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tubeguy@myshop.com: Dec 02 12:30AM -0600 How do you test a Selenium Rectifier?   Yes, I am aware that they should be replaced, but on preliminary tests of this 1956 Zenith tube AM-FM Radio, I want to know if it's working. My digital multimeter shows 1meg in one direction, 2.5 meg the other way. NOT DISCONNECTED FROM THE CIRCUIT. To me, that seems bad, but I have not worked with one of these in many years, and never had to replace one in the old days. My meter was climbing, probably from the filter caps. during this test.

Fox's Mercantile <jdangus@att.net>: Dec 02 01:26AM -0600 > worked with one of these in many years, and never had to replace one in > the old days. My meter was climbing, probably from the filter caps. > during this test.   A DMM won't read correctly. No enough voltage compliance on the current source to read ohms correctly. Just replace it with a 1N4007 diode and about 100 ohms series resistor.     -- "I am a river to my people." Jeff-1.0 WA6FWi http:foxsmercantile.com

tabbypurr@gmail.com: Dec 02 12:53AM -0800 > worked with one of these in many years, and never had to replace one in > the old days. My meter was climbing, probably from the filter caps. > during this test.   Selenium stacks have high Vf & high reverse leakage. DMMs don't apply enough voltage. Probably the simplest way to test is to power it up. They fail by Vf increasing, causing overheating & lots of toxic selenium fumes, so best not tested indoors.   Replacement is probably a wise option. But add a resistor & fuse, seleniums act as current limits. There are lots of old scopes still running with selenium EHT rectifiers in them.     NT

Cursitor Doom <curd@notformail.com>: Dec 02 10:57AM On Sun, 02 Dec 2018 01:26:41 -0600, Fox's Mercantile wrote:   > A DMM won't read correctly. No enough voltage compliance on the current > source to read ohms correctly.   True, but it *might* give some rough indication, like if the thing has somehow shorted out. I have a few of those lying around somewhere; I'll measure 'em with a DVM just out of curiosity and see if I get readings like those reported by tabbs.     > Just replace it with a 1N4007 diode and about 100 ohms series resistor.   Not kosher if you want to keep the internals original! Many collectors are extremely fussy about that.       -- This message may be freely reproduced without limit or charge only via the Usenet protocol. Reproduction in whole or part through other protocols, whether for profit or not, is conditional upon a charge of GBP10.00 per reproduction. Publication in this manner via non-Usenet protocols constitutes acceptance of this condition.

tabbypurr@gmail.com: Dec 02 05:03AM -0800 On Sunday, 2 December 2018 10:57:10 UTC, Cursitor Doom wrote:   > > Just replace it with a 1N4007 diode and about 100 ohms series resistor.   > Not kosher if you want to keep the internals original! Many collectors > are extremely fussy about that.   I replaced some parts on my 1934 set, but you'd never know by looking inside. The new parts are inside the old, which are repacked exactly as original. With selenium you could possible hide the diode somewhere not noticeable, keeping the selenium in place.     NT

Adrian Caspersz <email@here.invalid>: Dec 02 01:27PM > I replaced some parts on my 1934 set, but you'd never know by looking inside. The new parts are inside the old, which are repacked exactly as original. With selenium you could possible hide the diode somewhere not noticeable, keeping the selenium in place.   To maintain the authentic smell?   -- Adrian C

Ralph Mowery <rmowery28146@earthlink.net>: Dec 02 10:12AM -0500 In article <80v60e9fe9680kjb2aj25gn3kvol2m36ma@4ax.com>, tubeguy@myshop.com says... > worked with one of these in many years, and never had to replace one in > the old days. My meter was climbing, probably from the filter caps. > during this test.   The same way as with any other diode. However the selenium drop about a volt for each plate that is on it. Each plate is only good for about 25 volts , so you may have 5 to 10 volts to overcome. Therefore most meters will not have enough voltage to over come that drop.     Get a voltage source of around 10 volts or more (maybe even a 9 volt battery will be enough) use your meter on the voltage scale and put hte battery , diode , voltmeter in series. Then turn the voltage or diode around and measure again. There should be a couple of volts dropped one way and many more (almost all) the other.

Cursitor Doom <curd@notformail.com>: Dec 02 04:15PM On Sun, 02 Dec 2018 05:03:03 -0800, tabbypurr wrote:   > inside. The new parts are inside the old, which are repacked exactly as > original. With selenium you could possible hide the diode somewhere not > noticeable, keeping the selenium in place.   Yes, I'm aware of this practice, but for some super-fussy types, it's still not good enough.         -- This message may be freely reproduced without limit or charge only via the Usenet protocol. Reproduction in whole or part through other protocols, whether for profit or not, is conditional upon a charge of GBP10.00 per reproduction. Publication in this manner via non-Usenet protocols constitutes acceptance of this condition.

Cursitor Doom <curd@notformail.com>: Dec 02 04:17PM On Sun, 02 Dec 2018 10:12:01 -0500, Ralph Mowery wrote:   > battery , diode , voltmeter in series. Then turn the voltage or diode > around and measure again. There should be a couple of volts dropped one > way and many more (almost all) the other.   +1

etpm@whidbey.com: Dec 01 12:47PM -0800 To All, I need to power an amp that draws just under 1.5 amps at 110 volts. I measured the current it draws when powered from my variac. The voltage to the amp should be within 5% according to the documentation. The voltage in my house measures 122 volts to 126 volts, varying during the day. So bucking 12 volts should be fine. I am looking at a 120 volt to 12 volt center tapped 5 amp rated xmfr at PartsExpress. The VA of the xmfr is not listed in the description. I want to connect this xmfr in buck configuration. Since I will be bucking 12 volts at approx 1.5 amps this equals 18 VA. At least that's how I remember how to calculate VA from connecting big buck xmfrs to one of my machines several years ago. I think the 12 volts at 5 amps secondary means that the xmfr is 60 VA. But I'm not sure because it is center tapped. It shouldn't make any difference, right? If I used the center tap and just bucked 6 volts then the VA rating would be 30, wouldn't it? Thanks, Eric

Fox's Mercantile <jdangus@att.net>: Dec 01 05:36PM -0600 > I am looking at a 120 volt to 12 volt center tapped 5 amp rated > xmfr at PartsExpress.   The only thing that matters is the amp rating of the secondary. Equal or greater than the load.     -- "I am a river to my people." Jeff-1.0 WA6FWi http:foxsmercantile.com

Phil Allison <pallison49@gmail.com>: Dec 01 05:10PM -0800 > sure because it is center tapped. It shouldn't make any difference, > right? If I used the center tap and just bucked 6 volts then the VA > rating would be 30, wouldn't it?   ** You need to buck 1.5 amps and you have a tranny rated to do 5 amps.   Whether you use the whole or only half the 12V secondary is up to you.       .... Phil

Tom Biasi <tombiasi@optonline.net>: Dec 01 08:45PM -0500 > rating would be 30, wouldn't it? > Thanks, > Eric   If all the 110 volts does is make DC why can't you just clamp the DC?

John-Del <ohger1s@gmail.com>: Dec 01 07:27PM -0800 On Saturday, December 1, 2018 at 8:45:43 PM UTC-5, Tom Biasi wrote: > > Thanks, > > Eric   > If all the 110 volts does is make DC why can't you just clamp the DC?       What if it's a tube amp?   It's still easier to add a buck transformer than add a regulator circuit (not a great idea to "clamp" the DC).

Tom Biasi <tombiasi@optonline.net>: Dec 01 10:46PM -0500 On 12/1/2018 10:27 PM, John-Del wrote:   >> If all the 110 volts does is make DC why can't you just clamp the DC?   > What if it's a tube amp?   > It's still easier to add a buck transformer than add a regulator circuit (not a great idea to "clamp" the DC).   I didn't think a tube amp would be so fussy about the supply voltage.

Ralph Mowery <rmowery28146@earthlink.net>: Dec 01 11:38PM -0500 In article <ptvkht$17j5$1@gioia.aioe.org>, tombiasi@optonline.net says...   > > What if it's a tube amp?   > > It's still easier to add a buck transformer than add a regulator circuit (not a great idea to "clamp" the DC).   > I didn't think a tube amp would be so fussy about the supply voltage.   They are probably more fussy about the supply voltages. The filiments of the tubes burn out faster if the voltage is too high.

Tom Biasi <tombiasi@optonline.net>: Dec 01 11:55PM -0500 On 12/1/2018 11:38 PM, Ralph Mowery wrote:   >> I didn't think a tube amp would be so fussy about the supply voltage.   > They are probably more fussy about the supply voltages. The filiments > of the tubes burn out faster if the voltage is too high.   That's why most refurb guys put zeners across the filaments.

tabbypurr@gmail.com: Dec 02 12:55AM -0800 On Sunday, 2 December 2018 04:55:52 UTC, Tom Biasi wrote:   > > They are probably more fussy about the supply voltages. The filiments > > of the tubes burn out faster if the voltage is too high.   > That's why most refurb guys put zeners across the filaments.   surely that would overheat the transformer if they go into conduction. Also it does not prevent Vf rising too far, only reduces the rms rise.     NT

Tom Biasi <tombiasi@optonline.net>: Dec 02 10:17AM -0500 >> That's why most refurb guys put zeners across the filaments.   > surely that would overheat the transformer if they go into conduction. Also it does not prevent Vf rising too far, only reduces the rms rise.   > NT   Well its been done for quite some time. I would like to know the name of this product that specifies this voltage.

John-Del <ohger1s@gmail.com>: Dec 02 08:09AM -0800 On Saturday, December 1, 2018 at 11:55:52 PM UTC-5, Tom Biasi wrote:   > > They are probably more fussy about the supply voltages. The filiments > > of the tubes burn out faster if the voltage is too high.   > That's why most refurb guys put zeners across the filaments.     Zeners are a neat trick but I never liked using them in high current situations where a failure causes collateral damage. Consumer electronic designers fell in love with them in the 70s and 80s where they caused all kinds of mischief. I'll use them as high impedance voltage reference where they handle no appreciable current and I've also used them as crowbars following a fuse or low value resistor as a safety.

Lucifer <LuciferMorningstar@bigpond.com>: Dec 02 04:38PM +1100 I suppose an amateur radio group would be better but they are very quiet.   The mechanical tuning dial works as it should but the radio won't tune above .783 in each band. I haven't had the cover off yet but I'm thinking the VFO variable capacitor is being prevented from full movement.

Fox's Mercantile <jdangus@att.net>: Dec 02 01:31AM -0600 On 12/1/18 11:38 PM, Lucifer wrote: > won't tune above .783 in each band. I haven't had the cover > off yet but I'm thinking the VFO variable capacitor is being > prevented from full movement.   There isn't a VFO capacitor. The radio uses phase locked loops. Operating manual: <http://www.radiomanual.info/schemi/YAESU_RX/FRG-7700_user.pdf> Service manual: <http://www.radiomanual.info/schemi/YAESU_RX/FRG-7700_serv.pdf>     -- "I am a river to my people." Jeff-1.0 WA6FWi http:foxsmercantile.com

Lucifer <LuciferMorningstar@bigpond.com>: Dec 02 10:35PM +1100 On Sun, 2 Dec 2018 01:31:27 -0600, Fox's Mercantile <jdangus@att.net> wrote:   >> off yet but I'm thinking the VFO variable capacitor is being >> prevented from full movement.   >There isn't a VFO capacitor. The radio uses phase locked loops.   Thank you for your reply and the manual links, however you are wrong about the VFO capacitor. It uses the PLL to select the band and the VFO to tune within the band. The Kenwood R-1000 works the same way.

"~misfit~" <shaun.at.pukekohe@gmail.com>: Dec 02 09:53PM +1300 > is quite thermally conductive and does not have a tendency to crack > until you break it off. If it is in the chip you might get away with > putting a fan right on it.   Or you can get a PCIe - SATA card..... -- Shaun.   "Humans will have advanced a long, long way when religious belief has a cozy little classification in the DSM*." David Melville (in r.a.s.f1) (*Diagnostic and Statistical Manual of Mental Disorders)

tubeguy@myshop.com: Dec 02 12:30AM -0600 Anyone know where to find a Crosley Model 23 Dial Cord diagram? The cord is mostly gone, so I cant just duplicate the olds one ....   Dial cord replacement is NOT my favorite part of radio restoration..... But it's got to be done...... This oldie has a beautiful wooden cabinet in fair shape. I will be applying some new finish to to the cabinet. The radio works but hums, new filter caps are ordered. The only other broken item is the power switch on the rear of the volume pot, was fried, and left a burn mark on the chassis (before I got the radio). I doubt I will find one, so I will likely just use an inline power cord switch.   This is a 1941 radio. Google found me a schematic but not a dial cord diagram.   Just for grins, how does a person find a replacement pot switch that will fit?

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