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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment. |
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12th Mar 2023, 3:01 pm | #1 |
Diode
Join Date: Jan 2023
Location: Bristol, UK.
Posts: 5
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Trio TS-700 AGC time constant
I've resurrected my TS-700 for short wave duty and I find the AGC to be too fast, it's pumping the volume somewhat. I can mitigate this by backing off the RF gain but would prefer a proper fix.
I can't recall whether it was always like this, my memory isn't that good, the manual mentions having a slower AGC for SSB. Maybe other TS-700 users can say "yeah it's like that" and I'll leave it alone. Any pointers? I'm reluctant to dig too deeply inside and mess something up as otherwise the radio is working perfectly. |
13th Mar 2023, 9:57 am | #2 |
Nonode
Join Date: Nov 2015
Location: Welwyn Garden City, Hertfordshire, UK.
Posts: 2,013
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Re: Trio TS-700 AGC time constant
Been having a look at this and the AGC circuit is hard to read being that it is spread around different boards.
I can't see anything that changes time constant with the mode switch but is split across pages of the scan. The FT221 definitely changed them between SSB and CW. No sign of that in the TS700 so far. |
13th Mar 2023, 1:37 pm | #3 |
Diode
Join Date: Jan 2023
Location: Bristol, UK.
Posts: 5
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Re: Trio TS-700 AGC time constant
Thanks for looking Jon if you turn anything up do let me know. The only reference I can find to mode switched AGC is on page 4 of the user manual.
It may well not be true of course. |
13th Mar 2023, 3:06 pm | #4 |
Nonode
Join Date: Nov 2015
Location: Welwyn Garden City, Hertfordshire, UK.
Posts: 2,013
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Re: Trio TS-700 AGC time constant
I see that now. Right so how it's done needs to be found. Maybe I can join up my schematic halves or find a better version.
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13th Mar 2023, 3:43 pm | #5 |
Nonode
Join Date: Nov 2015
Location: Welwyn Garden City, Hertfordshire, UK.
Posts: 2,013
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Re: Trio TS-700 AGC time constant
Found it. I did locate a better schematic version. Mine was split right at the vital place.
There is a pair of diodes that generate "Is SSB". It drives a FET which changes the time constants. AM/FM and CW are all fast. SSB should be slower. |
13th Mar 2023, 7:45 pm | #6 |
Nonode
Join Date: Nov 2015
Location: Welwyn Garden City, Hertfordshire, UK.
Posts: 2,013
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Re: Trio TS-700 AGC time constant
I have one of these which is part converted from 2m to 4m. The RX works well but the TX PA is missing. It hasn't been on for a long while. On the whole I like them but the front end design is a bit hairy as it is built on single sided FR4. I'm surprised they got away with it.
I can't remember how far the TS700 is like the FT221 where the AGC and S meter are done using the SSB filter on all modes. Far from ideal. I think even AM RX for demod went through the SSB filter on a 221? In my FT221 (also converted for 4m) AM RX is diverted through a 7.5kHz BW filter so that both sidebands are demodulated and act on AGC. The TS700? I forget. I wonder how you are using one for short wave? Up conversion? Last edited by Jon_G4MDC; 13th Mar 2023 at 8:01 pm. |
14th Mar 2023, 11:06 am | #7 |
Diode
Join Date: Jan 2023
Location: Bristol, UK.
Posts: 5
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Re: Trio TS-700 AGC time constant
Good work Jon, I shall ponder on whether or not to dig inside to correct this irritation.
I am using the TS-700 with a Tokyo Hy-Power HX-240 transverter which makes a good receiver combo and also about 35W output. No WARC bands, but I don't have a resonant antenna for them in any case. |