can i simply plug a WZ-68 weber copper cap into my stock dynaco st 70 ? OR ...

do i need something else too .My 5AR4/GZ34 just went out so would i be better to replace it ? thank you

are changes needed to my two st-70's ? or does it need modification ? all i know is it sends power faster than the tube and that may do fillament damage ? THX Scott {new member}

I have not used a Weber copper cap but what little I know about them is there is a slight warm up time, maybe not as long as a 5AR4. The B+ might come on a little soon so your 525V rating of the quad capacitor might be exceeded for a few second.

The only thing you might have to do is readjust the bias.

I am sure Bob will chime in as he uses the Weber copper caps in his amplifiers.

Sal

Bob,

I have to chime in here.

I read all over the internet with interest how so many non-engineer tube types say how a rectifier so significantly changes the way an amp sounds (usually because it's now a vintage Mullard which costs hundreds of dollars). I have an electronics background, and I can say what I learned in the early 1980's applied to tubes,transistors, and ic's. The power supply in any well designed piece of equipment must provide a stiff voltage from idle to full output. The spec was usually 10% regulation or better. This was irrelevant weather the rectifier was solid state or a tube. How a rectifier makes such a significant difference in the sound of a properly designed amplifier is a mystery to me.

If the power supply was marginal, the addition of silicon diodes may help slightly. The use of them in an amplifier that was working properly would make little difference at best since the power supply was properly able to supply the needed voltages under all conditions with a tube rectifier.

Not to mention, there were many designs "back in the day" that used diodes in a good design. Take my Pioneer SX-34b receiver. It uses a voltage doubler circuit with diodes. The full voltage is available immediately. By no means does it sound like a solid state amp. It is as "tubey" as any i've heard.

End of rant.

To Scott:

1) Drop in the WZ68.
2) Reset the bias.
3) Enjoy your amp.

Tony

Just to point out something not always obvious when reading and digesting tube literature on the web-
There's a divide between tube amps being used for hi-fi and those for guitar and other instrument amplifiers. Especially when used as guitar amps, some of the tubes and circuitry are pushed to their limits; indeed PAST their limits! As such, different rectifier tubes or SS can sound differently.
Note that an amplifier can become something more than "just an amplifier"; it is part of the instrument itself.

Ok,

Blitzen is correct. If you push an amplifier beyond its limits there will certainly be a difference in sound. My education didn't include guitar amplifiers, and were not taken in to consideration in my above rant . But, when there is talk of changing a rectifier to alter sound quality in a garden variety amp be it Dyanco, McIntosh, Scott, Realistic, Lafayette, etc... I stand by my education and more importantly my ears. Keep in mind this is just my opinion. What do I know ?

Tony

anbitet66 wrote:Not to mention, there were many designs "back in the day" that used diodes in a good design. The full voltage is available immediately. By no means does it sound like a solid state amp. It is as "tubey" as any i've heard.

End of rant.


Tony

Yep, my citation II's and I think my mc240.
There is nothing "tubey" sounding with the citations though.
The 240 is another story.


Steve

anbitet66 wrote:
If the power supply was marginal, the addition of silicon diodes may help slightly.

On an old amplifier, if the power supply CAPACITORS are marginal, the silicon diodes may finish them off.

The reason: the process of "forming" the electrolytic dielectric layer in a capacitor is voltage-reliant; that is, if your
capacitors have been seeing 480 volts for umpteen dozen years and you put in a silicon rectifier, the capacitors
will "see" 500 volts or so, all of a sudden. But in effect, for all these years, even if the can is stamped "525 WVDC",
the electrolyte has actually "formed" for a working voltage of 480 volts. A new capacitor, or one in good condition,
with fresh electrolyte, will re-form itself to the new voltage. But an old, worn, dried out one may not, the result being
an arcover.

At the very least, bring the voltage up slowly with a VariAC or equivalent, the first time you fire up the amplifier with
its new silicon rectifiers. That will give the capacitors a fighting chance.

Also,

I can't seem to search right now, but I posted a while back Weber's response regarding the difference between WZ34 and a WZ68, and in an ST70, it seemed it might be better to stick with the WZ34. I think it had to do with the warm up time changed with current flow. Probably not a big deal, but something to check out.

Use Advanced Search on my id "j4570" and "weber" and see what comes up.

Now at home, and can search, here is the link:

https://dynacotubeaudio.forumotion.com/t489-wz34-vs-wz68-weber-copper-cap

Looks like the WZ34 would give more "sag" earlier, mimicking the original tube more, the WZ68 would be an improvement. I doubt there would be much difference, but since I don't run one yet, I am not the one to offer a real-world opinion.

Heed GP49's warning, this could be a good way to toast a marginal or old can cap. Also, if it's original, does that mean you have a selenium rectifier too? Just waiting to go up in smoke, literally.......might be time for a little updating, at least in the power supply section, for safety's sake.

I want you to get that ST70 back up and running, but safely.