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1bassleft
Lowdown Cack-hander
Joined: 16 Feb 2005
Posts: 3742
Location: "Hit The North"
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 Posted: Mon Feb 18, 2008 3:42 pm Post subject: |
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Now I think about it, none of my WEM Dominators has a standby, including the 30W and the RSC GP30 I've just sold (also cathode-biased, maybe Class A) didn't have one either. Bit mystifying, because I can't see any reason why cathode-biasing saves the valves from torture. EL84s were/are a lot cheaper than the EL34, but that doesn't explain the absence on the RSC. I suppose that cathode-biasing means that, if a tube goes kaput, you simply buy a replacement and drop it in, whereas fixed-bias amps would require a new set and re-biasing. Expensive and tedious enough to warrant fitting a standby circuit.
Incidentally, all Doms I've bought still had their 70s Mullard EL84s in there so a standby isn't the big deal you'd think. The only exception was that 30W version (parallel push-pull, still cathode biased), bought for 41 quid as a non-worker. It had three Hungarian Tungsrams and a nasty, dead, Chinese EL84 that can't cope with the screen current of old amps. Replacing the Chinee with a Tungsram got it working fine. |
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lee_UK
Rolling Stone No.8
Joined: 04 Feb 2005
Posts: 3243
Location: London, UK
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| Posted: Tue Feb 19, 2008 1:34 am Post subject: |
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| I also heard on a VOX amps website, the best way to preserve an amps valves is to put on the main swicch, leave for 1 minute before switching on the standby , but to switch off you turn the power off first to bleed the voltage for 30 secs then turn off the standby, one thing ive always done is after switching off not to move the amp til the last possible moment, the valves are very delicate when hot. |
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1bassleft
Lowdown Cack-hander
Joined: 16 Feb 2005
Posts: 3742
Location: "Hit The North"
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| Posted: Tue Feb 19, 2008 4:02 pm Post subject: |
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Yes, the standby is only for switch on. If you have a beer break, just turn down the vols and leave it running; don't go into standby. I also switch off the mains (and strum a chord for that frazzle-azzle-pfft thing), then flick the standby back into position for when I'll next use it.
The idea behind this is to drain the capacitors of their stored charge. Opinions are mixed on whether moving the amp while still warm is more likely to damage the valves, but it doesn't hurt to get paid and finish your beer before tering down  |
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