TX to my amplifier

Bob - WD8KND

I've had my 6300 for almost a month now and everything was working fine. I had an RCA cable running from my TX jack to my linear amp. All was working fine. Yesterday I noticed my receive was down and I started to investigate, and found my amp was keyed up. (Not transmitting, just the relay keyed) Upon further investigation, I found that my TX jack has 20 ohms on it from center post to ground. That is low enough to key up my amp. It's there all the time, until I transmit, and then it goes to about 30 ohms. Anybody have any ideas? Do I have a hardware problem, or did something change in my software to cause it?

Thanks,
Bob-WD8KND

George KF2T

Uh oh - tube amp with a relay? Could have hit your rig with a spike. Can you check the RCA jack on the rig and see if it is working? Check the relay enables, etc., in setup. A power-down software reset wouldn't hurt. Might be lucky.

Bob - WD8KND

When I check the RCA jack (TX) I see 20 ohms with nothing keyed up.

Mike_WB8CXO

Bob, can I call you on the phone? Or you can call me...on the phone? Mike WB8CXO

Steve N4LQ

When you key the 6300 the RCA jack's resistance should measure near zero ohms however polarity is important. It should read high one way and low the other. Meters vary so I can't tell you when lead is which. This is only when you key the rig. With the rig unkeyed it should read rather high with either polarity. 
What kind of amp is this? Were you keying an older amp that used more than 5 volts? If so then you may have blown the keying transistor.

Bob - WD8KND

7349800

Bob - WD8KND

My amp is a Heathkit SB1000. It's been working for a month. According to the Flex 6000 manual, it says: "The TX relay outputs are designed to handle signaling levels up to +40 VDC @ 140 ma"  The fact that there is 20 ohms on there all the time kind of indicates something is wrong.

Steve N4LQ

The Flex uses solid state, transistor, keying. The Heath probably has 110v at the key input so yes you probably blew the Flex. You need a keying interface on those old amps like this one http://harbachelectronics.com/shop/heathkit-sb220-sb221/sk-220-soft-key-keying-interface/

Bob - WD8KND

No, it uses a 12V supply.

Bob - WD8KND

The SB1000 is basically a Ameritron

Mike_WB8CXO

Bob, the keying spec for the SB1000 is 12vdc at 100ma that is within the 40vdc at 140ma Flex 6000 spec but looking at the SB1000 schematic there is no protection diode across K1 to suppress back emf... Looks like Ameritron didn't add one till the AL80B... FWIW Great talking to ya on the phone this evening.

Bob - WD8KND

Yea, I saw that Mike. If it is a bad keying transistor, I'm going to have to come up with a protection circuit for the future.

Steve G1XOW

Sounds like the final switching transistor in your radio has been blasted. Happened to me on an Anan-100. SDR don't appear to be as immune from Amp switching/HV relays as previous designs.

Bob - WD8KND

It's not a HV relay, it's 12 volts at a 100 ma. If these things are that sensitive, than maybe Flex should protective them better.

Steve G1XOW

My old Alpha 76a was the one that killed the Anan-100. The final transistor on the Anan was a pathetic miniature surface mount affair, like a spec of dust.

The alpha only had about 26v on open contacts but it was still enough. Not sure what Flex put in the final switch but I am guessing not much different.

The slight variation in on/off impedance is identical to what I saw after the incident.

...just one of the reasons I got rid of the Anan in favour of the Flex

Cheers, Steve G1XOW

Bill -VA3WTB

It is a very good idea to use a buffer unit to protect the Flex. Amaritron makes one I am using. I remember with my Flex 3000 I called Flex about using one and they said the 3000 uses a different method of keying and my Amaritron amp should not cause any problems. But they said if I switch to a 5000 then I would need it. I bought one anyways.

Bob - WD8KND

My only problem here is this. The Flex 6000 book says 40V and 140ma. I check into my amp and find it is 12V and 100ma. Well, below the requirement. If we need to use a buffer, than fine, tell me that before I hook up the amp. 

Bill -VA3WTB

Yes that is well below requirements, in normal opperation. But if something happens and there is a spike, sounds like that is what happened, that could damage things. As for what you knew or not and what Flex should tell people I won't comment on that.

KY6LA_Howard

It is normal standard practice to ALWAYS use a buffer when connecting any solid state device to a tube Amp. Why? Because tube Amps are notorious for generating spikes many times their official rated voltage. Designers of ancient tube amps were not that concerned with those random spikes when all they had to design for was tube based radios which could easily weather huge over voltages. In more recent years (1970's+) tube amps started to be connected to solid state radios. So the more recent tube Amps started to include protection circuits to clamp the spikes before they destroyed the radios. But even then Amp manufacturers always recommend using a buffer with solid state devices. Yes the Flex could handle +40VDC@140ma. But obviously that pre-protection circuit ancient tube Amo was generating spikes far in excess of these ratings.

Bob - WD8KND

My last radio, which is a solid state radio, has been keying this amp for 22 years. If the Flex is that sensitive, than a warning should be posted in their manual. Their only post says not to exceed 40V. I saw no suggestion in my amp docs or Flex docs to use a buffer. From the posts I'm reading, it seems that others are learning this valuable lesson the hard too.

Bill -VA3WTB

Your Flex uses a soft key circuit, It would not handle the spike it got from your amp. I take it you feel Flex is responsible for your problem, but how many people have you asked about connecting the two together? and did you ask Flex that?

Steve N4LQ

Why would he think about asking "people" and Flex? 

Bill -VA3WTB

You must be kidding ,Right?

KY6LA_Howard

I believe he's using a Heathkit SB1000 tube amp?

Was not that amp invented before solid-state rigs became popular?
So I'm at the amp docs were written well before it became standard practice to warn about the need for buffering which, of course, would explain why they contain no mention of buffering

Tim - W4TME

Steve - let's be more mindful of the sarcastic comments.  That isn't contributing anything productive to the thread.

Bill -VA3WTB

Tim, I wounder about making suggestions to people in the Insider or here. I am surprised this does not happen more often. Many of us just assume a buffer is needed with tube amps and some are worse than others. In Bob's case it seems he didn't know. I hope this does not happen to others going foreword.

Steve N4LQ

Hey...That was not being sarcastic. Some of you guys are jumping on Bob as if he was somehow supposed to know that tube amps produce spikes. He read the manual didn't he? Everyone can't be an expert.   

Tim - W4TME

I'll review the doc and see if additional information is needed.  Thanks.

Steve N4LQ

Tim:
And furthermore I totally reject your discipline.  
It contributes nothing productive except irritating the customer. 
We buy and help sell your products. 
Just read the post and take action to help. Update the manual and fix Bob's radio under warranty. 

Tim - W4TME

This issue is being handled through the HelpDesk as it appears to be an hardware issue.

Ferrell

I havent had time to look into it but I am having the same problem different jack of course. I use a antenna.radio switch to interface two radio to one amp. One of the radios is my flex 6400. I have been using the RCA jack on the rear called " TX REQ " been working fine. Now there must be a short because my al-600 stays keyed into TX mode all the time. I disabled that port i settings rebooted the radio ad still the same thing. AMP has the TX LED on puts out no power. Assigned amp PTT to another jack and it works fine.

Ferrell

n4frl