GZ34 Rectifiers

[WA4SWJ]

Hi Gang,

Came into the office this morning and turned on my Dynaco Stereo 70 clone with Shannon's board and the GZ34 rectifier I have in it flashed over and blew the primary fuse. It's a new JJ version of that tube that only had about 150 hours on it. This is a brand new amp I built from scratch with a new chassis and Uncle Ned's transformers. It has the standard size electrolytic can cap (new) so the tube was not working into capacitors that are too large.

Seems like I read somewhere that GZ34's aren't all that great and fail frequently during startup surge currents. Any comments on that? I have several old 5U4's that I'll put in there next. I'm quite sure they are much more rugged. The only problem is that my spare fuses and tubes are at home so I have to listen to solid state today. Heresy! :-)

Best regards to everyone!

[EWBrown]

These new build GZ34/5AR4s aren't quite up the standards of the old originals, this is especially true for some of the ones from China (some spell it MADE IN CHIAN) which aren't even up to pretending to be 5Y3s...
So far I've not had any JJs fail - yet...




/ed B in NH

[Thermion]

Hi Gang,

...the GZ34 rectifier I have in it flashed over and blew the primary fuse. It's a new JJ version of that tube that only had about 150 hours on it.

I have several old 5U4's that I'll put in there next.

I have been using a JJ GZ34 in my ST70 for almost two years now with no problems. Yours is the first I have heard of. I have been using Sovteks in my MKIII's for well over 10 years without problems, but of course the current is less. The JJ's seemed to be better built which is why I'm using one in the ST70.

I would recommend that you do not use a 5U4 in the ST70. The filament draws 3 amps and the PT is already working too hard.

JT

[WA4SWJ]

Thermion,

I just re-tried the JJ GZ34 by quickly powering up the amp with my hand on the switch and it flashed over immediately. So, it's definitely bad. I do have Uncle Ned's PA-060-S power transformer and it has a 5 volt, 4 amp heater winding for the rectifier. So, a 5U4 should be OK. Those draw 3 amps. Perhaps I just got a bad GZ34 from JJ.

I tried my only 5R4GY in the amp this afternoon. It sounded great for a while but it soon faded out due to low voltage - that tube is old, old and is tired and worn out. I'll have to order something else. I just don't have that many rectifiers laying around. I hate to have the amp down because it sounds so great when it's working. I do have an old 5U4 I'll try tomorrow. Maybe it's got a bit of life left in it. Hope so! I gotta get some stock built up.

Regards,

[Shannon Parks]

Seems like I read somewhere that GZ34's aren't all that great and fail frequently during startup surge currents. Any comments on that?

Just use Mullards! Yellow_Light_Colorz_PDT_04

Grab a Keystone CL90 inrush current limiter and put it in series with the primary. I believe Thermion has run his MKIIIs for a while in this config, and it is used in the ST35 project. I will probably do this myself in my ST70. Inrush current, even with the small original capacitance, really gives those glass rectifiers a workout.

JJ tubes are probably the best value/performance, but in my limited experience I feel their QC isn't the best. My 2 cents: the Sovtek 5AR4's are dirt cheap and seem very solid.

Shannon

[Thermion]

Grab a Keystone CL120 inrush current limiter and put it in series with the primary. I believe Thermion has run his MKIIIs for a while in this config.

I have not used the CL120's in my MKIII's or ST70. In fact, in my first ST35 clone, (not diytube) I had some problems and cut it out of the amp.

I think WA4SWJ just got the rare bad JJ. Shannon and I disagree somewhat on the JJ's. In my experience their QC is much better than the Russian or Yugo choices.

An ST70 pushes the rectifiers much more than a MKIII or Ike. Since you have the reserve filament current, a 5U4 may be a good choice, but your B+ will be ~30 volts lower.

JT

[EWBrown]

If you're using the "Uncle Ned" power trannie, it has a lot more gumption than the original dynaco iron, it will definitely test the capacity of any rectifier tube.

I was thinking of using an ICL on the primary, but wasn't sure just which one would be the right rated one.


I've been using the CL-90 on just about every SS rectified amp project, just to play it safe. I'll have to see how all those CL-50s can figure into the erquation (back when they were freebies with the early ST35 boards).

/ed B in NH

[WA4SWJ]

JT,

Yeah, I know the 5U4 tube drop is higher and I'd rather not use one of those for a long period. I was thinking about replacing the tube with a solid state rectifier but I'd rather not since I'll need to add some resistors to get the voltage back where it should be. I also like the look of the rectifier tube. It turns out the failed JJ GZ34 I have is under warranty and I'll get another one but I have to ship the old one back first. I'll do that but it's a little bit of a pain. I've been looking at the old Mullards but I just don't see the reason to pay a lot more (other than perhaps a reduced failure rate).

I am still enjoying the amp tremendously. I may take it home and bring in my Baby Blue and listen to it more.

Regards,

[erichayes]

Hi All,

Ahh... "So soon they forget..." Both Amperex and Mullard 5AR4s were notorious for imitating Roman Candles with annoying regularity, and the American versions weren't much better. My music teacher in high school had a Dyna stack and he replaced the rectifier in his Stereo 70 every six months whether it needed it or not.

As much as I love this tube, I concede that it has an Achilles heel: spontaneous, spectacular failure. That being said, I think the JJ is as good as the NOS stuff available; I've been using them in my Eico HF-20 rebuilds and they're working just fine. I talked with Bob Pletka of http://eurotubes.com about JJ's development of the 5AR4 a few years ago and he said that they were trying to make it as true to the Mullard/Amperex design as possible, and they tested it for more than a year before they released it.

[TerrySmith]

If you think aboot it, the '70 pulls a lot of current. I figure at 50ma bias, thats 200ma + 15-20ma the driver uses, all this at idle! If you played music with a lot of bass, I could only imagine what current that poor little GZ34 has to pass.

Then there's the choke thats only rated for 200ma.

Maybe a dual rectifier-coke-capboard could be crammed under there!

I guess this is why I like the MK-3 or MK-4 (or IKE!) layout a little better.

Just my early morning $.02 worth!

[EWBrown]

i've always had a liking for those "Chatham" style 5R4s, the flat top "potato masher" mil spec B-52 jobbies. Unfortunately their voltage drop is rather high, so they probably wouldn't be suitable as a drop in replacement in an ST70. Not to be confused with 5AR4s, these are a zebra of a different stripe...

So far, the JJ's I've been using in two different ST70s haven't yet gone pyrotechnic on me. And one of them has an SDS cap board, the other has a new 4 section "can" cap similar to the original.

/ed B in NH

[Shannon Parks]

...I meant to suggest the Keystone CL90. But even those freebie Keystone CL50's that many of you have would work great as they'll start out at 7 ohms and drop close to 1 ohm. Here's the datasheet again: http://www.diytube.com/cl.pdf

Shannon

[WA4SWJ]

Hi again guys,

I finally got around this morning to checking the HV output from the power supply using a 5U4GB rectifier instead of the GZ34 in my amp. The voltage at the first capacitor section is 380 volts instead of 435 volts as I've seen on the Dynaco schematic. That's after I re-biased the tubes all to 50 mA. The amp sounds fine and I don't need a lot of power since I'm using it in my office. Unfortunately, although I checked the voltage before with the GZ34 before it failed, I don't remember what it was. Seems it was in the normal range of over 400 volts though.

I'll try the CL-90 for surge reduction when I get my replacement GZ34. I've got a few of those laying around.

Just some comments for interest.

Best Regards,

[EWBrown]

My latest ( last year) ST-70 using Uncle Ned's PA060, JJ 5AR4/GZ34, "Winged C" EL34s, and NOS A470s, runs about 460VDC at the B+ connections on the OPTs. The driver board is Roy Mottram's VTA-70 using three 12AT7s. Those Triode Trannies do have a tad more "testosterone" than the original Dyna Iron...




Not a good idea to try the "bargain bin" EL34s in this one, they'd go into roman candle mode, most definitely. Yellow_Light_Colorz_PDT_05

My line voltage is between 120-123 VAC, and occasionally spikes up to 127 during "light load" times. Yellow_Light_Colorz_PDT_29


/ed B in NH