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Amp had a hum until you plugged a jack into the instrument inputs or the power amp input. Replaced all the cement resistors that tend to overheat but that didn’t work. Then ran a 220k resistor from a transistor )Q7)leg to D18 Cathode leg. Article from forum where I found this. https://music-electronics-forum.com/forum/amplification/guitar-amps/maintenance-troubleshooting-repair/976509-fender-fm212r-possible-muting-problem pertainent text.....from the article above by Wernersaurus: Right - here's the cause and solution: First - the humm is a medium to loud 100Hz (120Hz in the US) straight from the PSU Full Rectifier. It is definitively caused by the mute circuit but not every amp will do it - it depends mainly on three different things: - the value of the temp PTC (they are not very precise) - the HFE of Q6 and Q7 - the amount of residual humm on the -16V rail The problem ONLY occurs when the mute circuit is engaged - ie nothing plugged in either of the two input jacks or the effects return jack. What happens when R73 is pulled to ground - the circuit Q6/Q76 now becomes a current amplifier circuit who's efficiency is governed by the HFE's of Q6/Q7 and the value of the PTC. The idea is the shut down the constant current circuit formed by Q8, D20 and R82 - but depending on the amplification value the mute circuit now controls the current through the constant current circuit - in effect amplifying the residual 100Hz (120Hz) on the 16V rail. So - that is done - now the fix: Install a resistor 220kOhm or more (I tested 220kOhm and up to 1MOhm - they all work - depending on the amplification value of the mute circuit) from the collector of Q7 (attach it to the leg of R72) to ground Cathode of Diode D18 (is just on the diagonal other side of Q7). This absorbs the amplified current from the mute circuit and the humm is gone. Now - have fun with the Frontman 212R !!

I didn't lke the original Grote 6 saddle bridge design where the strings rattled against the saddle screws. The Grote Electric Guitar is made from the cheapest wood/paper mache known to man, so I thought why not expirement. So I made it into a Telecoustc, Acousticaster or Fender Acoustasonic Electric Acoustic Guitar.