Hot 5AR4/GZ34 arcing on powerup surge?

[rtsang]

Dear Kevin,

Would the series SS rectifiers add some switching noise and would be better served by HEXFREDs?

Or the tube rectifier would smooth out the noises?

Raymond.

[kevinkr]

Hi Raymond,
I haven't observed any significant switching noise with the ss series diodes, when the vacuum tube rectifier cuts off this disconnects the ss diodes from any large radiating current loop that would otherwise exist. I do recommend UF4007 if this is a concern, and/or a small ceramic cap (2KV min) in the range of 1nF to 10nF (0.01uF) across the ss diodes, but the hexfred is total overkill in this application - might as well eliminate the tube rectifier if going this route. I use mostly 1N4007 for this application and have no noise issues, and no distinguishable difference in performance other than not frying rectifiers on a regular basis.

[SA-12]

I had this problem with a st70, on advise from a friend I bought a electroharmonix rectifier tube and problem went away. Another crazy story is how I had 80uf on the first stage without any problems , I used it like this for over a year before I sold it. That electro tube held strong all that time, never changed the tube again.

On a side note I bought the new 6CA7 fat boys from russia, what a sweet change that made over the EL34's I was using. This thread makes me want to source another dynaco clunker

[Evenharmonics]

Originally posted by kevinkr
Interestingly enough placing a single UF4007 or 1N4007 diode in series with each plate lead will cure this and a lot of other issues with modern rectifier tubes.

I suppose this is a standard tube amp design these days? If not, shouldn't it be?

[kevinkr]

Originally posted by Evenharmonics


I suppose this is a standard tube amp design these days? If not, shouldn't it be?

No, oddly enough it isn't and it is really only required with the 5AR4 and strongly recommended when pushing the envelope voltage wise with the 5U4XXX (say 1KV)

I've been doing this for about 10yrs now, and have to admit that Eric Barbour originally suggested this to me when I was working on an Italian made dht based monoblock (572-3) using 5U4 at voltages in excess of 1.2KV. I applied it to the 5AR4 when I was having problems in my own products and this helped greatly despite the fact that I was not running them any harder than is the case in ST-70 and in a lot of cases not half as hard.

[mantha3]

I had read on another forum that you may hear "Switching" if you run the two IN4007 Diodes inline from the power supply/Power Transformer to the GZ34 as seen in this thread...

A solution was to use the UF4007 (Fast Recovery) Diodes in place of the 1N4007. this is in regards to running 2 1A / 1000Volt Diodes inline from the Power Transformer to the GZ34 as seen in the diagram of this thread.

I have the IN4007s now... Wondering about doing a switch over to UF4007 as I can do this for a $1.00.

Thoughts??