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Author Topic: $20 score  (Read 9212 times)
AC5UP
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« Reply #15 on: November 11, 2011, 08:07:53 PM »

Here's a working version of the link.......... http://repairbench.com/philco37.aspx

 Grin
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N4NYY
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« Reply #16 on: November 12, 2011, 06:48:49 AM »

I am dying to know how he gets the chassis that polished. I basically use Dremel, steel wool, sandpaper. How does he get the oxidation off of the tuner? Does he use naval jelly?
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AC5UP
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« Reply #17 on: November 12, 2011, 09:38:31 AM »

Next time you have a chassis in need, try some Brasso.

Last summer when I got the Fisher tuner I Brasso'd the tube shields just for grins and the results were much better than expected. It's on an aluminum chassis, which did take a shine, but there's no fix for the dull greyness of the metal. If it were nickel plated it could be dazzling. As it stands right now the chassis is a very clean aluminum grey with bright tube shields that look better than new.

This also means that if someone is doing a full teardown-to-the-chassis rebuild and happens to take a steel chassis to a local plating shop the results could be whatever melts your Kester 44.

In other news, the cleaning continues and I found three power amplifier modules that came out of Rat Shack's parts dump in Foat Wuth in the mid 80's. Probably paid two bucks apiece for them 'cuz they're on a super-heavy heat sink. Anyway, imagine a sink approximately 6" square and 4" deep. Heavy aluminum, deep fins, PC board on one side and one each of 2SK134 and 2SJ49 on the other side. This is a complementary pair of 100 watt Hitachi VMOS FET's in TO-3 packages and completely discontinued.

Did some web crawling last night and was amazed to find these are a hot item among audiophiles. Allegedly the newer versions don't sound as good.  Plenty of schematics for them and NOS originals can still be purchased for a paltry $100 each (average) if you're lucky.

Whoa...........................!

Who Knew?
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N4NYY
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« Reply #18 on: November 12, 2011, 01:56:48 PM »

Can you guess the capacitor value?

Below is what appears to be a piece left over from an exploded Bumble Bee cap.

From left to right, the colors are Yellow, Violet, Orange, Black, blank space, Yellow.

It appears to be 47000 something. I am guess pf.

http://i224.photobucket.com/albums/dd78/yankees_1996/IMG_2078.jpg
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AC5UP
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« Reply #19 on: November 12, 2011, 02:10:21 PM »

If this is accurate: http://classicamplification.net/Guitar/marking%20explanation.jpg

Yours would be 47000 mmf +/- 20% @ 400 vdc. Move the decimal three spaces to the left for Nanofarads and we have 47 nf, another three spaces to the left for Microfarads and it looks like .047 mf. That's a very common value and if you don't have one in the junquebox you're not trying hard enough.

If you have a .05 mf @ 400 vdc on hand use it. 20% tolerance gives you a buttload of slack.

It's the Philco way.  Tongue

BTW: This is the first time I've heard the phrase "bumblebee cap". I think Mallory called them Black Beauties or that may have been Cornell-Dublier. Either way they're 50's tech and it's my understanding they don't age well.
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N4NYY
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« Reply #20 on: November 12, 2011, 02:11:51 PM »

Bumble Bee cap are the black beauties, except for the written value, they use stripes that resemble a bumble bee.

Now, I think that is an audiophile term, and there are many audiophile that buy these pieces of crap as NOS. Those guys are kooks!

BTW, I should have plenty of these, unless I threw them out last week  Roll Eyes Roll Eyes Roll Eyes Roll Eyes Roll Eyes Roll Eyes
« Last Edit: November 12, 2011, 02:13:23 PM by N4NYY » Logged
N4NYY
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« Reply #21 on: November 12, 2011, 04:58:43 PM »

Nelson,

Anyway to measure impedance of the speaker. These damn things cracked at my slightest touch. They are connect to a 220 ohm step down transformer. The schematic does not say.

« Last Edit: November 12, 2011, 05:42:18 PM by N4NYY » Logged
AC5UP
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« Reply #22 on: November 12, 2011, 07:09:27 PM »

Are we talking about the Edsel radio? If so I located the schizmatic on page 124 of Beitman's 1958 most often needed, and you're looking at the 220 Ohm label on the primary of the output transformer... That's the DC reading and what you should see on your Ohmmeter if the transformer has good continuity and isn't shorted.

Note how the schizmatic sez all voltages measured with a 20,000 Ohms / Volt VOM........... NOT A DIGITAL METER! (your voltage readings should be higher)

You can ballpark measure the impedance of any speaker with your Extech. Try it and you should read ~4 Ohms, which would be typical of the 3.2 Ohm speakers that were common at the time. As for the transformer, the audio output tube is a 50C5 which is designed for a 2,500 Ohm load. The transformer should be a 2.5k to 3.2 Ohm impedance (AC) ratio.

A four Ohm speaker is close enough as a replacement part.
« Last Edit: November 12, 2011, 07:34:01 PM by AC5UP » Logged

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N4NYY
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« Reply #23 on: November 12, 2011, 07:19:20 PM »

I did one better. I measured three 8 ohms and three 4 ohm speakers, to see their DC resistance. All measure exactly 4 and 8 ohm. Go figure. Here is a replacement I have found:

http://www.amazon.com/BRS40-Replacement-Individually-Packaged-Clamshell/dp/B001RNNX8K/ref=wl_it_dp_o_npd?ie=UTF8&coliid=I3AL2NXKVMARAJ&colid=24YPLJX9FDJUX

I have to be careful with these damn things. These are so brittle, that they crumble.
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AC5UP
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« Reply #24 on: November 12, 2011, 07:26:05 PM »

Now that I have a schizmatic to look at............ Notice how C6 is a .047 mf jobbie wired across the AC line cord?

That wouldn't happen to be the one that blew apart, would it? Sure would make sense if it was, and the radio got hit with a line surge.  Shocked
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N4NYY
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« Reply #25 on: November 12, 2011, 07:30:13 PM »

Quote
That wouldn't happen to be the one that blew apart, would it? Sure would make sense if it was, and the radio got hit with a line surge.  Shocked

I think it was. One leg went to the AC line. I other leg went somewhere where I did not trace. It literally exploded. Should I replace that with a safety? I used a standard poly film.
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AC5UP
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« Reply #26 on: November 12, 2011, 07:37:09 PM »

Look at the schizmatic.......... Chances are the .047 mf condenser was wired across the line cord with one side on the PC board and the other on the power switch.

I would definitely replace that with a safety cap. The capacitance value isn't critical but the voltage rating should be 250 volts AC or better.
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N4NYY
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« Reply #27 on: November 20, 2011, 05:22:25 PM »

http://www.nostalgiaair.org/PagesByModel/933/M0013933.pdf

Nelson,

I am readying a parts list. Can I go 33uf instead of 25uf in the filter section, without screwing up the B+? They ask for 30/25/20. I can got 33/22. But the 25uf is an odd size, and I would rather go higher then lower. I always though the general rule was staying within 10%.
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AC5UP
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« Reply #28 on: November 20, 2011, 05:51:09 PM »

The 10% relates more to condensers in a tuned circuit like the local oscillator or IF. You can correct for typical part tolerances by alignment. In the case of filter condensers, the values were chosen based on parts price and availability plus what's needed to reduce the AC hum to an acceptable value. Going larger in a set like that does no harm and can reduce the hum a bit while giving the set more margin against the next repair. If a 25 mf condenser starts to hum around 8 mf, so will a 33 mf condenser. But the 33 mf part will take longer to get that weak. The downside of going too large is available mounting space and the risk of damaging a selenium or silicon rectifier with the cold start surge.

That's the long way of saying 33 mf will work OK for any of the three condenser sections and you'll probably use three separate condensers, 150 vdc minimum. If it were mine I'd probably tape them together in a triangle with Scotch 33 or 88 then tie the bundle to the chassis with a Ty-Rap or two.

BTW: I started consolidating my tube stash today. You'd schiz your BVD's if you saw the pile... Probably the first time I've seen them all in the same place at the same time and I'm definitely outnumbered.  Shocked
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N4NYY
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« Reply #29 on: November 20, 2011, 06:04:48 PM »

How did you know I wore BVDs?

Anyway, it appears the cap was replaced at one time, with a 30/30/30, so I will just do 33/33/33.

BTW, there is a dogbone resistor in a white ceramic cradle. According to the schitzmatic, it appears to be a tube saver resistor. Never heard of it. Should it be replaced?
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