[EdHolland]

Looking again at the bias voltages required to get uniform quiescent currents (anywhere from -16 V to -18.5 V) has made me think of investing in new output valves for this receiver. They are also something of a mixed bunch. Three are marked RCA, one Fisher, presumably the latter might be original. It certainly looks like it has seen better days - the Bakelite base is crumbling at the top edge from where the glass extends. They all look a bit well used. Sound wise, I have not judged the amp on a decent set of speakers yet - using either phones, or the cheap full range drivers on the workbench that are used for tests.

Since I plan on keeping this one, I looked around at the offerings for 7591a types, and also at reviews. There is a lot of concern for reliability with one brand, JJ. I can't confirm this, but they are certainly cheapest at ~$17 each. Better things are said of the Electro Harmonix brand, but they are packaged in a large envelope that doesn't look right, precludes addition of a wood cabinet, and puts everything even closer together. The last, probably best option is the Tung-Sol. Reviews are favourable (little report of trouble). They are quite expensive, at $30 apiece, but should last, now that bias is properly controlled. I have decided to go with the best option, and treat the Fisher to a secure future. These valves also look right, having the same envelope shape as the 60's types. I have the FM stage valves, but did need a few more 12AX7, so added those to the order.

Cheers,

Ed