WZ68 is not designed for use in HIFI amps??

Hi


I noticed a faint buzzing noise from the amplifier, not the speakers when I place my ear close to the amplifier.
Yesterday evening after a few hours of operation, I noticed the buzzing noise was much louder. The power transformer was hot to the touch.
With the benefit of hindsight, I now realise that my tubes were brighter than they usually are.
I did some research and found this on the tedweber.com…website states the WZ68 is for guitar amps and is not designed for hifi amps.
I am confused.
The WZ68 solid state rectifier was included in my ST120 amp kit and is also one of the options listed on the tubes4hifi website.

Dis you bias your amp?

Yes. Bias settings are within acceptable range.

The buzzing noise seems to be coming from the solid state rectifier. I’m not 100% certain.

I don’t understand why that website warns that the rectifier is for guitar amps.

My guess is that the "buzz" is unlikely to be from the WZ68, but more likely to be mechanical hum from the power transformer. The subject of that Weber warning has been discussed here in the past:

https://dynacotubeaudio.forumotion.com/t2639-weber-wz68-now-not-recommended-on-weber-website

There's plenty of discussion on the causes of mechanical transformer hum on the web:

https://www.google.com/search?q=dynaco+power+transformer+mechanical+hum&sxsrf=APq-WBuzfyF8kGgY4PUMZfGq4-Y0RDAwNw%3A1646213344235&ei=4DgfYpGBDs6WseMP4cuBsAg&ved=0ahUKEwiR8e3Mjqf2AhVOS2wGHeFlAIYQ4dUDCA0&oq=dynaco+power+transformer+mechanical+hum&gs_lcp=Cgdnd3Mtd2l6EAwyBwgjELADECc6CggjELACELADECdKBAhBGAFKBAhGGABQzhdYzhdg3lVoAXAAeACAAacBiAGnAZIBAzAuMZgBAKABAcgBAcABAQ&sclient=gws-wiz

Send Roy an email for advice: info@tubes4hifi.com

This thread shows what is inside a WZ68.

https://dynacotubeaudio.forumotion.com/t4654-wz68-copper-cap-tear-down

Diodes and resistors with a thermistor delay. Nothing that will buzz per se. The PT can buzz when new as it does its job... it could make the copper cap internals vibrate a bit, but I agree it is most likely the PT mechanical hum. Try grommets, and/or tighten/loosen mounting threads. Early on I put a small wooden block on top of the PT to absorb the slight buzz... worked well until things settled down due to heat and use.

The dropping resistors (vs WS1) simulate the sag of a tube rectifier to get B+ a little closer to what it would be with a tube. The WS1 does not have this (its just diodes), maybe the delay thermistor if ordered; as such you will get a higher b+. Who knows why weber made that caveat.. it makes no sense in the VTA world since we know what is under the hood in our power supplies.

Good luck!

Are you using a Variac to control line voltage......Where I live I'm seeing from 118V to 125V.....These amplifiers are most happy at a very solid 115vAC......I couldn't even own tube amplifiers where I live without a variac......$50 at Circuit Specialties

Hi

Thanks to everyone who replied.

The following day I switched my amp on and the noise seems to have disappeared although the power transformer Becomes warm after approximately half an hour of use and continues to heat up.

I thought about the situation and I noticed that my power transformer might not be the correct one for the ST120.
I have the 240V version although I noticed the lamination stack is not as high as was stated on the tubes4hifi.

What are the consequences for my amp if I have the ST120 output transformers and a ST70 power transformer, running KT88 valves?

Thanks

If you have the amp wired as a “120” there will be major stress on the power transformer due to lack of current capacity. You can look at tubes4hifi website and cross reference the various transformer capacities. This will also likely cause a buzz….

It turns out that Gabriel does indeed have a 240v version of the ST70 power transformer, however alot of people on this forum and elsewhere
are running KT88 output tubes in an ST70. A "hot" transformer is a relative term, especially to anyone new to tube amps.
Tube amp power transformers almost always run "warm" but not "hot". To me, a hot transformer is one which is too warm to keep your hand on continuously.
Part of the heat of course comes from the current used. The other part of the heat comes from being close to the output tubes, which of course ARE HOT at nearly 400 degrees.
The bigger issue for me has been that the ST120 and M125 amps run the rectifier tube at MAX rating continuously, which is why I now supply these amps with WZ68 solid-state rectifiers.
I chose a WZ68 even though Weber claim it's not designed for Hi-Fi amps. The reason they say that is because at high current, the resistors "sag" the B+ voltage down slightly.
Now this is something a guitar player likes. For hi-fi, it's less of an issue than the fact that a WZ1 has zero sag, but a WZ1 also sounds more like diodes than a rectifier tube,
because it contains absolutely nothing other than a couple diodes, and maybe a thermistor. The thermistor only gives about a 2-3 second delay at turn on.
A WZ68 gives 5-6 seconds delay at turn on.
At any rate, after going back and forth on the pluses and minuses of power supply current in the ST120 and M125 amps, I first decided the obvious advice was to use a WZ68 and a TDR.
Now after more experience and actual listening tests, I'm recommending two alternatives. One is to use a 5U4 rectifier tube, rather than the GZ34, because it has a 10% higher current rating.
But it will also start up faster (5-10 seconds) instead of around 20 seconds for a GZ34. The other recommendation for those two amps is to run them at lower current by turning the bias down
from 0.50vdc to 0.45vdc, which is 45ma per tube. With four tubes that gets you up to 180ma, plus the 25 ma the driver board uses. That's 205ma, rather than 225ma, and all the tubes will
run cooler, last longer, and the power transformer will run cooler and actually put out very slightly more B+, so no real change in output power.
That said, if someone prefers using a WZ1, that's fine, and use it with a TDR. Otherwise, use a 5U4 and either remove or bypass the relay connection on the TDR.

Roy thank you for this. Awesome.

Just FYI for anyone concerned, I have today shipped a new ST120 power transformer to Gabriel in Australia at my out of pocket cost of $150 for the transformer and $130 for shipping,
so once he receives that, all should be good.

"Just FYI for anyone concerned, I have today shipped a new ST120 power transformer to Gabriel in Australia at my out of pocket cost of $150 for the transformer and $130 for shipping,
so once he receives that, all should be good"

Fantastic customer service!

tubes4hifi wrote:
Now after more experience and actual listening tests, I'm recommending two alternatives.   One is to use a 5U4 rectifier tube, rather than the GZ34, because it has a 10% higher current rating.
But it will also start up faster (5-10 seconds) instead of around 20 seconds for a GZ34.   The other recommendation for those two amps is to run them at lower current by turning the bias down
from 0.50vdc to 0.45vdc, which is 45ma per tube.  With four tubes that gets you up to 180ma, plus the 25 ma the driver board uses.  That's 205ma, rather than 225ma, and all the tubes will
run cooler, last longer, and the power transformer will run cooler and actually put out very slightly more B+, so no real change in output power.
That said, if someone prefers using a WZ1, that's fine, and use it with a TDR.   Otherwise, use a 5U4 and either remove or bypass the relay connection on the TDR.

So I have the M125's on order with the new chassis design. Are you saying that using a 5U4 rectifier tube is a viable option if you run at a slightly reduced bias? If so, how will the new design top panel be configured? I don't see a socket for a rectifier tube in the pictures that have been posted so far.

The reason the WZ68 is not recommended for hi fi use is that some hi fi enthusiasts, myself included, prefer not to simulate the sag from tube rectifiers.  I prefer an amp to be as uncolored as possible, with as little unpleasant glare or hardness as possible.  That's why many serious high end tube amps, like VTL, use solid state rectifiers.  The sag most definitely affects bass transients--things like bass drum whacks.  I know this from my listening.  A guitarist, on the other hand, considers the amp to be part of his instrument, and chooses it for the sound desired, not accuracy.  The sag is often part of the desired sound.

The problem is, a SSR without the series resistor will overvolt the filter cap.  On the M125, at least (which I built), the 550 WV is a razor thin margin.  You would need a Variac to reduce the primary voltage to where the plate voltage runs at a safe level.  Another solution, one almost certainly not approved by VTA/Tubes4HiFi (you're on your own, in other words), if you're never going to use the 5 volt filament winding, is to connect it in series with the primary as a bucking winding.  Make sure to get the phase right or you'll boost instead (you can play with it at a safe level using a sine wave generator to get the right phasing).

Glad you got your transformer buzz straightened out.  I was pretty sure it was unrelated to the WZ68 being the "wrong" rectifier.