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Re: 5R4 Vs. 5AR4

The 5R4 is not a great choice for the ST70 - the B+ will be lower than desired and will sag significantly under load. Dynaco suggested the 5U4GB as a possible emergency substitution, but the 5AR4 is really a better choice in this amp.

The Chinese 5AR4's are better in quality lately and quite inexpensive (Ned has them for about $10 www.triodeel.com). My experience is that if they last the first few hours you can expect a long lifetime. They are not as nice as a Mullard/Amperex GZ34, but are a better option than the 5R4 in the ST70.

BTW, Schematics for the ST70 and all of the vintage Dynaco gear are on my web page below.




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