Looking at the schematic, the problem part is the voltage regulator. While substitutes will not be a pin-for-pin substitute, there are many regulators that...
Check this: http://nte01.nteinc.com/nte/NTExRefSemiProd.nsf/69d5aa3584d015ce85256e780056e56f?CreateDocument It may be impossible to locate the original part....
Everyone, I have a few of the 78MGT4 parts on hand. I have in the past had many of the MFC6030 parts. I was thinking recently that I should ask if there is...
Mark me down as interestd in gettin a set. also looking for a pwr supply, voltage and current regulated, 15v 5 amp would be fine. May have to build one, and...
Hello everyone. I have a question on the specific diode folks use to protect the meter in the SB200 amp. I read a post where the person used 1N5408 diodes. ...
I've got an old VTVM (RCA Voltohmist Jr) that uses the old selenium (?) diode that looks sort of like an old radiator. I would think that I could simply...
Just use 1N4007's. Normally the failure mode of the selenium was to open up so many shops simply soldered the silicon replacements across the Selenium Diodes...
I have the same unit, and have just been using it for years without opening it up. I would be interested in how this thread resolves. (I think I have heard...
In a message dated 03/02/2011 15:56:36 GMT Standard Time, jblair1948@... writes: I've got an old VTVM (RCA Voltohmist Jr) that uses the old selenium (?) ...
In a message dated 03/02/2011 15:56:36 GMT Standard Time, jblair1948@... writes: I've got an old VTVM (RCA Voltohmist Jr) that uses the old selenium (?) ...
... Selenium rectifiers have a higher forward voltage drop under load (on the order of volts) compared to silicon (0.7 volts nominal). They also have a higher...
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Mike McCarty
Mike.McCarty@...
Feb 3, 2011 5:05 pm
... Yes, that's a Se rectifier. ... You don't need that much current capacity. Those old Se used in VTVMs were good for 50 mA or so. You need a PIV greater...
Selenium rectifiers! Wow that brings back antique memories. I'd think a 1N4004 would do just fine as a replacement. Bob K5ZOL ________________________________ ...
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Mike McCarty
Mike.McCarty@...
Feb 3, 2011 5:06 pm
... Se rectifiers are less efficient than Si. It is common to put a 47 ohm 1 W resistor in series with a Se rectifier for two reasons. One is to reduce the B+...
19561
Mike McCarty
Mike.McCarty@...
Feb 3, 2011 5:09 pm
George F. Nemeyer wrote: [...] ... Those copper oxide rectifiers were used only in very early equipment, and not in VTVMs ever AFAIK. Certainly, the VoltOhmyst...
... They're often *inside* the meter movement case if it's an AC-only measuring movement. They'd be outside if the meter itself was used for multiple...
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Mike McCarty
Mike.McCarty@...
Feb 3, 2011 6:01 pm
... Yes, that's true. I wasn't arguing with you, only providing additional information. I agree fully with your assessment. I chose the words "some success"...
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Mike McCarty
Mike.McCarty@...
Feb 3, 2011 6:14 pm
Still under revision, but mostly complete. ... Steps to First Power On *** C A U T I O N *** The high voltages associated with the older tube type equipment...
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Mike McCarty
Mike.McCarty@...
Feb 3, 2011 6:18 pm
Still in flux and perhaps a little rough, but usable, I think. I solicit comments. ... Ok, now we have a working power supply. However, it still isn't time to ...
I have a HW-2036A that has been stored for years. I put it back on the air and it receives great but no transmit. I think there my be a loose wire due to my...
Excellent, Mike. Both Parts I and II. Thanks, Alan, KD5R ... From: Mike McCarty To: heathkit@yahoogroups.com Sent: Thursday, February 03, 2011 12:18 PM ...
I am retiring in 3 weeks and have a bunch of boat anchors to restore. This is very helpful....Many thanks, Bob K5ZOL ________________________________ From:...
Yes, you can and likely should replace a selenium with a silicon diode. You should also include a dropping resistor of sufficient wattage to make up for the...
The selenium rectifier has more resistance, and thus more voltage drop across it. By adding a dropping resistor of sufficient size you install the diode you...
... versions so far which ... Bob, The only markings on the unit is WV-77E then an ink stamp looks like 78631 which I suppose is a serial number. I removed the...
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Mike McCarty
Mike.McCarty@...
Feb 3, 2011 9:13 pm
... BAMA has full information on that VTVM. I have a few of them myself. ... It is possible to rig up an LM317 to run off the heater supply and do away with...
