Marshall 1962 Bluesbreaker (JTM 45) Reissue Hum

[ca7922303]

DC voltages look good.

See if disconnecting one end of the 0.22µ cap that connects to the tremolo intensity pot makes a difference.

Yeah, is there away to remove a wire off of tremelo intensity pot to check that cap? Otherwise I'll have to start desoldering wires to get to the bottom of the board. Wires are very tight on it.

[Helmholtz]

Yeah, is there away to remove a wire off of tremelo intensity pot to check that cap? Otherwise I'll have to start desoldering wires to get to the bottom of the board. Wires are very tight on it.

Just lift the wire that connects between the 0.22µ cap and the intensity pot, connect your guitar and see how it sounds.

[g1]

You should be able to disconnect the wire right at the pot, unless these pots are mounted on the circuit board?

[ca7922303]

You should be able to disconnect the wire right at the pot, unless these pots are mounted on the circuit board?

If I'm looking at this right, C2 is the 0.22u cap and it's not there. Tested resistance from all three(3) pot wires to both ends of C2 and reads(OL.)

[ca7922303]

If I'm looking at this right, C2 is the 0.22u cap and it's not there. Tested resistance from all three(3) pot wires to both ends of C2 and reads(OL.)

Also, C3 is reading(OL.) in circuit?

[ca7922303]

Also, C3 is reading(OL.) in circuit?

Also have plate to cathode voltages DC:
v1 1-3(183vdc) red probe on pin 1, black on pin3
6-8(193vdc) red probe on pin 6, black on pin 8

v2 1-3(190vdc)
6-8(128vdc)

v3 1-3(181vdc)
6-8(176vdc)

V4 1-3(165vdc)
6-8(201vdc)

[g1]

If I'm looking at this right, C2 is the 0.22u cap and it's not there.

No you are not looking at it right. Are you using the schematic from post #7 ? Where do you see C2 on it? I see a .22uF cap connected to the intensity pot with an * symbol beside it. According to the notes that means it is mounted 'off the board'. So I expect it to be mounted right at the pot lug.

[ca7922303]

No you are not looking at it right. Are you using the schematic from post #7 ? Where do you see C2 on it? I see a .22uF cap connected to the intensity pot with an * symbol beside it. According to the notes that means it is mounted 'off the board'. So I expect it to be mounted right at the pot lug.

In this photo, intensity is 2nd pot from right and it does not have a cap connected to it. The 3rd pot from the right(presence) does. Meanwhile I reconnected 16 ohm selector wire(purple) and now channel 2 has normal output, except treble, middle, bass do not function. Presence is working correctly.

[ca7922303]

No you are not looking at it right. Are you using the schematic from post #7 ? Where do you see C2 on it? I see a .22uF cap connected to the intensity pot with an * symbol beside it. According to the notes that means it is mounted 'off the board'. So I expect it to be mounted right at the pot lug.

Have a 100 ohm 5 watt Pot on order for a humdinger. Could you suggest and possibly draw a diagram on best way to wire it? I'm thinking I'll glue it down to chassis between PT and board.

[ca7922303]

Have a 100 ohm 5 watt Pot on order for a humdinger. Could you suggest and possibly draw a diagram on best way to wire it? I'm thinking I'll glue it down to chassis between PT and board.

More photos

[Helmholtz]

Does the tremolo work?

[ca7922303]

No you are not looking at it right. Are you using the schematic from post #7 ? Where do you see C2 on it? I see a .22uF cap connected to the intensity pot with an * symbol beside it. According to the notes that means it is mounted 'off the board'. So I expect it to be mounted right at the pot lug.

I have some pots in hand I'd like to try the humdinger wiring to see if it will reduce the hum. Can you tell me what values would also work while I'm waiting on the 100 ohm 5 watt Pot? Thanks

[Helmholtz]

I have some pots in hand I'd like to try the humdinger wiring to see if it will reduce the hum. Can you tell me what values would also work while I'm waiting on the 100 ohm 5 watt Pot? Thanks

See the link in post 71. Merlin uses a 500R/80mW pot. You shouldn't go higher than 500R. The lower the resistance the higher the wattage.
You can roughly calculate the required pot wattage from 50 divided by resistance.

[ca7922303]

See the link in post 71. Merlin uses a 500R/80mW pot. You shouldn't go higher than 500R. The lower the resistance the higher the wattage.
You can roughly calculate the required pot wattage from 50 divided by resistance.

I've got a 100 ohm 5 watt Pot on order per rob Robinette webpage about a humdinger. Will that pot not work?

[Helmholtz]

I've got a 100 ohm 5 watt Pot on order per rob Robinette webpage about a humdinger. Will that pot not work?

Should work fine, but a 100R/1W pot would be completely sufficient.