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jrethorst wrote:How can you tell when a 5AR4 needs to be replaced?
Corona wrote:Use a mullard GZ37. They're cheaper than 5ar4's, look better and are more durable. I've been using one in my st-70 without issue for months.
Bob Latino wrote:Corona wrote:Use a mullard GZ37. They're cheaper than 5ar4's, look better and are more durable. I've been using one in my st-70 without issue for months.
You can also use a GZ33 rectifier tube in the ST-120. A GZ33 draws more current than a GZ34 but the rectifier line on the ST-120 is rated at 5 amps and can handle the extra current draw with no problems. A GZ33 is a tall, coke bottle shaped tube. The nice thing is that you can still find NOS Mullard GZ33's for about half the price of a NOS Mullard GZ34. There is vendor on Ebay from Great Britain that sells NOS Mullard GZ33's for about $70 + about $7.68 shipping from GB. Not a bad price for a NEW Mullard tube. Check the link below.
NOS Mullard GZ33 on Ebay
Bob Latino wrote:
I wouldn't use EL34's in a Mark III. IMHO you would be pushing them too hard. KT88's or 6550's are better output tubes for a Mark III.