Wurlitzer Upgrading Model to 3700/3800 amplifiers to more reliable/stable 3800 late series amplifier.
Last revision September 21, 2007
Upgrading Wurlitzer (American) amplifier from 556 (3700) to 556 Rev. 3 (3800)
This was a factory recommended improvement, amp runs cooler and is more stable!
The changes follow two procedures, depending on your starting point (check for
missing/changed parts).
For the Wurlitzer 3700 amplifier:
Change your amp from basic 556 (3700) to (3800) Revision 3 amp.
1) R17 & R18 changed to 0R47 at 5 watts if the original is 2W.
2) R23 & R24 changed from 470R to 3K6R.
3) R12 changed from 2KR to 1KR.
4) R8 changed from 2K7R to 3KR.
5) Add fuses to green wire to each board's output (edge connector pin 4) - 1A25 slo-blo.
6) Zener diodes Z2 & Z3 removed.
7) Remove R25 (1K8R) & R22 (1K8R).
8) R21 & R26 (4K7R) removed.
9) Verify that Positive lead of C1 is connected to base of Q1 (reversed from original placement).
10) Change C5 from to 47ufd/50V and that the positive lead is connected to ground.
11) Transistor Q4 (138789-2) changed to PN2222A
12) Change Q1 & Q2 from 142346 to 140622 (many boards have this done already) (sub with 2N2919).
13) Change Q3 & Q11 from 142347 to 142623 (many boards have this done already) (sub with MPSA56).
14) Change Q5 & Q10 from 142348 to 142624 (many boards have this done already) (sub with MPSA06).
15) Label this board from 140617 to 142315 Rev.3.
Note that the 2NXXXX or MPSAXX transistors installed face the OPPOSITE DIRECTION from the original 13/14XXXX parts
For the Wurlitzer 3800 amplifier including the 7500 Cabaret, 1050, and SONOTA
Change amp from 556 "SI" (early 3800s) to 3800 last revision style amp.
1) Zener diodes Z2 & Z3 removed.
2) Remove R25 (1K8R) & R22 (1K8R).
3) R12 changed from 2KR to 1KR.
4) R8 changed from 2KR to 3KR.
5) Change Q1 & Q2 from 142346 to 140622 (many boards have this done already) (sub with 2N2919).
6) Change Q3 & Q11 from 142347 to 142623 (many boards have this done already) (sub with MPSA56).
7) Change Q5 & Q10 from 142348 to 142624 (many boards have this done already) (sub with MPSA06).
Note that the 2NXXXX or MPSAXX transistors installed face the OPPOSITE DIRECTION from the original 13/14XXXX parts!
8) Verify that Positive lead of C1 is connected to base of Q1 (reversed from original placement).
9) Change C5 from to 47ufd/50V and that the positive lead is connected to ground.
10) Label board 142315 Rev. 3.
That completes the changes!
:-#)#
|
Flippers.com 
