MK 3 Reverb problem

[xhavier]

Hi All I have a boogie MK III 100w simulclass combo with graphic and reverb, I have owed this amp for several 15 years I have used a delay unit with the amp never the reverb. I have recently come to try the reverb and it is very weak. I have changed the reverb driver 12ax7 and tested the cables to and from the reverb tank. The issues are the reverb sound is very faint and distorted in the mix, as I increase the reverb intensity the amp volume changes and the total sound becomes mildly distorted. I have taken the amp to local engineers but they just say in seems to work it may be a poor design and they don’t know how to fix it. Anyone have ideas?
Thanks in anticipation

 

[jonarobb]

Reverb transformers on Mark III's are known to overheat and cook themselves out. The distorted tone when you turn up the reverb is a dead giveaway. Replace the transformer and increase the value of the dropping resistor to the primary coming from the B+ rail.

 

[Boogiebabies]

The weak reverb and distorted tone in most likely a bad ground somewhere in the reverb circuit. When the circuit is held slightly
above ground reference by oxidation it can turn the reverb circuit into a miniature 1 watt amp, hence, when you turn the reverb up it is overdriving
the circuit. To start, all the grounds on the reverb jacks need to be cleaned as well as the outer surfaces on the tanks input and output jacks.
In most cases, the grey cable's outer connection is used to ground the tank. If the dropping resistor was blown, or the transformer, you would usually not even get a reverb signal.
No reverb whatsoever. In MK III's it's very common for the dropping resistor to blow as it was under rated for the job, but older Boogie designs did not even use a dropping resistor
and put about 400V straight to the reverb transformer. In any case, it may be a good upgrade to change the dropping resistor to a 33K 1 watt.
Any decent contact cleaner should be able to assist you in cleaning the grounds.

 

[xhavier]

many thanks will try these suggetions out tomorrow and report back,

 

[fantasyl]

revamping this old 3d just to say thanks.
The Boogiebabies info helped me in resolving my reverb issues (it was a bad ground).

 

[Boogiebabies]

Well, at least it helped someone...

 

[McBarry]

Another revamp of this thread..esp to BB.

Ed, my rev tranny is open on the primary side (mark IIB, seems all original)
Besides replacing the tranny, do U routinely ungrade the dropper resistor also?
The 10k/2w measures per spec, but obviously not under load with tranny out.
33k seems like a big jump, but yr ideas appreciated.
David