This Fender Musicmaster from the 'Silverface' era is up for eBay auction and is the same model as our BBer Dane's; single 12AX7 and twin 6AQ5s (6005s).
A friend of mine just bought one of these except that his is a twin 6V6 model, not 6AQ5. When the parts get here, I'm going to recap it for him. I went looking for the schematic and found the 6V6 version that includes an 'extra' transformer; Gibson GA35 shown on left for comparison:
According to Teagle and Sprung's Fender Amps, the Musicmaster was in production from 1970 to 1982. They go on to say that the function of the transformer is to couple the audio stage to the output and achieve phase inversion without the use of another tube and its necessary sidekick resistors and capacitors that, in most amps, act as the phase inverter. According to them, this is the only Fender design with a coupling/inverting transformer and explains why there is only one preamp tube, rare for a twin or push/pull amp. In this discussion of the differences between Black and Silverface Fender amps, they say the Musicmaster is a 'tone monster'! Additional Musicmaster specifications at Ampwares
In LTG's Voicing Amps thread, there's a lot of discussion about the effects of cathode bypass capacitors on tone and frequency response. The Musicmaster schematic below showing a large value 50uf cap on the left bypassing the preamp cathode resistor and a conventionally sized 25uf cap bypassing the output tube's cathode resistor on the right. The preamp cap acts like a low-pass filter; it prevents higher frequencies from passing while allowing the lower ones to pass. Every Fender Bassman has a 50uf cap in the same location.
So what? Nearly every high-grade boutique or home-built 'Deluxe' has switchable preamp cathode bypass caps mounted; normally 25uf in one switch position and .68 'Marshall' style in the other because the low value cap acts like a high-pass filter; stopping low frequencies while allowing higher ones to pass. The switchable cap provides a fundemental change in the amp's frequency reponse and tone. When I get my friend's amp on the bench, I'll try to get him to listen to a 25uf there; whatever's in there is coming out anyway for maintenance reasons. If you get the time or inclination Dane, you might try the same thing; ought to make the amp sound like it's running a little hotter, more twang, and if you're interested, I still have that single, low-use 6AQ5/6005. CJ
A friend of mine just bought one of these except that his is a twin 6V6 model, not 6AQ5. When the parts get here, I'm going to recap it for him. I went looking for the schematic and found the 6V6 version that includes an 'extra' transformer; Gibson GA35 shown on left for comparison:
According to Teagle and Sprung's Fender Amps, the Musicmaster was in production from 1970 to 1982. They go on to say that the function of the transformer is to couple the audio stage to the output and achieve phase inversion without the use of another tube and its necessary sidekick resistors and capacitors that, in most amps, act as the phase inverter. According to them, this is the only Fender design with a coupling/inverting transformer and explains why there is only one preamp tube, rare for a twin or push/pull amp. In this discussion of the differences between Black and Silverface Fender amps, they say the Musicmaster is a 'tone monster'! Additional Musicmaster specifications at Ampwares
In LTG's Voicing Amps thread, there's a lot of discussion about the effects of cathode bypass capacitors on tone and frequency response. The Musicmaster schematic below showing a large value 50uf cap on the left bypassing the preamp cathode resistor and a conventionally sized 25uf cap bypassing the output tube's cathode resistor on the right. The preamp cap acts like a low-pass filter; it prevents higher frequencies from passing while allowing the lower ones to pass. Every Fender Bassman has a 50uf cap in the same location.
So what? Nearly every high-grade boutique or home-built 'Deluxe' has switchable preamp cathode bypass caps mounted; normally 25uf in one switch position and .68 'Marshall' style in the other because the low value cap acts like a high-pass filter; stopping low frequencies while allowing higher ones to pass. The switchable cap provides a fundemental change in the amp's frequency reponse and tone. When I get my friend's amp on the bench, I'll try to get him to listen to a 25uf there; whatever's in there is coming out anyway for maintenance reasons. If you get the time or inclination Dane, you might try the same thing; ought to make the amp sound like it's running a little hotter, more twang, and if you're interested, I still have that single, low-use 6AQ5/6005. CJ