burn-in tubes before sticking the "Mesa" label on it, might actually be the case and not just salesman's talk.

My ST-70 hasn't done a fraction of the time I have put on my Mark IIIs. I don't know if this may be perhaps some indication that something is up with my ST-70 - it works and sounds fantastic otherwise.

-- JunkyJan

I guess I will do the "yellow sheet" forward diode modification on both of my Mark IIIs before I insert my new 5AR4s. I haven't heard of anyone having a bad experience attributed to adding that simple change.
...j

I would say the Sovtek 5AR4 quality is very questionable.
I have a modwrite power supply for the CD player and I have gone through 3 of these tubes in 14Mths; Probably less than 100 hours of playing in that time.
I have checked the heater voltages and it's all fine.
I am going to give the Shuguang GZ34 a shot to see how it goes.

For what it's worth... I think Shuguang makes some pretty good tubes these days... The KT88's... These Rectifier tubes.. Tubes from China etc get a pretty bad rap but these tubes are pretty good... At least the ones I've got.

I'll 2nd what J Beede said, always do the rectifier mod, it pretty much ensures reliability,
thanks to Mantha for the drawing

What a timely topic. I just blew what seems like a GZ34 in one of the new MK3's I finished building. I had powered the amp down for less then a minute, changed the input source, powered up and saw the JJ GZ34 internally arced and then blew the fuse. I had another in the ST120 that would sometimes show some arcing at idle (now have a Weber in that). I'm sure the short cycle didn't help anything either.

Will have to see tomorrow if anything is bad and pop in a new GZ34 and see what's up.

The question what do the 1N4007's do to protect the tubes? It looks like they allow only the positive side of the waveforms to hit either side of the tube, does that keep things from conducting across the 2 internal anodes which results in a blown tube?

Sandy

I think you answered your own question Sandy. The silicon diodes pre-rectify the AC--clipping the lower half of the wave form--meaning the 5AR4's function is reduced to providing a voltage drop and B+ delay at turn on. FYI: My $13 Sovtek 5AR4 are both holding up months after installation with the "yellow sheet" mod.

Did the 'yellow sheet' mod last night, thanks for the tips.

When I checked out the suspect GZ34 on the tester and back in the MkIII and it seems fine. I will be skipping JJ GZ34's and trying the Shuguang on the next tube order as well as some more fuses

What was interesting is that when I did the other amp's diode mods (The amp that did not have a problem), the bias was always bit more unstable, I swapped out the other JJ GZ34 and it seemed to have less instability and settle down quicker. Seems these tubes have a good bit of difference, but not sure if this is normal from tube to tube, but interesting to see a bit different rate of bias stabilizing.

Sandy