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Pioneer ER-420 Rebuild

audiomaniac2

audiomaniac2

Active Member
I'm Rebuilding a Pioneer Er-420 tube receiver. I traded a guy for it . Changing electrolytic caps and Pio caps.Also replacing bad tubes .
The power switch was defective which I've taken apart and repaired.Also the voltage selector switch in the back panel was also defective.
I'm thinking about replacing the solid state rectifiers.
Just wondering if there are any other modifications that someone could recommend.
I'm a solid state guy but I have worked on some tube equipment over the years.
I did download the service manual . If anyone has owned one , let me. know how you think it sounds. Thanks!
 
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I found working on the bigger Pioneer SX82 tube receiver quite a job, as in 'this is the last time I do one of these'. It was working well when I sold it, but I was glad to see it go. I seem to remember having trouble with resistors and pots in the bias circuit. I'm not surprised that you have found some of the switches faulty.

However, I have one of the smallest of the Pioneer tube receivers, with ECL82 tubes and it sounds sweet. I'm sure you'll enjoy this one, once you've shaken out all the bugs!
 
Dandy said:
I found working on the bigger Pioneer SX82 tube receiver quite a job, as in 'this is the last time I do one of these'. It was working well when I sold it, but I was glad to see it go. I seem to remember having trouble with resistors and pots in the bias circuit. I'm not surprised that you have found some of the switches faulty.

However, I have one of the smallest of the Pioneer tube receivers, with ECL82 tubes and it sounds sweet. I'm sure you'll enjoy this one, once you've shaken out all the bugs!
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I'm really looking forward to hearing this receiver. It's rated a 15 watts @ 8 ohms. Not sure if it's ok to run 4 ohm speakers on it.Just need to install 4 can type capacitors(which will defiantly take some time) and get 4 new output tubes and 1 rf amp tube which is on the way. Hopefully not to many bugs.
 
So I've worked on this receiver on off for a few months now. I've replace all the electrolytic and Pio caps. Replaced all 4 output tubes and a whole bunch of out of spec. carbon resistors.
It sounds really good to my ears. I have a question.
The B+ on the output tubes plates are running about 30 or so volts higher than the schematic specifies .The line voltage is around 3 volts higher than specified .The milliamps going through both audio output transformers is pretty close to specs off by 4 or 5 milliamps high(combined).
The power transformer and audio output transformers run pretty hot, but from what I've been reading it seems they do run hot normally .
Should I try to lower the B+ voltage or leave it alone. If I should lower it should I place a power resistor in series with the B+.
 
What you're seeing in terms of voltage and current seems well within the usual tolerance for a tube amp. Remember most things measured ±10% or 20% back in the day. The only time I get upset is if DC voltages are right up against the capacitor ratings, or if filament voltage is too far off. The latter affects tube life more than most other variables.

Jack
 
TriodeLuvr said:
What you're seeing in terms of voltage and current seems well within the usual tolerance for a tube amp. Remember most things measured ±10% or 20% back in the day. The only time I get upset is if DC voltages are right up against the capacitor ratings, or if filament voltage is too far off. The latter affects tube life more than most other variables.

Jack
Click to expand...
Thanks for the quick response,I appreciate your knowledge .What is your opinion on the transformers running hot. After running a few hours thew were running at around 150-160 degrees F. I must add that the receiver was out in my shop at the time and the ambient temperature was around 90F.
 
Funny, I just sent an inquiry to someone about one of my own amps regarding transformer heating. 150º for the power transformer probably doesn't indicate anything amiss if ambient is 90º. Output transformers don't usually generate much heat. They're probably being affected by the proximity of the output tubes.

Jack
 
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