Old Tube Equipment Turnon - Page 4

Victoria · 1st March 2006, 10:02 PM

I can still barely get FM stereo audio outout at full volume--barely hear it.
After looking at the bases of the three multi cap cans, it would appear that they never have been changed. (Probably also true of the coupling caps and the selenium rectifier).
So I have two more questions:
(1)Could a problem with any of these lead to the current situation? and
(2)Is there a way to check them to see if they are in bad?

Thanks again, Vic

anatech · 1st March 2006, 10:07 PM

Hey Vic,
Selenium rectifiers are just problems waiting to happen, if they already haven't gone defective.

What circuit is it in? If bias, just use 1N4006 or 1N4007 (I just buy 1N4007's, they are about the same price as the lowest ones). If they are for heaters, figure out what the current draw is and use a resistor to drop some voltage. They did this in my 400C control amp.

Don't check, just change. They will get you if you leave them in.

-Chris

rickl · 2nd March 2006, 04:48 AM

Quote:

Originally posted by Victoria

So I have two more questions:
(1)Could a problem with any of these lead to the current situation? and
(2)Is there a way to check them to see if they are in bad?

Thanks again, Vic

Get a schematic and start checking voltages at the pins. I know when I was debugging my Fisher tuner I just started checking and comparing with what was listed on the schematic. The problem I had was the final 'rootbeer barrel' caps were leaky and passing DC.

I wouldn't replace the PS cans until you know they are bad. Weak output isn't a ps problem. Hum, yes but not low output.

BTW, I have never seen a 500C let alone worked on one so there maybe something I'm missing.

Fisher 500C Schematic

rick

sklimek · 2nd March 2006, 06:53 AM

Quote:

Originally posted by anatech
Hey Vic,
Selenium rectifiers are just problems waiting to happen, if they already haven't gone defective.

What circuit is it in? If bias, just use 1N4006 or 1N4007 (I just buy 1N4007's, they are about the same price as the lowest ones). If they are for heaters, figure out what the current draw is and use a resistor to drop some voltage. They did this in my 400C control amp.

Don't check, just change. They will get you if you leave them in.

-Chris

Hi, I'm in the process of fixing a HP 410B that I got for nothing and one of the things everyone was saying is 'get rid of the selenium rectifier' I found a good article from Antique Radio that suggests replacing the selenium rec w/ just as you mentioned a 1N4007 and add a 2 ohm resistor in series with it to compensate for the added efficiency of the silicon diode. A small terminal strip will make thing easier. Another recomendation was to get rid of the Black Beauty caps as well. Sorry for the bad scan but maybe it will help.

Stan

anatech · 2nd March 2006, 01:46 PM

Hey Stan,
You're a lucky fella. HP stuff is great!

The scan is rough, but it illustrates things well.

Sometimes you need to play with the resistor value to get the expected voltage right. That is the correct idea, and yes, I try to use terminal strips as the dropping resistor can get warm.

-Chris

Victoria · 3rd March 2006, 06:58 PM

I have temporarily set the 500C aside and am currently looking at the Dynaco ST-70. But the very top of the 5AR4 tube is milky colored, not silver. Is that an indication that I shouldn't go any farther before I replace it. Or is that normal and I should proceed. I don't have a tube tester. Thanks, Vic

anatech · 3rd March 2006, 07:07 PM

Hey Vic,
The vacuum is gone in that tube. Careful as the glass may cut your hand if you pull it. Handle by the base only.

-Chris

tomtt · 3rd March 2006, 07:25 PM

david hafler remains a hero(rhymes with keros) for

many pepole however,

the transformers in the sansui are of much better quality

http://www.tube-amps.net/index.htm

Victoria · 3rd March 2006, 08:03 PM

Anatech
Thanks for the info and the alert!

tomtt,
I hear you and appreciate your help. I read about Hasimoto after your first comment about the 1000A. Is the site you linked to yours?

Thanks again guys, Vic

anatech · 4th March 2006, 12:57 AM

Hi tomtt,
I'm sitting here looking at a Sansui AU-111 (second version, original run). Should I pull the power and output transformers out of it and build a proper amp?

-Chris

3rd March 2006, 06:58 PM	#36
Victoria diyAudio Member Join Date: Jan 2006 Location: SF Bay area	Tube Condition I have temporarily set the 500C aside and am currently looking at the Dynaco ST-70. But the very top of the 5AR4 tube is milky colored, not silver. Is that an indication that I shouldn't go any farther before I replace it. Or is that normal and I should proceed. I don't have a tube tester. Thanks, Vic

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1st March 2006, 10:02 PM	#31
Victoria diyAudio Member Join Date: Jan 2006 Location: SF Bay area	I can still barely get FM stereo audio outout at full volume--barely hear it. After looking at the bases of the three multi cap cans, it would appear that they never have been changed. (Probably also true of the coupling caps and the selenium rectifier). So I have two more questions: (1)Could a problem with any of these lead to the current situation? and (2)Is there a way to check them to see if they are in bad? Thanks again, Vic

1st March 2006, 10:07 PM	#32
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hey Vic, Selenium rectifiers are just problems waiting to happen, if they already haven't gone defective. What circuit is it in? If bias, just use 1N4006 or 1N4007 (I just buy 1N4007's, they are about the same price as the lowest ones). If they are for heaters, figure out what the current draw is and use a resistor to drop some voltage. They did this in my 400C control amp. Don't check, just change. They will get you if you leave them in. -Chris

2nd March 2006, 01:46 PM	#35
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hey Stan, You're a lucky fella. HP stuff is great! The scan is rough, but it illustrates things well. Sometimes you need to play with the resistor value to get the expected voltage right. That is the correct idea, and yes, I try to use terminal strips as the dropping resistor can get warm. -Chris

3rd March 2006, 07:07 PM	#37
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hey Vic, The vacuum is gone in that tube. Careful as the glass may cut your hand if you pull it. Handle by the base only. -Chris

3rd March 2006, 07:25 PM	#38
tomtt diyAudio Member Join Date: Aug 2002 Location: kansas city mo, and on occasion, around the world ... Blog Entries: 15	david hafler remains a hero(rhymes with keros) for many pepole however, the transformers in the sansui are of much better quality http://www.tube-amps.net/index.htm

3rd March 2006, 08:03 PM	#39
Victoria diyAudio Member Join Date: Jan 2006 Location: SF Bay area	Anatech Thanks for the info and the alert! tomtt, I hear you and appreciate your help. I read about Hasimoto after your first comment about the 1000A. Is the site you linked to yours? Thanks again guys, Vic

4th March 2006, 12:57 AM	#40
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi tomtt, I'm sitting here looking at a Sansui AU-111 (second version, original run). Should I pull the power and output transformers out of it and build a proper amp? -Chris

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