Altec 1569at pwr tube meter

[altec342b]

Hello, looking for info on installing a altec pwr tube meter in a 1569a aka 1569at w/meter.These are the same meters used in the 128b I believe. What I'm looking for is how to hook the meter up to the power tubes and also any pics (for proper meter location) of 1569at's or 128b's . Thanks,.

[bfish]

Greetings!
This is a project I've been considering, but haven't yet committed to. I've never seen a schematic for the AT or BT versions of the 1500 series, but I did find one for the 128B after consireable googling, but can't find it again to send you a link. Email me at [email protected], if you can't find it, and I'll reply with a pdf copy.

On a 128B, the meter is centered in the front panel, but appears to be above center, due to the location of the bezel/trim plate. Front panel layout is almost completely different than a 1568a, but it looks like everything will fit if using the exiting holes, it just wouldn't look exactly the same unless you started a new front panel from scratch. Since I haven't yet begun restoration on the 128s, I don't know if there are other problems using its' circuit on 1500s or not, but as they use different xfmrs, it's possible. Adding a switch for the high-pass filters is an easy copy that does work.

An easier compromise would be to install a few test point probe sockets, but since the 1568 and 9 are so easy to access, it might not be worth the trouble. Using your DMM gives you more info, as the panel meter only has a 'green good' area, and isn't marked for V or A. BTW, the meter also checks both 'pre' tubes too, via the 4 pos switch.

Although the thermal protection of the 128b can't be copied without using those xfmrs, one could copy the thermal breaker circuit from the 1570b fairly easy to the 1568 or 9. I've been adding extra fusing too, as finding replacement xfmrs will become impossible at some point. If at any point, you should have the xfmrs unhooked for any reason, I recommend installing isolation mounts under them. Rubber washers on both sides of the chassis helps, but true isolation mounts (chassis-hung rubber assy with a rigid center bushing) really quiet cabinet hum, especially on 1570s. Any place you can improve mounting/fastening, and get rid of those cheap 'speed-nuts' is a good idea too.