Start up delay needed???

[losacco]

Just finished my first amp project, Walton audio 300b mono block and it sounds great. On power up, I get a lot of popping and hissing that goes away after 5 to 10min and would like to know if a time delay would help this? Not even sure what one is, just have done some reading on them.

Thanks

[richwalters]

Popping and hissing on startup I feel needs investigation. Whatever amp design should be without this on warmup and shutdown. Check tube sockets and anything loose.

Others agree ?

richy

[k9swc]

Yes... and check the tubes themselves. I've had amps that did that and replacing the offending tube cleared it up.

However, on a different note, I've always gotten into the habit of returning the volume control to minimum before turning an amp on or off - especially on. If there are any such sounds generated in the circuitry, they won't be heard - or potentially damage your speaker(s). Some amps "pop" when you turn them off...having the volume down minimizes the effect.

Bud

[el156]

I think all tube amps should have a delay for the HV,only after all the tubes are warm ,the HT should be aplied ! its not good for the tubes not to do that,it shorts tubes life!
A simple way to do that is to use almost any cheap tube,and connect it in serial with a 230V relay(10 ma),connect it between the plate and ´B+ of 350V or so! When that tube is enough warm it turns the relay ON ! dont forget the cathode resistor and grid to ground!
Silvino

[richwalters]

Originally Posted by k9swc

Yes... and check the tubes themselves. I've had amps that did that and replacing the offending tube cleared it up.

However, on a different note, I've always gotten into the habit of returning the volume control to minimum before turning an amp on or off - especially on. If there are any such sounds generated in the circuitry, they won't be heard - or potentially damage your speaker(s). Some amps "pop" when you turn them off...having the volume down minimizes the effect.

Bud

Curing "off" switch transient clicks that somehow get on the signal path can be difficult to eradicate: worse with high gain tube amps with wide audio b/w. Designing amps with input sensivities around 0dBu/0.775V or higher will help alot.
One solution is to make sure the input signal can be muted first and that needs to be quick. Reason: any DC offset caused by an SS opamp pre or line amp switching off is far quicker than the tube amp and must be "downed" before reaching the inputs. I've seen may opamp preamps and power amps go into oscillation on power down relying on the fast opening of a power relay in the LS circuit. Not an ideal solution.
It only takes a mere uV to create a click and there lies the problem. I try to avoid it, but never quite succeed.
........
K9Swc is right; in a mono amp with no feedback stuff, the tubes and hardware become the offenders.
........
El156....All commercial amps of the 1940,50,60 had no sensible HT delay.The TV business dictated a thermistor in the B+. It was the only limit,(not to brown outs) and only 1 component and was unreliable. It did spread to some audio amps but it was considered Too expensive. The only practical delay:- use an indirectly heated rectifier.
I believe the Walton audio block uses a directly heated 5U4;
This design avoids the B+ rocketing on near instant warmup as there is a large bleeder resistor from the raw B+ (450V) ext rectifier to chassis. I have to check the schematic. MAy be wrong. Rectifier/smoothing circuits have a nasty reputation ! In any case keep ones fingers OUT.

richy

[kmtang]

I built a few of the 300B and 2A3 with similar 6SN7 driver. It seems like there's problem from the 6SN7 driver tube.

It is important to have the 6SN7 filament potential lifted to around 70V to avoid excessive potential difference between the cathode and filament at the 2nd stage.

Remove the 6SN7 and power it up to see if the noise is gone.

Watch if there is some ARC over occurs at the rectifier tube during power up. Use 5U4G tube - they are much more robust in this amp.


Johnny

[losacco]

Johnny, whats the best way to check for arc at rectifier? Also the pins on my 300b's are a little loose, that can't be normal, right?

[thor61]

Just found this delay circuit > http://www.nervenet.info/HT_delay/ax_aug-2001.pdf

[Joshua_G]

Lets settle the b+ on cold tubes issue!

[Wavebourn]

There may be 3 reasons of popping and crackings:

1. HF oscillations

2. Voltages on cathodes in respect to filaments are out of specs

3. Bad tube, with curved/loose/naked filament that touches cathode during heat up / cool down.

Startup delay would hide such problems, like sweeping garbage under the rug.