Dating fender bandmaster amps
The C12n sounds very punchy, wide and deep in a 2×12″ cabinet.
See page How to select speakers for speaker recommendations. If you want cleaner and spankier preamp distortion charcteristics, you may replace the V1 or V2 12AX7 preamp tube with 12AT7 and 12AY7.
This mod does not alter the tone significantly when amp is played clean or when only the power amp section distorts.
You’ll have to increase the volume setting to achieve a similar volume as before.
The Bassman has a slightly bigger output transformer resulting in a firmer tone and more attack.
A smaller output transformer will introduce sag and compression in the power amp section.
The 70W model from 1978 with master volume and push/pull boost had a huge power transformer and big filter caps.
It reminds us more of a classic 80w Twin Reverb than a Bandmaster Reverb, and it shared its circuit design with the Pro Reverb and Super Reverb at that time.
This is caused by the lack of gain stage in the reverb recovery circuit which contributes to tube distortion and compression in the preamp section when the amp is pushed.Speakers The Bandmaster’s 2×12″ speaker cabinet was from the Fender factory loaded with either Jensen C12n or Oxford 12T6.Personally we favor the Jensen C12n for their natural and transparent “Fendery” tone and, most importantly, for not being to bright and harsh.The vibrato channel in the Bandmaster is even more clean than the Bassman because of the vibrato circuitry loading the signal chain and reducing the gain level in the premp section.Hence, the AA864 Bassman normal channel has more preamp “juice” and reaches the sweet spot at an earlier volume knob setting.