Weber WZ68 now NOT recommended on Weber website!

skriefal wrote:If the problem is heat, then it would be good if Weber would offer an option with pre-cut ventilation holes or slots in the copper tube.  Others have suggested adding such slots in prior threads here.

Exactly what I was thinking just now. I was measuring the temps. in my ST-120 in modest operating conditions. The hot-spot, while using a Mullard GZ-37, was the heater area of the rectifier tube - over 300F. The KT-88s are burning at around 200F, and the power tranny maxes out at 150F. I can't recall what I measured the Weber copper-top at, but it must have been getting warmer than I thought. So perhaps heat is the killer.
{Measurement  taken with laser therm from close proximity}.

The Webers are a brilliant idea but poorly implemented. It's like operating your rectifier in a copper oven. The diodes need to be isolated and far away from the hot sag resistor and thermistor. Heat shortens the life of components drastically and especially the semiconductors. Air flow and heat sinking all the parts would greatly increase longevity. And over spec parts by a wide margin.

I have though used my WZ68 in the ST-120 for close to 2 yrs without issue and it has clocked a lot of hours. Never needed the 2nd I bought for a spare.

well this is certainly an interesting development. I have heard both good and bad things about the Weber's, I used them in my builds for a while, and so far no failures, but, call it a gut feeling....I decided a while ago to switch to two tube rectifiers in parallel, especially on my version of the M125's.
This may of course be a problem with the M125 chassis, where to find the room for the extra rectifier, not to mention cutting the hole into the SS chassis.
It really is a simple solution to wire two rectifiers in parallel. Now you can use pretty much any suitable rectifier, as the load on each unit is about half...give or take.
I am even using the big bottle Shuguang 5Z4P, so far no failures, not to mention they look pretty cool!!

And here's another secret. I have also started using the Compactron Diode 6CG3. This tube is a single heater-cathode diode, originally used for TV dampening diode applications.
This tube is rated at 5KV and 350mA. Use two of them and you're set. Can be used in the M125, or ST70 and ST120, or any tube amp for that matter. And again, this is a really cool looking tube!
It uses a 6.3V filament rated at 1.8A

The suggestion that the inside may be sprayed with plasti dip may not be a good idea.
This copper top is a heat sink and applying plasti dip to the inside dip would lower the heat transfer capability significantly.
Note the spring in there to push the resistors to contact the copper cap to enhance heat transfer.

I think the holes are a good idea but I would only wrap the wire on the exposed top and the two wires on the bottom of the resistors and leave the heat sink mass alone.
Maybe soldering/brazing some copper cooling fins on the copper cap along with some holes would be a better option and done right could look cool!

Thanks for the Gut shot pic....hehe looks funky....






thanks for the site Bob.......................

I have Bobs earlier version of the vta-st120 amp with the 12at7 board . The amp works beautifully but
the rectifier is the weak link . I've used the WZ 68 copper rectifier for almost from the beginning and have
 various problems with them from the diodes shorting to the resistors going bad from the heat they generate so i
totally revamped mine . Changed the diodes to 1N5408 3a/1000v and to round resistors ,drilled 4 1/4 inch holes near the
bottom and cut the top off the copper can with a band saw and added a 30mm fan on top for forced cooling . My power
amp sits on a shelf i build in the basement so i don't see the amp . Its been there among others in the past 20 some years
 . Haven't had rectifier problems for over a year now . And no down time . Just pure music .

Just slightly O/T... the UF5408 diodes are MUCH quieter than the 1N5408 series. If you decide to modify your copper cap I strongly suggest you use the UF5408 diode. The cost difference is maybe $0.25 per diode.

Also - providing even a small hot air vent at the top of the cap and a cool air entry hole at the bottom (the bottom of the locating pin?) would be a huge help. And it might be worth trying a Pearl tube cooler to reduce the temps as well.

Finally, if you have a copper cap you can improve the copper's emissivity (ability to radiate heat) by a factor of 10 or more simply by painting it black, either with an air dry enamel or better yet an oil based paint. The thinner the coat the better, use just enough to ensure you have the black color; and use a self-etching primer first after cleaning up the copper surface before applying the THIN black coat.

Just my $0.02 worth!

The guts of the Weber looks like a death trap to me!   Slots in the copper cap bottom plus many small holes at the top would ventilate the inside at least.  Heat rises and pulls cooler air in from the bottom. The diodes would benefit next to the bottom slots. Oh, I wish I had a machine shop and knew what I was doing. But those insides look very scary!

What about a water cooled computer CPU heat sink adapted to it? There are hundreds of variations of CPU water cooled units sold in the aftermarket there must be one that could work.

Most of them have a tiny radiator or fins arrayed on a piece of copper tubing. They are usually already a cool copper color.

I didn't notice any noise from the diodes on my scope. I just plugged a stock spare in and made an A-B test on my amp with modded model but next time when or if I have another failure I will try the UF5408 diodes. What the heck.

Meanwhile I didn't mention it earlier but the leads on both 5408 types are thicker and either have to be filed a bit thinner or you have to do what I did which was to strip the little PCB completely then VERY CAREFULLY! ream out the holes a bit  to fit the thicker leads on the diodes.

I did this on a drill press with a tiny round machinist's file in the chuck. It had a tapered tip so it worked perfect. The PCB is of average quality and a bit delicate for drilling. Be careful!
BTW
Antique Electronics sells octal base blanks if you can't sweat the leads out of the original. Cheap too.

Good idea with the rounded resistors. it leaves a bit more space. Were they a wound type? Where did you get them?
Good thread!
I am surprised at all the feedback on the WZ68 I did not realize how many members have had to fix them.

Lots of different options ... just substitute a copper cap for the candles ...



Or add a riser underneath to get it more into the open air. It do get a bit crowded on a Dynaco chassis, especially with the competition of all the other heat sources.



Not sure if the vent holes around the socket could be done with the stock chassis - I do know they help, but you'd also have to vent the bottom plate to allow good air flow for a chimney effect. Air's gotta come from somewhere.

Or build a custom chassis ... lot more room for the big boys to breathe. As mentioned, I didn't roll with a copper cap for long, but had no problems when I did.

Or add a fan? Nice flat unit on top of the PT would be easy enough to do and blend in fairly well. Wouldn't even have to be permanent. Bend a plate to use the PT's corner screws, attach the fan to that with stand offs, and power it up with a USB wall wart. Some clever bending on the plate, and you could even direct the air intake for max effect at the rectifier. I've seen fans mounted to the back where they're not seen, and once again, a baffle plate could be use to cool both the big iron AND the rectifier.

Water cooling is an option ... make it adjustable for each valve ...  



~~~

Couple things to keep in mind before bad mouthing the design of the copper cap too much ... they're designed for musicians, for musicians, and we're not using them for their intended purpose. Also, a typical instrument amp will have the rectifier mounted horizontally which would induce more air flow across the entire shield, and have more air space below to allow improved chimney effect. So there ... ;-}

When I built my VTA ST-70 about 15 mos. ago, I enlarged the vent holes on the bottom plates using the following stepped drill bits:

HFT stepped drill bits

The bits cut right through the stainless steel without any problems. Not much luck, however, with standard drill bits. I believe this increased airflow. Also, the amp rests on Cardas myrtle blocks, lifting up the unit about an inch.

I didn't think of adding tiny little fans on top of the tubes, such as those employed by sKiZo.(See above). Then again, nobody has quite the breathtaking creativity which sKiZo has repeatedly demonstrated.

MontanaWay probably has best solution: Split the load between two rectifiers and include a small ventilation fan. BTW, he is closing out one of his ST-120 builds over on eBay:

Custom VTA ST-120

As you can tell, the price is very favorable. I would buy it myself, except I have a perfectly functioning VTA ST-70.

As i said i don't see this when the amp is in operation as it sits on a shelf in the basement near the ceiling . The resistors
are wired parallel then series  . The square resistors that came with the WZ 68 were 10 W 20 some ohms in series

So 2 50 ohm in parallel would amount to almost the same + an added extra watts . When the Amp is on i can put my
hand on the Copper cylinder .

That is awesome and a step in the right direction.  Run the fan on 6V to slow it down and it will be almost silent.  Good job!

Jim made mention of keeping an eye on the line voltage. Brings to mind my lil bucker ... this pic shows a GOOD day here at the farm ...



I'm sure even the bigger GZ rectifiers can benefit from lower line levels, as long as the amp can still deliver B+ to spec ...

I've mentioned earlier as well that I get some sonic benefits from the lower VAC line levels. Amp sounds a bit pinched when the power supply is hovering at 125 or thereabouts. Seems reasonable as the recommended level was 117 back in the day.

(And ya, I know ... the new iron is wound to handle todays higher average levels, but mine seems quite happy with the bucker in line.)

I've mentioned earlier as well that I get some sonic benefits from the lower VAC line levels. Amp sounds a bit pinched when the power supply is hovering at 125 or thereabouts. Seems reasonable as the recommended level was 117 back in the day.




Bucker well work also an can cost less than a Variac....I just like to set the sound I get....with A variac...go from fat soft big image sweet tone.....to tight full bass...an hard driven mids....clear highs....are anywere inbetween....hehe
I well not sale any tube amps are preamps with out a Variac in the sale............ never had anyone say anything but good things about the sound thay get by droping the B+....$50....for a variac...an all the stress is gone...
.I have never heard high B+ on a tube amp setup in... triode are UL  sound good...............now if like... Bob Carver...you run your amps in Tetrode...you can run the plate B+... up to 600-750....as long as screen grid 2 is feed lower B+ at about 380-400....but all the Dynaco an most others are UL.......I say tops for good sound is 480 UL.....going higher may sound ok.....but then looks to me like all this .....tube killing an over heating shows up.....justsaying


thanks for the site Bob.............................

This is a new one for me.
We run a pretty steady 120-122 VAC out of the wall here; would be nice to knock that down a bit. I've been through a couple of variacs but at least the $100 Chinese types seem not to live very long; I've had two that developed ground faults after just a few weeks on-line.
Is there an "off the shelf" bucker available (google search not too productive) somebody could recommend? And would 117 VAC be too low for s/s gear?
Many thanks
-d-
P.S. In defense of the Webers I've had no trouble with mine for a year. I do like Holger's idea of doubling down on rectifiers, as it opens up some tube options for the M-125s.

In the ST-120 I am thinking about wiring the tube rectifier 5V heater winding in series with the AC input to buck (not boost) the line voltage by 5V. I don't currently use the heater winding with a solid state rectifier so seems like an easy way to at least give it a try.

My Chinese variac also developed a ground fault problem, per deepee99 above. I have two used US-made Powerstats that work flawlessly, purchased on eBay.

I still use the Chinese variac, but I never switch it OFF. The ON-OFF cycle seems to be the culprit. Even tried it in our maintenance shop here at the apt. complex; same results.

deepee99 wrote:Is there an "off the shelf" bucker available (google search not too productive) somebody could recommend? And would 117 VAC be too low for s/s gear?

Not that I'm aware of, but it's a simple build. Hard part might be finding an appropriate transformer - lucky me, I just happened to have one in the parts bin, I'm thinking leftover from a Hammond chassis. Not to forget, it's got to handle peak draw from the amp. Mine is 6 amps which is plenty strong. Used to be a fairly common component, but not so much anymore.

Basically, you're taking a step down transformer and wiring the secondary winding in series with the primary.



Test it prior to using to make sure you've got what you're looking for on output. Wiring it up bass ackwards will BOOST the line level! You could also fine tune the power out with resistance, but that tends to run hot, so best to get the correct transformer in the first place.

PS ... I also had the old school power strip in the scrap heap, complete with switch, fusing, and pilot lamp. Those are handy and real popular with the bucker crowd.

As far ass ss gear goes, I never really felt a need to drop the line in for that ...

Bob Latino wrote:I have had the same two Weber WZ68's in my two M-125's for almost 5 years now .. These amps are not played daily but they do get use every week .. These two WZ68's have never given me a bit of trouble and still work fine ..

As to why Weber is not recommending them for AUDIO tube amps, I cannot say unless someone hears from them about why ? Some thoughts as to maybe why ?

1. Weber may know now that some of their WZ68's are going into KIT BUILT audio amps. If the high voltage storage system is not wired properly and has a short or a bad connection somewhere, then the WZ68 may go up in smoke at the first turn on. They may be wary of the WZ68 not going into a factory built and pretested amp.

2. Guitar amps do not usually run as high a B+ voltage as the VTA ST-120/M-125's (490 - 500 VDC). The Weber's probably (as baddog1946 has said above) could be made to stand up better to a little bit of abuse if they used the 1N5408 diodes instead of the cheaper 1N4007 diodes. As to "abuse", I am talking about voltages much above 120 VAC or amps being short cycled either manually or by sudden ON/OFF/ON power failures.

Bob

Will this WZ68 drop directly in place of the GZ34

Yes plug it in, set your bias and you are good to go, to be honest I was using a JJ GZ34 and switched it out for the heck of it (Never did fail have as back up) to the Copper cap Months ago and have just kept using it with no issues.

I have two Webers (WZ68s) and two Mullards (GZ 33s), and two M-125 amps. I am going for Holger's 2 holer rectifiers mod.
Question is, can a Weber and a Mullard live next door to each other, and how would this mess up the bias?
The obvious answer would be to put both Webers into one of the amps, and the Mullards into the other. But I am looking for the un-obvious. Not wanting to wreck things.

Bob, maybe I misstated my question. Could I put a Mullard tube and a Weber side-by-each on the same amp?