ST70 Rectifier Tube Alternatives

[dcriner]

Well, the Chinese Ruby 5AR4 lasted about 10 hours. Now, I'm trying a JJ 5AR4; hope it lasts longer.

Doug Criner

[erichayes]

Hi All,

As I have mentioned more than once here and on other threads, the 5AR4--any 5AR4--is being pushed to its absolute limits in a Stereo 70. If you look at the ST70's contemporaries, you'll see that almost without exception, they either have solid state rectification, or more than one rectifier tube. In trying to keep costs down, Hafler decided that a single rectifier, undersized transformer and dense topography were worth the downside of premature tube (and, unbeknownst to him at the time, filter cap) failure.

The best thing you can do for any ST-70 is put a whisper fan on it to get rid of the heat that accumulates. Your tubes, transformers and capacitors will thank you for it.

[Shannon Parks]

Sorry if you already mentioned this in another thread, but is this with a stock power supply?

[mesherm]

http://www.webervst.com/ccap.html
I know it it isn't a vacuum tube but I use the WZ68 in my ST70 clones for everyday listening and pack my 5AR4s away for later.

[WA4SWJ]

Hi Guys,

I converted my ST-70's (two) to solid state. In my opinion, they sound much more solid and punchy than with the 5AR4. I have 5AR4's in my Mark III clones and they work fine so far since they are slightly less loaded in total. I am thinking about converting them too.

Regards,

[TomMcNally]

I used the big-azz GZ-37's in my Poseisdon/MK-III clones ...
so far so good. They are hard to find and kind of expensive though.

[dcriner]

Shannon: Yes, this is a modern ST70 clone with the original power supply configuration, including a T/E PA-060-S power xfmr.

If my JJ 5AR4 rectifier doesn't hold up, I have a used 5AS4 which I will try; it's a GT shape and fits and works fine. The 5AS4 has a higher current rating than the 5AR4 (1A per plate vs. 825mA). Ratings-wise, the 5AS4 is close to a GZ37.

The 5AS4 draws 3A for the filament (rather than 1.9A for the 5AR4), but that should be OK since the T/E transformer's 5-V winding is rated at 4A.

But for the time being, I'll let my JJ 5AR4 ride, and see how well it holds up.

Doug Criner

[jeffdavison]

not taking cost or current draw into consideration..also assuming the power tranny is beefy enough (i.e. not the original Dynaco PA-060)....

How would a Western Electric 274b work out? Sophia make a very nice remake (for a few less bucks than the originals)
It's a direct heated tube so it hits the output tubes hard and fast like a 5u4. Now if you put a CL90 on the line voltage to the tranny and maybe a timer circuit to let the filiment heat up before the B+ turn on, and the choke helps a bit here also....could it work? They ae supposed to be marvoulous sounding.
Can it be tamed to take the place of the venerable 5ar4?


Jeff Davison