We have at least a three Almarro owners on the Haven, and I’m still hopeful one will sell theirs soon as these don’t come up for sale stateside often either.I have tried to get hold of a 205 for several years but they rarely appear on the used market in Sweden as the owners of these stubbornly refuse to let them go!
My assumption with the one I worked on was that the cathode bypass caps blew from being overheated, as they were super close to a giant wirewound resistor that otherwise was also very hot and cooking off its own lettering. The grid leak resistance was 100K IIRC whichthis seems to be a solution to the problems with early almarro A318 / A318B and blown cathode bypass capacitors, this is taken from a discussion on a european audio forum, any technical knowledgeable person who would like to explain in more detail what this is about ??
(constant current sinks / sources (CCS's)??
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So you’d not recommend buying one? If I do, would spacing out the caps away from the resistors be sufficient? I’d hate to have to redesign the thing. Really wanting to try a single ended el84.My assumption with the one I worked on was that the cathode bypass caps blew from being overheated, as they were super close to a giant wirewound resistor that otherwise was also very hot and cooking off its own lettering. The grid leak resistance was 100K IIRC which
These amps run mixed bias, meaning there is substantial resistance between cathode to ground but also adjustable negative grid bias. It's tough in a 6C33 amp to run cathode bias, as you may need 80V of bias at 200mA, so the resistor will dissipate 16W. This really requires a 50W resistor and some decent space/ventilation. Almarro instead develops less of the bias across a cathode resistor and the rest is obtained by negative grid bias.
If the grid to ground resistor is too large of a value, the grid voltage can wander, which also causes the bias to wander. If you put a CCS under the cathode of the 6C33, you can fix the current and as that grid voltage moves, the cathode voltage will move with it to maintain proper current. The issue with this is that the CCS will get super duper hot if that voltage grows too large.