Author: Provo Electronics

Case   345560  .   12/23/2024.  Poineer SX-880 . No sound. Unit in protection mode. Protection relay not clicking  after turn on .

After troubleshooting  found  –  only one channel causing this issue.  ( DC offset voltage test on protection relay) .  After we know what chanel is bad  we focus on this specific channel. Found bad 2SA899 driver transistor( you can use 2sa939 , 2sa914) and bad soldering   joints on board.  After changing transistor , rebuild joints – still no sound. Investigating voltages on this transistor  found resistor 330 ohm connected to base 2sa899 changed value to 10000 ohms. Same story in working channel  – from 330   to 1500 ohms. Changing resistors in  both channels solved the problem.  Our guess – resistor change value problem developed by bad soldering  joints on main board and   hard working transistors in line after  46 years . Or they getting older like people do   or something else  on chemical level .
Nice receiver , easy to work on it ,   enormous power .  All critical and major components designed on  one board.

Case 238791 , 12/21/2024. Chevrolet Corvette 1962 tube AM car radio.
No sound.
Interesting radio . Mixed technologies – vacuum tubes and solid state components used .  Use  5 tubes and 1 germanium old style output transistor. Tubes- 12DZ6 / 12AD6 / 12EA6 / 12VD8 / 12AL8. Speaker can be used with insulation transformer only.  Modern speakers   4-8 ohm  will not work.
We changed illumination bulb, paper capacitor 1000 uf x 6 v , multi-section aluminum cap . Aluminum cap shell was removed ,  opened , internals removed, new small 3 modern capacitors inserted inside old aluminum can. Can has been glued to chassis by Power grab. Mechanical moving parts lubricated, board cleaned. All tube tested ok , even after 63 years. Respect to  quality product from  RCA  and Silvertone tube production companies  .

25 Watt mono 3 way acoustic system inside . 3 speakers covers sound frequency from 20 Hz to 19000 Hz. Unique string control system for treble ,base range on front panel. Amp located in wooden cabinet 35 x17 x22 inch with removable legs. Simple 5 tubes amplifier based on   6BQ5 (2) , EZ81,ECC83, EF86 tubes .
All tubes original Hoffman tubes. EF86 tested and found bad. You can use soviet made in USSR tube 6Ж32П instead of EF86 with better results .Full analog.  In this case we replaced all  tubes for age reason. Cabinet refinished , tube replaced, all multi section capacitors replaced also. Speaker cloth cover replaced, all controls cleaned , illumination lamps #44 replaced, speaker foam replaced.
Has 4 RCA inputs – AUX, PHONO, TAPE, TUNER.    Power consumption from AC line -150-190 WATTS.
Unit has our warranty – 6 month.     Nice  piece of history.  Beautiful sound.