B+ Turn On Delay Question

[skidave]

Sorry if I am beating a topic to death... Question about B+ delay. Obviously with a tube rectifier, there is a ramp up of B+. With most turn on delay circuits, there is a lack of B+ for a specific amount of time as the heaters warm up and then a relay [or such] closes and completes the B+ path. Is there an issue with applying all of the B+ voltage at one time when the relay closes? Obviously ramping that B+ would be great, but much more difficult.

Looking for thoughts.

Thanks,

Dave

[Geek]

Depends where the relay is placed in the circuit. I know of amps that go from *pop* to *BANG!* as the relay clicks in.

However, unless you are using large DHT transmitter tubes, you don't require a relay.
(for a discussion on why cathode stripping is a myth, see: viewtopic.php?f=4&t=4832 )

Cheers!

[kheper]

If you think you need to ramp the B+ slowly and use a FWB rectifier, you can put a spst switch and resistor on one leg of the AC secondary - for cheap.



http://www.valvewizard.co.uk/standby.html

[skidave]

I guess the big question with SS rectification is delay or no delay. Especially if your B+ is near 500V? Sounds like there are positive and negatives for delaying.

I have used CL-xx in-rush limiters for other projects, and I remember seeing discussions about them around here as well. They have their purpose, but they are not my favorite.

Dave

[burnedfingers]

You hear on so many forums that stripping will occur and this scares the heck out of everyone. Just the thought of B+ coming on without a delay is enough to bring on a heart attack. Well, for years tube amplifiers have been made and guess what? They used a lowley 5U4 and B+ came up instantly and nothing blew up and the world kept revolving and yet another day passed. Want to use SS? Afraid of the sudden turn on? Use a damper tube and your problems are solved. Use that 5 volt winding and apply it to the damper tube for a nice controlled warm up. Problem solved..

Just a thought or two ... most forums recognize cathode stripping happening at around 1000vdc not 500. The thought of a switch in the secondary isn't quite the thing to do. Ever seen a switch rated at say 500 volts? Most are rated at say 250volts and something actually safe for 500 volts would be quite large. So contact ratings need to checked and recognized in order to be completely safe.

[kheper]

Here is the full, diytube thread of high voltage switching do's and dont's.

viewtopic.php?f=1&t=493

Below is Tom McNally's schematic for an Amperite delay relay, which he used on a 300B SE amp.

[burnedfingers]

The Amperite relay closes after 90 seconds, and puts
the 6 VAC DPDT relay into a latched "self hold" and
turns on the plate voltage by grounding the center tap
of the HV transformer, at the same time, the coil of
the Amperite relay is removed from the circuit so it
cools down. If you decide to go to a 5Z3 rather than
an 83 Mercury Vapor rectifier, you can remove the
Amperite relay and jump pins 5 to 7, and retain the
standby switch and relay.

The hand drawn schematic makes more sense with the discription that was with it. No need to use the 6N090 in certain instances.

[Blair]

Has anyone ever used these:

http://item.mobileweb.ebay.com/viewitem ... 7202788215

If the link does not work, go to fleabay and type "power supply delay".

I have three of them. Just curious about the safety, etc.

Blair