60's Kay 504 Tremolo Problem

[Enzo]

I feel like the "numbering each part" started with silkscreened PCBs?

Oh no, numbering goes WAY back. Maybe not as much in guitar amps. My 1950s era Seeburg drawings had part numbers.

[Enzo]

I feel like the "numbering each part" started with silkscreened PCBs?

Oh no, numbering goes WAY back. Maybe not as much in guitar amps. My 1950s era Seeburg drawings had part numbers.

[Perkinsman]

Clockwise, the ON/SPEED pot measures 166K-.8M. The STRENGTH pot measures 246k-130k. Both were measured in circuit, swept smoothly but neither goes to 0. I tugged on the shafts and both measured stable. I removed the pot and deox'd again, this time clicking on/off a dozen times. It seems to have resolved the problem but I'll try it thru the day & report back.

Update: I think that was the issue, a good pot cleaning and exercising worked out the kinks. I noticed another peculiar thing. Despite the Tremolo being totally off, if I turn the STRENGTH knob up on the Tremolo, the volume of the amp increases. How in the world can the tremolo circuit that is in the off position affect the amp volume??

[Enzo]

You are right, I was looking at the pots wrong. The speed control for example has the 220k resistor in parallel, so at one end you measure the pot only for about 1 meg, (You got 0.8M, close enough)Turn the other end for the 1 meg with 220k in parallel, and your 166k is close enough. SImilar thinking on the other pot. As long as they work smoothly, the value doesn't matter much.

When the trem switch is off, the trem doesn't oscillate. But the tube continues to conduct current. The left side of the trem tube is a cathode follower, and it shares a cathode resistor with the cathode of the second audio stage. The pot adjusts the cathode load of the trem tube from 240k to 130k, this in turn affects the current through the (shared) cathode resistor of the audio stage. And THAT is why it affects the volume.