MARK III Red Reverb Issue

[mgbanach]

Howdy yall. This is my first time on, as I have recently acquired a mk iii red stripe combo amp. Such a rad amp. Currently I am having issues when I turn my reverb up. When I turn it up, there is lou crackling and volume boosts, but when I turn it to 0 everything is fine. I figured it was a pre amp tube. Cant seem to find which is the preamp tube for the reverb though. My amp has two 6L6 power tube ports and 5 pre amp ones. I went through all of the pre amp tubes, with my one replacement pre amp tube, and couldnt find the port. I interchanged all of them but the port 1, silver encased one. Do I need to replace all of the pre amps and power tubs? Is it a circuitry issue?
Thanks so much for the help.

 

[stokes]

"When I turn it up, there is loud crackling and volume boosts, but when I turn it to 0 everything is fine".Do you get any reverb effect at all?

 

[tommyhawk13]

This might be the tube for reverb. I think the metal casing is for noise suppression. The old Boogie catalogs advertised a shielded tube for reverb. You can use a regular 12AX7, or even a 12AT7 like they did in the old days.

 

[stokes]

The reverb tube is V4.

 

[Promethean]

v4 should be the one furthest from the input jack. The preamp valve set behind is the phase invertor.

I always had a hissing, buzzy noise problem with my MK3 whenever I used reverb. I cleaned all the connectors from the amp to the reverb unit. They could be rusty. What finally sorted it was a mail to Boogie. They directed me to make an additional connection to earth from a transformer wire and that eliminated all the noise problems completely..

"120k resistor on the red lead from the smaller reverb transformer to ground."

I am not sure if that was resolved by the red stripe - mine is the purple one before. It was called the 'reverb glitch mod' so seemed common to the amps. I have a copy of the Mark 3 mod sheet from Boogie themselves.

I also added a 10k 1/2 watt resistor in series to the black wire going to the fx return jack. That significantly boosts the amount of reverb available. 3.3k or 5k would work too

 

[mgbanach]

replaced the reverb pre amp tube. still happens. called boogie, and they recommended I take it to a tech.