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 Post subject: K-488 Transmitter Kit Troubleshooting
PostPosted: Jan Sat 05, 2019 9:25 pm 
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I just purchased a K-488 transmitter kit to use for a science project for my 8th grade son. This is a bit out of our comfort zone so we were challenged building the kit. We tested with a volt meter when complete and it shows continuity throughout. When we plugged it in there is a VERY slight humming of the vacuum tube but no other true indications that it is working. I tried connecting my iphone and macbook using some headphones that I stripped. We also tried using an old cd player by stripping the component connections and connecting the wires to the AF-IN and Ground. After hours of trying we have had no success hearing any output on our AM radio anywhere on the dial. :( What are your suggestions for what we should try first to troubleshoot? Thanks for any help you can provide.


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 Post subject: Re: K-488 Transmitter Kit Troubleshooting
PostPosted: Jan Sun 06, 2019 1:42 pm 
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Here is the schematic for your transmitter:

Attachment:
AES K-488 AM Transmitter Sch.JPG
AES K-488 AM Transmitter Sch.JPG [ 46.2 KiB | Viewed 3653 times ]


My first thought would be to check to be sure that the oscillator coil (L1) is correctly connected.

Dave


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 Post subject: Re: K-488 Transmitter Kit Troubleshooting
PostPosted: Jan Sun 06, 2019 5:33 pm 
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With the lights out, is the tube glowing? Are you sure D1 is connected the right way?

Norm

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 Post subject: Re: K-488 Transmitter Kit Troubleshooting
PostPosted: Jan Sun 06, 2019 5:48 pm 
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Thanks both of you! Very helpful tips. We are traveling today but will check both suggestions as soon as we return home. Greatly appreciate it.


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 Post subject: Re: K-488 Transmitter Kit Troubleshooting
PostPosted: Jan Sun 06, 2019 8:59 pm 
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Make sure the volume control on your input device (CD player, etc) is all the way up.
Though the schematic states you don't need an antenna, attach a piece of wire about 4 feet long to the antenna terminal.

Tune to a quiet spot on the AM band with your radio.
Adjust the ferrite slug inside the coil till you can hear the transmitter on the radio.


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 Post subject: Re: K-488 Transmitter Kit Troubleshooting
PostPosted: Jan Sun 06, 2019 9:11 pm 
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skibama96 wrote:
When we plugged it in there is a VERY slight humming of the vacuum tube...

Where do you hear the hum? Is the carrier hum heard on the radio or do you hear hum even with the radio off? If it's the latter, is it transformer hum you hear? Or is it the tube itself that's humming?


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 Post subject: Re: K-488 Transmitter Kit Troubleshooting
PostPosted: Jan Tue 08, 2019 1:12 pm 
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SkyKing wrote:
Make sure the volume control on your input device (CD player, etc) is all the way up.
Yes, that's because many of today's modern audio devices often do not produce enough output voltage to drive some tube equipment. Even with the volume control all the way up, there still may not be enough voltage available to drive this one-tube transmitter without using an input transformer.

Dave


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 Post subject: Re: K-488 Transmitter Kit Troubleshooting
PostPosted: Jan Fri 11, 2019 9:57 pm 
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I wonder if we'll ever find out if it worked.


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 Post subject: Re: K-488 Transmitter Kit Troubleshooting
PostPosted: Jan Sun 13, 2019 5:11 pm 
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We are working on it again today. I'll definitely let you know if we get it working! Thanks again.... :)


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 Post subject: Re: K-488 Transmitter Kit Troubleshooting
PostPosted: Jan Sun 13, 2019 9:36 pm 
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ok friends, we have been troubleshooting all day. With a voltmeter the number 3 and 4 connections on the octal tube socket (where the vacuum tube plugs in) are the only ones hot. All of the other connections are not showing any voltage. Does that seem right? And, the vacuum tube is not getting warm or glowing.... Other thoughts? :?


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 Post subject: Re: K-488 Transmitter Kit Troubleshooting
PostPosted: Jan Sun 13, 2019 11:57 pm 
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What is the part number of the transformer? Also, it will be helpful if you can elaborate on the questions below:

skibama96 wrote:
When we plugged it in there is a VERY slight humming of the vacuum tube...

Where do you hear the hum? Is the carrier hum heard on the radio or do you hear hum even with the radio off? If it's the latter, is it transformer hum you hear? Or is it the tube itself that's humming?


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 Post subject: Re: K-488 Transmitter Kit Troubleshooting
PostPosted: Jan Mon 14, 2019 12:16 am 
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Dave posted schematic with voltages on tube pins. There is not supposed to be voltage on pin 4, but should be 7v on pin 8.

Also no small signal tube is supposed to hum.

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 Post subject: Re: K-488 Transmitter Kit Troubleshooting
PostPosted: Jan Mon 14, 2019 1:12 am 
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skibama96 wrote:
And, the vacuum tube is not getting warm or glowing.... Other thoughts? :?


There should be 12 volts across pins 2 and 7. If not, the tube won't light up.


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 Post subject: Re: K-488 Transmitter Kit Troubleshooting
PostPosted: Jan Mon 14, 2019 1:17 am 
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35Z5 wrote:
Dave posted schematic with voltages on tube pins. There is not supposed to be voltage on pin 4.


I see 105 volts on pin 4 (but the schematic is almost impossible to read)


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 Post subject: Re: K-488 Transmitter Kit Troubleshooting
PostPosted: Jan Mon 14, 2019 3:41 pm 
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SkyKing wrote:
skibama96 wrote:
And, the vacuum tube is not getting warm or glowing.... Other thoughts? :?


There should be 12 volts across pins 2 and 7. If not, the tube won't light up.
That would be 12 volts AC.

Also, keep in mind that, unless the tube filament is lighting up, you will not see any (AC or DC) voltage on pin 8.

Dave


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 Post subject: Re: K-488 Transmitter Kit Troubleshooting
PostPosted: Jan Mon 14, 2019 4:39 pm 
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SkyKing wrote:
35Z5 wrote:
Dave posted schematic with voltages on tube pins. There is not supposed to be voltage on pin 4.


I see 105 volts on pin 4 (but the schematic is almost impossible to read)

Yea that's it, schematic is hard to read. :wink:

Never mind the tube won't operate without screen voltage. :lol:

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