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Grommes console

I have the schematic for the 20LJ, but the 101GT didn't make it into Sams - dunno if it's anything like 102GT, 103GT...
 
Tom Bavis said:
I have the schematic for the 20LJ, but the 101GT didn't make it into Sams - dunno if it's anything like 102GT, 103GT...
Click to expand...

Tom,
Thanks for the Schematic!
dcgillespie said:
I built one of those Grommes amplifiers as a young boy, and loved it. It was my first really good stereo amplifier, with everything before it being little more than record player designs (not putting them down, but used for description). Your version is an earlier version, as mine used PECs for the tone controls circuits as well as the one shown for EQ duties. It's basically a stereo version of the Grommes Little Jewel LJ-7 amplifier, which was the last in that well received line of amplifiers.

Dave
Click to expand...
As Dave mentioned mine looks to be an earlier version. It is different than any I see referenced on the internet.
Along with what Dave notice on the tone controls, This one has only 2- 12AX7 tubes instead of the 4 12AX7s that the later version had and also in the schematic that Tom sent me.
I'm going to need some help here. So is this a Push Pull amp without phase inverter tubes? I thought they went hand in hand?
- Brad
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Please send me a copy of the schem. if possible please, as I'd like to see that design. What's that 3rd unshielded tube?

Thanks,


Regards!


Randy
 
This is very interesting! I've never seen one like that before. The only real answer is that this unit likely uses 6BM8/ECL82 output tubes, which contain a power pentode and high mu triode all in one envelope. That would effectively allow the unit to operate without the two additional 12AX7s used in the 20 LJK (K for kit) that I built, but effectively use the same basic circuit as if those tubes were present. A close look at your undershot pic shows that appears to be the case. Can you confirm this?

Dave
 
dcgillespie said:
This is very interesting! I've never seen one like that before. The only real answer is that this unit likely uses 6BM8/ECL82 output tubes, which contain a power pentode and high mu triode all in one envelope. That would effectively allow the unit to operate without the two additional 12AX7s used in the 20 LJK (K for kit) that I built, but effectively use the same basic circuit as if those tubes were present. A close look at your undershot pic shows that appears to be the case. Can you confirm this?

Dave
Click to expand...

Dave,
You are right, the output tubes are indeed 6BM8/ECL82. The tube novice that I am, didn't notice the difference from the 6BQ5 in the schematic and the 6BM8 clearly labeled on the amp. Thanks!
 
I was thinking the same thing too Dave, & if you look at those 4 tall tubes on the left one is clearly different in structure inside, but they all look to be the same height? Even that fifth unshielded may be fairly tall.

Randy
 
Shadowdog said:
Please send me a copy of the schem. if possible please, as I'd like to see that design. What's that 3rd unshielded tube?

Thanks,


Regards!


Randy
Click to expand...

Randy,
Just to note: This is not the version that I have, probably a later version of the 20LJ.

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  • Grommes_20LJ.jpg
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Randy -- the tall tube next to the power transformer is the 6CA4/EZ81 rectifier tube, which was consistent with the model I built as well.

Dave
 
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