2023 Monkeymatic Black Butte (from Ampex 620)

[xtian]

I got this CUTE Ampex 620 suitcase from eBay. Didn't have near enough gain for guitar, so I replaced V1 EF86 with 12AX7 (gain stage, tweed tone control, gain stage), same as my other Black Buttes. Now we're ripping! Just too much hum. I'd like to try gNFB, but since this isn't a standard LTPI, not sure how to implement. Suggestions, please? Attached schematic 1 is before mods, schematic 2 is after (V1 not shown).

schem1.png

schem2.png

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[beasleybodyshop]

Nice! These projector amp/film amp conversions never disappoint. I dig all the bumblebee caps in there too. Some fools will gladly part with $$ to buy those for Les Pauls it seems

[xtian]

I ran a gNFB line from the OT secondary, thru 15K resistor, to V1b cathode. Much better, lower noise, still enough gain. Putting out 3-4 watts into 8 ohms, a little better into 16R.

[Reeltarded]

That monkey is always busy and does great work.

[maxkracht]

Looks nice! I rebuilt one of those a couple years ago but never got the noise floor quite low enough for my taste. Input right next to the mains is odd, but maybe that was just a lazy excuse.

[xtian]

It's a super cute package!

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