Transistor (but not portable) table radio fixed

[wa2ise]

A Hitachi table radio, solid state, uses transistors. Not a portable, so by some definitions it's not a "transistor". In any event, got it at a garage sale, as not working. It's a "hot chassis" design, the audio output transistor is a high voltage one, and the rest of the circuits are conventional low voltage transistor circuits. As seen in many such radios, it uses a dropping power resistor in series with the rectifier diode. In this radio, that power resistor went bad apparently on its own. Replaced it, radio now works. But I relocated this resistor away from the "high" side of the powerline, to the "low" side (connected directly to the radio's B- line and the power switch (which switches the low side of the line)). Keeps a hot resistor away from the filter cap.

And the radio doesn't seem to notice that its "ground" is bouncing at a complex 60Hz wave above external ground.

[Sandy G]

...And THIS is why Yr Humble Narrator NEVER wanted to learn to work on these things... NO WAY could I ever remember all the little "Ins & Outs" that can get one KILLED if you momentarily forget...

[maxhifi]

That resistor sure looks out of place amongst all its Japanese neighbours! Cool radio, thanks for sharing.

[dieseljeep]

Originally Posted by maxhifi

That resistor sure looks out of place amongst all its Japanese neighbours! Cool radio, thanks for sharing.

According to the code date on the speakers, the radio is about a '70 model.
It seemed to be common practice,at the time to do it that way in the line operated radios. It could also be used on DC, unless it was a clock radio.

[maxhifi]

Originally Posted by dieseljeep

According to the code date on the speakers, the radio is about a '70 model.
It seemed to be common practice,at the time to do it that way in the line operated radios. It could also be used on DC, unless it was a clock radio.

I was referring to the specific
brown ceramic resistor he used, it looks very American made, and all other components are looking very japanese.

[dieseljeep]

I was going to do a post reply instead of a quote.
I'm aware of what you were referring to!

[maxhifi]

Originally Posted by dieseljeep

I was going to do a post reply instead of a quote.
I'm aware of what you were referring to!

Haha sorry, that makes a bit more sense.

[radiodayz]

How does it play, WA2ISE? Big sound, but I'm assuming not stereo.

[wa2ise]

Originally Posted by radiodayz

Big sound, but I'm assuming not stereo.

No stereo, but it sounds good. Somewhat similar to a tube table radio.

[dieseljeep]

Originally Posted by wa2ise

No stereo, but it sounds good. Somewhat similar to a tube table radio.

I understand the hi-voltage type output transistor is good for about 1.2 watts.
The impedence of the output transformer is about the same as one used with a 50C5.

[wa2ise]

Originally Posted by dieseljeep

... hi-voltage type output transistor is good for about 1.2 watts.
The impedence of the output transformer is about the same as one used with a 50C5.

The "plate" voltage is a little lower, about 95V on the transistor. But an AA5 output transformer and speaker would load it nicely. I've actually done this and it worked well.

[centralradio]

I love the sound on some of these old table radios.I have a Panasonic here from the 1970's and it sounds great.

Line powered.I'm surprised its not a GE.They love eliminating the copper power transformer way before copper prices skyrocketed.

this set could be a good candidate for converting it to FM and AM stereo since it already has the two speakers built in.Or probably not since its line powered.