Hey
When I powered up my 300b monoblocks I saw my full range drivers twitch, just moving without any input.
Just noticed this for the first time today.
I always turn the amps on last and off first. What’s the likely cause?
Thanks
When I powered up my 300b monoblocks I saw my full range drivers twitch, just moving without any input.
Just noticed this for the first time today.
I always turn the amps on last and off first. What’s the likely cause?
Thanks
Does it quit moving after a few seconds?
Is there an output DC blocking capacitor, or transformer?
Is there an output DC blocking capacitor, or transformer?
The solidstate power supply allows the B+ to come up very fast. The jump in B+ across the plate load choke and the output transformer (before the 300B starts conducting) causes a current surge in the primary of the output transformer. That surge generates a pulse on the secondary of the output transformer that is pushing the driver coils in the speakers. The duration and decay characteristics of the pulse are driven by the LC time constant of the plate choke, the coupling capacitor, and the output transformer primary inductance.
Thanks
Wish I understood my amp as well as you. Would you consider this detrimental?
Jcris
There are two very different cases for an amplifier without B+ delay, speaker protection circuits etc:
- Power on from cold. There should be no movement on the speakers. Cracks like sound may point to serious problems with the output/rectifier tubes or/and output transformers.
- Power on quickly after power off: Some speaker movement is expected, especially if using a silicon rectifier, B+ comes up very fast.
P.S I just noticed that you got silicon rectifiers. I would say a short reaction is fine, should be barely noticeable from cold, but easily heard from a warm start.
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There is a B+ delay on cold start of about 30 seconds. This does occur on both drivers. I usually turn on the preamp and let it warm up for a couple minutes and then turn on the amps. And also wait a few minutes before turning on the source (cdp).
Thanks guys
Thanks guys
Also,
It seems maybe the B+ delay is not working properly. Seems odd that both channels are doing the same thing. Perhaps this has more to do with the preamp. I just got this system running after replacing the sockets on the 300b’s and the 6sn7’s. I also rewired the preamp and amps putting the iec receptacles, inputs and outputs on the back panel. I never liked the way the cables laid out from the top. I don’t recall this cone movement previously but I’m not sure
It seems maybe the B+ delay is not working properly. Seems odd that both channels are doing the same thing. Perhaps this has more to do with the preamp. I just got this system running after replacing the sockets on the 300b’s and the 6sn7’s. I also rewired the preamp and amps putting the iec receptacles, inputs and outputs on the back panel. I never liked the way the cables laid out from the top. I don’t recall this cone movement previously but I’m not sure
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On start up this morning I did 2 things differently:
I turned the volume pots all the way down for both channels and I let the preamp warm up longer before turning on the amps. I observed no cone movement. While this eliminates the movement im not sure why
I turned the volume pots all the way down for both channels and I let the preamp warm up longer before turning on the amps. I observed no cone movement. While this eliminates the movement im not sure why
Try now to separate both cases. Do a cold power up with warmed-up preamp, and another one with cold pre-amp, high volume.