Rerurn to Romy the Cat's Site

Paul S wrote:

I got new 6C33Cs for V2s from Lamm because no one else wants to match them, let alone match them for gain…

There is no meaningful mutual conductance or bias matching for 6C33Cs (in context of ML2) besides gain matching, and to match gain of this tube is very simple with any special equipment or skills.

Paul S wrote:

but the loud thump through the speaker still happens just when one amp self-switches from warming its filaments to full-throttle operation.

Paul, I do not know if I misunderstood you or you juts mis-presented the case. As I understood you, you complained about the pulses when the amp was operations. THAT would be because the aged L2 tube. If you have pulse when the amp accepts B+ then it is totally different story.

Paul S wrote:

I don't know how this internal switching would happen without a relay or a thermistor, etc., but I'd like to find the source of the pulse and fix it before it blows a speaker.   Needless to say, I want to avoid shipping the amp from San Diego to Brooklyn and back, if possible.

I am sure it would makes sense to ask Vladimir about the possible reason but Vladimir has a tendency to do discuss problems with his circuits. In order to answer what is going on it is necessary to have the amp in hands. I do not know what kind delay it executes. As I remember it has only one relay switching and permeably it applies regulated voltage to 6C33C plate. I do not know how ML2 applies the plate voltage to the first and second stages perhaps Lamm does it the “cold” tubes at the initial start. Still if you hear an auditable pulse then you heard some voltage running across the primary of the ML2‘s output transformer. What might it be? A regulator, a 3200uF cap the transformer and then the tube…. I presume the bias is applied immediately as soon the amp is turned on. I really do not know. Perhaps that last large cap does it regulator create this  “ping”. Confirm that gas regulator holds the voltage during switching? Put a new amplifier tube in the regulator. Make sure that regulator does regulates and do not create any spike during loading itself to the plate of V2. Perhaps Vladimir was afraid to charge that 3200uF caps and has some kind of charging spreading mechanism in there that went out of the sync? Still, if you apply voltage to wormed and properly biased 6C33C then 6C33C should not generate any noise.  Hm… the ML2 uses global feedback… and perhaps something is coming from there… I remember the ML2 was very unusable when it was loosing 3-4dB of feedback…. Yet, without having it in hands it is difficult to say anything. Rehabs, some folks on this site who have some technical expertise would advise you.  Nevertheless, I do feel that Vladimir would perform an initial debugging with you over the phone… It is kind of his part of the game

Rerurn to Romy the Cat's Site