Ampeg SVT3 Pro turn on delay

[AJStrummer]

HI.

An SVT3 Pro I have has a really long time delay until the relay engages (20-25 seconds). Can someone explain how the circuit works? I found voltage increases form 0 to 40VDC, at the junction of R23 and C11, at that point the relay activates. Is there a way to speed up the time of the start up? I replaced C11 and C12 but it made no difference. Start up circuit is on page 13 of attached schematic. ampeg_svt-3-pro manual schematics.pdf

Thanks for any help

AJS

[g1]

So the 40V at C11 is slow to come up?
Is R23 (and solder connections) good? How long does the 65V supply take to come up?

[AJStrummer]

Hi g1

Yes the 40V starts at 0v and climbs steadily, but slowly up to 40v. The 65v is there almost immediately after start up (2-3 seconds). R23 was reading a bit odd in circuit, so I removed it. It read 109K, so replaced it to see what resulted. The 40V seemed to climb a bit quicker. Do you think playing around with the value of R23 will change the time it takes for the 40V to build up?

Cheers
AJS

[g1]

How long is it supposed to take? The heaters will always take at least that amount of time to warm up (20 - 25 sec.). Is it possible that is what they are waiting for?
If it is not normal, then the defect should be fixed, rather than modification to the timing circuit.

[g1]

A bit more digging says 20 to 30 seconds is the normal turn on delay. It's like an automatic standby circuit to protect the tubes.

[AJStrummer]

The relay is a speaker protect relay, afik, and as it's a hybrid, the only tubes are in the pre-amp. They are getting full voltage (450VDC) form power up, with no protection in there at all. I timed the delay, and its actually 40 seconds, so it really seems a bit long. I popped in a 47K, and it dropped the relay switch on time to 17 seconds!! Now to watch and see if anything goes bang!!

[g1]

That will work, as would decreasing the value of C11.
I guess with no standby switch, some people may have wondered why it didn't give sound instantly (due to heater warm up of preamp tube). So if they build in a delay, they can mention it in the manual?
Just speculation.
From completely cold, do you get sound now as soon as the relay kicks in? Wondering what the actual heater warm up time is. I'm guessing less than 10 seconds.

[AJStrummer]

I'll check in the morning, but I'm sure there is signal as soon as relay kicks in. But, I did find another issue now. When cranking the gain & master, the +65v is crashing and the relay is switching off, which it is supposed to do in low voltage conditions. That would indicate filter caps not doing their job??

BTW, thanks for your input g1!!