ST70 Tube Alternates

knowledge base for the classic Dynaco ST70

ST70 Tube Alternates

Postby dcriner » Sun Oct 12, 2014 4:36 pm

For the 5AR4 rectifier, a Mullard should last a lifetime. Some (maybe all) General Electric-branded 5AR4s were made by Mullard. The "Great Britain" and the Mullard plant code markings prove it. The GEs often sell for less than Mullard-branded tubes. I have had poor luck with newly-manufactured 5AR4s - Chinese, Russian, or Eastern European. NOS Sylvania "fatboys" are very good.

There are one or more batches of JAN Philips tubes marked 5V4GA that are actually U.S.-made, Sylvania fatboy 5AR4s. The larger glass envelope at the base and the copper holes in the plate edges are the give-away. The story is that in the mid-1950s, Philips' U.S. tooling for making 5V4GAs was kaput or gone, but they still had the old Sylvania tooling for making 5AR4s. Since the two tubes are nearly identical, except that the 5AR4's electrical data is a bit better, it seems that the Army and Navy went along with it - probably by that time, there were no other U.S. manufacturers that could supply "real" 5V4GAs. I was lucky to snag two of them. Keep your eyes peeled.

I have two pairs of JAN Philips 7199s, which will last the life of my amp. They are now priced out of sight, so maybe it's next best is to rewire the sockets for 6U8As (Google for instructions). There are several substitutions for 7199s, all of which I think require some wiring changes. If any of those substitutions are so great, I wonder why 7199s price has escalated so much? Maybe because of do-dos like me?

For EL34s, I've tried several of the newly manufactured "overseas" brands, and I can't tell the difference. There are various options.
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Re: ST70 Tube Alternates

Postby skidave » Mon Oct 13, 2014 9:17 am

Thanks-good info on the 5AR4. The last few times I needed a 5AR4, I purchased them from Parts Express. I had one fail right out of the box and called them about it. They shipped a new one at no charge. I have to say that is good customer service since a tube rectifier could be a topic of concern.

I just looked and their price has gone up significantly. ... e--072-320

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