Support HammondWiki. Donate!

Technical Service Bulletin #27

January 28, 1966
Affects Models M, M-2, M-3, S & S-1

As noted in our previous technical bulletin #8, the early electromagnetic speakers are becoming more difficult to recondition as regards to increasing prices and the availability of proper materials.

With proper circuit revisions, the AO-21066-1 and AO-21055-2 electromagnetic speakers, as used in the early Spinet and Chord organs, can be replaced with our AO-22748-0 permanent magnet speaker, selling at a list price of $14.00.

In place of the AO-21055-1 EM speaker field coil, a 1000-ohm 20-Watt resistor must be subsituted. For the AO-21055-2 EM speaker field coil, a 700-ohm 20-Watt resistor must be substituted.

One other revision must be made to the early Spinet and Chord organ power supply circuits.

In the case of the Model M Spinet, condenser C-57 .15mfd must be removed. Install a 25mfd 25WVDC electrolytic condenser between the -18 volt point and the chassis ground. This is applicable on all amplifiers of the Modem M Spinet Organ only. The Model M-2 and M-3 will not require this change as a 25mfd condenser is already incorporated in their circuits.

In the case of the S and S-1 Chord Organ, condenser C-240 .2mfd must be replaced with a 25mfd 25WVDC electrolytic condenser.

NOTICE: In both cases, the POSITIVE side of the 25mfd condenser must be attached to ground potential.

No other circuit changes will be required in either of the above models. all wiring and replacement must be done in a neat workmanship manner which reflects your service ability and knowledge.

We will begin shipment of the AO-22748-0 PM Speaker soon as our stock of EM speakers is depleted. there will be no allowance for returned AO-21055-1 or AO-21055-2 speakers against this replacement.

All old EM speakers speakers AO-21055-1 and AO-21055-2 from prior exchanges, must be in our hands no later than 30 days from the date of this bulletin or from the date of an invoice to receive proper credit.

The content of this page is Copyright (C) 2000, 2001, 2002 Geoffrey T. Dairiki and the other authors of the content, whoever they may be.
This is free information and you are welcome redistribute it under certain conditions; see for details.
Absolutely no warrantee is made as to the correctness of the information on this page.