Tweed Deluxe ....lost it's mojo

[Doc Stitches]

Customer said after he finished this Mojo Kit it sounded good but had a very loud

humm....so......he tore it apart and made some changes and now it plays fine except it

has lost that magical mojo/blues sound. He changed the board, and all carbon resistors

to film. I have read a lot of the other posts here on this amp. Just hoping to keep this

as simple as possible.

Doc

[MWJB]

If it "plays fine" & voltages are the same as when he first built the amp (changing board material & resistor composition won't change that), then either he changed something else that he is yet to mention, or during the strip down & rebuild time that it took to do the work, his perception of what the amp really sounded like has changed. Maybe the background hum was also colouring his perception? If he is adamant that the metal films have changed the sound, then sub them for carbon comps & charge accordingly...but my suspicion is that you are on a "hiding for nothing" in this instance. If he thinks that "last month/weekend/day it had a magical sound that has since disappeared" I suspect that you'll never recover it to his satisfaction.

Might be worth posting voltages & a few pics of the board & socket wiring in case of any obvious wiring flaws?

[J M Fahey]

Mojo is intangible and there's nothing physical you can do to restore it.
As said above, I firmly believe that resistor composition does not alter the sound (beyond the obvious higher noise) .
Now, there *was* a real, physical, measurable change there: it did hum a lot,now apparently does not.
*What* was changed?
Different grounding and even wire layout *does* change sound many times, and that's measurable.
Not as "Mojo" but as different frequency response, peaking at different frequencies (that's what happens when an unstable circuit is close to oscillation, but not reaching it), duller sound (lost highs because of unexpected parasite capacitances), etc.
Anyway, if there was a sound change because of that, it's lost because it was a random phenomenon,m impossible to repeat, plus you don't know what's in his mind.
Or maybe it's just a placebo effect: he read many Forums (not here) about the "sterile, cold" sound of metal film resistors or similar nonsense and he just does not like his amp any more.
Sorry.

[Doc Stitches]

Very loud POP when I chopsticked the board by V1.....suspect loose solder joint below board. I also noticed a lot of noise when I pocked the two bottom input jacks. I will try again to send some photos, and will post some voltages.

[Doc Stitches]

V1
1=190 2=0 3=1 4=24 5=24 6=192 7=0 8=0 9=0

V2
1=189 2=loud hum 3=1 4=24 5=24 6=232 7=21 8=55 9=0

V3
1=0 2=0 3=399 4=369 5=0 6=0 7=24 8=24

V4
1=0 2=0 3=397 4=365 5=0 6=0 7=24 8=24

V5
1=0 2=408 3=0 4=11 5=0 6=11 7=0 8=408

[Doc Stitches]

photos ?

[MWJB]

V1 pin 8 should be the same as pin 3.

If the heaters are dc biased via the cathode resistor in a twisted pair, then the cathode voltage should also be present on pin 9 of the 12AX7s.

OK I take back what I said, wire routing is pretty bad, get the power tube grid wires away from the heater wires, heaters to the preamp should either be suspended over the sockets, or run along the lip of the chassis, either way, should be well away from the speaker jacks, not tucked behind the board.

The red grid wires to V1 pins 2 & 7 can run straight from the 68K resistors to the socket pins, there's no point in sticking them through the board like that...other than to possibly induce noise & oscillations ;-)

[J M Fahey]

You can't have 24V DC on pins 4&5 and 0V on pin 9 in those triodes.

[sgelectric]

Incidental to "mojo", but 3 prong power cord is wired incorrectly by modern standards.

[Bruce / Mission Amps]

Wow... I don't think that is a Mojo Kit.... however... I can't tell if the power tube sockets are even wired right... it looks like a wire from the standby switch is running to a 6V6 socket and in one picture, where I expect to see a flying lead from lug 4 (screens) over to the other tube, it looks blank!!! That'll mess it up.