Engl valve amp disaster
On Tuesday, March 5, 2019 at 2:38:49 AM UTC-5, Phil Allison wrote:
Gareth Magennis wrote:
I still don't have the schematics for this amp, maybe putting the protection
diodes on the heater circuit instead of ground was a big design mistake.
I have moved them to ground.
** That the HV diodes connect to the heater line ( instead of chassis ground ) likely did not cause the failure, but it sure caused all the damage.
A tech working for the maker / importer is NO use to you when it comes to bad design problems. I see a lot of them these days in tube amps and have to modify circuits to effect a reliable repair.
I don't give a hoot what the amp maker or even the customer thinks of this cos *** I *** am the one liable for a repeat failure both financially and in terms of reputation.
the standby switch opening the cathode path to ground makes me nervous.
Maybe the switch arcs when it opens.
I'd find a different way to put the amp in standby or at least put a snubber cap across the switch.
Maybe wire a switch in series with R74 and let the negative grid bias go way up to cut the tubes off.