ADA MP-1: Sovtek 12AX7s don't work in it, but do elsewhere?

[fdesalvo]

Strange issue - I have an ADA MP-1 in great condition. It doesnt seem to like or function with SOvtek 12ax7-lps tubes. Every other tube I have works here, but not these. Have any of you experienced a similar issue?

[Rhodesplyr]

Over the years, there have been many different versions of the 12AX7, made by different companies, so they vary in the details even though they meet the general specifications for a 12AX7.

When choosing a current-production 12AX7 for an application, there are some general patterns, like the fact that the JJ ECC83 tends to be more resistant to microphonics than some other types, but, yes, occasionally you do run across an application where some minor characteristic of one 12AX7 version doesn't play well in that particular circuit. Sometimes you'll get heater hum in an amp that disappears with a different brand.

I haven't dealt with an ADA MP-1, but what you've noticed is not unheard-of.

[nickb]

The heater volts can be a bit low in these. Measure the DCV between pins 4 and 5 on tube sockets of the tube pcb.

[Jazz P Bass]

Unregulated 8Vdc.

[alexradium]

Unregulated 8Vdc.

[ATTACH=CONFIG]48369[/ATTACH]

that is veeery low! I had an amp with 5Vdc and it worked with Sovtek wa's but not with JJ.