Help to identify

[by the way]

Could use some help trying to identify and understand the four parts circled in red. Schematic shows them to be RCA 40428 Diode Temperature Compensating. Im not finding a cross reference to buy them. Thank you.

 

[E-Stat]

They are caps and may be polystyrenes as found higher up in the pic.

 

[cpt_paranoia]

Since it appears to be compensating for the temperature for the power transistor, which is germanium, I would imagine it should be a germanium diode. It's bolted to the device in question for thermal coupling. Probably has to be in a metal, filled package, too.

Early SS amp with transformer coupled stages & germanium transistors. what is it?

 

[by the way]

Since it appears to be compensating for the temperature for the power transistor, which is germanium, I would imagine it should be a germanium diode. It's bolted to the device in question for thermal coupling. Probably has to be in a metal, filled package, too.

Early SS amp with transformer coupled stages & germanium transistors. what is it?

The amp is out of a Seeburg HSC1 home stereo unit. The amp was modified in 1970 with no schematic. The picture refers to another amplifier from a duplicate HSC1 unit that I have. Those 4 pieces are the only thing I need to identify and locate so the amplifier can be restored.

 

[ecluser]

From my old RCA SC-15 manual.

 

[ecluser]

Beware that the maximum reverse voltage is only 0.5V. The datasheet is on two pages, lower part of page 657 and upper part of page 658.

 

[by the way]

Beware that the maximum reverse voltage is only 0.5V. The datasheet is on two pages, lower part of page 657 and upper part of page 658.

Thank you very much! That’s the first information I’ve seen on that part.

 

[by the way]

Thank you very much! That’s the first information I’ve seen on that part.

Do you by chance have a source for that part?

 

[cademan]

If they are not bad, don't replace them. Restore old capacitors, out of spec resistors, but leave any good transistors and diodes alone.

I will almost certainly guarentee that when you try and find obsolete parts that are are hard to find or are no longer made, any found substitutes will not work right or up to spec.

I have an old Sonab of Sweden amplifier booster with a blown transistor and a Boeing engineer could never find an original even direct from Sweden as it was discontinued years ago. He could only find the closest sub but it would never work right after that. I still have it 45 years later hoping that I will come across an original.

 

[by the way]

I agree 100%. Leave good parts alone. Unfortunately for me right now is the amplifier I'm trying to restore is missing these 4 diodes. They are the last piece needed for this project to come together. The picture I posted on this forum is of a second perfectly working amplifier I have from another HSC1 that I own. The amplifier I'm working on was modified some time ago and there isn't a schematic to match that work. I would like to restore it back to original and match the the known working one I have with a schematic. Hopefully someone who reads this post has these parts maybe form a parts amplifier or possibly from stock. Thank you for any help.

 

[cademan]

Maybe it was a factory revision and they were not needed in the one you are restoring.

Did it ever work for you originally?

Hopefully no one before you needed just those diodes. It would be quite a rare possibility.

 

[by the way]

There was an external unit/heat sink that was installed and then the configuration of the amp changed. I bought the console this past December and never turned it on knowing capacitors were over 60 years old and needed replacing. My thoughts were to return this amp to original design which would give me a schematic. But without these diodes, I think I have reached the end of my ability. All my paths to find them are dead ends. I’m truly at a loss on what to do now.

 

[cademan]

Ramp it up slowly on a variac and see if it works. Unless a capacitor is shorted, they usually reform nicely enough to see what you got going there.

 

[ecluser]

These diodes are needed for biasing properly the power transistors. In fact, the bias transistors are biased by the resistors and the diode. Without these diodes the bias will be too high and the transistors will go in thermal runaway. It would be possible to replace the original diodes by another germanium diode and adjust the value of the 22 ohms resistors to have acceptable bias. Another possibility is to replace the diodes and transistors by silicon devices.

 

[by the way]

These diodes are needed for biasing properly the power transistors. In fact, the bias transistors are biased by the resistors and the diode. Without these diodes the bias will be too high and the transistors will go in thermal runaway. It would be possible to replace the original diodes by another germanium diode and adjust the value of the 22 ohms resistors to have acceptable bias. Another possibility is to replace the diodes and transistors by silicon devices.

Very interesting. Thank you very much. I do have some options apparently.

 

[cademan]

These diodes are needed for biasing properly the power transistors. In fact, the bias transistors are biased by the resistors and the diode. Without these diodes the bias will be too high and the transistors will go in thermal runaway. It would be possible to replace the original diodes by another germanium diode and adjust the value of the 22 ohms resistors to have acceptable bias. Another possibility is to replace the diodes and transistors by silicon devices.

But then why would anyone steal just those specific diodes? Unless a rare event in which the previous owner needed them for a HSC that he had.

 

[by the way]

But then why would anyone steal just those specific diodes? Unless a rare event in which the previous owner needed them for a HSC that he had.

The amp was modified back in 1970 according to sticker on amp.
The first picture shows the heat sink added and everything else associated with it disconnected in amp.
The second picture shows 56uf electrolytic’s circled in red where .1 capacitors use to be, plus some other changes in the same area.

 

[cademan]

Okay, so if it was modified, didn't it work? Is this the one you were afraid to plug in due to old capacitors? I think we're getting sketchy info here on both units.

One you are restoring, the other was missing the diodes but was modified in the 70's so shouldn't the modified one also work

 

[by the way]

Okay, so if it was modified, didn't it work?

I bought this unit in December 2022. I never plugged it in until replacing caps. The previous owner said it played but it had a slight buzz and hum. After recapping, the buzz and hum he talked about is still there. It does work and sounds pretty good, but I would like to locate the cause of the noise.

 

[cademan]

I bought this unit in December 2022. I never plugged it in until replacing caps. The previous owner said it played but it had a slight buzz and hum. After recapping, the buzz and hum he talked about is still there. It does work and sounds pretty good, but I would like to locate the cause of the noise.

So is this the one with or without the diodes?