HQ-140x mute

[W9BHI]

Hello all,
I have a Hammarlund HQ-140X that I use with my Valiant II.
I am using a Dow Key relay to switch the antenna between the two as well as
controlling the mute function on the receiver.
The receiver has a really loud annoying pop when the contacts on the relay close after releasing the PTT on the mic.
It us unbearable when using headphones.
Any thoughts on how to cure or reduce this annoying problem?

Don W9BHI

[ke7trp]

You can use a snubber circuit across the relay contacts, Or if your dowkey has the dual contacts, You can also cut the speaker line. 

If you cut the speaker line, I like to but a low ohm resistor on the open side contact, this way the radio's transformer sees a 10 ohm load during transmit.  If you dont add this, the radios audio transformer will see no load and voltages could arc inside.

Some recievers mute circuits only remove a section and do not completely kill the receiver.

This problem is excacerbated when the owner of the radio has increased the size of the filter caps. For example, On a radio that uses a 20 UF filter and you used a 47 or 100 uf to lower hum even further. Now you are asking that relay contact to take a huge hit from that charged 100 uf cap. In this case, You can increase or add a bleeder resistor on the filter cap to bleed it down faster.

A simple cap and resistor across your contacts will likely fix it though.

[W9BHI]

Thanks for the reply.
The Hammarlund mutes by removing the plate voltage from the last 2 IF stages as well as the detector.
You can see the schematic on BAMA site.
What do you recommend for the R/C values?

Don W9BHI

[KA2DZT]

You can try some caps from each side of the contacts to ground.  Maybe 5-10ufd from the contacts to ground.  Or maybe a cap across the contacts as suggested.

[ke7trp]

The short story is I dont remember what value of R and C, I used.  Someone here suggested the values. If someone does not chime in, I will have to remove the reciever off the shelf and have a look.  I think it was a .01.  I just dont remember right now. 

[w3jn]

A much better and safer way to do this is to switch the RF gain circuit instead.  Remove the wires from the standby terminals and short them together.  Lift the ground end of the RF gain control and run it out to the standby terminal, ground the other terminal, and put a 50-100K or so resistor across the terminal so there will be a return path to ground thru the RF gain.  It's bad having B+ out on the relay terminals.

Another problem could be switching sequencing, ie, the transmitter is on the air before the contacts actually switch the RX into standby.  I use a DPDT switch for transmitter keying; I use one side of the switch for the xmitter and the other side for RX muting, so the RX mutes immediately with no mechanical delay thru the relay.

[KM1H]

The last thing you want to do is go beyond a nominal 40uF maximum for the input cap and 47uF is fine since the original cap has a +50% tolerance anyway. Too much C and the 5U4 could arc. If there is really PS ripple as verified on a scope then increasing the output C sections might help.
Otherwise Id start looking for tubes with H-K leakage.

Carl

[ke7trp]

Muting with the RF gain control is great.  However, Lots of us out here just dont want to mod the receiver like that.  I have often contemplated doing that modification after having relay contacts fail after a year of us from arc.  But the snubber circuit is the cure to stop that arc and pop.

Good points Carl.  I use close to the correct value for the input and when you double the output cap, that ripple goes away. 

C

[WQ9E]

A much better and safer way to do this is to switch the RF gain circuit instead.  Remove the wires from the standby terminals and short them together.  Lift the ground end of the RF gain control and run it out to the standby terminal, ground the other terminal, and put a 50-100K or so resistor across the terminal so there will be a return path to ground thru the RF gain.  It's bad having B+ out on the relay terminals.

John,

I posted the same solution to the originator's thread on the Antique Radio Forum.  I don't like having B+ running out to a relay-particularly those exposed contact Dow Key coax relays. 

The modification is simple and easily reversible and also avoids the drift issue that often results from B+ interruption.  I like the way Hallicrafters implemented it in the SX-88 with the auxiliary gain control pot that allows the receiver to function as a monitor during standby.

[w3jn]

Hmmm..... ANOTHER one that loves to post the same problem in multiple forums 

[KM1H]

Ive used snubbers on the 240VAC contacts of my NCL-2006 for about 4 decades and no more welded contacts. I can look for the values in my manual notes if wanted.

Yeah, Im another who replied over there also as well as to others who come here to get a second opinion

[W9BHI]

So whats the problem with posting the same question on multiple forums?
Some of you post the same answers on multiple forums.
I'm not looking for second opinions, just more solutions and ideas.

W9BHI

[w3jn]

So whats the problem with posting the same question on multiple forums?

Particularly when someone poses a troubleshooting question, it's difficult to follow the track on multiple forums.  You end up with two different troubleshooting tracks which end up not helping the person with the problem at all by sending them on wild goose chases as information dribbles out.

Some of you post the same answers on multiple forums.
I'm not looking for second opinions, just more solutions and ideas.

You've been provided with several good solutions here.  Which of them have you tried?  Why ask for additional ones until you've tried the ones you've been provided?

W9BHI
[/quote]

[W9BHI]

I tried the solution that WQ9E suggested and it works great, no switching noise at all.

Thanks,
W9BHI