A temporary customer reference number is assigned to each customer only while they are shopping on
zZounds.com. If you call our customer service department for assistance, this number makes it easier
for us to answer any questions you have about products, services or purchases.
Electro-Harmonix 7591A EH's are available in platinum matched sets. Our platinum matching process consists of a 24 hour tube burn-in period followed by a bias (plate) current measurement in milliamps. Please specify matched tube grouping (ie. pair, quad, sextet, etc.) when ordering (no odd-quantity groups, please).