Pioneer ER-420 valve amp/tuner

[tiv48]

hi rob i just re read post about 1 meg resisistor i meg is right, i was assuming the resisistor was an earth lift between mains earth and chassis, but of corse you have no mains earth, so i repeat this resistor must be 1 meg .the reason older valve amps were not earthed .was that preamps tunners record decks ect might of been .so the chance of getting a hum loop was high.from a safty point of view you have a double wound mains transformer, these can and do go leaky or as you discovered the mains lead could get damaged . so i would fit a 3 core mains lead with the eart connected to the chassis ,if this causes hum when useing say a record deck fit a 10 ohm 5watt resistor between the earth and chassis
sorry about confusion i will edit above post
rob t

[Robjkmannering]

Thanks once again,
I have fitted a 3 cope mains lead and am happier with safety now!
HOWEVER, I cleaned the function and stereo switch which are made of multiple wafer assemblies.
I won't tell you what I used as cleaning agent, I had run out of servisol and being in a hurry, I used what was to hand. Big mistake! It obviously contained some form of carbon compound and on switch on,
FIREWORKS!
Now I have a working function and stereo switch, FM stereo now sounds great. But I have reduced volume, what have I upset?
The HT rectification is handled by 2 ancient silicon diodes, Me thinks the HT may be low as the fireworks may have seen one of them off. Better go hunt for the 1N4007s
Back to circuit diagram......
Regards,
Rob

[Robjkmannering]

Whoops, too late!
It went bang! I think I had better service the wafer switch with some proper servisol, have a look at replacing caps and then rebuild power supply....
Rob

[tiv48]

ht line should be 350 volts, where did the fireworks come from?
rob t

[Robjkmannering]

The mode selector and stereo selector switch wafer assemblies!
The diodes and power supply have survived and I am now cleaning carbon from the switches.
Anybody know a safe solvent to clean the carbon off please?
A mistake I won't be making again!
I dont't want to dissasemble the switches as they have 4 wafers and a lot of connections.
Rob

[Robjkmannering]

Hi,
I have disassembled the selector switch, the part that controls power to the various modules is carbonised and beyond repair.
As I don't intend to sell the amp, I wondered if it would be possible to switch the FM tuner or aux inputs to the amp using relays powered off a circuit fed from the heater supply.
A rotary switch could then replace the selector switch to maintain the visual appeal.
I have traced out all the connections from the four wafers (front and rear) and although complex, there are many inputs and stereo/mono functions that I don't really need.
Regards,
Rob

[Robjkmannering]

This is now working fully!
I once again dissasembled the wafer 4 wafer switch and cleaned the carbonised wafer with solvent and a toothbrush. Reassembly was a nightmare and involved tracing and replacing the wiring as the wires were too short to solder with the switch assembled.
As an aside, even the stereo pilot light works now!
Valves sound so much better than transistor amps! Can't wait to hook it up to my mp3 and enjoy it.
Regards,
Rob