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Author Topic: How do you disable the preamp on a Radio Shack 2 meter amp  (Read 3101 times)
KC4YJI
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Posts: 27




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« on: November 04, 2010, 11:09:37 PM »

I am cleaning out the shack and found a "Radio Shack" 2 meter amp ( HTA-20 ).  I hooked it up to try it out and it attenuates the signal about 20 dB's, it transmits fine but you can hear  only very strong signals.  How do I fix this correctly and also how can I bypass the preamp altogether.  I know very little about electronics and have no experience fixing my radios,  so please be very detailed in any answers.  I am trying to learn more of the electronics and I figured this would be a good project to learn on.  You can find some info about the HTA-20 at the following link…

http://www.repeater-builder.com/radio-shack/radio-shack-index.html


Thank you for your help,

Scott - KC4YJI
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WB2WIK
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Posts: 20612




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« Reply #1 on: November 05, 2010, 10:06:00 AM »

I am cleaning out the shack and found a "Radio Shack" 2 meter amp ( HTA-20 ).  I hooked it up to try it out and it attenuates the signal about 20 dB's, it transmits fine but you can hear  only very strong signals.  How do I fix this correctly and also how can I bypass the preamp altogether.  I know very little about electronics and have no experience fixing my radios,  so please be very detailed in any answers.  I am trying to learn more of the electronics and I figured this would be a good project to learn on.  You can find some info about the HTA-20 at the following link…

http://www.repeater-builder.com/radio-shack/radio-shack-index.html


Thank you for your help,

Scott - KC4YJI


The problem might be the FET preamp transistor, a 3SK189, which would be easy to replace if done by a competent technician using an ESD safe soldering station, but it might also be a bad relay RL1.

The design is very "robust" (good!) and they've employed quite a lot of protection for the preamp transistor.  The problem might be the transistor or the relay.

Do you have a local 2-way service tech shop anywhere nearby?
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KC4YJI
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Posts: 27




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« Reply #2 on: November 08, 2010, 07:10:18 PM »

Sorry it took me so long to respond, I been working a lot the past few days.  Thanks for replying so fast.  To answer your question, no there are not any radio repair shops close by (that I know of.)  How do you check to see which one is bad.  If it is the relay, how could I bypass it?  The only test equipment I have is a multimeter.

I did find where someone had a similar problem, but the did not tell how it was done.

http://forums.qrz.com/showthread.php?t=65481&highlight=hta+20

http://forums.qrz.com/showthread.php?t=85399&highlight=hta+20

Thanks again
Scott, KC4YJI
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WB2WIK
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Posts: 20612




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« Reply #3 on: November 09, 2010, 07:54:55 AM »

Sorry it took me so long to respond, I been working a lot the past few days.  Thanks for replying so fast.  To answer your question, no there are not any radio repair shops close by (that I know of.)  How do you check to see which one is bad.  If it is the relay, how could I bypass it?  The only test equipment I have is a multimeter.

I did find where someone had a similar problem, but the did not tell how it was done.

http://forums.qrz.com/showthread.php?t=65481&highlight=hta+20

http://forums.qrz.com/showthread.php?t=85399&highlight=hta+20

Thanks again
Scott, KC4YJI

If you strap the two common pins of the relay, RL1(a) to RL1(b) that bypasses both the preamp and the relay itself.  This would take 1/2" or less of wire, and a soldering iron.

73

Steve WB2WIK
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KC4YJI
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Posts: 27




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« Reply #4 on: November 16, 2010, 04:44:26 PM »

Sorry once again, I am working two jobs plus dealing with several personal matters and just have not had the time to reply.

I'm sure I will look stupid for asking this, but when looking at the schematic below just exactly which wires do I connect?  At the top of the schematic where RL1a and RL1b are, do I connect the two wires that are at the bottom (the two that are not connected at the present time?)  My understanding is that this is in the receive mode.  When you transmit RL1a and RL1b move from the contacts at the top and connect with the bottom contacts.  Or am I completely off and this is in the transmit mode?  If this is the case would I connect the two wires coming in from the sides (the two connected now?)  

I told you I knew very little about this stuff, but I do want to learn.  I even bought one of those 200 in 1 electronics project labs on eBay.  I haven't had time to go through many of the projects yet, but hope to soon.  I am the type that doesn't get a real understanding of something until I put it to use practically.  The electronics theory is one thing when I read about it, but I want a practical knowledge.  Something I can use to build things with.


http://www.repeater-builder.com/radio-shack/hta-20/hta-20-schematic.jpg


Thanks again for your help, I appreciate it more than you know!

Scott - KC4YJI
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WB2WIK
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Posts: 20612




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« Reply #5 on: November 17, 2010, 09:12:27 AM »

You'd jumper the "center" of RL1A to the "center" of RL1B, on the schematic where three connections are shown for each half of the relay.

The "center" connection is the "common" one, for each side.
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KC4YJI
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Posts: 27




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« Reply #6 on: November 17, 2010, 07:35:10 PM »

Thanks, I'll try to work on it this weekend.

73,  Scott
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KC4YJI
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Posts: 27




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« Reply #7 on: November 23, 2010, 03:21:41 PM »

Works great!  Thanks for your help!!!!

73, Scott
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