For Sale: Rebuilt Altec 128b Monoblocks


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I know we're Altec speaker nuts here, curious to see what love there is for Altec tube amps.

These are among Altec's last tube amplifiers, a deluxe version of the 1568 amplfier. Whereas the 1568's intended uses were in general P.A. duties, the 128b went into service as a amplifier in recording and television production studios. From what I've gathered, the 128b improved on the 1568 through three means:
  • A much beefier output transformer with lower distortion and increased bandwidth (max output of 40 watts at 2% THD from 30-20,000 hz.)
  • Front panel meter to monitor tube health
  • Improved power transformer with copper shielding and thermal protection relay patented as their Thermoguard system
This is a well executed Williamson circuit utilizing a 6CG7 front end, PP EL-34 outputs, and a 5AR4 rectifier. Great Plains has a copy of the data sheet here: Altec 128B Specs & Circuit

As can be seen from the photos, this is not a matched pair - one amplifier (serial #613) had obviously seen some use; its partner (#1200) was unused in its original packaging. I purchased these in 2018 and had them immediately rebuilt by a trusted tech in north Texas, Frank Muffich. Frank worked to preserve the external appearance of the amplifier, leaving the original power supply caps in place and routing new caps inside. The only change to the circuit is the addition of bias pots for each output tube inside the amp. Frank is an EE who distrusts the boutique cap market - not sure I agree with him, but the caps he chose have sounded excellent and have provided stable service.

Included here is an internal pic - I have to applaud Frank for his very clean work. Should anyone want to play with different (larger) caps, there's lots of room inside to do so. Note that one piece of work should be done to amp #613 - the power switch on the front panels needs to be replaced, at the moment it works for checking tube health but can not be switched to turn off the amps.

I absolutely love these amps but have decided to stick with my current direction of lower power amps, especially given the speakers I have been enjoying as of late.

Asking price of $1,700 includes an extra supply of 6CG7 tubes and a pair of 60's Mullard XF2 EL-34's that originally came with the new amp (#1200). If this sells here, 5% of the proceeds will be donated to the Haven. PXL_20210321_174926879.PORTRAIT.jpgPXL_20210321_175051023.PORTRAIT.jpg