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 Post subject: Need assistance with circuit
PostPosted: Feb Sat 03, 2018 10:35 pm 
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Joined: Jan Mon 16, 2017 3:08 am
Posts: 212
Location: Boise, Idaho
At this point in my project I have reduced the bad voltages on the tubes from 68 to about 17 but am stuck right now.

V13 is supposed to have 245 volts to pin 2 but I have zero. Looking at the enclosed, the line that goes to left through the 150k resistors shown vertically goes back to a relay that receives power on transmit, not receive. That leaves only the circuit on the right from pin 2. Pin 1 should be 0, and has 0.

I have included the overall schematic in 3 page format and (iteration 12) of my spreadsheet of tube voltages. Sorry I cant a copy I have with circuits traced out in color to a file size the site will accept. There is a definite problem with the IF circuit if you look at it. One symptom is with RF gain at max I get noise and drops off sharply at 10 o'clock. At 12 o'clock noise is low enough to turn AF gain to max. If I tap on the chassis I hear the tapping through the speaker. That leads me to believe there is either a wire going to ground that should not be or a wire simply going to the wrong location. I have found more than a few of those. Last one being V8 pins 4 and 5 were reversed, who knows why.

Anyway..thanks for looking and hopefully someone can help me understand figure out why there is 0 voltage to v13 pin 2.

Oops, forgot tube voltage pdf.


Attachments:
v13.pdf [185.66 KiB]
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pg1.pdf [90.41 KiB]
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pg2.pdf [108.96 KiB]
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pg3.pdf [102.73 KiB]
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current Tube Voltage Checks.pdf [3.81 KiB]
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 Post subject: Re: Need assistance with circuit
PostPosted: Feb Sat 03, 2018 10:52 pm 
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Joined: Sep Thu 01, 2016 3:56 am
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Location: San Jose, Ca.
Hi Gibson, Is the bypass cap on pin 2 leaking or shorted? Is the tube shorted internally? Is the tube socket ok? Does R1303 have voltage on the relay side? Try pulling the tube and measuring voltage on the socket.

Regards, Larry


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 Post subject: Re: Need assistance with circuit
PostPosted: Feb Sat 03, 2018 10:58 pm 
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Location: Hudson, MA
It looks like you should get 215V on pin 2 of V13 (from pin 10 of K1 )
Is C1301 shorted to gnd
Does R1303 measure 150k ohm

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 Post subject: Re: Need assistance with circuit
PostPosted: Feb Sat 03, 2018 11:01 pm 
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Is the T/R relay actually switching to transmit? Have you measured the 150K resistor to make sure that it is intact? If the relay is switching and the resistor is intact then I suspect you have a broken wire or bad relay contact. With the power off check for 150K measuring from the tube pin contact back to the relay base.

Swan shows a bit of a voltage discrepancy since they are showing that fed from a 215 volt source but since you are measuring 225 volts on pins also fed from a 215 volt source I suspect that is a "strong" 215 volt source :) Once you find the problem you will have about 225 volts on pin 4 I suspect.

Rodger WQ9E


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 Post subject: Re: Need assistance with circuit
PostPosted: Feb Sun 04, 2018 12:30 am 
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Joined: Jan Mon 16, 2017 3:08 am
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Location: Boise, Idaho
Lar H wrote:
Hi Gibson, Is the bypass cap on pin 2 leaking or shorted? Is the tube shorted internally? Is the tube socket ok? Does R1303 have voltage on the relay side? Try pulling the tube and measuring voltage on the socket.

Regards, Larry


Hi Larry,

C3101 and 1303 did no show sings of leakage up to 500 volts, maxing out my tester. They have been replaced anyway since I had them out.

Checking tube for shorts in tester...no shorts. It is a new tube and even tried another tube. Voltage is still zero with tubed pulled

R1303 is not supposed to have voltage on it in R (receive). It goes back to pin 6 on the relay. Its a direct wire connection, no stopping along the way. Voltage on pin two, is 249.

Tube socket....hmmm. Not sure what I would be looking for other than tight pins and being clean.


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 Post subject: Re: Need assistance with circuit
PostPosted: Feb Sun 04, 2018 12:39 am 
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Joined: Jan Mon 16, 2017 3:08 am
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Location: Boise, Idaho
Eddy wrote:
It looks like you should get 215V on pin 2 of V13 (from pin 10 of K1 )
Is C1301 shorted to gnd
Does R1303 measure 150k ohm


I know its hard to tell in a 3 part schematic, but it gets voltage from K1 pin 10 via pins 6, but only in transmit. Otherwise voltage from pin 10 is on pin 2 with goes to screens on V6 and v7.

C1301 is grounded, yes, to same point as pin 1 ground.

Yes R103 measures 150. Brand new, checked again anyway.


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 Post subject: Re: Need assistance with circuit
PostPosted: Feb Sun 04, 2018 1:00 am 
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Joined: Jan Mon 16, 2017 3:08 am
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Location: Boise, Idaho
rsingl wrote:
Is the T/R relay actually switching to transmit? Have you measured the 150K resistor to make sure that it is intact? If the relay is switching and the resistor is intact then I suspect you have a broken wire or bad relay contact. With the power off check for 150K measuring from the tube pin contact back to the relay base.

Swan shows a bit of a voltage discrepancy since they are showing that fed from a 215 volt source but since you are measuring 225 volts on pins also fed from a 215 volt source I suspect that is a "strong" 215 volt source :) Once you find the problem you will have about 225 volts on pin 4 I suspect.

Rodger WQ9E


The TR relay switches, when called upon. The 150k resistor measures 150. I was going to replace it the other night but did not have one. I picked up a pack today so I suppose I could put another new one in. From tube to (solder connection) to pin 2 K1 is exactly 150 ohms..

That is not my problem though....v13 pin 2 does not get voltage from K1 at all except in transmit, and then it is only 85 volts. Right now it gets 70, but I am thinking it will come up once I get this to a point where an alignment and PA adjust can be done. I am not there yet, checking transmit voltages. I am still trying to get receive voltages in line. Per my tube voltage chart a crap load are more than 50% out of tolerance still.

On pin 4 I have 225 volts, its pin 2 (v13) that is the problem. I don't see how it gets 245, maybe 215 per the schematic but that is a moot point right now. I get zero. I asked a buddy to measure his 350 and he told me that he is getting around 225-230 on pin 2. His 350 works...my does not. LOL

And you are right, my 215 volt circuit is high at 249. I need to dig through the box and see if I have another 750 ohm 10watt. It ohms right 750 ok, but the voltage out is not right, even though voltage into it is spot on at 275.


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 Post subject: Re: Need assistance with circuit
PostPosted: Feb Sun 04, 2018 1:56 am 
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Pin 2 should be zero volts during receive, that is why its voltage is switched via the T/R relay. The 245 volts is a misprint in the manual. I didn't realize you were trying to measure pin 2 voltage in the receive position which is why I asked whether the T/R relay was actually working.

The 150K resistor will drop the 215 volt source voltage to around 85 volts during transmit.

Rodger WQ9E


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 Post subject: Re: Need assistance with circuit
PostPosted: Feb Sun 04, 2018 2:55 am 
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Joined: Jan Mon 16, 2017 3:08 am
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Location: Boise, Idaho
rsingl wrote:
Pin 2 should be zero volts during receive, that is why its voltage is switched via the T/R relay. The 245 volts is a misprint in the manual. I didn't realize you were trying to measure pin 2 voltage in the receive position which is why I asked whether the T/R relay was actually working.

The 150K resistor will drop the 215 volt source voltage to around 85 volts during transmit.

Rodger WQ9E


Darn it.....I would have sworn on my life I included "in receive" in my OP. I was sure thinking it though. There is no way to get even 215 to pin 2 because it has to to go through the 100 and 47k and C1301 shunts to ground. My buddy swears he is getting 230 on pin 2. I think he is wrong.

I pulled the 750 ohm 10 watt out and measured again. 739 ohms, within spec for sure. The only other 750 ohm I have measures 719.

I know there is one more crossed wire somewhere that is making my grid circuit go sideways. At this point I don't know if I did it or the other guy did and that's why he dumped the radio.

I want to ask this again:

With the RF gain at max I get noise and drops off sharply at 10 o'clock as I turn it down. Note that voltage drop is smooth as measured at the pot and V6 pin 2. As I turn gain down, at 12 o'clock position the noise is low enough to turn AF gain to max. In fact, if I don't turn up the AF gain I hear nothing. At this point if I tap on the chassis I hear the tapping through the speaker as if the chassis is a microphone. Does this sound like an issue of something going to ground when it should not, or something not getting a good ground? Or not ground related at all?


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 Post subject: Re: Need assistance with circuit
PostPosted: Feb Sun 04, 2018 3:03 am 
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The noise you hear from tapping is most likely a microphonic tube and some tubes that will work fine are slightly microphonic under unusual conditions. If it is OK with the RF gain at normal I wouldn't worry about it because it is VERY rare that you will have any reason to reduce the RF gain control. The AGC takes care of reducing gain with strong signals and for most applications with modern gear the only reason to run the gain control lower would be to set it where band noise is no longer audible but I have never cared for this type of operation.

When you run your AF gain at max with no background signal any slightly microphonic tube in the latter stages of the receiver is going to show up making noise but unless it is noticeable in normal operation I wouldn't worry. Microphonic tubes (or other microphonic parts) are best found by lightly tapping with an insulated object (like a cheap ball point pen).

And if your buddy is really getting high voltage on pin 2 of V13 in receive mode he is unfortunately in need of a new 7360 tube because his has an internal short :(

Rodger WQ9E


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 Post subject: Re: Need assistance with circuit
PostPosted: Feb Sun 04, 2018 3:46 am 
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Gibson wrote:
The TR relay switches, when called upon. The 150k resistor measures 150. I was going to replace it the other night but did not have one. I picked up a pack today so I suppose I could put another new one in. From tube to (solder connection) to pin 2 K1 is exactly 150 ohms..



Are you saying the 150k Ohm resistor measures 150 Ohms and not 150k Ohms?

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 Post subject: Re: Need assistance with circuit
PostPosted: Feb Sun 04, 2018 3:59 am 
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Joined: Jan Mon 16, 2017 3:08 am
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Location: Boise, Idaho
It measures 150k, sorry, lazy typing.


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 Post subject: Re: Need assistance with circuit
PostPosted: Feb Sun 04, 2018 4:05 am 
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Joined: Jan Mon 16, 2017 3:08 am
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Location: Boise, Idaho
Thanks for the information, Roger. I can now green out one more cell in my chart.

The micro-phonics is good to know. I will then turn my attention back to my remaining voltage issues.


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 Post subject: Re: Need assistance with circuit
PostPosted: Feb Sun 04, 2018 4:22 am 
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Grab the early Swan 500 manual because there are a lot of similarities between the 350 and the more deluxe 500 which came out slightly later and I see the voltage chart is corrected for V13 in the 500 manual. Note that there ARE differences but if you find confusing data for one radio sometimes looking at a later version will provide enough information to clarify the situation.

http://bama.edebris.com/download/swan/500/500.pdf

Note that the 350 and 500 had numerous updates over their long production life so don't be surprised to find changes in the circuitry made by the manufacturer that differ from the schematic or modifications made by the owner often to try to imitate changes made by the manufacturer in later production.

There is also a big PDF of Swan stuff on the web and it contains some user created modifications that may shed light on changes in your 350: http://www.w0btu.com/files/misc/Swan_Co ... m_Rev4.pdf

Rodger WQ9E


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 Post subject: Re: Need assistance with circuit
PostPosted: Feb Sun 04, 2018 5:09 pm 
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Joined: Jan Mon 16, 2017 3:08 am
Posts: 212
Location: Boise, Idaho
One would think that Swan would have corrected voltage errors in their charts over the course of years of production. Even the white face 350's showed 245 volts on pin 2, that spans several years of error. That is not the only error in the chart either.

Based on my serial number I know my radio was manufactured in November of 1968. Just a coincidence that is when Swan issued the one and only schematic with a date on it, as I posted.

This radio has had several mods done to it. Some were done correctly, others I have no idea what they were doing or why and some were simply wrong and reversed voltages. PITA.

Your link does not work, but looking a the Rev4 in the title leads me to believe it is for the Compendium....I have it, thanks.


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