Icom: IC-7300 to HeathKit SB-200 to Manual Tuner

[HamHill]

New member here with first post, be gentle! Received my Canadian Basic (with Honors) back on April 4th this year. Had reasonable success with DX so far considering Summer band conditions.

I currently am using a Icom 7300 hooked to a MFJ-971 manual tuner, hooked to a DX LBPlus multiband center fed dipole up at 30' in the center, 4' at each end. The antenna orientation is East-West.

DX contacts include Russia, Japan, New Zealand and Romania 9and others) so I am content. But when band conditions are good I am missing QSO that I just to weak to have them hear me well.

One of the Net control oldtimers has found me old HeathKit SB-200 in nice clean shape, and a MFJ ATR-30 manual tuner. I have downloaded all manuals (haven't received the Amp or Tuner yet), and read through each.... Watched as many you-tube videos as my search ability will allow... BUT, I am concerned by what I haven't found. Even in a Google search I am left wondering a few things. Lots of warnings about hooking the IC-7300 to the Amp, and not releasing the expensive magic smoke...

I don't know IF there have been any mods like a "Soft Start" done to this Amp. So what I'm looking for is some advice from someone who has connected something similar together. Advice is always welcome. and light to carry around. And my wallet would appreciate not taking a hit for another transceiver!

Brent
VE5BMS

 

[HamHill]

Anyone!

 

[arg0s]

BUT, I am concerned by what I haven't found. Even in a Google search I am left wondering a few things. Lots of warnings about hooking the IC-7300 to the Amp, and not releasing the expensive magic smoke...

What did you not find? Warnings about what? Magic smoke from the amp or the TRX?

Adjust the TX delay to at least 20...25ms to avoid hot switching. At first use more TX delay, you can always optimize the timing later. Adjust the CW delay (Semi-BK) to about 0.25...0.3 seconds if you do CW. For PTT you have to use an external keying relay. The Icom TRX can only switch low voltages (max 20V @ ACC connector, max 16V @ send RCA jack), the Heathkit amp uses > -100V DC for PTT. An example is given in the manual in section 18 "connector information". If you connect the ALC line use a 4.7...5.6V Zener diode across the ALC RCA connector to limit the max. voltage seen by the transceiver. The IC-7300 works with ALC voltages between 0 and -4V DC.

 

[HamHill]

The Amp arrived. On inspection I saw it has both a Soft Key and Soft Start installed. I tracked down a MFJ-962D tuner. This Amp is not equipped with a by-pass. Several people have told me (and tracing the Wiring Schematic) I should be able to tune the antenna with the radio, amp and tuner connected and the Amp powered off. I was able to log the initial antenna tuning presets for the Bands I frequent, the the wheels fell off the wagon. I lost the audio and the waterfall screen showed no peaks.

I disconnected the amp, hooking the Transceiver to the Tuner and all is well. Putting the Amp back in the circuit all came back so I initiated the Amp power. This is where I come to a grinding halt. Any of the instructions or videos I watch are consistent with what I am seeing... I am afraid I may bugger up either my IC-7300 or the tuner (needles go wild even with only 5% input to the amp.

I have put the Amp aside. Perhaps some day I will find someone who has the same set-up as mine. But all the old hams around here have gone silent key or moved on to digital...

 

[prcguy]

I use a simple relay to interface some of my radios to amplifiers. The 7300 has an amp key line that goes low on transmit and it will sink enough current for a small relay. Get a SPDT or DPDT 12v relay with contacts rated 250VDC at an amp or more and coil current less than 50ma then put one side of the relay coil to constant 12v and the other to the 7300 key line. Then connect a relay common contact to ground and the NO contact to the SB220 key line. I would also put a 1N4004 or similar diode across the relay coil (stripe to +) to snuff out voltage transients.

When you transmit on your radio its amp key line will go low and key the relay which will ground the SB220 key line which is now isolated from the radio. I would also add more TX delay in the radio from what is mentioned above as the new relay will delay the amplifier keying by 20-30ms.