TBS-50C - - leaky cap problem?

[stevef]

My TBS-50 is drawing current from the HV power supply in standby.  In CW mode, with the key up, it draws 13mA.  In Phone mode, it draws 97mA standby.

Is this a leaky cap (or several) symptom?

Steve
KK7UV

[WQ9E]

Steve,

In Standby, the TBS-50 is designed to interrupt the HV supply (which is everything except filament power in the TBS-50 series).  For example, using the Harvey Wells APS-50 supply the HV transformer primary has power removed when in standby. 

What supply are you using?  If homebrew then you will need to provide a means to remove HV during standby.

[stevef]

Yes - I built my own supply for it.  I should not have used the term "standby" - what I should have described was that I wired my mic PTT to the PHONE/CW switch common terminal - so that the PTT grounds the keyline when pressed.

So, with the switch set to "Transmit", but the PTT/Keyline ungrounded, I get current draw as stated in my initial message.

[WQ9E]

Steve,

With the power supply set up this way that sounds normal (but undesirable).  In CW mode with voltage applied and with the key up you will have current flow through the 25K pot to ground (the drive pot).  In AM mode then your 6L6 modulator tubes are drawing normal idle current added to the current draw through the pot.  The figures you report sound right in the ballpark for metering current directly from the supply.

With the TBS-50 you have a lot of tubes in a small space so you really don't want to leave the plate voltage on during receive; particularly in the AM mode.  That is why the Harvey Wells power supply was set up with a relay (and they had similar instructions for using dynamotor supplies).

The Gonset G-76 is similar in this manner and I had to add a relay to the Drake supply I was using with mine.  Since I couldn't switch the primary I had to use a relay in the HV lead.  If you aren't using separate filament and HV transformers in your homebrew supply you will need to do the same thing.  A regular relay with 240 volt rated contacts will work fine to switch the relatively low HV needed for the TBS-50 series but you should use a "snubber" across the relay contacts to minimize arcing on break.