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Old 11th Aug 2018, 5:02 pm   #11
Sideband
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Join Date: Oct 2003
Location: Croydon, Surrey, UK.
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Default Re: Marshall JTM45 Guitar Amplifier- Mains (Primary)Fuse Blows

I've checked a few of these in the past and it's been the GZ34 rectifier. They don't seem to fare too well in these amps and I think it is because of the HT switch. When the HT switch is off (standby) and then switched on when the rectifier is fully warmed up I've seen them flash quite badly when they have to supply the current instantly to charge the reservoir cap. Valve rectifiers were never designed to operate that way. I did suggest to Marshall that if they insist on having an HT switch, they should consider fitting surge limiters in each anode of the rectifier. Whether they ever did I don't know.
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