carr mercury - anyone had a look inside?

[tubescent]

checked out a couple of youtube demos of these things and i am curious about the 3 position boost. it also says that the mercury takes an extra 12ax7 preamp valve so i was thinking it might be almost like a channel switching champ where the input is channeled to a more hotly biased 12ax7 when engaging the boost. i've had too much time to think lately but if someone out there has a mercury and could tell me if this is true, it would curb my amp curiousity for maybe... half a day.

 

[teleamp]

I think the extra 12AX7 is for the reverb. the boost switch just varies the amount of the tone stack being taken out of the circuit IIRC.

 

[tubescent]

there's a 12at7 in there as well and i summised that was for the reverb?

 

[meyekel]

It has 2 12ax7s and one 12at7. I haven't opened it up to look or the knowledge to really know what's going on in there anyway. The boost switch does lift the tone stack but has it's own distinct tone for position 2 and 3.

 

[tubescent]

champs normally use one 12ax7 for preamp/driver and i've seen quite a few schematics for a one tube reverb (12ay7?) so am wondering if one of the boosts is tonestack lift and the other is an extra tube engaged to add gain?

 

[nvilletele]

I have a Carr Mercury but not sure I would even know how to exactly begin to answer the OP's question, or the one last raised above either. But here is some related info from the Mercury manual, in case this info is of any help:

3 Position Boost–
Position 1: 60s American sound with great warmth
Position 2: Increases gain by defeating the tone controls (Treble and Bass) while trimming low end for a focused overdrive tone
Position 3: Further increases gain from the tone stack and reverb circuit while the low-end focus is refined. Tone controls are defeated.

=============================================

V1, V2, etc. for preamp tubes and P1, P2, etc. for power tubes.

Mercury Tubes------P1----------V3------------V2--------------------V1
Type----------------E34L------12AX7--------12AT7----------------12AX7
Manufacturer--------JJ-----Groove Tubes--Electro-Harmonix--Electro-Harmonix
Function------Single-ended--Reverb return--Reverb send-----Initial gain stage,
----------------power stage----and mix-----------------------post tone-stack recovery
==========================================

We recommend biasing EL-34s at the factory bias point of .045Vdc. We recommend biasing all other compatible tube types at .052Vdc.

 

[teleamp]

OK, so V1 is the preamp tube (circuit very similar to a Champ), V2 & V3 are for reverb and V4 is the power tube (fixed bias). From the schematic I saw, the boost takes the tone stack out in stages, not being fully defeated until the last stage.

Steve's work is beautiful and just about bullet proof... I've seen the insides of some of his amps, very impressive craftsmanship.

 

[tubescent]

"Position 3: Further increases gain from the tone stack and reverb circuit while the low-end focus is refined. Tone controls are defeated."
this sounds like the unused half of the 12ax7 reverb return is being used as a further preamp boost which is what it sounded like in a demo i listened to.
cheers for the info